Principles of Yacht Design [First American ed.] 0070364923, 9780070364929

Citation preview

BELVEDERE TIBURON LiBRARr

3

1111

01616 612^

LARS LARSSONa ROLF E ELIASSdN

•Bm

O^

r

1

30 years a revolutior

The evidence

,igr

f'

J last

oiising yachts

IS

plain to

'

,

'/ r

-

nght through to the

j'.'.

uilr.'

i

place

in

yacht

whole vanety of

j

'ugh tech racing

machines. Simultaneously the impetus given to yacht research has been tremendous, stimulated partly by the

demands of

such high profile media events as the Amenca's Cup,

BOC

or

Whitbnead campaigns. This

book

the

IS

for

first

many

years to examine every aspect

of the process of yacht design. Throughout the book the

authors have used a

nev\/ly

designed 40-footer to demonstrate

the practical application of yacht design theory.

Beginning with the yacht's specifications, the authors explain

the geometry of the

CAD

by means of

waves are descnbed

keel

as

in detail,

and introduce

lines plans

techniques. Hydrostatics and stability

well as hull,

hull

is

in

calm water as

the design of the

and rudder. Next the aerodynamics of the

the influence

this

has on the shape of the

sail

plan

sails

and

is

examined. Methods are introduced for finding the balance of the yacht and there

a short chapter

is

on

selecting the correct

propeller and engine.

Structural aspects of the design are treated comprehensively

throughout. Loads acting on the

methods

for

hull

and ng are identified and

computing them introduced. There

is

also a

discussion of different fibre reinforced plastics, including

sandwich laminates.

Finally, practical

matters such as the layout

of the cockpit, deck and cabin are discussed, and a complete

weight calculation

The book

is

is

provided for the 40-footer.

nchly illustrated with explanatory diagrams, and

although the subject

is

complicated, the authors treat

remarkably clear and concise manner, making

it

it

in

a

easily

understandable for both professionals and amateurs interested in

the pnnciples of yacht design.

Front cover photograph by Roger Lean -Vercoe

Notm: Boundary taymr thicknmam

mxoggmrafmd

Smaltmr 4ddl»t Turbufmnt boundary

Smparatlon

layr

Lorgmr mddlmt Transition

Laminar boundary laymr

,

natural frequency (in

(Dg

V

frequency of wave encounter volume displacement

Indices c

canoe body

k

keel

r

rudder

u

upper lower

1

roll)

XVI

Principles of Yacht Design

Conversion factors

To To

convert metric measures inlo

inipcricil measures, mullipiy by .v convert iwpera/ measures into ineiric measures, multiply by y

Metric

Imperial

Length

(mm)

Inches

Centimetres (cm) Metres (m) Metres (m) Metres (m) Kilometres (km) Kilometres (km)

Inches

2.540

Inches

0.(325

Feet

0.305

3.281

Millimetres

Area Square Square Square Square Square

(mm-)

millimetres

centimetres (cm-)

metres (m-) metres (m-) metres (m^)

25.40

0.039 0.394 39.37

Yards Geographic miles

.094

0.914

1.609

0.621

Nautical miles

1.853

0.537

Square Square Square Square Square

inches inches inches feet

yards

1

645.10 6.452 0.00063 0.0929 1.1968

0.0016 0.155 1600.00 10.764 0.8355

Volume Cubic centimetres Cubic metres (m^*) Cubic metres (m^)

Cubic inches Cubic feet Cubic yards Cubic inches Cubic feet

(cm-*)

Litres (L) Litres (L) Litres (L)

US

Litres (L)

Imp

gallons

gallons

16.387

0.0610

0.0283

35.315

1.309

0.764 61.024 0.0353 3.785 4.546

0.0164 28.317 0.264 0.220

Weight

Grammes

Ounces Pounds Pounds

(g)

Kilogrammes

(kg)

Tonnes, metric (T) Tonnes, metric (T) Newton (N) Kilonewton (kN)

Tons, long

Pounds Pounds

28.350 2.2046 2204.60 1.0160 0.2247 224.73

0.0353 0.4536

0.00045 0.9843 4.450 0.0044

Density

Kilogrammes/m^ (kg/m^)

Pounds/cubic foot

0.0624

16.026

Pressure, stress, work, energy

Newton/mm- (N/mm-)

Kilonewton-metres (kNm)

Pounds/sq inch Pounds/sq inch Pounds/sq inch Pounds/sq inch Pounds/sq inch Pounds/sq inch Foot-pounds Foot-pounds

Horsepower (metric) Kilowatts (kW)

Horsepower (imp) Horsepower (imp)

Kilonewton/mm- (kN/mm-) = Pascal (Pa) Wm-) = Kilopascal (kPa) kN/m-) Megapascal (MPa) = N/mm-) Gigapascal (GPa) = kN/mm-) Newton-metres (Nm) (

1

1

(

1

(

(

Speed Metres per Metres per Kilometres Kilometres

1

second (m/s) second (m/s) per hour (km/h) per hour (km/h)

Feet per second

Knots Miles per hour

Knots

144.95

0.0069

144950.00 0.00014 0.14495

0.0000069 6899.00 6.899 0.0069 0.0000069

144.95

144950.00 0.7370

1.3568

737.00 0.986

0.0136

1.340

0.7463

3.2808 1.9425

0.3048

0.6214 0.5396

1.0142

0.5148 1.6093

1.8532

INTRODUCTION

the During generally

30 years yachting has expanded from being, speaking, a minority sport - too expensive for the large majority of people - into a major recreational activity past

practised by millions coastal areas were

be

all

still

over the world. In the 1960s,

relatively free

difficult to find a suitable

many

attractive

from pleasure boats: today

mooring place

racing has increased correspondingly at

for the night.

all levels,

The

it

can

interest in

from dinghy racing

Cup and around the world races. During this period, many new yacht designs have

to

the America's

number of

appeared, and the

amateur designers has increased steadily. In fact most yachtsmen have a keen interest in the principles behind the design of their yacht and the theory of sailing. Most yachting magazines have design sections, and articles on design professional,

as

well

as

principles feature regularly.

At the same time, yacht research has boomed. The total expenditure in one round of the America's Cup is now in the region of £150-200 million, about one tenth of which is spent on research and development. Yacht research is presented regularly at several series of conferences,

such

as

the

SNAME/AIAA Symposium Symposium on

HISWA Symposium on the

US West

in

Holland,

the

Coast and the Chesapeake

on sailing theory are frequently found in scientific journals on hydrodynamics and fluid mechanics. With this background, it is surprising that there is no good up to date book on yacht design available. More than 60 years ago, Skene wrote his now classic Elements of Yacht Design, which was revised several times by Kinney. This work is still used at design offices all over the world and by many amateur designers, but while several of the methods explained in the book are still useful, many sections dealing the East Coast. Papers

with building materials, design principles

Two

etc.

are obsolete.

books on the same topic are Sailing Yacht Design by D Phillips-Birt and Sailing Yacht Design - An Appreciation of a Fine Art by R G Henry and R T Miller. These books were first published in the 1950s and early 1960s, respectively. They are now out of print and do not seem to be widely used any longer. However, the latter was updated in an interesting paper: Sailing Yacht Design - A Ne^v Appreciation of a Fine Art by R T Miller and K L Kirkman at the Annual Meeting of the Society of Naval Architects and Marine Engineers in 1990. The most well-known books on sailing theory are the excellent ones by C A Marchaj: Sailing Theory and Practice, first published in 1964, other,

more or

less classic

Principles of Yacht Design

The Acyo-Hydiodynaniics of

Sailini;,

in

Forgotten Factor in 1986. Other books

1979 and Seaworthiness

the

same category are The Science of Yachts, Wind and Water by H V Kay and Technical Yacht Design by A G Hammitt, both published in the early 1970s. However, neither one of these is useful for the designer, since they do not cover in

the

methodology, statistical data for existing yachts or design evaluation techniques. Furthermore, these books concentrate on the hydro and aerodynamic aspects of the problem, while, for instance, loading, strength and structural problems for example, as well as practical design considerations, are either not mentioned, or are treated very briefly. Two more recent books on the topic are Modern Developments in Yacht Design by D Connell & J Leather and The Design of Sailing Yachts by P Gutelle, both out of print. The former is not very useful as a textbook, since only a few selected aspects of the subject are covered,

and the

latter

falls

in

the

same category

as

those

in

the

previous

paragraph. Gutelle, however, refers to a future second volume of his

book, where the more practical aspects of design will be treated. A comprehensive review of the literature and research in sailing theory may be found in L Larsson's Scientific Methods in Yacht Design. published in the 1990 Annual Review of Fluid Mechanics. There is thus no modern textbook comparable to Skene's as a guide for the yacht designer. Trying to replace this classic text with a

modern

an exciting challenge, and a successful result would satisfy a deeply-felt need among professional and amateur yacht designers all over the world. With the present book the challenge has been taken up. For a book of this kind to be successful, two conditions must be

one

is

satisfied:

• •

must cover all aspects of yacht design Although it must be comprehensible for amateurs, it must be advanced enough to be of interest also to professional designers. It

There follows a short presentation of this book and an explanation of the strategy adopted for satisfying these two requirements. The book begins with a description of the methodology recommended in the design process. Specifications of the yacht and the design concept are discussed in Chapter 2, and Chapters 3 and 4 cover the geometric description of the hull and the hydrostatics and stability in calm water and waves. The hydrodynamic design of the hull, keel and rudder, and the aerodynamics of the sails are explained in Chapters 5, 6

and 7, and methods are introduced for finding the balance of the yacht in Chapter 8. Chapter 9 deals with the selection of the correct propeller and engine. Structural aspects of design are treated in Chapters 10. 11 and 12. Loads acting on the rig and hull are identified and methods for computing them introduced. Dimensioning according to the ABS (American Bureau of Shipping) rule is explained and complete calculations carried out for one example. There is also a discussion on different

FRP

(fibre

reinforced plastics) materials, including sandwich

Introduction laminates.

cabin are discussed

Chapter

in

means

for evaluating the design.

out

Appendix

in

The

To

complete weight calculation

is

carried

requirement above, the material must be well

we have

Yacht design

is

tried to

by

its

professional or amateur,

know

not enough to

made thicker, What he needs

is

keel.

A

14 presents different

2.

the second

satisfy

skin

and Chapter

13,

different aspects of the design process are therefore well covered.

presented, and

is

and

Practical matters, such as the layout of cockpit, deck

skin thickness

this in a

number of ways.

A

nature a quantitative process.

much

not

designer,

helped by qualitative reasoning.

that the hull can withstand a greater load

or that stability to

and the

all

amount of

more

increased by

is

know, as exactly as

least

yacht to be safe under

compute

is

accomplish

possible,

is

if

It

the

lead in the

the

minimum

lead needed in the keel for the

possible conditions.

he

If

is

not able to

may be slower and more expensive it may be unsafe. Therefore, a basic

these quantities the yacht

than necessary and, worst of

all,

book has been

formulae or diagrams for all aspects of the design process. The reader should be able to evaluate principle of this

to provide

quantitatively every step in the design procedure.

We

are fully aware that

many

potential readers

may

be intimidated

book as being too technical. To avoid this, the equations have been removed from the text and inserted into the figures. A serious designer will need to work through the formulae himself for the reasons just explained, but we believe that the book could also be of interest to yachtsmen in general, by a

text

loaded with formulae, and would

since

many may have

They

will

reject the

a keen interest in the basic physics of sailing.

be able to read the text without digging too deeply into the

quantitative aspects.

On

the other hand, the equations are not very complicated

from a

mathematical point of view. They are numerous, and they may be lengthy, but they are all of the algebraic type. Higher mathematics, such as integral or differential calculus, have been completely avoided, and everyone with a basic mathematical background from, say, secondary school should be able to understand them.

To

help

principles

reader

the

understand

and formulae presented,

the

practical

the design of a

application

new

of the

yacht, called

YD-40

(Yacht Design 40 footer) is followed throughout the book. Thus, after most of the formulae the computed value for the YD^O is given, and all drawings (like lines plan, interior and exterior layout, rig plan and general arrangement) are for this modern cruiser/racer. This does not mean, of course, that the book

is

limited to this type of yacht.

The material covers other cruisers and racers, traditional or modern designs and different rig types. To a certain extent dinghies are also included, but there is not much discussion on multihulls. and reference to power boats is made only occasionally. The YD^O is specified in detail in Appendix 1, where all the data is given. There are

condition, with

two

all

different

sets

of data.

One

is

for the cruising

the necessary equipment and the tanks half

full.

Principles of Yacht Design while the other

or an even lighter one,

latter version,

new

material for

for the light version, without cruising equipment.

is

YD-40 in To evaluate

yachts.

The weight

normally used

is

calculation in

in

Appendix

The

advertising 2

is

for the

the half loaded condition, including crew.

it

in

a

new design and

its

with other yachts. Sections with

many of

qualities

statistical

Median values

the chapters.

is

it

important to compare

data are therefore included

for existing yachts are given

and the spread, within which approximately 95% of all yachts lie, is indicated. There is also a discussion on the effects of deviating from the median, which will enable the designer to create a yacht with special

The

qualities.

shown and

YD^O

position of the

within the statistical data

a motivation for this position

is

yacht specification in Chapter 2 and Appendix

is

also

given in the light of the 1

In order to satisfy the more qualified readers of the book there are sections

on advanced design, where the methods and

tools described are

not normally available to non-professionals. Also, throughout the book, the results of the

Much

of

this

is

most recent research

not discussed

in

yacht design are presented.

yachting literature.

in

Finally, some general remarks on the principles and style of the book must be made. With few exceptions the SI system of units is adopted.

Unfortunately, the

ABS

chapter on this rule

we have had

rule does not follow this standard, so in the

to

adopt other systems. Otherwise

only the yacht speed that does not follow knots.

At the present time

metres per second (m/s). units

may

A

it

is

in

the SI system;

it is

it

is

given in

probably premature to give the speed

in

conversion table between the SI and English

be found on page

xvi.

Another standard adopted

is

the

nomenclature

specified

by

the

Towing Tank Conference (ITTC). This has been developed over a very long period of time and is agreed by all members of the ITTC, which include all reasonably sized towing tanks in the world, as well as most universities teaching Naval Architecture. The symbols in International

this

A

system are

listed separately at the

may

beginning of the book.

end of the book. The list is arranged in alphabetical order by the first author's surname. No reference numbers are given in the text, but contributions from different individuals or groups are identified by the author's name, and it should be easy to find the relevant publication in the list. It should be noted reference section

that there are in the text.

more

be found

references in the

at the

list

than are specifically referred to

DESIGN

METHODOLOGY Yacht design

is

To

beforehand.

and

iterative, 'trial

has

result

final

an

to

requirements,

certain

satisfy

procedure where the

error'

specified

achieve this the designer has to start with a

number of assumptions and work through

the design to see

if,

at the

most certainly not be the have he to change some assumptions and repeat the process, normally several times. The sequence of operations is often referred to as a spiral, where the designer runs through all the design steps and then returns to the starting point,

end,

satisfies

it

case in the

first

whereupon

a

the requirements. This will iteration, so

new

After several turns the process

begins.

'turn"

have produced the desired

more

will

We

result.

may

design spiral in

will describe the

detail below.

manually the procedure can be very time consuming, and it is tempting to stop the iterations before the initial specifications have been fully met. A huge saving in time and accuracy is possible if modern computer aided design (CAD) techniques are adopted, and we will discuss this possibility in the second part of the chapter. If

The design

spiral

all

In Fig

1.1

identified,

Fig 1.1

The design

steps

taken

are

shown. Eleven different segments may be segment corresponds to an operation by the

the design spiral

and each

is

spiral

Chapter numbers within brackets

Update o f data for next

feration

(.2)

Evaluation (14)

/

^ yC^

and

stability

\

^^-^^ 1

(^"tU/C p~iiY \^

Weight

1

I

III

calculations (Appendix 2)

—

dimensions

CO)

Hull

\

1

\

and deck

W^

\

\ ^.^'^^A^^

Keel

\

\

and rudder design

\

(6)

f^]~N

|

Vx^^^^v

tP\

vX

scantlings ^"' '^^

N

/~---/\

[pmklffii:t^^

\

V Rig

(3.

/^\

y^*\.

/

and deck

design 5)

^v

>^^

/

(4)

Hull

S.

'

\

Hydrostatics

tK.

^

^T

/^""''w'mUMmlrrm^

1 ""mJim

\

y\. / rC'^ yC

1

/ -v/

1

Sail

/

>L-J^-^ "X/ /^

"T' \

1

Propeller

engine (9)

and

General

arrangement (13)

and

design (7. 8)

rig

Pi

iiKiples of Yacht Design

Not

designer.

all

operations have to be earried out

tools used in each operation

more and more segments

may

in eaeli lurn.

are included, and better and better tools are

used, as the process converges towards the final solution.

shows this

The

figure

that each sector corresponds to a chapter (or possibly two) in

book.

From its

and (he

vary (Voni lurn to turn. In principle,

the start the designer has only the specifications of the yacht,

ie

requested capabilities. Based on his experience, or data from other

he

yachts,

parameters

main

assumes

the

such

displacement/length

ratio, heeling

as

data

arm and metacentric

of

height

the

hull.

ratio,

sail

Non-dimensional area/wetted

area

may thus be computed, and a made based on statistics from

rough check of the performance may be other yachts. The procedure is summarized in Chapters 2 and 14. In this first spiral turn the designer jumps from the first to the last segment

and the evaluation

directly,

In the

is

very rough.

second turn, after having adjusted the main parameters,

it

be time to begin the actual design of the hull, keel, rudder and plan.

The theory

for this

is

given in Chapters

3. 5. 6. 7

and

layout of the interior and exterior design (see Chapter 13)

8.

may

may sail

A

rough

be

made

an initial weight estimate, needed for the stability calculation, (see Chapter 4). It is likely that neither the weight, nor the stability will be correct, so several turns may be required to satisfy these too,

give

to

requirements reasonably.

have to be redone stability

for

the

in

Of

course, not

all

may

previous operations

each turn. Having found a reasonable weight and

yacht,

the

next

turn

may

include

the detailed

hull

and the dimensioning of the rig, as well as the 9, 10, 11 and 12). Only at this stage can an exact weight calculation be carried out, as shown in Appendix 2. As the designer approaches the final solution he may want to evaluate the design more carefully, and to do this a Velocity Prediction Program (VPP) is required. Such programs are described in Chapter 14. where other, even more accurate, techniques are also presented. The amateur designer may not have access to either of these tools, however, so his evaluation of the current design will have to be based on scantling calculations

choice of the engine (see Chapters

experience. It

should be pointed out that

required. This

is

some segments

particularly the case in

requirements for volume and

beforehand, and

in

it

may

its

internal iterations are

the hull design area.

distribution

are

Here,

probably specified

take several iterations to satisfy them. If the

manual, iterations between the different views to fair the lines are also required, as will be described in Chapter 3. In the hydrostatics and stability segment iterations are required to find the proper sinkage and trim when the hull heels at large angles. process

Computer Aided Design

(CAD)

is

computer aided design (CAD) may be carried out efficiently on PC or Macintosh computers. mathematics required a Since fairly extensive calculations are coprocessor is recommended to enhance the computing speed. It is also

Thanks

to the rapid

development

in recent years,

Design methodology advantageous to have a high resolution colour graphics screen of least

EGA/VGA

standard, or preferably a screen with

much

at

higher

and special graphics software. A laser printer will produce reasonably good small-scale graphical output, but professional designers use pen plotters of various sizes to produce drawings up to full scale. The most important module of a CAD system for yacht design is a powerful program for generating the hull lines, and such programs have been available since the early 1980s. The hull is represented mathematically, either by two families of lines, one running longitudinally and the other transversely on the surface, or by surface patches matched at the intersections by some conditions of fairness. In either case, any point on the surface may be found from the mathematical representation, or more precisely, if two coordinates of a point are given, the program computes the third one. Thus, if the user provides the distance from the bow, X, and the distance above the waterline, Z, the program computes the local beam, Y, at this location. By specifying several points, any cut through the surface may be obtained, for instance, any station or waterline. There are principally two different problems in connection with the surface representation. The task can be either to generate a new hull, or to duplicate, as accurately as possible, an existing one. The latter problem is more difficult, and software for yachts has not yet been developed for this purpose. It is certainly possible in an iterative process to approach a given shape, but it can be time consuming. Fortunately, resolution

the designer

To

is

normally interested

achieve this he has to

in the first task:

work with

creating a

hull.

a set of master curves close to, but

not normally exactly on the surface. Each master curve set

new

is

defined by a

of points (vertices) lying on the curve. The number of curves and

vertices varies

from case

to case, but are often in the range 5-15.

By

moving one vertex the master curve changes and the hull surface is locally deformed in such a way that it is still smooth. In most programs the curvature of the surface

may

be plotted, thus enabling the designer

lines even on a small

and with the relatively low resolution of the screen. Some programs use points on the hull itself for defining its shape, but all the major programs on the international market use master curves. There seems to be a consensus among yacht designers that this approach is very effective for creating fair lines. In Chapter 3 we will show how the hull is generated by the master curves. Some hull geometry programs have the capability to rotate the hull and show it in different perspectives on the screen. In other cases the hull image is transferred to a special visualizer. The possibility of showing a perspective plot of the hull is important and is a major improvement compared with the manual approach, where only three standard views are employed (see Chapter 3). For example the shape of the sheer line may look quite different in perspective compared with the side view, since the line that meets the eye is influenced also by the beam distribution along the hull. Hulls that look good in a side view to generate fair

may

look quite ugly

in reality.

scale,

8

Principles of Yacht Design

The

detailed drawings are normally

done

in

a general

CAD

system,

based on a two-dimensional representation of the body. The input to this

system

Some

is

of

obtained from the hull geometry module or the visualizer. the

more

programs

advanced

superstructure as for the hull model,

represented

in three

may

dimensions and

other programs they are treated

ie

include

the

and

deck

these parts of the yacht are

be displayed

separately.

in

perspective. In

To compute

stability

at

and cockpit need to be modelled, and this is frequently done in a separate module where these parts are added relatively crudely, section by section. A keel/rudder module is often available in yacht CAD systems. The designer may choose between a number of different profiles for the cross-section and specify the planform of the keel/rudder. The code computes the volume, weight of the keel, centre of gravity and centre of effort of the hydrodynamic force. The latter is required in the balancing of the yacht, as explained in Chapter 8. For this the sail plan is also required, and some systems have a simple sail module which computes sail areas and centres, given the sail corner coordinates. The total weight and centre of gravity location (in three directions) are computed in a weight schedule monitor, which accepts the weight and position relative to a given reference point of all items on board. Appendix 2 presents the input and output from such a monitor. Very important modules of the yacht CAD system are the hydrostatics and stability programs. These compute all the quantities discussed in Chapter 4, including stability at small and large heel angles, weight per mm of sinkage, and moment per degree of trim. In the stability calculation the correct sinkage and trim are found for each heel angle - a very time consuming procedure if carried out manually. The Velocity Prediction Program (VPP). mentioned earlier, may also be regarded as a module of the CAD system. As explained above, this program computes the speed, heel angle and leeway angle at all wind speeds and directions of interest, based on a set of dimensions for the hull, keel, rudder and sails. The very simple pertbrmance estimator, based on a few main parameters and used in the first iteration of the design spiral, may also be a module of the system. Finally, more or less advanced programs for the structural design of the yacht may be included. Such programs can be based on the rules given by the classification societies: the American Bureau of Shipping, (ABS), or Lloyd's Register of Shipping. The ABS guide will be described in Chapter 12. Other methods employed in the rig and scantling calculations may be based on basic strength theory or finite large angles of heel the deck, cabin

element techniques.

Computer

aided

design

may

manufacturing, which can be used

be

extended

in the

computer

to

aided

production of the yacht. For

example, the very time consuming lofting process, where the builder

produces

full-scale

templates,

may

be eliminated.

Traditionally,

the

builder receives offset tables from the designer. Based on these offsets the templates are

drawn

at full scale

with a reduction

in

dimension for

Design methodology the skin thickness of the hull. This

is

necessary, since the templates are

used internally during the building process.

If the hull

has been

CAD

designed, however, the full-scale templates with the proper reduction

may

be plotted directly, provided a sufficiently large plotter Plate expansions may also be obtained from the

is

available.

CAD

simplifying the production of steel and aluminium hulls.

system,

PRELIMINARY CONSIDERATIONS Before

we must have

actually starting the design work,

picture

of the

what

purpose:

yacht's

are

the

requirements,

and objectives of the design? In this chapter we the considerations that form the starting point of the design. limitations

list

Choice of boat-type

a clear

Regardless

of

whether

the

client

an

is

individual

owner

will

or

a

have definite ideas as to the type of boat he wants. Most people have a particular yacht in mind which, with changes in dimensions, style, arrangement, rig or hull form, satisfies boatbuilding firm, he

their

demands.

will

These

preferences

are

often

by

modified

other

considerations, such as local conditions, economic considerations and the intended use. Personal opinion often governs the choice of type to

such an extent

that

the

more

become of secondary concern, Intended use

if

logical

and

scientific

arguments may

not set aside entirely.

The intended use of the yacht is a matter that comes first on the list of considerations. The first distinction is that between racing and cruising. For the racer we must naturally decide to which rule the boat should be designed, and in which class it will be racing. This gives us a good starting point regarding the size of boat and crew, rig size and type, by comparing it with existing successful designs. Having established the type and size of boat, we can proceed with the design process described in the following chapters, making adjustments so as to conform to the rule we are following. For the cruiser the primary requirement influencing the type of design to adopt regarding hull, deck, accommodation and rig, is the yacht's intended use in broad terms

open or is

ie

unlimited ocean passagemaking,

restricted offshore use, or coastal or sheltered use. Obviously,

easier to reach high standards of safety, stability

it

and performance

crew to handle the vessel. This brings us to the question of the need for compromise. The

with a big yacht, provided there

is

sufficient

requirements of speed, seaworthiness, dryness, weatherliness, ease of handling, comfort and other qualities often conflict, but the fewer the

compromises the better the design will be. We must decide at an early stage what particular qualities we desire most, or require to the greatest extent. By getting our priorities right from the start we know where compromises can be made with the least harm. Too many yachts are designed on the assumption that it is possible to achieve all of the qualities of the perfect yacht without regard to the limitations of the

chosen type and

its

intended use.

To

achieve a good design

it

is

crucial

Preliminary considerations

1

to define the intended use. weigh the requirements that these

the yacht and choose a type of yacht

When

need.

the type of yacht

whose design elements

chosen we must

is

impose on

Of course there will be that many major changes

the whole design process.

stick to

it

fulfil

that

throughout

alterations along the

way. but if we find arc necessary it will probably be best to start the design work from square one. The intended use is not only about sailing area, performance and range, but also about who is going to use the boat and under what circumstances.

a

design

intended

for

charter

the

use.

number of berths and a roomy accommodate everyone when sailing. The time at sea will be

requirement cockpit to

we take

If

will

usually be a large

most sleeping

harbour or at anchor and the be understood by novices. By contrast, an experienced owner who wishes to make extended passages with a small crev\ will have the opposite requirements. restricted,

be

will

in

handling systems must

Main dimensions

It is

generally agreed that increasing the size of the boat will produce a

better design in terms of performance

the boat might be

more

difficult to

and comfort; on the other hand

handle by a small crew. Size

is

also

linked to the intended area of use: unlimited ocean use naturally places

demands on

greater

a boat

compared with

sheltered water use.

Not

need to withstand strong winds and heavy seas, but it will also need to carry more fuel, water and stores - all of which point to only

will

it

the bigger yacht. However,

it

is

not self-evident that size

in this respect

measure would perhaps be displacement, since this describes the volume of the boat. Take two boats of similar displacement; the longer one will usually have better performance but

means

its

length; a better

carrying capabilities will be roughly the same as for the shorter one.

The requirements of on

size,

engine, rig and deck equipment depend largely

weight and length as well as beam.

To

reach a certain speed

under power with a limited power source the length weight ratio vital

importance, while the stability required to carry enough

more dependent on

the

beam and

weight. In this context

it

is

is

of

sail

is

noticeable

power of 3. while the increases with size to the power of 4. So scaling a boat up does not produce a design compatible with good performance

that the heeling forces increase with size to the stability

linearly

and stability. The changes

in

proportions with increasing size have been calculated

from Lq^^ = 7m to Lq^^ = 19m by H Barkla of the University of St Andrews, Scotland (see Fig 2.1). As we can clearly see. different dimensions and parameters scale differently with length. The scaling factors shown in the figure produce boats of similar behaviour regarding performance and 'feel" when scaled in either direction from a base model. The 'L' in Fig 2.1 refers to the length relation between the base model and the derivative. For example, if we increase the length of the boat by 50%, ie 1.5 times L. the beam, depth and freeboard will be increased by 1.5"'' = 1.33 times the original value for an allometric series of yachts

M

to

keep the boat within the same performance-family.

Principles ot Yacht Design

12 Fig 2.1 Proportions versus

PRIMARY RELATIONS - Indapendonf of basic modal

size (B,ukbl

Scale Factor

Assumad:

L

araa

l_

Sail

i.es

Beam, depth, freeboard Keel

&

l_0

70

1^0.70

rudder span, chord, thickness

Derived: 1.40

areas — section

l_

- wetted -

— keel —

—

lateral

1.70

hull

l_

&

^1.40

rudder

1.70

hull

— kaal

l_

&

^ 1.40

rudder

volumes — hull

l_2.40

- keel

l_2.10

ratios

- Lwl/^^'^^ («x-keel) - SA/^^/^ (ex-keel)

l_0.20 l_0

Second moments of watarplane —

—

1^3.

lateral

longitudinal

SECONDARY RELATIONS - dependent

to

some

25 10

l_3.70

extent on basic

model

Total

volume of displacement

l_2.jg

Total

wattad area

l_

Sail area

/

1.6 J

0.22

wetted area

l_

Sail area /^^'^^ (tncl-keel)

l_0.26

Distance of VCB below

l_0.64

Lt/yi_

BM GM

l_0.72

0.45 l_

moment

l_2.B3

Separation of centres of effort (lead)

l_o.a6

Initial

righting

Fig 2.2 Preliminary

dimensionless ratios

Design

LoA

YD-40

12.

40- Yacht on Market

LoA LwL

Bmax T V

SA

SW DLR LDR SDR

DSF

LwL

Bmax

a5

10.02

3.71

2.07

12.27

9.88

3.93

2.15

= Length

overall [m] waterline

T

SA

DLR

LDR

SDR

SA/SW DSF

7.3

75.4

205

5.2

20.0

2.79

70

7.8

78.4

229

5.0

19.9

2.88

70

V

[m] = Maximum beam [m] = Maximum depth from waterline [m] •= Light load volume displacement [m^] = Nominal sail area, main + 1 00% fore triangle [m 2] = Wetted area of hull and appendages [m^] = Displacement Length Ratio [28300-1/ L^i^ ] = Slendarness Ratio [Lwl/i'^^ ] = Sail area Displacement Ratio [SA^^-y^^/^ ] = Dynamic Stability Factor, described In Chapter 4 — Length

in

Preliminary considerations

A

very good

way of

13

establishing dimensions for the hull

and

rig

of a

new design before there are any drawings or calculations, is to decide on some vital dimensionless ratios that can be checked against known designs. Chapter 5 deals in more detail with this, and explains what

YD

factors are involved. Fig 2.2 shows, for the

40. the values of the

from first estimates of the main dimensions. Comparison is made with an existing yacht of the same size. Once we are satisfied with the numbers we have a good starting point for the design. ratios derived

No

one

is

interested

having a boat

in

built

more expensively than

Taking only that prerequisite into account, the obvious answer seems to be to build the boat as small as possible, since building costs relate directly to size (or rather weight). However, in going for light weight we might be forced to use exotic materials and advanced building methods which in turn might increase the cost compared with using heavier materials and a more conventional building technique. At the other end of the scale are the heavy building methods needed for steel and ferrocement. for instance, which certainly provide cheap materials but produce heavy boats that need much power (sail and engine) to drive them, and robust deck equipment for handling them, all of which cost money. necessary.

A common

when designing

pitfall

a boat in the smaller size range to

down, is to miniaturize. Everything might look well on paper, but in practice the design may not work because the human being cannot be scaled down. Moreover, trying to squeeze too much into a small volume would not produce a costkeep

costs

proportioned

found

effective design, not only because everything

would be there, but due to lack of space. The hull form

also because

it

in

a bigger yacht

would be so much harder

to

fit

in.

hydrodynamic and hydrostatic requirements, while the form of the deck is more open to the whim of the designer, to fashions and trends, and to what is

'character" the design

and

sharp

turning

construction) the corners.

construction

is

basically

derived

intended to radiate.

points

is

much more

from

A

deck with

difficult

to

lots

of angles

build

(FRP

compared with one with smooth areas and large radii in Here we have a choice that most definitely will affect the Designing decks

cost.

multiple moulds to

make

or

parts

of decks

mould-release possible,

will

that

also

require

make

the

We

have to be quite sure that the benefits of such a design outweigh the increased cost that goes along with it. To some extent the same reasoning can be applied to the accommodation. Obviously, a flat panel attached to another at a square angle is much cheaper to produce than a curved one attached at an

costs higher.

oblique angle.

On

the other hand,

rounded panels and oblique angles

can be used to achieve better space utilization which, in the end, will make the boat so much better that the increased building costs can be justified. Another way of increasing usable space is to let areas and compartments overlap one another. It is not always necessary to have

Principles of Yacht Design

14

iho

lull

toilet

cabin licighl over

llic

full

length of the boat. I'or example a

can be under a cockpit seat with the

rest

the superstructure. Instead of thinking of the

dimensional jigsaw puzzle,

it

dimensional puzzle so as to

A word

YD-40

accommodation

might be

fruitful to think

utilize the

space available

of in

it

as a two-

as a three-

the best way.

much might raise way might be to make the

of warning though: complicating things too

the cost out of

Fig 2.3 Preliminjry Liyout

of the head area under

proportion, so a better

all

whole boat bigger and simpler in order to fulfil the requirements. The amount of standard equipment also plays an important role in the overall cost of the boat, regardless of whether she is light or heavy. By this we mean whether to have an airconditioner/heater, running hot and cold water, a watermaker, a freezer/refrigerator, electric winches, full electronics with radar, a chartplotter and auto pilot, self furling - sails and so on. All these items can almost equal the cost of the rest of the boat.

Main Accommodcifion Areas Passagm s immping

Harbour

Soclalliln

ar»a

ar»a

\

ar»a

s lumping

Gal »X aroa noar It.

pitch contra, but wall, off companlonway with two good soa borths and lockor

Aft cabin

\ \ \

spaco.x^

I

I I

I

Saloon with fixmd tablo jt sattaas long onough to bm usma as sma — ^•'^''^ / Doublo borth and lockmr ^P'^'^* In for* cabin, / b» usad In harbour \

\

/to \

Forapaak 'with bulkhaad

collision to

Good cockpit lockar spaca Haad

accommodation

part of tha boat Mast position crucial to

saloon lay out

pitch cantra with spaca for stall

Dackhousa ovar

In

shov/ar

Sc

wat gaar

Nav station with full siza chart tabia and good communication vflth

tha cockpit

haadroom araas

full

Preliminary considerations

15

Checklist of considerations

To summarize the above considerations the following 1

Define the intended use and

5

limits.

2 Collect information about similar boats.

3 Decide on the main dimensions and ratios. 4 Decide on the preliminary layout and

Checklist for the

we must

brief for this yacht

we

is

are

now

first

approximation of weights and

form parameters. 6 Check against 3 and correct if necessary. 7 Produce a preliminary design to work

ready to lay

decide on a specific one, and

in this

down

To make that YD-40. The design

a preliminary design.

book we

will

use the

as follows:

An ocean-going

yacht, with long-term

accommodation

for four, to

be capable of

being handled by a crew of two. The performance shall be good enough for it to be successfully entered in club level racing. The ocean-going requirement demands carrying capabilities for water and stores for up to a month without reprovisioning. 2 See Fig 2.2 for comparison with a similar yacht.

3

a

YD-40

Having considered these points

1

Make

can be applied:

from.

exterior.

meaningful

list

The main dimensions and

ratios are also

derived from the comparison

4 Figure 2.3 (see opposite)

is

a

in Fig 2.2.

first

sketch of

the yacht showing the principal areas of

accommodation. Basically they are designed around the assumption that they will be functional under way with a crew of four. This means four good sea berths, two in the aft cabin and two in the saloon, a galley, head and navigation area in the pitch centre of the boat. The saloon shall be big enough to accommodate the occasional racing crew, and other social entertaining in harbour, and the forward cabin shall be used as an in-harbour master cabin. The accommodation shall not be pressed into the ends of the boat to enhance performance, and judged on a length-only basis this will reduce the building costs.

Having established the main dimensions, type of boat and area of use we can proceed with the more precise design work. Comparing with Fig 2.2 we can see that the design brief is met quite well, with the main dimensions and their connected ratios chosen.

HULL GEOMETRY The

hull of a yacht is a complex three-dimensional shape, which cannot be defined by any simple mathematical expression. Gross features of the hull can be described by dimensional quantities such as length, beam and draft, or non-dimensional ones like prismatic coefficient or slenderness (length/displacement) ratio. For an accurate definition of the hull the traditional lines drawing is still a common tool, although most professional yacht designers now take advantage of the rapid developments in CAD introduced in Chapter 1. In this chapter we start by defining a number of quantities,

frequently

referred

to

in

yachting

features of the yacht. Thereafter, traditional

drawing

recommend

a certain

drawings and, in a

Definitions

finally,

CAD

modern

The

list

used

in defining a

we

literature, will

describing

the

general

explain the principles of the

and the tools required to produce it. We work plan for the accurate production of the we show briefly how the hull lines are generated

program.

of definitions below includes the basic geometrical quantities yacht

hull.

Many more

quantities are used in general

ship hydrodynamics, but they are not usually referred to in the yachting

A

complete list may be found in the International Towing Tank Conference (ITTC) Dictionary of Ship Hydrodynamics.

field.

Length overall (Lq^)

The maximum

length of the hull from the forwardmost point on the

stem to the extreme after end (see Fig

3.1).

According to

common

practice, spars or fittings, like bowsprits, pulpits etc are not included

and neither

is

Length of wateiline

The length of

Length between

This length

perpendiculars

(

L pp)

ships.

is

the rudder.

the designed waterline (often referred to as the

not

much used

in

yachting but

The forward perpendicular (FP)

designed waterline, while the aft

is

DWL).

quite important for

forward end of the perpendicular (AP) is the centre of the is

the

rudder stock.

Rated length

Beam (B

or By/^^J

The

most important parameter in any rating obtained by considering the fullness of the bow and more or less complex way. single

The maximum beam of

rule.

Usually L

is

stern sections in a

the hull excluding fittings, like rubbing strakes.

Hull

Geometry

17

Fig 3.1 Definitions ofttie niain dimensions.

Beam of water line

Draft

(

The maximum beam

The maximum

T)

waterhne.

The

Depth (D)

T^, is

Displaeement

draft

Could be

designed waterline.

of the

yacht

when

on

floating

the

designed

the draft of the hull without the keel (the "canoe" body).

vertical distance

(see below).

at the

D^, is

from the deepest point of the keel

without the

to the sheer line

keel.

either weight displacement

(W

or A)

i.e.

the weight of the

volume displacement (V or V ), the volume of the immersed part of the yacht. W^., A^,, V^, and V^, are the corresponding notations yacht, or

without the

Midship section

keel.

midway between the fore and aft perpendiculars. For yachts it is more common to put it midway between the fore and aft ends of the waterline. The area of the midship For

ships,

section

this

section (submerged part)

that the keel

Maximum

area section

is

(Cp)

is

denoted A^^, with an index

'c'

indicating

not included.

For yachts the maximum area section midship section.

Prismatic coefficient

located

is

Its

area

is

denoted

A^

is

usually located behind

the

(A^c)-

volume displacement and the maximum section area multiplied by the waterline length, ie Cp = V/(Ax L^O- ^^^^ value is very much influenced by the keel and in most yacht applications only the canoe body is considered: Cp^ = ^c/(^xc ^wl)- See Fig 3.2. The the fullness is representative of of the yacht. The prismatic coefficient

This

is

the ratio of the

*

"

Principles of Yacht Design

18

Hull

volume =

V.

Circumscribed cylinder = L„volume = V A^ WL X CYL

Max. area

C = p

Fig 3.2

CYL

=

L

A^

•

WL

A X

The prismatic coefficient

Max. area

= A

Circumscribed box volume - L BWL Tc V WL BOX

= ^'i

p^ ^ »

^

"0

/>^^

A/

=

5

^ O 'N O Q - N N N O rN ^!^ ^*:'^^t? fN ^ &.;,|.',v;,|

iiiin

w

/:y:::-:::-;/-':/-;'-:/''^---:;::';

ivivXv/Xy

',

fs

=

0.1 14

m

s

s/2

]

,',',",",',','.'.',',".".'.',;:::::^>^::::v:v::^^^^^^^

s/2l ^0

Ordinate No.

O

Ordinate value Yo

[ O.OOO ]

Y,/2 [ 0-7^B J

1/2

Area

= A Product

S.M.

0.5

2

0.5Yo

2Yl/2

—

[ 0.000 ] [ 1-472 ]

1

y,

/ 0.977 J

1.5

2

Y2

[ 1.217 ]

4

4Y2

[ 4.868 ]

3

Yj

[ 1.364 ]

2

2Y3

[ 2.728 ]

4

Y^

[ 1.473 ]

4

^Y*

[ 5.892 ]

5

Ys

[ 1.562 ]

1

Y5

[ 1.562 J

1.5Y,

Sum

A

nwi

mw

^

.

/'

^iirr»

A^= 2 A [A^= 1.367 n

'•**

«*-..,W.#^*«.

)

(both sides)

of products

[ 1.465 ]

[ 17.987 ]

is

Hydrostatics and Stability Fig 4.4 Calculation

35

of the

volume displacement

Curve of soctional aroas

sro

X

Xq

X2

Xj

m

[ s

=

A

Areas calculated as

:

1.000

Ordinate

x^

x^

] In

Fig 4.3

Ordinate value

hJo.

Product

S.M.

A so

[ 0.000 ]

1

A so

[ 0.000 J

1

As,

[ 0.160 ]

4

4 As J

[ 0.640 ]

2

As2

[ 0.470 ]

2

2As2

[ 0.940 ]

3

Asj

[ 0.832 ]

4

4Asj

[ 3.328 J

4

As4

[

1-1 44

]

2

2As4

[ 2.288 ]

5

Ass

[ 1-332 ]

4

4As5

[ 5.328 ]

6

As6

[ '-^^' ]

2

2As6

[ 2.682 ]

7

As7

[

156 ]

4

4As7

[ 4.624 ]

8

A SB

[ 0.805 ]

2

2Asa

[ 1.610 J

9

As9

[ 0.364 ]

4

4Asg

[ 1.456 ]

10

Asw

[ 0.000 J

1

1.

[ 0.000 ]

Asio pro'ducts

V

=

-f-

('

Sum

of products )

[ 7.632

[ ^^-5^^ ]

m^ ]

the product of the force and the distance to the axis (the lever arm).

This concept can be used for finding the centre of gravity of a body. By definition, the centre of gravity is the point where the mass of the body may be assumed concentrated. The gravitational force may be assumed acting at this point.

from an body arbitrary axis, is to add with respect to this axis. This gives a resulting moment, which must be equal to that of the concentrated mass at the centre of gravity. This method is explained in Fig 4.5. where the axis chosen is located

One way

to calculate the distance to the centre of gravity

the

moments of

the different parts of the

athwartships at the FP.

A

corresponding computation can be performed for the centre of gravity of the displaced volume of water, ie the centre of buoyancy. Let us first

compute

the

longitudinal position,

LCB,

using the same axis as

36 Fig 4.5

Principles of Yacht Design

Methods

ol tindin^

the centre of gravity

DWL Transverse

FP

axis at

m^9 g = acceleration of gravity ( ^9.81 m/s^ •-^,^,9

X— Values forward of FP and z — values below DWL

are negative.

Centre of gravity measured from FP along x—axis. "^toi^'^G

^G

'^7

*

9^,

rn^9^-t- rrijgXj-h

•1^1

tot '^G

= '"tot

=

m, + m. +

=

=

+

+

'",

m, ^ + m2 -^•' ^3 X^-H 1^ m, + /T^ /- /77j +

^1^1 ^

+

m.gx.-i-

"J "J nrij

+

.

"-',

Centre of gravity measured from

^G

...

^^2+

m^ + m^ + mj

"^3^3+ -h

...

+ ^, ^• + +

...

DWL along z—axis:

- + ^J^! + + m^ + ...

-

Each section of the hull may now be considered as contributing to the moment by an amount proportional to its area multiplied by its distance from the FP. Thus a 'curve of sectional moments" can be before.

constructed in a similar

way

to the curve of sectional areas.

under the new curve represents the

total

moment, from which

of the centre of buoyancy can be obtained as explained

in

Fig

The area

the position 4.6.

There is a simple alternative method, which is used frequently for determining the LCB. If carefully employed, this method is probably as accurate as the numerical one.

The

sectional area curve

out in a piece of cardboard and the cut out part

is

is

simply cut

balanced on the edge

Hydrostatics and Stability Fig 4.6 Calculation

37

of the

longitudinal centre ot

A^x

buoyancy of the canoe body

Curve of sectional

moments

f s = 1.000 m ] A : Areas calculated as

Ordinate No.

In

Fig

4.3

Ordinate value

Product

S.M.

Aso- ^O

[ O.OOO ]

1

A so

'0

f O.OOO ]

Asj- X,

[ O.160 J

4

4 As,

X,

[ 0.640 J

2

As2

'B

x|

[ 91.10 J

2

2 bg

xl

[ 182.2 ]

9

1=9

x|

[ 93.27 J

4

4 bg

xf

[ 373.1 J

bio-

"%

[

0°

Sum

of

r

191B 4 J1 ''^1^-4

^w x%

io

[ O.OO ]

1

.

products

'lfp=^

-(

Sum

[ 812.2

of products )

rrf

[ 1.7 J

[ 305.1 ]

1-

J

]

K4oment of Inertia around centre of floatation

[ 93.

'l= 'lfp- ^w- -;

A = watarplane area

=

X

1

m" ]

[ 22.61

distance from FP

to

m

7

centre of flotation

[ 5.674

m

]

same way as the sectional area curve and the location of the VCB can be found. However, the areas of the waterlines might not be known, since they are not normally required for other purposes. Another possibility is to cut out all sections of the hull from a piece of paper and

treated in the

glue

them together

centre of gravity for this

Water plane area

The water plane is

important

mm

body plan. The vertical paper body is the desired VCB.

just as in the

area,

ie

the area inside the designed waterline

in several respects: first, its size

immersion',

ie

position of the

determines

'the

(DWL),

weight per

the additional weight required to sink the hull a

Hydrostatics and Stability

39

Fig 4.8 Calculation of the

transverse

moment

of

inertia

Curve of cubic

boam

half

m

[ s = 1.000 b

=

half

]

beam

Ordinate No.

Ordinate value

&/ bf

[ O.OOO ]

1

[ 0.080 J

4

2

fc/

[ 0.528 ]

3

5

6/ 6/ b/

6

O

Product

S.M.

i>/

[ O.OOO ]

4

bf

[ 0.320 ]

2

2

fe/

[ 1.056 ]

[ 1.412 ]

4

4 bj

[ 5.648 ]

[ 2.527 ]

2

2

[ 5.054 J

[ 3.498 ]

4

i,/

[ 3.974 ]

2

7

6/

[ 3.767 ]

4

a

fc/

[ 2.888 ]

2

9

6/

[ 1.529 ]

4

bf 4 bf 2 bf 4 bf 2 bf 4 bf

bfg

[ 0.000 J

1

1

4

io

[ 13.992 ] [ 7.948 ] [ 15.068 ]

[5.776] [

= ^

(

Sum

V=|--

J

[ O.OOO ]

bfo

[ 60.978 ]

pro'dufts

A

6.1 16

of products )

[ 13.6 m* ]

certain distance: secondly,

its

centre of gravity

trimmed, when moving

is

located on the axis

around which the hull is on board; thirdly, the so-called moment of inertia (sometimes called the second moment of area) around a longitudinal axis determines the stability at small angles of heel; and fourthly, the moment of inertia around a transverse axis through the centre of gravity (of the area) yields the longitudinal stability,

ie

the

moment

a weight longitudinally

required to trim the hull

a certain angle.

The

calculation of the area

exactly as

shown

in

Fig

is

4.1. If the

straightforward, using Simpson's rule

area

is

denoted A^v^l

(full-scale value),

40

Principles of Yacht Design

m\ The hull, is

mm

A DWI weight of this volume, corresponding to the applied weight on the when

Ihc additional displacement

p

sinking the hull

1

Apvvi where p is the water density. thus calculated from this simple formula.

0.001

•

•


.

— ^ "^^

100

""""

' '

^ 3

5

4

^m.

V

7

6

^

( mefrfc units )

Fig 5.21

Displacement/

length against i

length/displacement ratio *

0.60 >

y/

/

0.55

t

//

//

/ /

/

/

.^

^

r

/

r

r

/ 0.50 >

Fig 5.22

// 0.35

0.30

Optimum

0.40

0.45

prismatic coefficient

result

is

The designer has to decide optimum performance. Upwind

given in Fig 5.22.

yacht shall have

its

at in

what speed his light wind the

prismatic coefficient should be 0.5 or even lower, while

more wind

the coefficient should be 0.6 or slightly higher,

the traditional heavy or

medium displacement

type.

downwind

if

the hull

is

in

of

Normally, hulls are

designed for maximum performance beating upwind in a breeze. The Froude number is then around 0.35, which gives a prismatic of 0.56.

80

Principles of Yacht Design

The

may

increase in residuary resistance,

if C'^

dilTers

from ihe oplimum,

also be obtained from the formula, in Fig 5.23 the increase

is

given

Froude numbers: 0.30, 0.35 and 0.40. These cover the upwind speed range for most yachts. It can be seen that the largest increases occur if C|, is too small and the speed is relatively high. for three different

Fig 5.23 Resistance

increase

(in

% of

displacement) due to non-

i

Incremonf of R^/^

,

[%]

optimum prismatic

1

coefficient

1

0.5

0.4

\

\

0.3

1

\

\

1

1

.

1

\

r = 0.40

\

1

0.2

1

O.I

^v ^>w

1

1

F = 0.30

. -1

1

^^^^ —

—

~"

1

^^^ ^^'''^^'

"*''**~-i

_---'^^ = 0.35

1 1

"~

_..

^^

^""""'T^ ^'^^^^

—

C

1

0.52

0.54

0.56

0.58

0.60

For lightweight hulls, which can reach the semi-planing region at Froude numbers above 0.45, the situation is more complicated. To attain high downwind speeds and surfing capabilities the aft part of the bottom has to be flat and relatively horizontal. The best solution is in fact to have a submerged transom, as on power boats, but this is hardly possible for a sailing yacht, which has to operate in a wide speed range. The low speed characteristics of this solution are not acceptable. For transom stern hulls the optimum prismatic increases to about 0.70 at Froude numbers of 1.0, due to the fact that the transom should become larger as the speed increases, but if a transom has to be avoided the requirement of a flat horizontal bottom automatically means a small prismatic. No optimum value can be derived from the high speed formula of Fig 5.19, since Cp is not even included. Neither is it possible to derive useful relations from the general hydrodynamics literature, since submerged transoms are always assumed in this speed range. In practice, the designer has to some extent to sacrifice the upwind characteristics in the low speed range and use a somewhat smaller prismatic than the optimum from Fig 5.22 to obtain better downwind performance.

lull

Centre of huoyuney

Design

81

optimum location of the centre of buoyancy. LCB. the medium to high displacement hulls. Obviously, the

Fig 5.24 gives the

Again

this

variation

means

for

is

very small over the speed range. Note that a negative sign aft of midship, and that the numbers given represent the distance is

from this section in percentage of L^l- As in the case of C^ the increase due to a non-optimum LCB has been computed and ihc result is given in

Fig 5.24

Fi2 5.25.

Optimum

location of centre of

Li

buoyancy i

-4

-

^^

-3

"~^

^ -2

-1

0.30

0.35

0.40

0.45

Fig 5.25 Resistance

increase

(in

% of

displacement) due to non-

optimum LCB

location

increment of i

F

^

=

n

0.

0.40 1

10

/

0.05

s.

f

\

/

v\

/

"^ ^^

/ >

/

r

/ Xy ^ / — — ^ — ^"v: ^ !^ •«L— **— — ^ ^ F^t*J — — 1

1

o

^

-4

^

--

-3

'

/

/

/

/ — =

-2

F = 0.35

/

/

r = 0.30

^^^ ^^^

^^.^^

LCB [%]

i^*"^"^

-1

a

82

Principles of Yacht Design

The reasons why Cp should be the speed

increases in

the

LCB moved

inereased and

when

aft

low speed range have been mentioned

A

connection with the viscous pressure resistance.

full

stern

in

increases

component, while the wave resistance is reduced, due to the fact that the thick boundary layer and possible separation makes the effective hull longer. At speeds corresponding to Froude numbers in the range 0.40 0.45 wave resistance dominates, and a full stern is better, while the opposite is true at lower speeds where the waves are small. As in the case of Cp the optimum LCB value in the high speed range depends on whether or not a submerged transom can be accepted. If so, the LCB should move aft to about 6'yii of L^^^ from the midship al a Froude number of 1.0. This is also related to the fact that the transom should increase with speed. However, if a transom cannot be accepted, the LCB automatically moves forward relative to the locations given in this

Fig 5.24, since the stern region has to be

flat.

A

problem occurs when applying the above results to hulls with an integrated keel, since the measurements were made with fin-keel type of yachts. The quantities above are for the hull alone. It is therefore necessary to make an artificial separation of the hull and keel and compute the parameters for this new hull. Len^th/heam and beam/draft ratio

The effect of made between

these parameters the

first

is

very small.

A beam

variation

three models in the Delft series, keeping

was

all

of

the above parameters constant. Naturally, this variation caused changes

both

in the

length/beam and beam/draft

ratios,

but the result showed

narrow boat (B^^/T^. = 3.0) had the smallest residuary resistance up to a Froude number of 0.375. Thereafter, the medium boat (B\v'l/T^ = 4.0) was the best. The beamiest boat (B^l/T^ = 5.35) was worse than the others in all but the highest speeds above Fn = 0.4, where it became better than the narrow one. It is possible to extract the effect of B\^[/T^. alone from the low speed formula. Since the coefficient A3 is positive an increase in this ratio that

the

should result

in

a slight increase in residuary resistance. Unfortunately,

conclusions cannot be drawn on the influence of L^^l^^wl alone, since it is not included in the low speed formula. Neither is it possible to draw

any general conclusions on this parameter alone from the high speed formula, where the parameter occurs in several terms. Often, the effect on the wetted surface, and hence the frictional resistance, is as large or larger than the effect on the residuary resistance when beam is changed. There are also other aspects on beam variations, above all the hull stability, which increases with beam to the third power. The effect on the added resistance in waves is also quite important, and a large

beam, or large

resistance

fullness in the

bow

component considerably.

region in particular, increases this

Finally, there

is

an important

effect

on the resistance due to heel, as will be seen below. The YD 40 has been designed to have its best performance upwind in a tYesh breeze, when the Froude number is about 0.35. As appears from Figs 5.22 and 5.24, the prismatic coet^ficient should then be 0.56

Hull Design

83

and the longitudinal centre of buoyancy should be located 3.5% behind midship. Both these requirements are met. The choice of other shape parameters

will

be discussed

connection with hull

in

statistics in a later

section.

Heel resistance

When

the hull heels due to the side force from the

sails,

two resistance

components develop, as explained in the first section of this chapter. The induced resistance is by far the most important one, but it will not be discussed here, since it is mainly caused by the keel and rudder, which generate the major part of the hydrodynamic sideforce. Less important

is

the heel resistance, which represents the change in upright

(viscous plus wave) resistance due to the heel angle.

One way

to obtain

component would be to compute the hull parameters for the heeled and use them in the formulae above. By comparing with the unheeled results the effect of heel could be obtained. However, if this technique were to be used, there is no need to treat the heeled resistance this

hull

as a separate Fig 5.26

Heel Resistance

component.

Heel resistance coefficient:

C^

= [6.747 (ryr) + 2.517 (B^/TJ + 3.710 (B^/TJ

[ 21.61

1

(T^

/T)]

1

o'

10-']

Heel resistance:

RH =

0.5- p-V^- S-

p

:

V

:

Density of water [1025 Boat speed [S.5 m/^sj

S

n W CH r^-

[ 99

i

Watted surface of hull

*

.-

Heel angle [rad]

=

in

^ '* 7

A

kg/m

SO

more common technique,

N J

]

uprighit position

[degj

[ 25.2

m

]

[ 13.6 deg ]

simpler, but

more approximate,

is

to use

an entirely empirical correction to the upright resistance. From the Delft series the formulae of Fig 5.26 may be obtained. It may be seen

two geometrical quantities of interest are the hull draft to the total draft, T^./T, and the beam to hull draft ratio, B^^l^T^., as mentioned above. The resistance increases with Froude number squared and is that the

proportional to the heel angle.

When computing

the heel resistance of the

YD-40

in

Fig 5.4 the heel

which should be appropriate for about 8 m/s of wind, has been taken as the Dellenbaugh angle (defined in the previous chapter). This angle is 13.6°, and yields a heel resistance of 99 N, 6.5% of the total. angle,

Note

that

the angle shall be given in

radians (degrees/ 57.3) in the

formula.

Added waves

resistance in

Chapter 4 introduced some basic safety factors when sailing in waves, and presented and discussed the solution of the equation for the rolling

Principles of Yacht Design

84

molion.

was pointed oul

ll

thai similar equations hold

lor the other

types of motion, provided the coupling between them can be neglected.

Here we shall deal with a special aspect of seakeeping, namely the added resistance caused by the waves. As pointed out in Chapter 4. the theory of seakeeping is quite complex and cannot be treated comprehensively in this book. We will explain only some fundamental concepts related to the added resistance, and give some guidelines on

how to reduce it. When a yacht moves are

the

When

coupled.

seaway, the waves impose motions of

The most important

kinds on the hull. view,

in a

all

ones, from a resistance point of

heave and pitch motions, which are usually strongly the hull heaves and pitches it generates its own wave

system, which carries energy

away

in

much

same way

the

as the

still

water wave pattern, thereby creating a resistance force.

Of some importance for a sailing yacht is which, as we have seen, creates vortices at rudder,

also the rolling molion, the

tip

of the keel and

a kind of induced resistance, similar to the one created by the

ie

when the yacht is sailing in smooth water (see Chapter following we will concentrate on heave and pitch.

tip vortices

In the

As

in the case

pitch.

When

of rolling the yacht has natural frequencies

the frequency of encounter of the waves

is

in

6).

heave and

equal to the

natural frequency of one of these motions resonance occurs, and the corresponding motion amplitude gets very large. The added resistance is particularly serious

if

resonance occurs

in pitch, since the resistance

may

then increase considerably. Ocean waves are normally considerably longer

than the yacht, and the frequency of encounter natural frequency, so resonance waters, however,

it

may

much

To move away

as far as possible

resonance, the natural frequency should be increased

of encounter Fig 5.27 Calculation of

the

mass moment of - L 'YY

is

smaller and vice versa, so practically

it

to have as high a natural frequency as possible. This will

most

important

quantity

in

connection

DWL

Mass moment of I

YY

when is

from

the frequency

always beneficial

means

that the hull

follow better the contour of the waves.

The

inertia

smaller than the

unlikely to occur offshore. In sheltered

is

happen.

is

—

ni

2

X 11

Cyradius:

+

l
if the

The more narrow wake

wind

velocity,

velocities quite well.

that

it is

be seen that at

sail

V-A)

is

much

optimum roughness

but a height of

Note

may

roughness height

also disturbs the

a double gain. Unfortunately, the

the

It

Q.5% of less,

1

the

so there

height varies with

covers most of the interesting

the apparent

wind that

is

of

interest.

Sail

and Rig Design

Drag of circular cylinders with sand

145

Fig 7.15

Drag [Z]

roughness

=

Unstimulated level (C^

1.2)

100

SO Grain size

of mast diameter

Apparent windspeed

[m/sj

10

Fig 7.16 Position of trailing

on

edge separation

s

:

n

:

with

stimulators

no stimulators

a sail with three

different masts

Ellipse

Pear

sn Delta

from measurements made by one of the plate sail with different masts, with and without roughness, was tested in a wind tunnel, and the position of the rear separation point was measured. The mast sections were the most common ones: ellipse, pear and delta. Practically no difference could be detected in the separation location for the three smooth masts, while the positive effect of the roughness was largest for the ellipse and pear masts. It can be seen in the figure that a considerable increase in the Fig

shows

7.16

results

authors and his students.

effective length of the sail test

A

is

obtained

in all cases.

The roughness

in this

was 1% of the mast diameter and was created by sand grains of

uniform

size

indicated that

glued to the front half of the mast.

much

less

disturbance

is

Later

tests

have

required. In fact, a small riblet

of the same height put at the leading edge of the mast produced the

same

effect.

Note

that

when

the sail

is

working, the stagnation point on

146

Principles of Yacht Design

mast

the

always on the windward

is

leeward side of the

sail

so

side,

has to pass the

ihc

Mow entering

even

riblel,

if

it

is

in

the

the

symmetry plane of the mast. There is no effect, however, on the flow on the windward side, so a better solution might be to put one riblel on each side of the mast, at 45°, say, on each side of the symmetry plane. Streamlining

The windage of

the mast and rig is considerable, as we will see in and all means of streamlining different components, such as 9. spreaders and shrouds, are valuable. A striking figure is that of Fig 7.17, which shows two 2-dimensional bodies with the same drag. The upper one is a streamlined foil, where most of the drag comes from friction, and the lower one is a round bar, for which pressure drag dominates. The drag coefficient for the bar is around 1.0, while it is only about 0.03 for the foil, based on the front area. The diameter of the bar thus has to be more than 30 times smaller than the foil thickness for the same drag.

Chapter

Fig 7.17 Effect of

streamlining

from wind-tunnel tests at the Davidson Laboratory in New York. Drag measurements were made for three different types of shroud: a wire, a circular rod and an elliptic rod. Fig

In

It

may

7.18

results

are

presented

be seen that the wire has the highest drag, somewhat higher than

At first sight this might seem contrary to the findings rough mast has a smaller drag than a smooth one), but the difference is that the wire has such a small Reynolds number (due to the small diameter) that the turbulent boundary layer never appears, that of the rod.

above

even

(that a

if

The

the surface ellipse

wire. This

is

is

is

rough.

outstanding with a drag that

is

so in spite of the fact that the ellipse

of attack of

19°.

considering

the

Small as fact

this

that

may

the

seem,

sails

it

%

only

was

probably

is

guide

the

longitudinal direction than the apparent wind.

It is

of that of the

tested at an angle realistic

more

flow

upwind, in

the

quite important that

the angle of attack does not get too large for the ellipse, as can be seen in

Fig 7.18(b). This diagram shows the relative increase

when small,

the angle increases from zero.

but at 20° the drag

Thereafter, the increase

is still

is

Up

to

resistance

10° the additional drag

three times larger than

faster.

in

the

is

minimum.

and Rig Design

Sail

Fig 7.18

and

147

Drag of shrouds a) Drag of wire,

stays

Drag per metre

rod and proflla

[N/mJ 1

6

1

\

'

13

mm

Rod

mm

X 6

mm

.

7^13

5

-

4

-

3

-

2

-

mm

Wire

1

/

//

-

1

//

/

^ 10

b) Imporfanca of angle of attack

26

-^

1

a

Ellipse

idegJ

20

Drag a^O Drag a — O (

\

6

-

S

-

4

-

3

-

2

-

1

1

1

_^

/ f

\

1

20

10

A

practical

sail

and

model

rig

aerodynamics

for

A by

model

G

for the

aerodynamics of

Hazen. This model

is

sailing yachts

used, with

was presented

minor modifications,

Velocity Prediction Programs (VPPs), for instance in the system. later

We

will describe the original

JO

model

first

IMS

in in

1980

many

handicap

and then introduce the

improvements.

model the

and viscous drag of each sail are prescribed as functions of the apparent wind angle. The corresponding coefficients are given in Table 7.1. Only five angles are given in the original model: 27°. 50°. 80°. 100° and 180°. Interpolation between these angles is supposed to be done using spline functions. Manual fairing, for instance In Hazen's

lift

Principles of Yacht Design

148

Area Main:

Jib: A^

Sail

=

A,^

0.5

MIzzen: A^

sheer

-PF

=

1.15 -SL-

= 0.5-PY-EY

Mizzen staysail: A^^

Foretriangle:

\

Nominal area

CE^ = 0.39 P + BAD

= 0.5-J 1^ + J^ -LPG

Spinnaker: A^

area and

height of centre of effort above

Centre of effort

A

=

=

0.5

0.5 YSD (YSMC + YSF

•

I

•

CE,

= 0.39I

CE^

= 0.59-I

CE^^

= 0.39-PY -hBADY

CE^ = 0.39PY + BADY

J

~ ^'''^m'^'^y

Lift

^ _ ^L>^-\-^^U-^J-''=LS^S-^^LY-\-'^LYS^YS

VIscous/parasltIc drag

C

Induced drag

%, = '=t-( ^rhAR-'o-oo^)

=

close hauled:

AR _

other courses:

AR = W-

(EHM + FA)) N

(1. 1

^

•

EHM N

DO

and topsldes Total

Flattening: Multiply

Multiply

^

^2 (BMAX

a) + (EHM

I

EMDC)

N

CD = CDP -hCDt +cDO

drag

Reefing: Multiply

_

Q

Drag of mast

C by

flat

C and C

factor

F

by reef factor R squared

height of CE by R

Standard lOR notation:

P E

Mainsail hoist Foot of mainsail I : Height of foretriangle J : Base of foretriangle LPG : Perpendicular of longest SL : Spinnaker leech length PY : Mizzen hoist EY : Foot of mizzen

Mizzen staysail depth Mizzen staysail mid-glrth YSF : Mizzen staysail foot BMAX : Max beam of yacht FA : Average freeboard EHM : Mast height above sheer EMDC : Average mast diameter BAD : Height of main boom above sheer BADY : Height of mizzen boom above sheer

YSD

:

:

YSMG

:

fib

:

Newer

additions: battens: Increase Blanketing and fractional rig Full length

Fig 7.1 9

Hazen's model

for rig

of main by 15% for angles up to 60 degrees exposed mast correction, see paper by C.L Poor on IMS.

lift

and sail aerodynamics

Sail

and Rig Design

149

using physical splines, is

is

also possible of course, but linear interpolation

too approximate. Coefficients are given for five

mizzen

To

staysail.

main,

sails:

obtain the total

jib,

spinnaker, mizzen and

or viscous drag (sometimes called

lift

P)

the parasitic drag, which explains the index

the area of each sail

be multiplied by the corresponding coefficient and final coefficient is

sum of

the foretriangle,

triangular,

given.

ie

There

the roach

no

is

of the mainsail

is

which

sail area,

areas. All areas are

the

is

computed

as

neglected. In Fig 7.19 the relevant equations are

explicit interaction

by the mizzen

quite crude, but

Table 7.1

main and mizzen

to

is

between the

sails,

taken

account

into

but the blanketing in

the

mizzen

view of the previous discussion on interaction the method

coefficients. In is

obtained by dividing by a nominal

is

added. The

sails

all

it

has proved to be useful nevertheless.

(a)

Sail coefficients,

Angle

Main

27 50 80 100 180

1.5

lift

Spinnaker

Mizzen

Mizz. stays

1.5

0.0

1.3

0.0

1.5

0.5

1.5

1.4

0.75

0.95

0.3

1.0

1.0

1.0

0.85

0.0

0.85

0.8

0.8

0.0

0.0

0.0

0.0

0.0

Spinnaker

Mizzen

Mizz. stays

jib

Table 7.1 (b) Sail coefficients,

Angle

27 50 80 100 180

viscous drag

Main

lib

0.02

0.02

0.0

0.02

0.0

0.15

0.25

0.25

0.15

0.1

0.8

0.15

0.9

0.75

0.75

1.0

0.0

1.2

1.0

1.0

0.9

0.0

0.66

0.8

0.0

The induced drag, which is more important than the viscous drag for upwind sailing, is computed from the simple wing theory presented in Chapter 6, Fig 6.5 in particular. The induced drag coefficient is thus proportional

to

proportional

to

the the

square aspect

of

ratio.

the In

lift

the

coefficient,

present

and

method

nominal sail plan is considered when computing the aspect the induced drag is computed for all the sails together.

inversely

the

entire

ratio,

and

1

so

Design

Princ i[)les of Yacht

The

aspect ratio of a wing was defined

divided by the average chord. This Since the projected area the aspect ratio

may

is

may

in

Chapter 6 as the span

be expressed

equal to the span times the average chord,

be defined also as the span squared divided by the

area. In the present model this definition

is

used.

However, due

mirror effect of the water surface the effective span of the height of the masthead above the water,

When

hauled.

the jib

is

if

to

taken to be

the yacht

is

some 10%

1

close-

eased and the gap to the deck opens up, only

is

the mast height above deck level should be considered,

height

another way.

in

and

1

\0"Ai

of this

used in the aspect ratio definition (see Fig 7.19).

is

Hazen argues

some of

that

the viscous drag, originating from the

separation on the leeward side of the

sail,

is

proportional to the

lift

he introduces an addition to the induced drag to

squared as

well, so

account for

this effect.

It

appears as a constant, 0.005,

in the

expression

for the induced drag.

model the drag of mast and topsides are included

In this

frontal area of the topsides

maximum beam,

to be 1.13.

The

taken as the average freeboard times the

computed as the mean mast height above deck. The drag coefficient is In Chapter 9 we will discuss this drag component

while that

diameter times the

assumed in more

is

as well.

of the mast

is

drag is found as the sum of the viscous, induced and mast/topsides components. The height of the centre of effort of each individual sail is given in detail.

The

total

Fig 7.19. For the main, mizzen and mizzen staysail

it

39% of the at 39% and

and spinnaker it is above the sheer

luff length 59'Mi

above the boom. For the

jib

is

taken to be at

of the fore triangle height, respectively,

line.

computed for the YD-40 are presented in Fig 7.20 for apparent wind angles from 0° to 180°. The curves were obtained from the tabulated values above, so only five points were computed on Sail coefficients

each curve. Splines were therefore used to find the intermediate points. As is common practice, the curves have been drawn horizontal below 27°.

Angles smaller than about 20°

force then

An

becomes too

not be reached, since the driving

small.

feature

interesting

will

of

the

model

sail

considering reefing and flattening of the actions

is

quite

different.

Reefing

defines the reduction in sail height.

The new height of

R

is

the centre of effort

new area

sails.

The

specified

is

equal to is

the

is

possibility

effect

of these two

by a factor 1

R

which

for the unreefed

thus obtained as

of

R

sail.

times the

found by multiplying by R-. This means that both lift and drag (excluding mast/topsides) are reduced with R-, while the major part of the heeling arm is reduced with R. The flattening factor F specifies the reduction in lift due to the for the normal flattening of the sails. This factor, which is equal to original height, while the

is

1

sail,

cannot be directly related to the

sail

geometry, but the smaller the

camber the smaller the factor. Note that F has no effect on the heeling arm, and that it has different effects on the lift and drag. Since the lift is

proportional to F, the induced drag

is

proportional to F-. This

and Rig Design

Sail

151

Forcm coafficiant I

i

2.0

Total

drag

1.0

Apparent

-^ wind angle

30

Main: A^

Jib: A^

=

=

0.5-15.1 -4.7

=

Foretrlangle: A^

1

=

.1 5 -1

0.5

6.6 4.3

-1

6.9 -4.3

= 56.2

= 82.0

=

36.3

N = 36.3 + 35.5 = 71.8

, u I ^ AR AD hiauled: close

Aspect

ratio,

other courses:

Fig 7.20 Sail coefficients

[dog]

sail area: A.,

t, ratio,

n Drag ofX

180

150

= 35.5

A Aspect J.

120

0.5-Jl6.S(^ + 4.S^-6.45

Spinnaker: A

Nominal

90

60

u II hull

=

AR =

(1»

1

-(16.9 + 1.30)) ' "

^^'I'/f'^^

^ mast: — r' 111 (3.78 and CDO = 1.13

- YD-40

t.

_ 5.58 ^a = I-

.,

=4.81

-1 .30)

+

71.8

(1

6.9 -0.173)

— n = O.Ilor 23

152

Principles of Yacht Design

means

that flattening reduces drag

rotates forwards.

It is

more than

lift,

ic

the resulting force

therefore better to flatten the sails before reefing,

most VPPs optimum values of R and F are conditions, thereby providing information on the best sail

as pointed out above. In

found for

all

setting.

The

model are the lift and drag components. To be useful for predictions the components parallel to. and at right angles to, the direction of motion arc required. Fig 7.21 explains how lift and drag can be converted to driving force and side force. Another geometrical transformation has to be made to obtain forces for the heeled condition. As has been seen above, no account has been taken of the effects of heel. This is done separately, in a somewhat forces provided by the

sail

unusual

way.

Rather

than

modifying

the

coefficients,

all

apparent

windspeed and direction are computed in a plane that heels with the yacht. This can be done quite easily, as shown in Fig 7.22. The component of the apparent velocity along the hull is unchanged by heel, while

the

component

at

cosine of the heel angle.

right

For

angles

thereto

simplicity,

is

leeway

proportional is

the

to

neglected in

this

computation, so the two directions to consider are along, and at right angles to, the direction of motion. Since the original presentation of this aerodynamic model, full-length

become popular. This is now accounted for by increasing by \5°A) for upwind sailing. Blanketing functions have been

battens have the

lift

introduced, as well as a correction for fractional the mainsail

is

now computed more

Fig 7.21 Relation between aerodynamic force components

exactly.

rigs. Finally,

By using

the size of

the chord length

Resulting force

Side force \Llft

(L)

Apparent wind direction

^

Direction of

Driving force

(^r)

=

L- cos(p) + D

sln(p)

A^= L- sin(fi) - D

cos(p)

A^

motion

Sail

V--

153

VA We

velocity (see Fig 5.2)

Effective apparent wind velocity

A We

^AW ^AWe i

Apparent wind

and Rig Design

'

:

'

''2

Apparent wind angle (see Fig 5.2) Effective apparent wind angle

^^

Heel angle

Apparent wind velocity along direction of motion ^^- Apparent wind velocity at right

^^

»^;--

angles

to

mast and

^^^

^/^

of motion

direction

^AWa

\

""l

=''

-'''aw-^''^(^aw)

""i

^2^''aW-''"(^AW^

"^AWa

^AW.

=

/ of the local chord at the waterline and at the tip of the keel by a straight line, and finding the point at 45% of the simplification for

draft

on

this line.

The procedure

The obvious disadvantage of

is

shown

in

Fig

the proposed

be used only for fm-keel yachts. In principle,

8.2.

method it

is

that

it

should

could be tried also for

long keels considering the whole lateral plane as a wing, but we lack experience of how to relate the CLR thus obtained to the centre of effort

of the

approach.

sails,

For long

and keels

do not want to propose only feasible method is to use

therefore the

this

the

Principles of Yacht Design

160

CLR

geometric

and

relate this empirically lo the sail plan.

standard rule of thumb used for centuries and there

This

is

liic

considerable

is

experience available.

Centre of effort of the

When

sails

completely separated. The centre of effort (or CE, as

wind

the

denoted)

is

is

at

90° angle of attack to a

sail

the flow behind it

then at the geometric centre of gravity of the

it

is

normally

is

sail.

This

is

what happens on a run. For other courses the angle of attack is usually considerably smaller and the CE further forward. As pointed out above, this centre is at the 25"A> chord for a plane wing of large aspect ratio. Now, the sail is not a plane, so even if it works like a wing at

CE

smaller angles of attack, the

not normally be located that far

will

forward. Fig 8.3

CE moves

shows how the

different sail cambers. This

seen

that the flattest sail

30% 37%

of the chord

is

the

for a sail of aspect ratio 5.0.

is

for the full sail with the

camber

1/7.

A

has

Fig 8.3 Centre of effort for

20 30 40 50 60

ro

varying angles of

be required for the

1

1

1

1

1

1

1

It

CE

may at

be

about

moved back

to

flat

to a full sail.

latter.

80 90

70

1

its

for

practical implication of this

the change in balance caused by changing from a will

of attack

angle

with a camber ratio of 1/27 has

at small angles, while this point

More weather helm

sails at

with

1

100 1

^

^

^

attack (Marchuj)

10

^V

20

1/27 /

50

1/13.5^

X

\

:

Distance from leading edge % of chord

In

40 li

SO

1 60

I 70

1

BO

I

90 '

Angle of incidence a [deg]

normally a considerCE (corresponding to 50'M) of the principle, it should be possible to plan based on, for example, 35'!/() of

Another implication of Fig 8.3 is able distance between the geometric chord) and the aerodynamic CE. In determine a centre of the total the chord, but this approach

sail is

that there

is

not normally used. Instead, only the

employed. Fig 8.4 shows how this is found for a sloop rig. The centre for each sail is found first, as the intersection between straight lines from two corners to the mid-point of the opposite side. The fore and main triangles are used in this method. geometric centre

Having found

is

the individual centres they are connected by a straight

Balance

161

Fig 8.4 Definition ot lead

line,

and the

shown

in

total

CE

is

obtained as a point on the

line,

located as

50% of its area The common centre

the figure. If the yacht has a mizzen, only

should be counted

(cf the

rudder efficiency above).

main and jib then has to be found as shown in the figure, and then the main plus jib area at this point is combined with the reduced mizzen area at the mizzen CE, in the same way. for the

162

Principles of Yacht Design

Lead

obvious from the above discussion that the positioning of the sail plan relative to the underwater body is too complex to be handled entirely theoretically. Regardless of which method is used for finding CE It

is

and

CLR

yacht

is

their relative location

has to be based on experience,

to be as well balanced as possible

under

all

conditions. In

if

the

all

the

methods used CE is in front of CLR, and the horizontal distance between them is called 'lead' (see Fig 8.4). The amount of lead depends, first, on which method is used for finding CLR and secondly on the type of yacht under consideration. In principle the following

• A

large

beam. The beamy

thereby creating a

moment

hull

to

•

is

front of, the

this

of the

CE

larger for a high sail.

larger

displacement to leeward of the CE.

The

chord and

The leeward displacement

stability.

yachts.

25%

hull the longer the keel.

A low

We recommend

heel,

windward.

large aspect ratio of the sails.

with heel angle

more asymmetric under

gets

• A long keel. The real CLR is at, or in moves more and more forwards on the • A

will increase the lead:

Hulls with low stability obviously heel

the geometric

method for finding the L^^ should then be

lead, in percentage of

more and cause a

CLR

of long keel

as follows:

• Masthead sloops: 12-16% • Sloops with

a fractional rig:

10-14%

• Ketches: 11-15

For

extended keel method proposed here (Fig 8.2) should be used. The following leads are then recommended: fin-keel yachts the

• Masthead sloops: • Sloops with a

Rudder balance

5-9%

fractional rig:

3-7%

Since the yacht should have a certain weather helm,

tiresome to steer balanced.

it

for long periods of time

The moment on

if

the rudder stock

it

the rudder is

could be quite is

not properly

equal to the side force

developed, multiplied by the distance between the centre of the stock

and the centre of pressure (see Fig 8.5). The position of the centre of pressure may be obtained from Fig 8.6 for the actual aspect ratio. Note

Balance Fig 8.5

163

Rudder bdlance

Centre of pressure

Fig 8.6 Position

,.^J

'44

of centre

of pressure for plane

c

wings of varying aspect

n

ratio

0.4

0.3

0.2

-

O.I

-

AR

X

=

C =

that for a rudder ratio

is

Distance from leading edge to centre of pressure Ctiord length

hung below the bottom of

the figure that the centre of pressure

when It

(ie

moves towards

6). It is

seen in

the leading edge

the aspect ratio goes to zero. is

has

will

the hull the effective aspect

twice the geometric one (as explained in Chapter

of the utmost importance that the rudder its

is

not over-balanced

centre of pressure forward of the rudder stock centre), since

then become unstable.

A

centre of the stock. This will

without tiring the helmsman.

mm

it

behind the give a good feeling for the rudder force, suitable location

is

50

PROPELLER AND ENGINE most

Since

today have auxiliary power,

sailing yachts

may

under different circumstances. There having an engine

in

crowded, and

difficult to

is

it

a

sailing

some harbours

Secondly,

sailing conditions

if

yacht.

it

is

important

first

propeller

be a life-saver under

important,

three

since

only

however, that the

reasons

for

yacht harbours are often sail in

the limited space

are not perfect, if

many

cruising skippers

they are short of time. Thirdly, the

critical

conditions in rough weather.

not put any major demands on

case does

design,

be

not even permitted for safety reasons.

prefer to use the engine, particularly

may

First,

manoeuvre under

available. In

The

is

consider the design of the propeller and the power required

to

engine

it

the

engine-

power is required. It is propeller works reasonably well when

very

limited

going astern. In the second case, speed is an important factor, while in the third case enough thrust should be developed to escape from dangerous situations even against strong winds and heavy seas. These

two

latter

important

cases to

put

find

different

a

good

demands on the propeller, and it is compromise to achieve a reasonable

Perhaps the most important performance in both situations. requirement is that the propeller allows the engine to work close to its optimum under severe weather conditions. In the first part of this chapter we will consider the total resistance of the yacht based on our discussion in Chapter 5. This will serve as a basis for the propeller design in calm weather, while for the rough weather case we will also introduce the added resistance in waves, and the windage from the above-water part of the yacht. Having found the

two conditions we will show how the optimum propeller and the required power may be obtained under each condition. The final choice of the propeller has to be a compromise between the two requirements, and we must also consider what is available from manufacturers, both as to the propeller and the engine. combination we will investigate its After selecting a suitable performance. Finally, we will discuss the added resistance due to the resistance under the

propeller It

will

fine

when

sailing.

should be pointed out that the calculations

in the

be more approximate than those of Chapters 5 and 6, tuning of the yacht and appendages was discussed.

suitable propeller/engine combination this accuracy is

also very difficult to obtain, since

not

present chapter

known

with great accuracy.

many

is

in

To

which the obtain a

not needed, and

it

of the influencing factors are

Propeller and Engine in calm and rough weather

Resistance

The

was discussed extensively

resistance

particular).

165

Since

we

are

forget about the heel

we can

fouled

water

now

in

interested

and induced

in

resistance,

Chapter

5 (see

in

the

upright case

we can

and

if

the hull

not too

also forget about the roughness drag.

What

then the friction and the residuary resistance.

is

Fig 5.4

is

is left in

How

calm

the friction

computed was explained in detail in Fig 5.8 and the residuary was presented in Figs 5.18 and 5.19. However, the formulae of the latter figures are quite complex and we could do with a more approximate estimate for the present case. As was pointed out in is

resistance calculation

Chapter

5,

more or

the residuary resistance, in percentage of the displacement,

is

same for all yachts at a given relative speed (Froude number), and we have plotted this approximate relation in Fig 9.1. From Figs 5.8 and 9.1 the reader can thus obtain an estimate of the less the

resistance in calm weather. Fig 9.1 Estimation of

residuary resistance

\

g.A

0.06

0.05

1

0.04

/

/

g- A

= ''r

/ /

0.03

gr.A

J

0.02

/ 0.01

^

a.

0.2

1

^ /y 0.3

/ r

0.4

0.5

rn

rough weather we also have the added resistance in waves (mentioned in Chapter 5), and the windage (discussed in Chapter 7). Let In

us start with the

latter.

Fig 9.2 gives the appropriate formulae for calculating the windage of the hull, mast and rig separately. In principle they have already been but they are repeated here for clarity and some missing coefficients are also included. The frontal area of the hull and superstructure may be taken simply as the maximum beam times the given in Chapter

7,

freeboard forward, and the drag coefficient is assumed to be 0.5. Often, somewhat higher values are used, but considering the fact that the

windspeed at the level of the hull is significantly smaller than at 10 m height, where observations are made, this should be accurate enough.

Principles of Yacht Design

166

WIndaga of

hull

^w

"ah

= if"^-

V

Apparont windspoed [m/s]

:

C

^AH

^r

Wind resistance coefficient

:

of

BMAX

:

(^0.5)

tiull

beam

f^ax

m]

[3.71 "

-'

Freeboard forward [1.39

/^:

Windage of mast ''am

m]

:

= ip-'f-^AM- M

M

AM

Wind resistance coefficient

M

Average mast tfilckness [

of

L,^

:

M

mast

('

~

t^ast length

Windage of

rig

I.OJ O.

139

m]

m]

[16.9

;

y~RAR = -!-p ±o.v'. 2^ o C ^AR .

•

t

R

Wind resistance coefficient ''ar

of rig

r~

1-2)

Thicltness of stays

[0.00 8 and 0.01

and shrouds

m]

Length of stays and shrouds [76.7 and 23.9 m]

(Add

^p-'*

f^''

different lengths

and

thickn esses)

"a

Fig 9.2 Estimation

windage

of

- "ah "^

"am'^ "ar

For the mast the tYontal area is taken as the mean thickness times the height, and the drag coefficient is set to 1.0, somewhat lower than the undisturbed

value

of

1.2

used

for

the

stays.

This

is

reasonable,

from spinnaker halyards etc. which act as turbulence stimulators. The drag of stays and shrouds may have to be added over components with different diameters. Geometrical values for the YD^O are given within square brackets, as usual, but no drag values are given, since the windspeed will vary in the example below.

considering disturbances

Propeller and Engine

The most

quantity to estimate

difficult

waves. In Fig 5.4

it

167

was assumed

to be

is

the

10% of

added resistance

the

sum of

in

the other

components, which may be reasonable for the conditions in question. However, now we will have to consider much worse conditions for the rough weather case. We will make use of the added resistance curves of Fig 5.30 computed by Prof Gerritsma et al. These were obtained for 10 m LwL yachts at a Froude number of 0.35 and a wave angle of 135° measured between the directions of motion of the waves and the yacht. The waves were thus 45° from head seas. To make use of the results some assumptions must be made. First, a dimensionless resistance is obtained by dividing by the weight force (weight displacement times acceleration of gravity). This can be done for each curve of Fig 5.30, since the length/displacement ratio is known, as well as the length (10 m). If the waves and yacht were geometrically scaled, and the Froude number was the same at two scales, the dimensionless resistance could be used for

all scales.

comparatively higher,

This ie

is

not quite true, since the shorter waves are

steeper,

but

if

we

restrict

the discussion to

with an L^.^ between 5 and 15 m we can adopt this approximation for the present purposes. The second approximation is related to the Froude number. Although 0.35 corresponds to a reasonable speed by engine, we do not know whether we will obtain that speed exactly. However, we are only yachts

interested in the

maximum

value of the added resistance,

the peaks of

ie

Fig 5.30, and these are likely to be about the same for other speeds (although they will be obtained at different wave periods). Finally,

head seas

we assume that the maximum added as in the computed 135° seas. This

resistance is

is

the

same

in

reasonable, since the

between roll and pitch is not considered in the which calculations, take into account only heave and pitch. It should be mentioned that if the computation is to be carried out for other waves than those of Fig 5.31, a good approximation is obtained by multiplying the values presented in Fig 9.3 by the square of the ratio between the actual wave height and the present one. The specification of the waves is the most uncertain part of this computation. The waves of possible

coupling

Fig 5.31 are typical for unsheltered waters off the coast

in

many

sailing

areas of interest. However, on the oceans the waves are longer, and in certain other cases (such as in a shallow area or a

narrow passage with

waves could be considerably steeper. The result of the above discussion is shown in Fig maximum added resistance in dimensionless form head

seas), the

9.3. is

The estimated plotted

versus

may be used for yachts of different the YD-40 are included, and it can

length/displacement ratio. This figure

and slenderness. Numbers for be seen that the maximum added resistance for this hull is 730 N. This value has been used in Fig 9.4, which shows the total resistance of the YD^O in calm and rough weather. The different contributions at 7, 8 and 8.5 knots are given in the table. To be on the safe side we have here assumed a wind speed of 15 m/s, which is somewhat higher than the speed for which the maximum added resistance occurs. sizes

I 168

Principles of Yacht Design

D AW.max

i

i

0.02

/

/ /

/

YD-40

/

^WL

9.85

V^/^

y 0.01

*a--

___ ___

y^^

y

:

"

=

-/ 'a

6.95' ''

-^-^

0.01 07 (diagram)

R^^ = 0.0107

9.81

6950 = 730 [N]

A

3

'

7

6

i''

Fig 9.3 Estimation of

maximum added resistance in

R [N] A

waves

Rough waathor

6000

5000 Calm woather

4000

3000

2000

1000

O

V [knots]

•-

Speod [knots]

Up rig tit (Fig 5.3)

Resistance [N]

Wind (rig

9.2)

Waves (rig 9.3)

Fig 9.4 Resistance in

and rough weather -

YD-40

calm

Total

7

8

8.5

1300

2750

4000

1327

1400

1439

730

730

730

3357

4880

6169

(Calm weather)

(Rough weather)

Propeller and Engine

169

Propeller

Propeller blades act as wings

characteristics

through the water. Fig

A

when

the propeller rotates

and advances

section of a blade at a certain radius

is

shown

in

can be seen that the resulting velocity, to which the blade is exposed, is composed of the axial component (due to the forward motion) and the tangential component (due to the rotation). The former 9.5. It

normally not exactly equal to the yacht speed, but somewhat lower, since the propeller operates in the wake behind the hull. This effect can be quite significant for bluff ships, but for a sailing yacht with the

is

propeller below the will neglect

it

bottom of the

in the following.

hull

The

it

should be

tangential

less

than 10%, so we

component

is

proportional

and the rate of revolutions. It thus increases linearly which means that the angle of the approaching flow gets

to the local radius

with the radius,

smaller and smaller towards the twisted to

Therefore, the blades have to be

tip.

become more and more

at right angles to the propeller shaft

normally designed so that the sections at all radii would advance the same distance for one turn of the propeller, had they been free from the others and cutting through a solid further

out.

This

body.

In

fact,

distance

propeller

the

is

called

the

is

pitch,

and

is,

together

with

the

diameter, the most significant property of the propeller. Fig 9.5

Cut through a

propeller blade

"\

Sue fion side

/ V

-.

-^ Y.

n 2n- n -r

/ The

/

^ Pressure side

pitch should be large

•

r

n

:

Wafer velocity at propeller Local propeller radius

Rate of revolutions fs~'j

Local force

enough

to create a suitable angle of attack

between the section and the approaching flow

A

[m/s]

[m]

(as

can be seen

in

Fig

more or less at right angles to the flow is then developed. Had there been no resistance the angle would have been exactly 90°, but, since we have both induced and viscous resistance, the resulting force points more backwards (as explained in Chapter 6). The force has one component in the axial direction, the useful thrust, and one in the tangential direction, giving rise to an unwanted torque. These components may be made dimensionless in a similar way as described 9.5).

resulting force,

170

Principles of Yacht Design

i

1

Advanca

^^^ /^""^^ ^'

^*^^^

^^^

X^

1

^— D n

K —

^

po'n^

K —

mnfflrlnnf

Thrii'st

\

^y^

1

y

=

°

^V^^

/^^^

J

:

Trrauo coofffcfenf

\

/^

ratio

Propoller offlcloncy

V.

-

^

^

D = Propallor diamotor [m]

\ >v

:

^

\

T

- Thrust [N]

V^' Fig 9.6 Propeller

earlier for the various resistance

characteristics

typical velocity in the present case

revolutions,

and a

typical area

the normal velocity

Fig

9.6.

To make

is

power

However, a

the diameter times the rate of

the diameter squared. If these replace

and area a thrust

coefficient

The advance

may

be defined as

in

ratio, defined in the figure,

measure of the angle of the approaching

effective

Hft.

the torque dimensionless another diameter has to be

included in the denominator. a

is

components and the

(thrust

times axial

velocity)

flow.

by the

is

By dividing the delivered power

(torque times angular frequency), the efficiency of the propeller can be

found.

The

It

may

be expressed as seen

in the figure.

and torque coefficients and the efficiency are called the propeller characteristics and they are normally given as functions of the advance ratio (see Fig 9.6). To obtain this diagram the propeller is run in free water, often on a long shaft in front of a very slender hull containing the measuring equipment. Systematic variations in advance ratio are made either by varying the speed for a given rate of revolutions or vice versa. At zero speed a large thrust and torque are thrust

developed, but the efficiency

is

move

zero, since the propeller does not

forwards. At high speeds both the thrust and the torque go to zero,

At

since the angle of attack of the blades goes to zero.

still

higher

speeds the propeller works as a turbine and negative thrusts and torques are developed.

When

the thrust

some intermediate speed

is

zero the efficiency

the efficiency reaches

its

is

At

also zero.

maximum, and

it

is

important to design the propeller for this condition. A final remark should be made about Fig 9.5. Propeller specialists

normally deal with the induced resistance

in a

way

different to ours, as

Propeller and Engine described in Chapter

71 In their approach, induced velocities from the

6.

traihng (hehcal) vortices are employed.

would

be

sHghlly

If

more complicated.

equivalent and the following discussion

these were introduced. Fig 9.5

The

is

methods

are,

however,

valid for both.

Design of an optimum

To

propeller

of the propeller, the thrust (or power) and the rate of revolutions. As we have already noted, the advance velocity is normally smaller than the speed of the yacht, due to the fact that the propeller operates in a

design the

optimum

we need

propeller

to

know

the advance velocity

wake. Considering the other approximations we will neglect which is small for a sailing yacht. Another approximation we is

the assumption that the thrust of the propeller

resistance of the yacht. This

is

is

this effect, will

adopt

equal to the total

not exactly true, since the propeller

itself

reduces the pressure around the stern, thereby increasing the resistance, but this effect should be very small for a yacht with the propeller below the hull

Fig 9.7 Principles for

using the

B^- 8 diagram

and

well in front of the stern.

There are several systematic series of propellers documented, but only a few of them include two-bladed propellers, which are of interest in connection with yachts. One series which does have two blades is the so-called Troost propeller series, developed and tested at the Netherlands Ship Model Basin (presently MARIN, Wageningen). The results are presented in the form of B^ - 6 diagrams, where B^, is a thrust coefficient and 6 is an inverted advance ratio. Both are defined in Fig 9.7, which also explains the way to use the diagrams presented in Figs 9.8 (two blades) and 9.9 (three blades). (If the power is known, similar so called B - 6 diagrams may be used.)

P

:

Gfven

P/D

'


10yjZ WL

(= Max Slamming Pressure )

Fig

1

1

.7

Longitudiniil

hvdrodynamic loads (ABS)

Bottom Pressure KPa

150

€^

"*'iJi|i!|

'%< #e

100

''*lllllllt

niiiii

liii

m

-4^ iiii.

"Hi, III!

Typical Design Pressure (P^ ) for a 42' LOA ABS— yacht excluding safety factor

""

'"M,^,

#2

50

# 1

2 3 4

5 6

5.0

Wind

Constr

LoA 39' 54' 42' 42' 37' 41-

Alum FRP Plywood ColdM

Alum

5.5

m/s

25 30 22 30 25 Not known

Steel

6.0

6.5

#•5

y.o Slenderness Ratio

Fig

1 1

.8

.2Pb

Calculated pressures from bottom failures Ooubert)

Lqa

214

Principles of Yacht Design

and cracks developed when the were slamming of the boats from a crest down into

All these deformations, dclaniinations

boats were on the wind. loads,

coming from

the trough (a

fall

The reason

the free falling

of 3

m

(10

ft) t)r

for the failures

more).

The pressure loads on the shells of the boats have been calculated 'backwards' by knowing the construction of each vessel. Depending on the calculation method, ic using simple beam theory or taking membrane stresses etc into account, different pressures are reached. The more sophisticated calculation methods gives a much higher pressure before the collapsing of the skin than does the beam theory. Fig 11.8 shows the result using the beam theory, with the boats ordered after slenderness ratio (LOA/(Displacemcnt)/). and for comparison the basic design head

Transverse load distribution

is

ABS

represented by the dashed band.

So much for the bottom pressure, but what about the sides? The longitudinal distribution follows that of the bottom, but transversely the pressure diminishes the higher up the topsides you move. And there is a difference between sail and power. Relatively speaking, a sailboat that in

some

the

side

is

compared to a slamming on its bottom.

plating,

subjected to

On

more loaded in planing powerboat which is more

instances has her topsides completely buried

falls off to zero at about 1.5 the from full bottom pressure at the waterline. On a planing motorboat the side pressure according to ABS is 20% of the bottom pressure plus a minimum static pressure head corresponding to

a sailboat the topside pressure

freeboard

height

half hull depth (0.5

D^,).

Deck and superstructure design pressures are functions of boat length and a constant. We will give more details of this when showing an example of a calculation using the ABS rule. Fig 11.9 shows typical transverse load distributions for sailing and motor yachts. Local deformations

The Whitbread study of deformations made at KTH in Stockholm on different methods of stiffening a hull (Fig 11.10), shows that it is very important to have the forebody sufficiently stiffened. The hull is the same in all cases, with a different number of frames in the forward part. The hulls are basically stiffened by an inner space frame. The C boat has this space frame only, whereas the In addition to this the

stringers per side.

before the mast, and the

The shaded

areas

in

F boat has Fig

subjected to slamming loads. hull with only the space

The reason

for this

is

11.10

D

boat has two additional

E boat has one

three ring-frames in the forebody. represent

As can be

deformed

the

seen, the difference

frame and the hull with stringers

is

hull

when

between the

not that great.

that lacking transverse stiffeners the stringers get too

long a span to effectively keep the deflections at a reasonable

By introducing

ring-frame

level.

frame spacing is 4.5 m, the deformations are diminished drastically, and by increasing the number to three the vessel starts to look like a boat even when under load (hull F in Fig 11.10). This ability to withstand slamming pressures a ring-frame into the forebody.

ie

215

Hull Construction

Pmin

Sa fling Yacht Fig

1 1

.9

Transverse load distribution (NBS)

Hull

Fig

1

1

.1

Motor

£

Deformations due

Hull

to

slamming

(Hunyadi & Hedlund)

F

Yactit

216

Principles of Yacht Design

for the

F

hull

shows roughly the same performance

As we have

transversely frame-stiffened hull will give.

when

the picture changes

dealing with

that a traditionally

longitudinal

seen previously, loadings.

So,

to

summarize, the hull must be stiffened lengthwise as well as transversely to withstand the rigging and slamming forces. This can be done either by a separate stiffening system, by a monocoque structure or by a combination thereof. Forces from the keel

shows an example of a calculation for stresses from the ballast keel on the YD 40. The 'design-attitude" for the boat is 90° heeled over and situated totally in air. Regarding the hull as in the air and applying a factor of safety of 4 to 6 takes care of the added loadings from dynamics, which are not incorporated in the formulae. A simple calculation of moments around the keelbolts gives the transverse keel moment (M^,). and by dividing this moment with the distance between the windward keelbolts and leeward keel-edge (OF^oi,) Fig

11.11

the keelbolt load

The

Assuming

this

it

reasonable to take a

is

the keel to have six pairs

becomes

bolt

(P|.|^

N

in

our

case).

along the root chord of the

OFt,o|, typically varies

account for each

can be calculated (81156

(P,^,)

=

mean N.

13526

required dimensions of the keelbolts

When

21

mm. The

when using

(d^^;,).

OF(,o|,s.

calculating

material that shall be used, not the ultimate strength.

diameter of the keelbolts

to

the

(oj of the The required of 5. becomes

the yield strength

is

it

all

of keelbolts. the loading on

{n,^h)

P|.,/n|,j,)

and

keel,

value of

a safety factor

from the formulae in Fig 11.11. strength used in the example above is 206 N/mm- which

as can be seen yield

corresponds to stainless

steel

AISI-316. The diameter obtained

is

the

minimum

core diameter of the bolt, so the nominal bolt size will be a

M26-bolt

in the

On

metric system or a

1

in bolt in the imperial

system.

must be and hull.

the leeward side of the keel the tension in the keelbolts

absorbed as a compression by the mating areas of the keel Since only the area nearest to the leeward edge is effective, it is reasonable to assume that 25% of the total area must be able to withstand a pressure corresponding to the total load on the bolts. The

minimum

A 1

17

required keel/hull area

13873 mm-.

(A,,,|„) is

compression for a glassfibre laminate is The actual keel has a 25'/o area of approx-

typical ultimate strength in

N/mm-

in

compression.

imately 150000

mm-,

so the factor of safety

is

considerable

in this case.

Each pair of keelbolts is connected to a floor which has to absorb the moment induced by the tension in the windward keelbolt. The factor of safety for the floors is taken to be the same as for the keelbolts; in our example it is 5. So the bending moment working on each floor becomes the total transverse keel

moment

(M,^,

5)

divided by the

number of floors,

our example, which gives a bending moment (M,-,) of 18598 Nm. The required section modulus (SMp) to withstand this moment

six in

calculated

by dividing the floor bending

laminate's

ultimate

glassfibre

strength

in

tension,

laminate, and in this case

it

moment typically

{M^^) by

becomes 150

the floor

N/mmcm\ The

125

is

for

a

result

217

Hull Construction

BmIn —

-^

Floor

HBight [O. 12

In

H

C/L,

Afi/t s Bnnin

Bnntn

p

Aflf f,

m]

f

O.St

i SM

[

\

cm3] Y

(o

260 240

f

/

/

ISO J

60

/

/

/

/

/

/

f

/

f /

f /

J f

/ i/

140

/

/

t

f

/ r

i

r

f

/

/

/

t

1

/ J/

220 200

1

f

/

H [cm]

0'

/

/ J

/

/

/

/

/ / / f/ J / / / f r / ^ / ^' f '( / / 100 ^ J i / ,^ / ^ BO f f '/ 4 / / J J f r , ^M ^ i> f 60 «» ^ K" ^A / '/'^/ ^ ^ * 40 S r ^ ,/ >/ / ^' 20 > J' ,

i'

120

e

6

.

A

i

,

y25

r/

1.

ry

/ / / /y / / / / ^ / n y / / V r y / \» [

[ 125150 N ]

/ / r/ y J

r ^ /

i^c

22

20

2.2

tg Com]

^

30 Afl

Required Floor Section Modulus

^^f

Fig

1

1

.

1

2

=-^

[ 750

Loadings from grounding

cm^

]

(SMfi

tcm2]

Section viodulus. Including offoctlvo width of plating, for 9e ctfons as functlona af flange :

Three layers of UDR held together by

a light stitching

WR, to

B 8- K I- i£ ;: « s a y t

BR or TR sewn

a layer of CSM

228

Principles of Yacht Design

Tho total

N.B.

relnforc&ment welglit Is In

\

Tensile Strength

of one ply of

[N/mm ^J

all

the

same

cases.

WR (600 g/m^)

220 Biaxial Ro ving

200

1

^

llll

"^Sjg.

80

"""""Illlllll,

"""'«»«l

"

1

60

mill, , '

mil

1

40 3.5

2.5

5.5

4.5

6

Crimp (W [deg])

(wy

Fig 11.18 (Top) Flexural

strength vs angle of

weave

Fig 11.19 Tensile strength vs

crimp (Hildebrand

Holm)

&

together by a binder.

which

is

dissolved

The binder

is

of either an emulsion or powder type,

when wetting out is slightly easier to work with because and must be handled with care. One

by the styrene

in

the

The emulsion type powder type is more fragile drawback with the emulsion type, however, laminate.

so in the outer part of a laminate

at least the

resin

is

that

it

is

the the big

prone to osmosis,

powder type should be

used.

229

Hull Construction

While

CSM

is

more or

isotropic

less

has the same strength

(ie

in all

much more sensitive to the direction of become an advantage when building the lay-up, if one lines

directions), the other types are

load. This can

up

the fibres with the primary load directions in order to lake the best

advantage of the available reinforcement materials. The use of rovings to take care of the primary loads is a good idea, but to ensure sufficient inter-laminar practice

is

strength

to

put

(strength

a

in

layer

between of

of

plies

CSM

between

reinforcement),

each

roving

the

layer.

Manufacturers of glass reinforcement have noted this, and they have come up with a mat/roving combination: a roving sewn to a mat so that one can achieve the proper mix in one lay-up process. The most direction-sensitive type of reinforcement

the unidirectional type, which has virtually

is

no

strength in the 90° direction (see Fig 11.18).

The maximum

slope of the fibres (crimp) in a

woven roving (WR)

has a strong influence on the tensile and compressive strength of the

The tested laminate consists of two plies of 600 g/m- WR, and between them and also on the faces, one ply of 450 g/m- CSM. The fibre angle (W) is a measure of fibre curvature in degrees. The fibre curvatures in the warp and weft directions are not always the same in many woven roving products, so the tensile strength may vary up to 20% depending on direction. As can also be seen from laminate, (see Fig 11.19).

Fig

11.19

a

biaxial

corresponding to a

stitched

fibre slope

roving

has

higher

a

tensile

value,

2°.

of approximately

Another very important parameter regarding strength properties of the laminate

is

the fibre content, often expressed as a percentage by

weight of the total laminate weight, (see Figs 11.20 and Fig

11.21).

Generally speaking the higher fibre content that can be reached the stronger the laminate becomes, as long as the fibres are wetted out and

not subjected to resin starvation. In practice, fibre content higher

is

it

than 37%, and lower than

not realistic to count a

27% when

lay-up with a mat laminate. With a mix of mats and the laminate the fibre content usually varies

using wet hand

woven rovings

in

from 35% to 45%, and with up to 55%. The thickness

multidirectional material (rather than woven)

of the cured laminate varies with fibre content as shown

in

Fig 11.22.

To calculate the strength properties of a glass mat/roving composite we can use the values from the mat-only and roving-only values. The combined properties can be approximated by calculating the average weight of the respective reinforcements

as:

where: P^,

P^

= =

property of the mat/roving composite property of the mat portion, having the same fibre content as the

Pf

=

X

=

mixed composite. Fig

property

of the

roving

11.20.

portion,

having

the

content as the mixed composite. Fig 11.21. ratio of

mat

to the total mat/roving

composite

same

fibre

230 Fig

I

Principles of Yacht Design

\.10

CSM-polyester composite

200

&

15000

A=4421 B=149

C=0. 037

Teti)

ISO

N

100

SO

jd

^ 4

pjp^

c=o.aa 12500

N

i

ftf

10000

A

W

7SOO

W^ A=2799 B=10S

A=16.1

C=0.018 IS

A ^ A

Hi

B=1. 14

2S

3S

Ffbrm Content

4S

sooo

[N/mm ^]

250

25

IS

Wf [%]

Compressive Strengttt

C=1.29 35 45 Wf [%]

Flbrm Content

[N/mm^]

Compressive t^odulus

20000

A

A=36.3 B=2.44 C =0.0 19

200

\

ISO

^

100

[N/mm ^]

Tans Ha Modulus

A=22. 1 B=3.32

properties

(Oiprino

[N/mm ^]

TensHa Strength

w

pr

A=4331 B=1 13

^

C=0.96

15000

10000

il#

5000

piiw-

\

^

A = 2619 B= 10S

A=16.1 B=2.24 C=0.

SO 15

25

Fibre Content

Flexural Strength)

C= 1.04

1

35

^.nflHill

iHi

45

O 15

Wf [%]

[N/mm ^]

400

25

45

35

Wf [%]

Fibre Content

[N/mm^]

Flexural t^odulus

12000

A=3930 B=SS C=1 \

A=46 B=3.42 C=0.036

300

90OO

200

6000

gH

\,

piiw--

gUi 3000

100 A =49. B=3. 74 C=0. 03 15

25

35

=3630 £1=37 C^=0.61

45

Fibre Content Wf [Z]

15

25

35

Fibre Content

Ttie curves follow the general expression: Strength/I^odulus = A + B(Wf) ¥- CCWf)^

45

Wf [%]

Hull Construction

Fig 11.21

400

&

Tensile

A =2452

B=244

C=0.037

Teti)

C=1.59

300

18000

\

200

100

^

^ iii»=

^ 15

_,^ pF i

12000

t

|jj>>*^

6000

1

A -14. 1 B=3. 18 C=0. 032

25

35

15

Wf [%]

[N/mm ^]

200

25

C=1.22 35 45 Wf [%]

Fibre Content

Compressive Modulus

[N/mm^j

20000 A=36.4 B=1.92 C=0.009

A=3959.6

B=186

C=1.21

250

15000

100

10000

5000

SO

15

25

Flexural Strength

[N/mm ^]

~^

^

15

300

ii giP

^P

25

Wf [%J

V

\

-.i

12000

nT

6000

IP

^^ A = -1234 B=

1

60.

C=2. 13

45

15

25

35

Fibre Content

Wf [%]

The curves follow the general expression:

Strength/Modulus

45

[N/mm ^]

il'

35

Fibre Content

35

A =3495 B=259. C=1.71

A=12.i? B=2. 715 C=0.0,59

15

25

Flexural Modulus

18000

\

1

Fibre Content

A =53. 1 B=3. 72 C=0. 064

A

ifF"

^

C=1.04

24000

600

^rfil

A=2619 B=105

A=28.3 B=1.28 C=0.011 35 45

Fibre Content Wf [Z]

150

^

A=742 B=238 45

Compressive Strength

4 W

jftrTl

Jl^ \p^

rtf

Fibre Content

450

[N/mm ^,]

Modulus

24000 A=22. 1 B=3.32

properties

(Caprine

[N/mm ^]

Tensile Strength

WR-polyester composite

231

= A + B(Wf)

-h

C(Wf)^

45

Wf [Z]

232

Principles of Yacht Design

Roinforcomsnf weight [g/rnrn^ ] to build 1 laminate

y

mm

l\

700

650

600 y A

550

B C

A + B(x) + C(x)^ 51.6931 8.58526 a. 1396

500

450

400 30

45 Fibre content by weight [%] Fig

1

1

35

40

>X

.22 Thickness v fibre content (NBS)

Flex Strength /I

[N/mm^]

Flex.

Modulus

[N/mm^]

Modulus Curves

12500

10000

300

7500

250 H«ll+*+.

C a ti

IJ

'V

U

V

*n

"*

y "n iiiiinii

'S "N "V

O o v~ o

4

1

1

1

1

1

1

-^ c

E

I.-

Ti

n

1

^ cQ Q Q C •C + • Q Q Q c 10 tN ^ n a- Q *^ *^

to

ih':iii|

i:

;:::iii'

7^

;^ (0

„,,

'I

Q

1

c

4-

4-

C ^ ^ ^ ^w >j O o m •0 * N N o Q ^

**

tN

>»

Q +

?

K h

M C

t

2:

-> b n c p

1

Q C

a:

c c Q

-J 10

t^

t

1

s

^

I,

5"

«2

g ^

•^

«^

"»^

« u

s

t)

Fig

1

2.4 Design heads for plating

Ql

n

0

1

1:

St

1 « ^

^ ,^ i: 1

«

1 1 1 ID

Ql

10

to

(0

« to

ti

•

tj

^

Ql

252

Principles of Yacht Design

Design head reduction

It

might seem strange that there

long lengths and panels of big

factor

design head

is

a reduction factor for stiffcners of

is

sizes.

The reason

for this

the boat actually encounters are

acting over a very limited area.

is

Cp

plating, but with a separately calculated

the formula in the figure.

Fig 12.6

at the

&

for hull plating

/

Fr 1.0

and

1

\,

O.B

The deck

bottom of the

Design head

reduction factor - F

the

spread out.

Fig 12.6 shows the F-factor which applies to the

shown

that

slamming loads of very short duration, So the longer the stiffcncr or bigger the

panel the more the slamming pressure

as

is

considered to be a static pressure, but the peak pressures

\,^

plating has

1

fmin

:

1

reduction factors

for hull plating

1

CIT for

^S,.

^^

own

its

= O.SO

1

\^ v^

o.e

and the

figure.

Internals

1

stiffeners

plating value according to

Cf

^v^

=

1

1

shell plating:

- 254

s

54.2 L + 559

"""-^ 0.4-

"^ 0.2

O.O

F and Fig 12.7

Panel calculation

Thickness of a)

t

',

Fs

;

Fs

hull,

for dock

Fs

= =

&

0.4

0.6

bulkhead plating

where s ^ 254mm 1.1 02 - 0.0004.S where s >

deck and bulkhead plating

(^

0.5

0.7

O.B

or b)

t

to

0.9

' min Fsmin

254mm

= =

be the greater of

= O.JS-s-c-'Uo^MnilEIEl V

0.02-

[mm]

Efr

= the design head, given In Fig 12.4 = the short span of the panel. In mm, given In Fig 12.4 F = the design head reduction factor, given in Fig 12.6 k = the aspect ratio factor, given in Fig 12.8 ki = the aspect ratio factor, given in Fig 12.8 C^ = minimum design stress, in kg/mm2, being half of the ultimate flexural stress, given in Fig 12.3, or calculated and tested. £>-= minimum flexural modulus, in kg/mm^, given in Fig 12.3, or calculated c = curve correction, c = (1—A/s), not to be less than 0.7 A = curve depth, in mm, as shown below h s

"'"

1.6

:

1

= s-c-MMI^IEIE. '

0.3

0.2

O.I

O.JJ o.so

The ABS Guide

253

1 I

5, ^

"

-^

o

v!

•0 0)

1

>f

5

r t.

0)C\,

>

o^

1

v.*

5

^^o

>

r*\n^

1

1

s

o Q

o Ol

"J

V

V.

c

V

E

- N

l


ts

Q v.

—

-J

'

(,

1

» ^-

f^

Ol

0

^I'tJ

•^J

„ t

1

d 1^

•

d

•^5 •.

:? c.

^ • 3-

18

^c ^£ i *

5 5:

D

kk

IN

•c-c

c c « «

1

"^

> 2 AV d k

c< 10

c

Fig

1

2.5 Design heads for internals

.?:

k5

k

o'^

•0

+

d

II

II

+

1

• «

lOO (NO :? d"^

U.

OO V.

,^ -^ ^^ ^ -' ^^. ^^ ^

riJ-

--•

,y\

1.0

l03

(i^

^ -^

0.6

= (6800 -h 13200)/ 2 Oj Et

[ 15.8 [1 197 [ 15.7

1

1

PANEL

&

11.21

kg/mm^J

kg/mm ^] kg/mm ^] kg/mm^ ] kg/mm ] kg/mm^ ]

from Fig 12.4

j^lg

= 5.86

h

[1111 [ 24. [1019

11.20

m

= 2000

I

mm

= 1200

s

mm

A

= 180

11.1

mm

mm

Reduction factors from Fig 12.6 Cr = 0.818 ; F = 0.31 < 0.5 (min) Reduction factors from Fig = 0.0259 k = 0.485

12.8

Single skin calculation according to Fig Curve correction, c = 0.850

^

001

0.

12.7

5- 5.86- 0.485

=

a)

t

= 1200-0.850

t.)

t

= 1200-0.850-0.75-'s[^^^^^^%^^fijf- 0259 =

sandwlcti panel

Trial

0.5-24

Equal skins

:

with)

If

a) SM,

= QQQ

15.8

1^

b)

11. SM^- QQQ,

c)

I

24 J^ y

and

t

^

=

15

mm

cm^/cm

OK

I

35 cm ~^/cm

OK

I

= 0.312 cm-^/cm

a) SM,

=

0.35

r, Ti ^ y = 0.314 cm J~^/cm

b) SM^

=

0.

J .9-^ 4 ^ ^^ = 2.37. j12000- 11019 154 = 0.294 cm y/cm 1

.

c)

I

=

0.39 cm'* /cm

OK

12.

14)

J

= (1197 + 1111)/2 = 1154 kg/mm

TC All

12.13

Fig 2

to

mm

Actual panel section modulus (Fig and moment of inertia (calculated)

Sandwich panel requirements according

=2.5

mm

11.9

criteria

are exceeded

witfi

the panel suggested

.

The shear strength requirement for the core is calculated from the last equation in fig. 12—13, using reduction factors from Fig 12.15 = 0.394 < 0.40 (min) V = 0.492 ; F^^

T -Tait -

0.492 -O.OOI 0.40-5.86 -1200 ('JO 25)/2 0.5

_ -

^ i,^/^^i> ,^, kg/mm ^-^^^

-t-

The requirement gives a PVC—core of 80 kg/m -^ according to Figs 11.35 or 12.16 and a core of 25 a total panel thickness of 30 The trial panel is satisfactory if 30 thick, shear strength of core is dimensioning.

mm mm

with

Fig

12.17 Calculation of panel for YD-40

hull

As can be be 11.9

mm

mm

.

seen from the results the equivalent sinale-skin laminate will thick,

weighing 18.5 kg/m- compared to the sandwich's 10.5

kg/m^. At the same time

the stiffening system

is

not as dense (see also

Fig 11.16), which contributes to a lighter structure. The skins of the

264

Principles of Yacht Design

BULKHEAD

=

h

1

.90

from Fig 12.5

/^2

m

;

I

mm

= 2450

;

Reduction factors from Fig Fs = 0.50 ; F = 0.35

12.6

Reduction factors from Fig k = 0.440 ; k, = 0.0217

12.8

s

Single skin calculation according to Fig

.

,

j)

t

..

t

0.001 0.33-

.,_ f/ = 1425-y

0.001 0.33- 1.90-0.0217

1.90-'0'. 440

0.5-24

=

9.1

:

Equal skins with

tf

°) ^^

\

,

= °-^^

'"^ ^""^

a) SM-

=

^^

b)

^-^^

1019 -1

154-

^

mm

1.5

and

t^

= 20

mm

J

'^^'^

4 .

.

^'-^^

"^'^

c)

/'^'^

=

SM.=

I

=

0.23 cm-^/cm

OK

I

cm^/cm

OK

I

0.35 cm'^/cm

OK

0.23

I

= (1197 + 1111)/2 = 1154 kg/mm

Ej^ All

o T7 = 2.37-^2000

=

Actual panel section modulus (Fig 12.14) and moment of inertia (calculated)

Sandwich panel requirements according

mm

,„ ^ 12.5mm

'

0.02-1019

sandwich panel

Trial

12.

,--_ ,/ = 1900-\J ,

.

b)

mm

= 1900

criteria

are fulfilled with the panel suggested

The shear strength requirement for the core is calculated from the last equation In Fig 12. 13. using reduction factors from Fig 12. 15 V

= 0.466

T Ta/t -

;

/^5

= 0.40

0.466-0.001 0.40- 1 .90 -1900 0.50 C2J + 20)/2

_ -

-

n nf^^ kg/mm ^„ /^^2 °-°^^

The requirement gives a PVC—core of 60 kg/m^ according to Fig and a core of 20 mm. a total panel thickness of 23

mm

with

Fig 12.18 Calculation of

sandwich bulkhead

YD-40

for

sandwich are 2.5

minimum

mm

thick

and

this

11.35

might be regarded a practical

thickness, so that the boat will not to be too sensitive to impact

and crowded docking manoeuvres. By using better fibres. S-glass, Kevlar, carbon etc, it is possible to get enough strength and stiffness with

forces

The ABS Guide

INTERNAL #1 from Fig h

=

1.465

m

:

1

=

265

12.5 ( side stringer )

2.0

m

=

s

:

m

1.02

.-ag:=

kg/mm 2

7.85

Stiffener requirements according to Fig 12.10

^^ ,

'

83.33-1.465 -1.02 7.85

26041 1.465 -1.02 —2^= 270 cm*A 1 154

-

Dimensions from Fig

and moment of

mm

H = 90 1

= 63 cm^

=

t^

;

1 1

for SM—req.

1 1

inertia (calculated)

= 491 cm*

10

OK

mm

mm

B = 50

;

!

mm

Dimensions according to Fig 12.9 : W = 264 ; = 75 F = 50 tj= 5 C = 50 ; h ; ;

mm

mm

mm

INTERNAL #2 from Fig 12.5 ( /?

= 2.393

m

:

=

I

1.4

m

;

=

t

mm

11.9

mm

^^

/

=

mm

^O

of 3 keel bearing floors )

1

=

s

m

0.6

;

=

Oa

kg/mm^

7.85

:

N =

1

Stiffener requirements according to Fig 12.10

SM = SM,,=

183.5 -2.393 ^

I

=

0.

I

^_ _ cm 3 = 58.6

way of

In

cm^ + SM =

ballast keel

57290- 2.393 -0.6- 1 .4^

.

TT54

and moment of

H =

160

mm;

t

= 2649 cm*

214 cm^

( 0.5 -1-55.2

:

f\gMA9

mm

Calculation of

internals for

YD-40

SM-req

)

)/58.6 = 1.32

;

(N

=

0.5)

,__ cm 4 = 196

-„ , 1.32

inertia

=

12

OK

mm

;

B = 80

mm

!

mm

Dimensions according to Fig 12.9 : W = 305 = 1 42 C tj = 6 ; ; ; h

F = 50

(

11.11 for SM—req. (calculated)

Dimensions from Fig

I

6- 1.4 ^

'^^^^'°^^ = 155.2

Increase of I

pg

y

mm

mm

thinner

skins

desirable necessarily

and

lower

the

design

true

from

if

cruiser/racer.

is

a

:

t

= 80

=

mm

weights,

meant practical

12.5 ;

which for

mm

t2= 12

is

of

and

satisfactory

high-level

point

mm

racing,

view

for

but a

it

indeed is

cruiser

not or

LAYOUT

The

term 'layout' covers a wide area, and

in this

chapter we

will

accommodation, cockpit, deck, instrumentation, hatches, ventilation and safety equipment. These different matters will be

discuss

dealt with in general terms, but

show one way of meeting

to

we

the

will

use the solutions used

in

YD-40

demands.

Generic space

Before using the boat there are some general requirements that must be

requirements

met, in order to live

make

to sail

and

aboard. Fig 13.1 shows some important dimensions concerning the

man

space required for a

we

and comfortable

the vessel practical

m

standing, sitting and lying.

The 'module man'

Optimizing for a bigger or smaller person done by interpolating the values according to size. When standing up (Fig 13.1(A)), the reach forward measurement are using

meant

1.8

is

show

to

tall.

the

practical

is

restricted.

movement forward

maximum The eye

to

height

reach

shown

is

is

when

controls

just that; in

is

order to see over an obstruction, (the deckhouse for example) this height has to be decreased by at least 100 the figure

the

is

minimum

mm. The

comfortable; a greater distance makes

comfortable to stand but on the other hand more wheel when

The

sitting

seat height

down. and depth shown

position, for instance

more

when

difficult to

in (B) is for a rather

and depth

is

more

reach the

upright seating

mm

but at the same

reduced by the same amount, to keep the

900

it

eating or sitting by a navigation table. For a

relaxed sitting the depth can be increased by 80

time the height

seat/wheel gap in

sum of

height

mm

which produces a comfortable sitting geometry. and 15° from vertical. Fig 13.1(C) shows the width requirements when sitting down. It is worth noting that when the seat is beside a bulkhead the width required is greater than when it is free-standing. The picture in Fig 13.1(D) shows the minimum measurements for a comfortable seagoing berth. The narrowing of the ends are not necessary but this often happens due to the form of the hull. If the berth is a dedicated sea berth these measurements are adequate, but if the berth is also to be used in harbour it might feel a bit cramped. will remedy this and doubling it will produce a Widening it by 100 usable double berth for harbour use, with a width of 1300 mm. If the double berth is free-standing with the sides not 'walled in" the width should be increased to 1400 minimum. A standard length of a to

The angle of

the backrest can vary between 5°

mm

mm

berth

is

2000

mm,

need to add at

least

but to tailor a berth for a specific body length, you

50

mm

to this

body length

at

each end.

267

Layout Tha mmasuramants corrmspond

to

a body length of 1.8 m.

-1000-700-

5'- 15'

1800 1500

900 800 L

7Q0

100-150",

300-400

@ 370-5OO @+ ® =

900

Max.

530

800 A) Standing Profile

350 1100

—

B) Sitting Profile

Min

-800-

420

—

SJ:A- BERTH

750

200 '^^._ff.arbour Bertn

-50

+ 100

50-Mln.

1900-

400 C) Sitting Front

Fig 13.1

D) Lying Plan

The human figure

Accommodation

Looking

at

the

YD-40's accommodation (Fig

13.2),

there are

some

general features to consider. Basically the layout follows the principle

motion of the boat, so that they can be used when under way. The lounging and sleeping areas, as well as stowage areas, are grouped forward and aft. As we have discussed previously, the aim with this design is to produce a comfortable offshore yacht for four persons, so we do not have to fill the boat to its extreme ends with bunks and accommodation. The numbers below (1-13) refer to the circled numbers in Fig 13.2. that the activity areas are situated near the centre of

268

Principles of Yacht Design

Looking

more

we

with the forepeak. This part is entirely given to deck stowage for items like extra sails, fenders, lines etc. By burying the headsail furler here we get a clear foredeck with the genoa tack low down. Since this space has nothing to do with the rest of the accommodation the bulkhead to the forward cabin can easily

I

in

detail

depth while folded down. On a boat with a shallow hull like this one it might be a problem to locate water tanks big enough, so here we use the space under

start

the settees for tankage.

5

be made watertight.

Thanks

opening of the door to the forward cabin, the L-settee on the port side is deep enough to contain a big fixed table, while leaving a wide passageway to to the offset

starboard.

2

Another advantage of not pushing the accommodation too far forward is the position of the anchor windlass and chainlocker, They can be placed comparatively far back so as not to hamper the rough weather performance. Such heavy items placed far from the pitching centre play quite an important role in forming the gyradius of the boat. •

allows us to

This far back cabin. This

is

we

cabin for

harbour use, and that is why the double is placed here, a berth type that cannot easily be converted to a comfortable sea-berth. To achieve an acceptable width the berth is raised, and berth

since this is too high to sit on, a separate seat is included. To make a cabin like this habitable, there

a dresser

is

a hanging locker,

and a general stowage space

for personal belongings, so they

do not

have to occupy the more public areas. 4

Moving further aft to the saloon there are some other points to consider. There must at least be enough space around the table people who can sleep on the boat can also eat onboard. This is no problem for the YD-40, but on boats with an that

all

exceptionally large

number

of berths

table fixed also

a proper locker

scale dining there

is

a drop-leaf

starboard side of the table, so

it

on the is

possible

to use the starboard settee as well.

6

Especially in boats under about 10 ft) it is

often hard to

and

table

fit

m

(33

a full-size chart

in

may be 300

seat. Big charts

1

x

mm when opened out,

so the table top should ideally be this size. In the YD-40 this is possible by aligning the

are in the forward

laid out as a

install

underneath with a door, instead of the more usual small opening top. For big-

800

J

Making the

it

might be. The saloon settees must be long enough (in our case) to sleep on, since the forward double berth is unusable at sea. This dual function means that the backrests must fold up in order to have the berths wide enough to sleep on, while retaining a proper sitting

table along the hull side.

possible

we

should

If

this

is

not

at least strive for

an

area of 800 x 650 mm, ie a big chart folded once. For the navigator to be able to brace himself when the boat heels over 30° the seat must have a sturdy backrest (when aligned the way it is in the YD-40), or have a concave sitting area (when aligned athwarthships). Fig 1

3.3

shows

clearly

what

is

in

is

like

when

Another thing to

sailing at a heel angle.

bear

it

mind when designing the

interior

the narrowing of the boat the further

down you

get,

and the

of hull and other items. in Fig

1

3.3

shows

effect of thickness

The

just this.

circled area

It is

not

deduct the sole width according to the relevant waterline on the lines plan without further deducting the hull and sole thickness. In this case they amount to a further deduction of 80 sufficient just to

mm compared to the hull Further

demands on

a

navigation station require

waterline.

good it

to contain

plenty of stowage space as well as bulkhead areas for books and electronic

Layout

^^

Fig

1

3.2

Accommodation

lay out -

YD-40

269

270

Principles of Yacht Design

instruments.

A stowage

bin under the

Most of these instruments are quite small and can generally be surface-mounted. Since many of them need input from the

working area is a good place to keep the charts fiat, and by making it 50 mm deep it is possible to stow up to 200 charts unfolded, or, if the area is not enough, 100 charts folded once can be stowed per 50

operator they must be placed within easy reach of the navigator. Radars and high resolution chart plotters are bulky, since the screens they use are quite deep, heavy and hungry for electrical power. Flat screens are now coming on the market (1 994), but their resolution remains on the low side; for chart plotters the image should be in colour so that they are more readable and on a par with paper charts.

mm depth. The best place for a

overhead bookshelf

is

on an

athwartship's bulkhead, so the books

in

it

can be handled on either tack without falling out when removing the retaining fiddle.

Space requirements for electronic instruments will vary depending on owner preferences and the intended use of the boat. The single most important instrument that any boat should have is the compass. The primary one should not be electronic, but independent of the boat's electrical system, and it should be placed up in the cockpit to steer by. Instruments in the navigation area can be divided into three groups: (a)

Navigation instruments (compass, speed and distance meters, depth sounder, Loran-C or Decca receiver, satellite navigator, chart plotter

and

radar). (b)

Weather and communications instruments (barometer, wind speed and direction, air and water temperature, multiple band radio receiver, weather fax, VHF and other radio transmitters).

(c)

Boat performance instruments (with the raw data gathered from instruments in (a) and (b), added to data such as heel angle, course and speed over ground from a satellite navigator, the processing unit in the

boat-performance instrument package can calculate VMG, leeway, direction and strength of current, time and distance to the next mark or waypoint, and calculate polar curves for the boat in actual conditions.

7

Galleys in the past could be placed almost anywhere in the boat, forward, along one side of the saloon, or aft. Today, the common location for galleys is next to the aft companionway, and there are good reasons for this. This is the area where the violent pitching motions are smallest, the cook is not isolated from the rest of the crew, the ventilation through the companionway hatch is good and food may be passed to the cockpit easily. In the YD-40 the galley is placed to port of the companionway, and thanks to the size of the boat it is sufficiently offcentre not to place the cook in the general traffic between the cockpit and saloon. The planform is J-shaped, with the 'hook' of the J forming a bracing for the cook when the boat heels. As we can see from Fig 1 3.3 it is important that the distance from this 'bracing-hook' to the stove be great enough to allow the cook to take up the boat's heel angle. The heel angle shown is 30° which is certainly greater than the normal sailing angle, but

temporarily, in squalls for example,

it

is

not an exceptionally large angle. Another way of keeping the cook in place is by

using a restraining belt. The disadvantage with this method

is

that the

strapped in and cannot escape if cook an accident, such as a boiling pot falling over, occurs. is

271

Layout

Seat with backrest r Navigation instruments

Enougfi space to brace

Sinks above waterline

Gimball

30.0' lieel

STN No 6

Fig

1

3.3

Heeled section - YD-40

As an added safety factor a crashbar should be set across the stove front to keep the cook from accidentally falling on to the burners. Another vital feature to bear in mind when designing the galley is to make sure that there is enough space behind and in front of the stove to gimbal

•

A

lock on the oven door, to keep

things inside

it

in

rough weather.

Several stove fuels are available:

(a)

approximately 60°. There are many stoves on the market,

freely over

but generally the following features are desirable:

Alcohol has the coolest flame and therefore cooks the slowest. It is fairly safe, with no risk of explosion, and a fire can be put out with water. It has a tendency to smell sometimes to the point that crew members may be sick.

• • •

•

Stainless steel construction

Removable top gratings, for easy cleaning A high fiddle rail around the burners with pot-holders, to keep pots from falling over Sturdy gimbals positioned for good dynamic balance when the boat is rolling

•

An oven

(b)

Kerosene has the hottest flame. It the most common stove

was once fuel,

more

but

it

is

becoming

difficult to obtain,

getting

more expensive

increasingly

and

is

as well.

requires a vaporizing priming

procedure to be smell bad.

lit,

and tends

to

It

272

Principles of Yacht Design

LPG

(c)

petroleum gas) is the second hottest in flame heat. It is stored in liquid form and

and

automatically vaporizes as it is released, so it can be lit just like

insulated boxes cooled plugged into the boat's

(liquefied

awkward

LPG

is

that

it

is

heavier than

On

and mixed with air it forms an explosive mix. If it escaped inside the hull and settled in the bilge this could be highly dangerous. Therefore, it must be stored and handled with care:

Stow LPG bottles in separate airtight compartments that drain overboard.

•

Install

in

a cut-off valve that

is

need an

situated

as well as

on the

top burners.

CNG (compressed

(d)

unlike LPG,

is

natural gas),

lighter

than

air.

if it leaks, it will rise and can be ventilated away. It is not as widely available as LPG, however, and it is more expensive.

Therefore,

The

sink must be

deep enough not

should be adequate counter space with high sturdy fiddles, with work areas on both sides of the Finally, there

to

even with a half-load of dishwater, which means a depth of at least 1 80 mm. Having two sinks is a good idea, one for washing dishes and the other for rinsing and emptying cooking water etc. By making the bigger sink round we make the most of the volume, ie we use

up

amount

of water to

to a given level.

Fig

1

fill

YD-40

are

placed high enough and sufficiently inboard to allow them to drain when the boat is heeled over.

Some because

sort of refrigeration

ice

is

is

Having the stove directly against a bulkhead is not a good idea, since it is an uncomfortable place to stand in, and the process of preparing a meal benefits from having an area each side of the stove.

stove.

the sink

As can be seen from

3.3, the sinks in the

more

item.

spill

a smaller

polyurethane or

thermally efficient (since cold air does not pour out when opening the box). However, you often need items from the bottom of the box and to reach them you have to rearrange some food on the box top, where it will be warmed up during the search process. A way around this problem is to make the top opening as big as the box itself, and equip the box with 'modular inserts', stacked beside each other, containing food sorted by type, meal rations or any other system that is suitable, so that the entire contents of the box do not have to be disturbed when looking for a specific

a stove with a flame-out safety

oven

is

the latter considered to be

a leak-warning system in case

shut-off in the

we

efficient

insulating material

of leakage into the bilges. Install

YD-40,

permanent

a

PVC-foam. The door to the refrigerator can be either side or top-opening, with

stowage compartment, also operable from the galley.

•

2-volt system.

box or cabinet to hold the refrigerator. By far the most important component is the insulation. There must be at least 100 mm of insulation all round the compartment. A very good

the galley, and preferably an

Install

we need

home, and

at 1

refrigeration system. To start with

electric solenoid valve in the bottle

•

handling). Even small boats

bigger boats like the

however,

air,

•

mention the

carry refrigeration in the form of

household gas. The big drawback with

difficult to find (not to

essential,

increasingly expensive

8

Like the galley, the head area traditionally

has been placed almost anywhere in the Today just two areas are preferred: between the saloon and forward cabin, or (as in the case of the YD-40) close to the companion way. The advantage of the vessel.

latter

position

is

the

same

as for the

273

Layout

motion of the boat is least felt here, so the head can be used underway in rough weather. As can be seen the

clothes stored here, there

galley: the

a hot air

is

outlet from the heating sytem into this

WC

aligned fore-and-aft. This is the proper orientation for use at sea regardless of

locker.

is

10

A

'landing platform'

formed by the top

heel direction, provided the distance

between the surrounding counter and bulkhead is not less than 650 mm and not greater than 750 mm. Anything smaller will render the WC useless, and made greater the ability to offer good

two

steps down from the cockpit. Enclosed by the longitudinal bulkheads to the head and aft cabin this gives a very secure companionway entrance. The locker behind the step is very useful

if

reduced. One disadvantage of placing the this way is that the wash-basin is forced outboard, and will not self-drain on a port tack in fresh weather. Two solutions are given: either we install a holding tank, or pump out the waste water via a loop that goes up under the sidedeck. The free area in front of the wash basin should be approximately 700 x and bracing

for

is

stowage of boots,

WC

11

is

where space

is

Foul weather gear

is

is

stow. Not only

dampened by essential to

is it

salt

it

YD-40

it

is

usually

room

the

the berth

for a quarter-berth at

YD-40 we have

a proper

makes entering and leaving easier, especially when two

this

people are using it. To be suitable as a double sea-berth, there is a solid, fold-up dividing bunk board, stowed under the cushion when not in use. Lee cloths are good, but only when used on single berths. To separate effectively two sleepers in a double-berth we need a substantial divider. At the centreline along the berth there is a row of stow bins. It would have been possible to extend the berth into this area, but by not doing so the berth is not completely under the cockpit sole, where a claustrophobic feeling might have been experienced. At the same time we gain some stowage bins, of which there can never be too many.

is

situated directly

of the head, so this compartment is used to take the wet gear without wetting the rest of the interior. There is also a hatch on top of the locker leading directly to the cockpit so that people do not have to come down to get their foul weather suits. To make it possible to dry

of the boat, as there

motion here compared to the

to less

because

have a separate wet gear

locker. In the

to place the sea-going

aft part

cabin containing sufficient stowage and hanging locker space for two persons. There are some features in the berth area worth considering. To begin with, there is a notch in the head of the berth,

to

water. Therefore

the

in

least. In

greater.

troublesome bulky but also

good idea

a

tools, flares etc.

forward part. In smaller boats where it is impossible to fit a proper aft cabin there

showering area. It is not necessary, though, that the sole be completely flat: the hull might still show, especially if the head is placed aft in the boat since the hull lines are rather shallow in this area. Having the head situated between the saloon and forepeak does prevent it from being used comfortably in a seaway, but since it is possible to use the full width of the boat here, it might be the only place to locate it in order to get enough elbow space, especially in smaller yachts. It also puts the saloon further back in the boat,

It is

berths

WC 700 mm to be usful as a washing and

9

is

of the engine compartment, situated just

aft

12

Extra sails, lines, fenders, fuel

and water

jerrycans, inflatable, outboard engine,

cleaning compounds, lubricants etc. are just a

few things

that

most cruisers

carry, in

274

Principles of Yacht Design

addition to the personal gear and food for

1

3

The aftermost

part of the boat (the

the crew. This type of accessory does not

lazarette) contains the steering

belong in the accommodation, but should be placed in a cockpit stowage space. On the YD-40 it is situated under the

mechanism, stowage for the liferaft, LPG and lighter items such as fenders. The compartment just aft of the steering quadrant on the YD-40 contains a

starboard cockpit seat. This

is

bottles

quite large,

but in real life it should be subdivided with fiddles and dividers so as not to

become

a giant gear-mixer

when

folding boarding ladder, integrated with

the transom platform, and by being at

low level it from the water.

the going

this

gets rough.

To

Deck layout

design a deck layout

that

suits

all

is

possible to reach

types of boats and

it

people

is

impossible. Like the accommodation, the intended use of the yacht has a

profound influence on the layout. different

compared

On

a cruising boat the priorities are

The racing deck

to those of a racer.

is

a working

platform that has to perform efficiently for a well-defined crew with

must work with a smaller space to sunbathe, protection from bad weather, and at the

specific tasks.

crew, offer

In contrast, the cruiser's deck

same time not be in conflict with the interior arrangement. On top of this we must not forget the performance side of it. The YD^O is intended to be a performance-oriented cruiser, and looking at the deck more closely we can see what compromises are made in comparison to a pure racer. The numbers below (14—33) refer to the circled numbers in Fig 13.4.

14

Originally, forward-raking sterns like this

one were developed on racing yachts to minimize deck weight, or to reduce the rated length under the lOR rule. It is interesting to note that on yachts designed to race under the IMS system (which does not measure the length in the same way as lOR), the transoms do

1

The cockpit

must be long enough to lie down in, even under way. This can be achieved even in quite small boats if considered

itself

in

the early design stages.

It

might not be possible to have a long

enough cockpit together with a heavily raked transom on a small yacht, and in this

case the cockpit length should be

On

not rake forward as heavily, since

given

cockpit space can be gained this way.

lying-down requirement that dictates the

On

a cruiser

we

can take advantage

priority.

length, but rather the

be working

of the forward-raking type of stern by

that shall

recessing a transom platform into

the layout of the

it.

This

good deck to board the yacht from a dinghy or floating dock. It also

a racer

YD-40

sail

it

is

number in

not the

crew the cockpit, and of

On

handling gear.

the benches are over 2

m

creates a

the

makes

and on the starboard side the bench contains hatches to the cockpit stowage space and the wet locker.

it

easier to recover a person

who

has fallen overboard, eases stern anchor

long,

handling and makes a nice showering

and towelling area

after a bath.

16 Generally speaking a steering wheel

Layout

Fig

1

3.4

Deck

layout -

YD-40

275

276

Principles of Yacht Design

takes a

space when under way than but the opposite is true when at

up

tiller,

less

anchor. The feel of the boat

is

system

much

tiller,

made more

length has to be almost 2

m

it

highly impractical

this

turns from hard over port to hard over

two on a performance-oriented boat, while on a heavy slow-reacting cruiser the number

starboard should not exeed

On

21

a cockpit as wide as that of the

YD-40,

against the opposite cockpit seat

when

the

extended forward to contain a cockpit table with a stowage space and a foot rest.

The primary winches

Fig

is

in

1

for the

the helmsman's seat

removable, and there

is

a door

aft

cockpit coaming to enhance the accessibility of the

transom platform.

system for the main, with the sheet to a

winch on the coachroof.

YD-40

The genoa winches

should be at

least of size

The

On

a cruising boat

the

sail

it

is

desirable to have

control lines (such as reefing lines,

outhauls, halyards and kicking strap)

18 Mainsheet handling systems often collide with other cockpit requirements on cruisers. Therefore, it is becoming common to employ a mid-boom sheeting

coming

foresails.

mainsheet winch working through a tackle of 3:1 ratio should be of size 24.

22 the

of

On

is

in

way

52, but preferably size 54.

same reason

the cockpit sole each side of the wheel

YD-40

the cockpit, to give a free

determining the sheet loads from the

17 To give the helmsman a chance to remain behind the wheel, an arched helmsman's

the

are situated well

3.5 gives another

main and

should be angled approximately 20°.

be out of reach of

coaming area as large as possible. The sizing of winches can be taken from most winch manufacturers' catalogues.

boat heels. Therefore the steering pedestal

seat should be fitted. For the

will

aft

forward

impossible to brace oneself

it is

an end-boom

edge of the bridgedeck, with the sheet and traveller control lines led into the coamings and aft via sunken rope clutches to winches which can be reached by the helmsman. The sheet is double-ended so that it can be operated from either side of the boat. The coamings are wide, and angled to be comfortable to sit on when the boat heels. the

tiller

to reach three.

to

consists of a mainsheet track recessed into

enough rudder action the number of

may be allowed

compared

The system we have used

19 and 20

cockpit design. To achieve a quick

of turns

greater

be

the helmsman.

to equal the

on

of the

that the sheet loads will

mainsheet winch

wheel-steering power on the YD-40. This

makes

is

The disadvantage

lines in

sheeting system, and the position of the

,

discussion of rudder forces, the

no

there will be virtually

the cockpit.

better with

and course adjustments can be quickly, which is especially important broad reaching in heavy weather, when broaching is most likely to happen. The disadvantage with a tiller is most obvious on a larger yacht. As we have shown in Chapter 11 in the a

way

this

which lead to the cockpit. For this reason the utility winches are placed either side of the companionway hatch, where they are easily reached from the cockpit. This tight

grouping of winches

not necess-

on a racing boat, where crew members might get in each

arily the best

different In

is

other's

way when

operating the boat.

277

Layout

Foresail sheef load (F^ ): Ffr

= 3.45 V^A^ [

53.5

3.4-5 -lO^-

= 18458 N ]

Main sheet load (F^): ^^ -

^-^5

•

10^ _ 7875 N ] [3.45- 4.70-15.1^ 15.65-3

^;_''^,:^^

Foresail sheet load [N]

= Mainsail sheet V = Windspo id Af = Foresail area £ = Mainsail foot P = Mainsail luff Ll = Mainsail leech r» = Mainsail tackle

load [N] [i^/^] [m ^]

I'm

Winch power

Fig

23

1

sail

ratio

(Pu/ )'

18458 = 52.7 350

^w

=

F^

= Crew power on

3.5 Calculation of

Leading

ratio

[nry]

[m] [m]

200 — 500 [N]

handle,

winch size (Marshall)

control lines to the cockpit via

on the coachroof, puts the roof under tension and exerts lifting

turning blocks

pressure. Therefore, install tie

7875 = 22.5 ] 350

is

it

25 As we can see from the deck plan the genoa tracks might be moved slightly

important to

rods between deck and hull

inwards, especially

in

the forward end,

as long as attention

is

paid to the

coachroof. The position of the chain

in

the mast area. Line organizers are used to

plates

direct the different lines to the cockpit.

To

a

good idea

to extend the

is

It

companionway

is

dictated by the rig calculation.

move them inwards would mean

higher rigging loads due to a narrower staying base. This in turn

since stepping on exposed lines

a heavier mast section

on the

deck can be very dangerous.

standing rigging.

It is

to find the proper

24

would require and stronger

hatch garage to cover these lines as well,

On

a racing yacht

we

an

process

iterative

geometry

that

fits

the

available mast sections, wire/rod and

usually have the

opportunity to place the genoa tracks at

intended deck layout. By using a three-

an optimum location. This means a

spreader

foresail sheeting

and the

10°.

angle of between 7.5°

in

accommodation.

sheeting position, since the tracks are

because

this

is

is

in

plates inward to the

It

is

difficult to

please

everybody.

not bad,

the sheeting position for a

small headsail, used

in

interfered with the saloon

the foremost

parallel to the centreline. This

might have succeeded

deckhouse, but then they would have

1

with the greater angle

we

moving the chain

The sheeting angle obtained on varies between 0° and 1 2°,

YD-40

rig

hard weather,

and by being sheeted slightly outboard does not backwind the main.

it

26

and ventilation are needed below, and the deck is the obvious place to let both of them in. When a skylight hatch is open it ventilates and no other Light

ventilation

is

needed. Ventilation

is

278

Principles ot Yachl Design

when

required, however,

closed.

the hatch

The obvious place

ventilator

in

is

standard 100 ventilator

the hatch

to ventilate a

itself.

fit,

cabin for

A shell

and is sufficient two people in

temperate climates.

27 Making the companionway hatch of smoke-tinted acrylic privacy

is

lets

maintained.

It

the light

in

but

forth in

an open

over the companionway increases the is

it

the

main

the boat's ventilation system.

wind is forward it acts as and when the wind is aft great amounts of air.

When

sailing with the

hatch open

factor in

When

the

To determine the

we must

fresh air that

is

1

and the other a up, built solidly and

ventilation. Quarter-berths or aft cabins

can become hot and uncomfortable if not properly ventilated. For obvious reasons the head also needs in particular

the

YD-40

these

requirements are taken care of by two ventilation skylights

needed below. For each

minimum

3.6

preferably 0.4

shows how much

with wind-speed.

air

CMM.

Fig

ventilation a

each side of the

companionway. 29 One very common, and good, ventilator is the dorade type. It consists of a scoop-

It

is

in

rough weather

sailing with the hatches closed that the

ventilators

exhaust

must provide

air. If

we

all

intake

and

consider a six-person

crew the required fresh air is 6 x 0.4 CMM = 2.4 CMM. The two 00 mm dorade vents on the YD-40 provide 2.8 CMM at a windspeed of 6 m/s. The exhaust area must at least equal the intake area, and we have two 100 mm 1

exhaust vents

28 As a general principle each compartment in the vessel should have its own

On

with the amount of

certain size of vent provides, varying

companionway

tight.

ventilation.

start

area

supply of 0.3 cubic metres per minute

scoops

ventilation openings,

good

total ventilation

person there should be a

it

lighter construction with built-in

set

needed

(CMM) and

wash boards may be secured so that they do not fall out if the boat is knocked down. It is a good idea to carry two sets of wash boards: one good-weather set of

heavy-weather

as handholds.

huge exhaust,

extremely important that

it is

lines

around them; these also serve

a

in

To prevent

being snagged, guards should be

it

ventilation; in fact

letting in water.

installed

does not slide back a seaway. Installing a dodger

position, so that

and

in

By directing the scoop into or from the wind it can act either as an exhaust or an intake ventilator. By placing the ventilators high on the roof and as close to the centreline as possible, as on the YD-40, they can be left open during rather rough weather trap.

without

should be

possible to lock the hatch

type ventilator placed on top of a baffled

water

to put a

mm diameter clam

easy to

is

is

the skylight hatches that

in

take care of that.

30 The to

and most important safety factor consider on deck is the danger of first

falling

overboard.

length grab

rail,

A

vital

item

is

so that you can

a full-

move

from the cockpit to the foredeck and have something to hold on to all the way. This rail also makes a good attachment for the safety harness. On the YD-40 this rail is bent inwards at the cockpit so that it is possible to clip on the harness before leaving the cockpit.

279

Layout

c MM ( One person requires

CMM =

\

supply

air

= 0.3 to 0.5 CMM ) Cubic Metres per Minute

In

t

10

1

1

1

1

1

1

1

-

9 J

/V

8

7 -

- WIndspeed [

m/s

6

/ 7

^\

>

y ^ / / X ^^ y^

-

>

,

5 4 .>

3

^^y^

^^"^ ^^

2

.^"^^ 1

:z..^r=r^

;;_,=—

25

50

75

_

100

^^

:

"

s^>^^

-

^^^

-^_^___, J^^-r^"^^ -

— ^-^rizl 125

1

-

,

50

200

175

Vent.

diam. Fig

1

^'"'"^

3.6 Airflow through ventilators

For boats with sail-handling systems (reefs,

a

on the mast it is incorporate a mast pulpit.

halyards,

good idea

to

lifts

etc)

32 The bow is an area where the combination of heaving and pitching

movements

is

the greatest, so here

it

is

have something to hold on to, ie the pulpit. Being a wrap-around structure it is possible to design it to be strong enough to bear the load from a essential to

31

The

chance of rescue before

last

the water rests with the height

is

often a

lifelines.

hitting

Their

compromise between

looks and function. To be safe the height

should be at least 750

mm

but the desire

good looks combined with efficiency has established a height of 600 mm, with

for

double

lifelines.

For small boats of

even 450 mm is accepted by the Nordic Boat Standard. As can be seen from the profile drawing lengths

below 8.5

m

YD-40 has a lifeline gate at the maximum beam. This is very convenient when boarding the boat lying alongside a dock or when boarding from a dinghy. the

The demands on the stanchions supporting the

lifelines are quite high.

falling

body.

A

disadvantage of being

wrapped around

when boarding

means

must be

points for the safety harness because a

centreline.

human body thrown

foresail furler the

10000 N (one

can reach a force of

tonne).

is

an obstacle

33 To have access to the forward deck stowage we must ensure that the deck hatch can be opened when the anchor is down and the chain is crossing the deck.

they cannot be trusted to be strong

roll

it

folded up.

In

during a violent

that

from a dock or shore when moored stem to. By making the forward part folding down we can have both good accessibility to the foredeck when folded down, and strength and security when

They must be throughbolted, but even so

against the lifelines

is

the boat over the bow,

practice this

offset or

that the hatch

divided at the

Thanks to the recessed deck is clear and unobstructed to aid anchor handling.

DESIGN

EVALUATION

A

aim of

basic

book has been

this

to provide the reader with the

for evaluating a design,

tools required

not only qualitatively,

but also in a quantitative way. Detailed formulae have been

provided,

enabling

of

characteristics

the

yacht.

information presented with an existing

designer

the

fleet

it

In

compute

to

combination

also possible to

is

performance

the

with

compare

the

a proposed design

of yachts.

This chapter summarizes the use of non-dimensional

composed of

statistical

parameters,

main data, for quick estimates of the performance properties of the design. These parameters have all been defined in earlier chapters but they are collected here, and their usefulness in the

evaluating the total concept

We

discussed.

is

then describe one of the most important tools available to the

namely the Velocity Prediction Program (VPP). This computer program predicts the speed, heel, leeway, apparent wind and many other quantities for a yacht under all possible wind conditions. By systematically changing the program input, yacht

professional

designer

today,

while specifying the yacht, the designer

may

optimize his design with

respect to different qualities.

The formulae given

information available from

are

largely

much on

the extensive series of yacht tests

of Technology, while

comes from wind-tunnel

based on empirical

of different kinds. The hydrodynamic

tests

part, for instance, relies very at the Delft University

book

this

in

and

much of

the aerodynamics

These kinds of results have been statistically evaluated to obtain the useful formulae in the book. The same kind of formulae are used in the VPPs. If more exact information is required on a specific design the traditional way has been to model-test it. This, however, is quite expensive, and is done only in connection with large projects like the America's Cup or Whitbread races, or perhaps for very expensive luxury yachts.

A modem

We

way

flow calculations,

will

tests

decribe briefly

to study a ie

full-scale experiments.

new

how

this testing

design in detail

using a technique

known

Dynamics (CFD). This technique has become

is

is

done.

to carry out numerical

as Computational

Fluid

possible through the rapid

development of computers over the last few decades which enables very detailed studies of the flow and resistance properties of the design to be made. Its advantage is that it is faster and cheaper than model-testing, but the technique is still under development and must, so far. be considered less reliable

CFD

than the

tests.

We

will give a brief

account of the status of

applied to yacht hydrodynamics at the end of this chapter.

Design Evaluation

281

Non-dimensional

The main data

parameters

displacement, wetted area and

relevant to a yacht's speed potential are the length, sail area.

To

estimate stability the heeling

arm and metacentric

height are also required. For judging seaworthiness

the beam, hull draft

and some information on the righting moment

at

large heel angles are also required.

Since the

sail

area

is

a measure of the driving force, and friction

is

component at low speeds, the sail most important speed parameter in light airs. This value should be above 2.0, otherwise the yacht will be very slow under these conditions. High performance will be obtained for ratios above about 2.5. Note that the sail area is defined here as the sum of the main and fore triangles. predominant

the

resistance

area/wetted area, S^/S^y,

is

the

much more complex. Not only carrying capability come into play. As

In stronger winds the situation resistance, but also the sail

the resistance,

we have

increases. In fact,

is

it

component due

seen that the

wave system becomes

of a

increasingly

for

to the generation

important when

speed

the

so important that most hulls will never be able to

leave the displacement speed regime at F^ interest in this respect

the

is

=

The parameter of

0.45.

the length/displacement ratio, L^^J"^

is

^'^

(or the

English equivalent, displacement/length ratio: see Fig 5.21). For a hull

reach the semi-planing region

to

around

has to have a ratio larger than

it

150), which is very rare. Dinghies, of course, and so are the Ultra-Light Displacement Boats (ULDBs), like the Whitbread 60 footers and the America's Cup yachts. Production boats can seldom reach higher values than 5.2 (smaller than 200), and most yachts are well below this value if the real sailing

5.7 (smaller than

are well above this limit

displacement

The

is

used.

vast majority of cruising

displacement speed region,

Froude number

is

in

essentially

and racing yachts thus operate in the which the wave resistance at a given proportional

to

the

A

displacement.

parameter often used for the medium to strong wind performance therefore the sail area/displacement ratio, S^/V ^'^. This parameter also a

measure of the yacht's acceleration

for reasonably

good

sailing

ability. It

It

is

should be above 15

performance. Very good performance

be expected for ratios of 20-22.

is

should be noted that the

may sail

area/displacement ratio says nothing about the influence of length on speed.

The

If this

is

A

simple and reasonably accurate

compute sail

ratio indicates the ability to reach a certain

Froude number.

given the speed varies as the square root of the length.

way of checking

the stability

is

to

the Dellenbaugh angle (as described in Chapter 4). Inserting the

area,

heeling arm,

displacement and metacentric height into the

formula of Fig 4.21 the heel angle

in a breeze

of approximately 8 m/s

is

The figure yields the variation between tender and stiff yachts. The seakeeping qualities of the yacht are best checked by computing the dynamic stability factor (DSF). as explained in Fig 4.22. This takes

estimated.

into account the proportions of the hull, the sail area, the shape of the

righting moment curve and the speed. For ocean sailing, above 40 are recommended, while 25 should be enough

DSF

values

for offshore

282

Principles of Yacht Design cruising and

should be above

DSF-

Inshore,

racing.

10,

while lower

values are sufficient in sheltered waters.

The

Velocity

Prediction

(VPP)

Program

The most important module of

VPP

a

equations for equilibrium, discussed

we

when

see that

the yacht

Chapter

Returning to Fig

5.

equilibrium,

in

is

in

routine for solving the

a

is

moves on

ie

5.1,

a straight

moments in each of the three More specifically, the following

course at constant speed, the forces and

main directions cancel each

other.

relations hold:

1

Along the direction of motion the driving force from the equal to the

sail

is

total resistance.

2 At right angles to the direction of motion the side force from the

sail is

in

the horizontal plane

equal to the side force from the

underwater body. 3 Vertically, the buoyancy force vertical

components

is

of the keel

equal to the gravity force and the

and

sail

forces are

assumed

to

cancel each other. 4 The heeling moment from the sails is equal to the righting moment from the hull. 5 The pitching moment from the sails is equal to the restoring moment from the hull. 6 The total yav^ing moment is zero, since the hydro and aerodynamic forces act along the same line in the horizontal plane. (See Chapter 8.)

These are the equilibrium conditions

in all six

degrees of freedom. In

assumed automatically satisfied, and so is the balance of the pitching moment (5). Very few programs include the yawing balance (6) in their equations, but the most advanced ones have a model for non-zero rudder angles and may practice the vertical force balance (3)

is

therefore consider this relation.

Most VPPs thus take transverse

forces,

and

into

account

only

the

longitudinal

and the moment around the longitudinal

As

and

axis,

ie

formulae for the resistance components are required, and those most commonly used are given in Chapter 5. The aerodynamic driving force is normally computed as shown in Chapter 7. Relevant formulae for the hydrodynamic side force are given in Chapter 6, and the opposing aerodynamic force in Chapter relations

7.

1,

2

4.

for the

first

relation,

The moment equation can be formulated using

of Chapter

4,

the stability relations

together with the heeling forces from Chapter

VPP the VPP

7.

Thus

the

have already been presented. In fact, they developed by one of the authors. are the ones used in Using the formulae of Chapters 4, 5, 6 and 7 relations 1, 2 and 4 may be formulated mathematically. The method for solving them is not obvious, however. It is necessary to use an iterative procedure. Thus, formulae required

in a

Design Evaluation 14.1

283

VPP flow diagram

True

wind velocity given

True

wind direction given

Boat speed

guessed Apparent wind velocity and direction from wind triangle

Heel angle

guessed

Aerodynamic forces from sail model h

Heel angle from heel equation

I.

jl

I

No

Boot speed from X— equation

No

Leeway angle from Y— equation

Yes

Yes

the value of

some

variables have to be guessed at the start. Based

quantities guessed.

process in

is

repeated.

is

obtained, which includes

each iteration get closer and closer to the

obtained

in the

on

new values of the These may now be used as a new start and the If the procedure is convergent the computed values

these values a solution

previous iteration, and

when they

initial

ones,

are close

ie

those

enough the

284

Principles ol Ydclit Design

solution

is

considered converged.

Some

care

is

needed

in

the present

case to obtain convergence, but the general sequence of operations

is

given in Fig 14.1.

The program moves

systematically

through

a

set

of given

true

windspeeds and for each speed a set of given wind directions is considered. These variations correspond to the two outer loops of Fig 14.1. For a given combination of true windspced and direction the procedure starts with a guess of the boat speed. The apparent windspeed and direction may then be obtained from the wind triangle, (see Fig 5.2). Now the heel angle has to be guessed, and this angle, together with the apparent wind, yield the aerodynamic forces from Figs 7.19, 7.21 and 7.22. The heeling moment may be computed and the heel angle found from the heel equation (4). If the computed angle is not close enough to the guessed one. the latter is updated and the process repeated with new aerodynamic forces. This is the innermost loop of the diagram. When the heel angle has converged, a speed may be found that gives a resistance which is equal to the known is thus employed. The guessed aerodynamic driving force. Equation speed may now be updated, a new apparent wind computed, etc. This is the outer loop to the right in the figure. Upon convergence of the speed the leeway may be solved from the side force equation (2). The result of the VPP calculation is often presented in the form of a polar plot (see Fig 14.2). Each curve represents a certain wind velocity, and the yacht speed may be found as the length of an arrow from the centre to the curve. The angle between the arrow and the vertical is the true wind angle. Points of special interest are the upper and lowermost 1

Fig 14.2 Polar plot I

True

wind dirocfion

Boat speed 12 [knots

Speed made good — maximum

True wind speed:

4 [m/s] 6 [m/s]

8 [m/s] [m/s]

10

150° '

Speed made good

minimum

285

Design Evaluation

ones of each curve, since these represent the best upwind and downwind

performance of the yacht. The arrows to these points thus give the optimum pointing angles upwind and downwind. The latter information is particularly valuable, since it is normally very difficult for the

helmsman

A

downwind.

to find the best course

polar plot

is

who can

of interest not only to the designer,

evaluate

different alternatives rapidly, but also to the racing yachtsman.

from the information on the best course the best setting of the sails

possible conditions

optimum

may

may

to

sail,

Apart recommendations on

be obtained, and a target speed for

be computed. The size of the

flattening of the sails are normally

computed

sail

to

its

to evaluate

ability

area and the

program, Chapter 7.

in the

based on the reefing and flattening functions mentioned

Due

all

in

performance VPPs are also becoming

The new International Measurement program very similar to the one described

useful in the handicapping rules.

System (IMS) is based on a here, and this system seems to be the natural successor to the lOR rule. The weakest feature of all VPPs is their ability to predict the performance in waves. This is because no simple methods are available for estimating the etTect of waves on sailing hydro and aerodynamics. The most promising work in this area is that of Professor Gerritsma and his co-workers at the Delft University of Technology, described briefly in Chapter 5. It is likely that general formulae for the added resistance in waves will become available soon and this will certainly improve the predictions. A problem that is still unresolved is the effect of the motions on the aerodynamics, even though interesting studies of this effect have been made at Massachusetts Institute of Technology, where most of the early research on VPPs was carried out.

Towing tank

testing

There are principally two different techniques for testing sailing yachts in towing tanks. The apparently most natural way is to tow the yacht at the correct centre of effort of the sails and, by means of an active rudder, let it attain its equilibrium heel and yaw angles. Each measured point

in

such a

number of

test

test

points

represents

may

is

kept fixed in

and the towing

pitch,

sailing

realistic

condition,

so

the

be kept to a minimum.

In the other technique the hull

except heave and

a

all

degrees of freedom,

side

force,

force

and

their

moments are registered for systematically varied speeds, heel angles and yaw angles. To evaluate such a test a special VPP is required. Rather than using the empirical formulae of the standard VPP, the measured forces

and moments are introduced

into the program. In this

way

the

evaluation will be specialized for the hull in question and the results

may

be expected to be more exact. The process

is

not straightforward,

however, since the means for interpolating the measured data to any possible speed/heel/yaw combination must be developed.

The

first

technique

is

captive. Obviously,

more

equipment required

is

called free-sailing

less

test

and the second one semi-

points are required in the

latter,

but the

complicated and the results are independent

of the stability of the model, since the heel

is

fixed. Different stabilities

286

Principles of Yacht Design

Carriage

Y— force .Universal joint

Fig 14.3

SSPA's yacht

dynamometer

(principle)

may

VPP. The free-saihng technique also calls for is required and the vertical centre of gravity has to be correct. At present, the semi-captive technique is by far the most common one in towing tanks all over the be evaluated

in the

more expensive models,

since a lead keel

world. In

Fig

14.3

the

test

rig

used

SSPA Maritime

at

Consulting

in

Gothenburg, Sweden, is shown. The towing force is applied to a mast approximately at the height of the CE via a transverse bar from the carriage. The bar is hinged at both ends to allow the mast to move vertically. At the point of attachment to the mast the longitudinal (X) and transverse (Y) forces are measured. The mast is always kept vertical, and when the hull heels it pivots around an axis through the mast at deck level. The foot of the mast may be locked at any sidewards position to fix the heel angle. To enable rapid yaw changes the mast is free to rotate at the point of attachment to the transverse bar. Fore and aft there are posts, free to move vertically and longitudinally, but locked in the transverse direction.

They

are attached

is by universal joints, and the side force at measured. A major advantage of this equipment is that it is stiff. Exact settings of the yaw and heel angles may be made, and they do not

to

the

each joint

hull

change under load. horizontally,

rather

A

disadvantage

is

that

the side force

is

applied

than at right angles to the mast, so there

is

a

component missing. This is can be determined beforehand. Since the weights constitute only a small correction to the displacement, there is no need to know them very accurately. Fig 14.4 shows a 12 m hull under test at SSPA. vertical

compensated for by weights, which

287

Design Evaluation Fig 14.4 12 test at

m

hull

-^

under

SSPA

seri^n

me: bj^"—^^^Lt^Jf^ ^s^

frl^i--'*^ ^^^^\

^^i J

\

'jg^kjpi^^

'^^i^^^^^H

^^^HIHiH^^^^^ ^^^^H^^^ajb

^^^^^^^H

....

'

»

-:^i$|^^^-; -•^ -

Computational Fluid

Dynamics (CFD)

—

"

,-

.

-

There are two main types of CFD methods used in naval architecture: methods for wave resistance and methods for viscous resistance. The reader is referred to Chapter 5, and Fig 5.4 in particular, for a description of these resistance components. The former type is based on the assumption that viscosity may be neglected, which makes possible a special approach called potential flow theory. This also includes lift and induced resistance. In the second type either the fundamental equations of fluid mechanics, the Navier-Stokes equations, are solved, or a simplification

known

boundary layer theory is employed. As explained in Chapter 5, the boundary layer is the thin region of water surrounding the hull, where the velocity relative to the hull changes from zero on the surface to approximately the yacht speed at the outer edge. By assuming that as

this layer

is

thin relative to the hull length the Navier-Stokes equations

assumption breaks down under certain circumstances, such as in the hull/keel or keel/bulb junction. For most ships the boundary layer assumption also breaks down in the stern region, but yachts are normally sufficiently slender that the theory may

much

can be

be used

all

simplified, but the

the

way

to the stern. Bustles or skegs

flow, however, particularly

if

may

complicate the

separation occurs.

Referring again to Fig 5.4, the frictional and roughness resistance components may be obtained using boundary layer theory, while

normally the full Navier-Stokes equations are required for the viscous pressure component. Wave and induced resistance may be found from potential flow theory, while the heel resistance

is

irrelevant in

since the calculations are carried out for the heeled hull.

resistance in waves, finally,

flow theory.

It is

may

the

same

thus possible to compute

as that

The added

be obtained from unsteady potential

resistance, as well as the side force, is

CFD,

components of the total so the output from the calculations all

from the tank. To evaluate the

results a

VPP

is

288

Principles of Yacht Design required, where ihe C\ I) oulpul

inlroduced

is

in

liic

same way

as the

from the tank. two advantages of CFD are that it is faster and cheaper than the tank. Another advantage is that very detailed information may be obtained on the flow everywhere around the hull. Pressure distributions, streamlines and velocity vectors are normally produced by the CFD programs, and especially interesting regions may be zoomed in. To obtain all this information from the tank would be extremely expensive. On the other hand, the CFD technique is new and experience so far limited. The approximations involved also tend to make the results less accurate than those from the tank. Therefore, CFD at present is a tool to be used when optimizing a design. Absolute accuracy is then not necessary, but the method must be able to rank alternatives in the right order. Furthermore, the detailed ilow results

As

stated above,

information

may

guide

the

designer

search

the

in

for

a

better

alternative.

SHIPFLOW is a CFD program developed especially for hydrodynamics problems by one of the authors and his co-workers. It includes a potential flow module, as well as both kinds of viscous flow methods: one based on boundary layer theory and one solving the Navier-Stokes equations. Although its major use is in ship design, the code has been used also for several yacht projects. Most results are some

confidential, but Figs 14.5-14.8 present

and measured wave resistance - Ant lope

calculations.

Fig 14.5 Calculated

C

10 1

1

6.0

e

Horreshoff

& Newman

(1967)

measurements

\

\

/

\

/

Larsson (1979) calculations

4.0

Larsson (1987) calculations

2.0

-^..^

-

1

1 1

y^

Kirk man (1974)

measurements

^-• 2.0

4.0

6.0

B.O

10.0

S

•

'O

Fig 14.9 Pressure

distribution

on

a sailing

yacht computed by

SHIPFLOW. (Copy of a colour photo, where each colour corresponds to a pressure interval)

both speed and leeway angle. with Froude

number

It

appears that the

lift

increases slightly

for a given leeway.

Fig 14.9 shows the pressure distribution on a yawed and heeled

This is

is

the type of plot used for detailed studies of the flow.

hull.

Normally

it

plotted in colour, which gives a good presentation to the results, but

this

has not been possible in this book.

APPENDIX

1

Main

particulars of the

YD-40

Refer to List of Symbols on page x

Half-loaded displacement: '

*

• • •

Lqa ^WL ^MAX

^WL Tc

T

•

Vc A

•

BIst

•

I

•

J

•

P

•

• • •

SMW

•

SAP

•

SAM

•

7.75 m-^

6.95

m^

8.12

t

7.25

t

3.25

t

3.25

t

12.05

= =

0.57

= = = = — = =

E SL

2.04

m m m m m m

= = = =

zz

10.02 3.71

3.17

2.07

SA

—

71.8

•

SW,

24.9

•

c,.

•

c„

•

T,

•

c,.

= = = = —

•

c.

=

T,

z=

•

Ak

•

Ar

•

LCB

•

Cp SA/SW,

•

SA/Vc^''-'

•

Loa/B Lwl/T ^WL ^C

•

• *

/\7

'/-^

•

T

*

Lqa /L^l Ff / L^L F,/F, Blst Rto

•

• •

= = = = = = — — — — =

m m m

m 4.3 m 15.1 m 4.7 m 16.6 m 7.75 m 36.3

= = =

m m m

16.9

— -

•

Light displacement:

35.5

mm' m2 m-

1.85

1.05

1.50

0.68

0.32 1.47

m m m m m m

12.05

9.85 3.71

3.12

0.54

m 4.3 m 15.1 m 4.7 m 16.6 m 7.75 m 16.9

36.3 35.5 71.8 24.1

1.85 1.05

1.50

0.68

0.32 1.47

21°

21°

14°

14°

-3.5

%

m2 m2 m2 m-

-3.5

m m m m

%

0.57

0.57

2.88

2.98

18.33

19.71

3.25

3.25

4.84

4.80

17.63

17.91

5.06

5.20

1.20

1.22

.142

m m

.144

1.22

1.22

0.40

0.45

APPENDIX

2

WEIGHT CALCULATION The weights

are

given

in

kilogrammes and

measured from the forward end of the waterhne and positive in the aft direction, denoted 'a" in the table, with negative values forward of the waterline, T. TCG is measured from the centreline with Group

is

1

"s"

Vessel

Name: YD-40

Condition: Half loaded

Structure

Item name

Hull gelcoat

Hull GRP Hull sandwich core Hull sandwich filler Keel strake e.xtra

Deck flange extra Deck gelcoat Deck GRP Deck sandwich core Deck sandwich filler Coamings GRP Roof GRP Roof sandwich core

Weight

LCG

TCG

VCG

45.000 450.000 87.000 50.000 47.000 46.000

5.37a

0.00

0.18

5.37a

0.00

0.18

5.37a

0.00

0.18

5.37a

0.00

0.18

5.18a

0.00

0.29

5.69a

0.00

1.24

16.000

6.08a

0.00

1.35

100.000

6.08a

0.00

1.35

17.000

6.08a

0.00

1.35

11.000

6.08a

0.00

1.35

40.000 105.000

8.20a 4.80a

0.00

1.39

0.00

1.52

12.000

4.80a

0.00

1.52

95.000 55.000 55.000 37.000 50.000 15.000 34.000 5.000

4.89a

0.00

0.16

4.90a

0.00

-0.44

4.00a

0.00

-0.40

5.00a

0.00

-0.41

7.15a

0.00

-0.37

0.85a

0.00

0.74

3.00a

0.00

0.68

6.55a

0.00

0.68

.000

9.75a

0.00

0.35

75.000

4.65a

0.00

0.37

120.000

4.90a

0.00

0.40

1588.000

5.30a

0.00

0.41

Item name

Weight

LCG

TCG

VCG

Sole 15 ply

5.000 6.000

0.40a 0.00

0.00

0.24

0.00

0.80

14.000

0.50f

0.55 0.77

Bilge stringer

Bottom stringer Mast step #1 to #4 floor Engine bed #1 bulkhead #2 bulkhead #3 bulkhead #4 bulkhead

GRP

taping

Misc

Group

Group

total

2

Purler housing

Group

1

1

Forepeak

Shelfl2piy Misc

1

3.000 total

28.000

in

the

and negative to port. 'p\ VCG is measured from the waterline with positive values above and negative values below the waterline. table

distances in metres.

LCG

positive values to starboard, denoted

1

5a

0.00 0.00

0,1

6r

0.00

0.

1.00

293

Weight Calculation Group

Forward Cabin

3

Item name

Weight

&

framing

LCG

TCG

VCG

20.000 5.000

2.15a

0.70p

0.60

2.35a

0.17s

0.05

1.07a

0.33p

1.08

1.38a

0.49s

0.67

Seat^

9.000 17.000 8.000

1.85a

0.50s

-0.01

Chain locker

10.000

1.38a

0.00

Dresser

14.000

0.74s

0.65

7.000

2.25a 2.49a

0.60s

-0.27

13.000

2.15a

Berth top

12

ply

Berth front

Overhead locker Hanging locker

Sole 15 ply

Berth cushion Seat cushion

Roof

liner

Side liner

Saloon door Misc

Group

total

Group 4

&

fronts

Stbd settee tops & fronts Bookshelves & lockers Chain plate knees Table Sole 15 pl\ liner

Side liner

Port cushion

Stbd cushion

Misc

Group Item

Nav Nav Nav Nav Nav

total

5

0.63

0.00

0.00

0.00

5.000

2.00a

0.00

1.45

5.000

1.60a

0.00

0.90

6.000 13.000

3.02a

0.39s

0.65

2.02a

0.05s

0.56

135.000

1.89a

0.03s

0.53

Weight

Port settee tops

Group

0.70p

3.000

.

Saloon

Item name

Roof

0.00

Nav

LCG

TCG

VCG

22.000 15.000 27.000 25.000

3.80a

0.90p

0.10

4.07a 4.35a

1.05s

0.10

0.00

0.90

3.80a

0.00

0.90

15.000

4.25a

0.1

5p

0.10

33.000 8.000 8.000 13.000 10.000 15.000

4.20a

0.15s

-0.26

4.25a

0.00

4.25a

0.00

1.00

3.80a

0.90p

0.10

4.07a

1.05s

0.10

3.97a

0.03s

0.26

191.000

4.07a

0.01

0.37

1.52

Station

name

Weight

LCG

TCG

VCG

table top 12 ply

8.000

5.75a

1.25s

0.65

table fronts

5.75a

0.95s

0.05

table seat

0.000 7.000

5.50a

0.45s

0.10

table bookshelf

7.000

6.30a

1.15s

1.05

table electr panel

7.000

5.75a

1.62s

0.90

5.000

5.85a

0.55s

-0.26

3.000 4.000

5.70a

0.90s

1.60

5.70a

1.78s

0.95

3.000

6.22a

0.60s

0.12

7.000

5.80a

1.05s

0.50

71,000

5.82a

0.98s

0.40

Sole

Roof

liner

Side liner

Cushion Misc

Group

total

294

Principles of Yacht Design

Group

6

Galley

Item name

Weight

Counter tops 12 ply Counter fronts & shelves Overhead locker

Drawers Icebox liner Sinks

&

Taps

&

insulation

plumbing

Stove Sole 15 ply

Roof

lining

Side lining

Misc

Group

Group

total

7

VCG

().()()()

5.50a

o.yip

0.65

5.60a

0.80p

0.30

7.000

5.90a

1.05p

1.30

12.000

5.22a

1.65p

0.90

7.000

6.38a

1.33p

0.29

15.000

5.30a

1.33p

0.31

5.000

5.38a

0.7()p

10.000

5.20a

0.7()p

22.000

5.88a

1.30p

0.47

15.000

6.01a

0.25p

-0.26

3.000

5.85a

1.03p

1.60

4.000

5.85a

1.82p

1.02

10.000

5.62a

l.OOp

0.39

132.000

5.65a

1.05p

0.43

LCG

TCG

VCG

0.38 -0.

1

Head

Item name

Wash Wash

TCG

12.000

1

Side locker

LCG

Weight

basin countertop 12 ply

5.000

7.15a

1.32s

0.56

6.000 7.000

7.06a

1.04s

0.15

7.02a

1.56s

0.97

12.000

6.44a

1.24s

0.65

6.000

6.58a

0.54s

0.64

Side bulkhead

12.000

7.15a

0.22s

0.69

Aft bulkhead base Wash basin & plumbing

12.000

7.75a

0.88s

0.65

5.000

7.41a

0.60s

-0.12

5.000

6.88a 7.39a

1.21s

0.29

15.000

0.64s

0.08

8.000

7.01a

0.73s

-0.26

2.000

7.21a

1.04s

1.60

1.000

7.09a

1.65s

0.90

10.000

7.03a

0.88s

0.45

106.000

7.10a

0.87s

0.44

LCG

TCG

VCG

basin counterfront

Side locker

Fwd bulkhead Door

WC

WC &

plumbing

Sole

Roof

liner

Side liner

Misc

Group

Group

total

8

shelf

Aft Cabin

Item name

Hanging locker Berth top Berth front

Fwd

&

bulkhead

Weight

&

dresser

12.000

7.37a

1.40p

0.72

15.000

8.81a

7.000

7.98a

0.66p 0.55p

-0.09

0.73

0.06

9.000

6.63a

1.15p

Door

6.000

6.63a

0.70p

0.75

Stow bins C/L bulkhead

4.000

8.72a

0.12s

0.45

15.000

8.81a

0.32s

0.31

Sole

10.000

7.26a

-0.26

7.000

7.96a

0.75p 0.70p

Side liner

5.000

8.88a

1.40p

0.73

Cushions Misc

14.000

8.81a

10.000

8.10a

0.56p 0.59p

0.33

114.000

8.07a

0.64p

0.35

Roof

liner

Group

total

1.00

0.13

295

Weight Calculation

Group

Cockpit Stow and Lazarette

9

Item name

Weight

LCG

TCG

VCG

Locker sole 5 ply Locker bulkhead

15.000

8.52a

0.80s

-0.15

8.000

8.25a

0.94s

0.10

Lazarette sole 15 ply

20.000 25.000 8.000 7.000

10.09a

0.00

0.05

9.98a

0.00

0.45

9.95a

0.00

0.85

9.47a

0.28s

0.24

83.000

9.53a

0.26s

0.23

1

Lazarette bulkhead

Lazarette hatches

Misc

Group

total

Group

10 Installations

LCG

TCG

VCG

Item name

Weight

Engine Prop shaft

207.000

7.04a

0.00

-0.06

12.000

7.80a

0.00

-0.37

Shaft sleeve

6.000

8.25a

0.00

-0.33

Shaft coupling

3.000

7.52a

0.00

-0.25

4.000 4.000 2.000 2.000 2.000 2.000 12.000 100.000 75.000 19.000 13.000 10.000

9.42a

0.00

-0.50

9.20a 7.40a

0.00

-0.30

7.44a

0.25s

0.18

7.26a

0.29s

-0.34

6.60a

0.28p

0.15

7.85a

1.05p

-0.10

8.04a

0.25p

-0.25

7.10a

0.00

5.22a

1.25s

1.00

5.30a

1.30s

-0.10

8.31a

0.40s

0.30

26.000 29.000 8.000 3.000 8.000 4.000 17.000

10.31a

0.00

-0.50

10.14a

0.00

-0.07

10.09a

0.00

0.06

10.08a

0.00

0.44

9.32a

0.00

0.40

8.78a

0.00

1.50

8.65a

0.00

1.05

4.000

8.54a

0.00

33.000

8.70a

0.40s

-0.15

38.000

0.00

-0.13

71.000

4.72a 7.30a 7.32a

725.000

7.54a

Propeller

P bracket Fuel

filter

Water filter Water intake

&

piping

Fuel piping

Shore power Batteries

Wiring

Nav

stn instr

Cool compressor Heater

Rudder Rudder Rudder Rudder Rudder Rudder

&

&

piping

ducting

blade shaft sleeve

quadrant linkage

wheel

Steering pedestal Pedestal instr

Fuel tank & piping Water tank & piping

Holding tank Misc

Group

total

&

piping

1

1

.000

0.20p

0.18

0.40

1.62

1.40s

0.20

0.00

0.01

0.05s

0.02

296

Principles of Yacht Design

Group

1

Deck t^uipment

1

LCG

Weight

Item luiDw

TCG

VCG

0.00 0.00

1.80

I'ulpit

15.000

0.65f

Slaiicliions

12.000

4.95a

I'ushpit

10.000

(),()()

1.45

Lifelines

10.000

0,00

1.65

Sheer

28.000 4.000 3.000 6.000 2.000 3.000 35.000 22.000 15,000 4.000

70a 4.70a 4.75a 4.70a

0.00

0.00

0.00

1.50

3.93a

0.00

1.65

5.50a

0,00

1.30

8.45a

0,00

1.20

6.50a

0.00

1.60

7.90a

0,00

1.39

8.90a

0.00

1.37

6.85a

().()()

1.80

8.50a

0.00

1.15

3.90a

0.00

1.20

l.OOf

0.00

1.39

.031"

0.00

1.35

.04a

1,12a

0.00 0.00

0.00

I0.38a

0.00

0.85

0.60a

0.00

1.36

2.50a

0.00

1.60

4.30a

0.00

1.60

6.50a

0.00

1.65

5.80a

0.00

1.65

4.66a

0.00

1.37

rail

Bollards

Mast turn blocks

Genoa tracks & cars Genoa foot blocks Rope clutches #1 winches #2 winches #3 winches

Main

&

track

blocks

Chain plates

8.000 12.000

Bow roller Bow anchor Anchor windlass Anchor chain Aft stay attachment

Fwd Fwd

deck hatch cabin deck hatch Saloon deck hatch Companionway hatch Companion garage

Deckhouse windows Deck ventilators Misc

Group

398,000

total

Group

Rig

12

&

&

Weight

spreaders

Boom

mm mm mm

Stays 7 or 8

Shrouds Shrouds

Runn

8

8

rigging

Spinn pole (on deck) Rigg screws & toggles Jib furler

Winches

&

stoppers on mast

Genoa hoisted Main hoisted Rodkick & blocks Mast top fittings Misc

Group

total

1

1

1.31

1.35

5.15a

0.00

1,65

4.04a

0.00

1,06

3,98a

0,00

1.06

TCG

VCG

Sails

Item name

Mast

20.000 25.000 70.000 4.000 4.000 5.000 5.000 10.000 16.000 7.000 3.000 40.000

9.

&

lines

LCG

24.000 23.000 12.000 10.000 17.000 12.000 13.000 9.000 18.000 7.000

4.15a

0.00

8,92

6.42a

0.00

2.70

15.000 15.000

5.68a

0.00

9.40

4.15a

0.00

12.00

4.10a 4.06a 2.15a 3.87a

0.00

4.60

0.00

9.40

I.lOp

1.45

0.00

0.00

1.08a

0.00

8.62

3.90a

0.00

2.16

3.50a

0.00

6.80

5.80a

0.00

7.80

6.000

4.85a

0.00

1.70

3.000

4.20a

0,00

18.60

35.000

4.16a

0,05p

7.28

319.000

4.16a

0.05p

7.28

Weight Calculation Group

13

Ballast

Item name

Keel

Group

total

Group

14 Payioad

Item name

Helmsman 2 crew

Forepeak gear

Fwd

cabin gear Saloon gear Nav stn gear Galley gear Head gear Aft cabin gear Cockpit Ikr gear Lazarette gear 1/2 water 1/2 fuel 1/2

holding tank

Group

297

total

TOTAL ALL GROUPS

Weight

LCG

TCG

VCG

3250.000

4.96a

0.00

-1.27

3250.000

4.96a

0.00

-1.27

Weight

LCG

TCG

VCG

80.000

9.10a

0.00

1.75

160.000

6.00a

0.00

0.70

60.000 65.000 35.000 40.000 85.000

0.60a

0.00

0.80

1.80a

0.10

4.00a

0.60p 0.50p

5.95a

1.35s

0.75

6.20a

1.40p

0.50

15.000

7.20a

1.30s

0.05

25.000 80.000 50.000 175.000 50.000 60.000

7.20a

1.30p 0.90s

-0.10

8.90a

0.08

0.35

10.00a

0.00

0.45

4.72a

0.00

-0.15

8.70a

0.40s

-0.13

7.30a

1.40s

0.20

980.000

6.07a

0.04s

0.42

8120.000

5.36a

0.00s

0.00

REFERENCES The

literature

on

sailing theory

Larsson below. The

Abbott,

1

following

and yacht design

list

is

extensive.

H, von Doenhoff. A E 1949. Theory of Wing New York: McGraw Hill.

Gutelle,

a

comprehensive

list

of references, see

1986-1993. Guide for Building and Classing Offshore Racing Yachts. American Bureau of Shipping,

P

1984. The Design of Sailing Yachts.

London:

Nautical Books.

Sections.

ABS

For

contains essentially the references referred to in the book.

Hammitl, A G 1975. Technical Yacht Design. London: Adlard Coles Nautical.

Paramus. Hazen,

ABS

and Classing Motor American Bureau of Shipping,

1991. Guide for Building

Pleasure Yachts.

G

S 1980.

A Model of Sad Aerodynamics for

Diverse Rig Types.

New

England Sailing Yacht

Symposium.

Paramus. Henry,

AIAA Symposium

Allen,

H G 1969. Analysis and Design of Structural Sandwich Panels. Oxford: Pergamon Press.

Cannell, D, Leather, Yachts.

J 1976. The Design of Sailing London: Adlard Coles Nautical.

Caprino, G, Teti,

Handbook.

R II

1989.

R

G,

Miller,

R T

1963. Sailing Yacht Design -

An

on the Aero/Hydronautics of Sailing. Held annually since 1969. Western Periodicals Company. North Hollywood.

Appreciation of a Fine Art. Transactions Society of Naval Architects and Marine Engineers, New

York. Herreshoff L E 1974. The Common Sense of Yacht Design. New York: Caravan-Maritime Books. Hildebrand, M, Holm, G 1991. Strength Parameters of Boat Laminates (in Finnish). Technical Research Centre of Finland. Research Notes No. 1289,

Sandwich Structures

Helsinki.

Prato - Pelf SpA, Padua.

M

Chesapeake Sailing Yacht Symposium. Held bi-annually since 1974. Society of Naval Architects and Marine Engineers,

DIAB

New

1991. On the Bending and Transver.se Hildebrand, Shearing Behaviour of Curved Sandwich Panels. Technical Research Centre of Finland. Research

Notes No. 1249. Helsinki.

York.

Manual H-Grade. AB, Laholm.

1991. Divinycell Technical

Divinyceii International

Honey, R

A

1983. Fibre Reinforcement Plastics in

Boatbuilding. University of Auckland.

Department

of Mechanical Engineering, Auckland. Gentry,

A E 1971. The Aerodynamics of Sail Interaction. AIAA Symposium on the Aero/Hydronautics

2nd

Hunyadi.

B.

Hedlund. P 1983. Strength Comparison of

Two

Constructional Concepts for a 25 Metres Racing Yacht (in Swedish). The Royal Institute

of Sailing.

A

with Yacht Keels. Seahorse Magazine, March/April

of Technology (KTH). Department of Lightweight Structures. Publication No. 83-16,

1985, pp. 23-26.

Stockholm.

Gerritsma,

J,

Keuning,

J

1985.

Model E.xperiments

Gerritsma, J, Keuning, J A, Onnink, R 1992. Sailing Yacht Performance in Calm Water and in Waves. 12th Symposium on Developments of Interest to

Yacht Architecture, Amsterdam. Gerritsma,

J,

Onnink, R, Versluis.

A

Committee on Safety from Capsizing.

1985.

Final Report of the Directors. United States

Yacht Racing Union, Newport and Society of Naval Architects and Marine Engineers. New York.

1981. Geometry.

Resistance and Stability of the Delft Systematic Yacht Series. International Shipbuilding Progress 28(328): 276-97.

Joint

N 1982. Strength of Bottom Plating of Yachts. Journal of Ship Research, Vol. 26, No 1, March

Joubert. P

1982, pp.

45^9.

299

References Kay,

H F

1971. The Science of Yachts.

London:

GT

Wind

uiul Water.

Foulis.

Kinney. F S 1973. Skene's Elements of New York: Dodd. Mead & Co.

Milgram, J H 1971. Sail Force Coefficients f)r Systematic Rig Variations. Technical Report No. 10, Society of Naval Architects and Marine Engineers. New York.

Yac/it Design.

R

Miller,

K L

T, Kirkman,

1990. .Sailing Yacht Design

-

A New

Appreciation of a Fine Art. Annual Meeting, Society of Naval Architects and Marine Engineers,

Lackenby. H 1978. ITTC Dictionary of .Ship Hydrodynamics. Marine Technology Monographs. Royal Institution of Naval Architects. London.

New

NBS

York.

1990. Nordic Boat Standard. Del

Norske Veritas

Classification A/S. Oslo.

Larsson. L 1990. Scientific Methods

in

Yacht Design.

Annual Review of Fluid Mechanics. Vol

22. pp.

H

1 979. Balance of Helm of Sailing Yachts - a Ship Hydrodynamics Approach on the

Nomoto, K, Tatano,

349-85.

Symposium on Development of Yacht Architecture, Amsterdam, pp 64-89.

Problem. 6th Lewis,

E

V, ed 1988. Principles of Naval Architecture. Society of Naval Architects and Marine Engineers,

New

York.

to

Obara,

C

J,

van Dam.

C

P

1987. Keel Design for

Interest

Low

Viscous Drag. 8th Chesapeake Sailing Yacht

Symposium.

Lloyd's 1978-1993. Rules and Regulations for the Classification of Yachts and Small Craft. Lloyd's Register. Yacht and Small Craft Department, Southampton.

C A

1966. Sailing Yacht Design.

London:

Adlard Coles Nautical. Poor.

Marchaj.

D

Phillips-Birt.

1979. .4ero-Hydrodynamics of Sailing.

C L 1986. The International Measurement System. Offshore Racing Council. London.

London: Adlard Coles Nautical. Rousmaniere. Marchaj. C A 1982. Sailing Theory and Practice. London: Adlard Coles Nautical.

Marchaj.

C

.A

1986. Seaworthiness. The Forgotten Factor.

London: Adlard Coles Nautical. Marshall,

R

1980.

Race

to Win.

New York

London:

W

DM

Street.

1990. Designed to Cruise.

London:

New York

and

W W Norton & Company.

&

2.

1973 and 1978. The Ocean Sailing Yacht. Vol

New York

and London:

R

1979. Designed to Win.

Coles Nautical.

London: Adlard

W.W

Norton

&

Company.

Symposium on Developments of Marshall.

New York and

W W Norton & Company.

Sponberg. E 1986. Carbon Fibre Sailboat Hulls: How to Optimize the Use of an Expensive Material. Marine Technology. Vol. 23, No. 2, April 1986. pp. 165-174.

1

R

Desirable and Undesirable

and London:

W W Norton & Company. Marshall.

J eds. 1987.

Characteristics of Offshore Yachts.

Interest to

Yacht

Architecture. Held bi-annually since 1969.

Amsterdam.

HISWA,

INDEX

ABS,

cardboard method

36, 40.

aspect ratio reduction 253, 260

cavitation 178 79

basic laminate 249,

Centre of buoyancy

definitions 248

width 254 guide 2, 246. 247 panel calculation 252, 253 sandwich panels 257, 259 stiffener calculation 254, 255 accommodation 13-15, 267-73

America's Cup Anilopc 288-90

1

7

1

1,

72. 107,

280-81

area,

of of of of of

foretriangle 148. 182, 183 keel

and rudder

130, 220, 221

mainsail 148, 182, 183

waterplane 38^0, 74, 76 wetted surface 33, 82 sectional 34 sectional correction 209

aspect ratio 99-107, 120, 124, 134-38. 152-53, 163 Australia If 107

balance, general 155, 157

rudder 162-63

M

Barkla,

beam

1

boundary layer

60, 62, 63, 118, 144.

287 bulb 106-7

buoyancy, centre of

19,

66, 81. 82. 183

178-79

155-61, 220, 221

content 229-32. 237. 249

229

20

fiarc 19.

flattening factor

Chesapeake symposium chord 99-100 cockpit 274 Computational Fluid Fynamics (CFD) 107. 180. 287-88 Computer Aided Design (CAD) 27, 28 Contessa 3 246 Copenhagen ship curves 23, 24 crimp 228, 229 curvature of lines 28

1

50

Floor.

bending moment 216 of inertia 255 section modulus 216 218. 254. 255 freeboard 19. 94-5 frequency, of encounter 47. 84 frequency, natural 47. 84

moment

Froude number

1

71 (definition)

Fibre Reinforced Plastics (FRP)

2.

227 galley 270. 271 3,

genoa track 274. 275 Gentry. A E 34 1

Gerritsma, J 73. 88. 114. 159. 167. 285 ghost transom 21 ghost stem 21 glass

Davidson Laboratory 107, 146 deck, compression 209, 225 design 13. 273-84

mat 227-30

Glass reinforcement, types 227 binders 228 glass roving 227-29, 231. 249, Grimalkin 46. 49. 51

rig forces 207,

P

Gutelle,

2

gyradius 85-90

34-8, 43. 65,

Delft University of Technologv 73.

Dellenbaugh angle depth 17

canard wings

D

1

157

230

arm

designed waterline 26 diagonal 21, 26 displacement/length ratio 78, 79 displacement, general 17. 26. 76-8 volume 32 weight 34

heeling

draft 17

hogging and sagging 49. 50. 205 Holm, G 228 hull girder, bending moment 208. 222 section modulus 205-9 human figure 266 humps and hollows 72 Hunyadi and Hedlund 214 hydraulically smooth 66 hydrostatics 30

23^ Stability Factor

(DSF)

53.

281

2

cant angle 108-9

G

52, 83, 281

design spiral 5

Dynamic 1

half breadth plan 20

Hammitt, A G 2 Hazen. G 147 head area 272 heave 46. 84, 89

113, 115, 280, 285

duck

camber 139^2

Caprino,

fibre

fibre angle 228.

drag bucket 121 drag 100, 148-52. 289

buttock 21, 26

Cannell.

34-8. 43. 65.

from slamming 214. 215

16

beam/draft ratio 82 beam of waterline 17 Bergstrom and Ranzen 138 bilge factor 32 biplane theory 111. 157 block coefficient 18, 19. 205 boom requirements 195, 197

Burrill

19.

Centre of flotation 40 Centre of gravity 19. 35, 36, 183, 293-98 Centre of pressure 163 Centre of lateral resistance (CLR) 157-62 chart table 268

openings 207 deformations, from 208

ballast 95

10

Fastnet disaster 45. 51

Centre of effort (CE) 98, 148. 150,

effective

allometric series

fairing 109

66, 81, 82. 183

design heads 250-52

advance velocity

44

elliptical force distribution

110

98-9. 103,

182. 183

Heller and Jasper 212

Henry,

R G

Heyman.

G

Hildebrand.

HISWA

1

124

M

228

symposium

1

Index mass moment

instrumcntalion 269

Standards Organization

liitcrnalional

(ISO) 53. 55

Towing Tank

International

Conlcrcnce (ITTC) 4 International OlTshorc Rule (lOR)

Measurement System

(IMS)

52. 147. 153,

inverse taper

oi inertia 84 90 Massachusetts institute of Technology 134, 285 mast

285

10

1

Joubert, P N 212 junction angle 108-9

H F

added 59, 83-8. 165, 167-68 components 58, 59

holes

m

induced 59, 111, 287. 289 propeller 180-81

rake 199

residuary 74-8. 165

transverse stiffness 183, 194, 195

roughness 287

moment 218. 219 transverse moment 216. 217 impact

Kelvin wave system 69 Kinney, F S

R T

Miller.

Reynolds number 63 Ridder, S

mirror image 98 modulus of elasticity 204, 236, 237

crew to windward 182 floor bending 216, 217 hull bending 208 impact 218, 219

153

laminar 60. 62. 63 laminate exotic 234. 235 fatigue 233 microcracking 233. 234 prepreg 235

of inertia 39, 40, 204. 210. 255,

properties (E-glass) 230, 231, 235,

properties, typical 201

transverse loads 185-87

weight, handling, price 193 types 183, 184, 189 wire versus rod 191-93 righting roll 46.

rudder and keel 221. 222

Royal

J

E 53

(definition)

107

breaking strength 191 fatigue, corrosion, elongation 192

righting 182. 183

Moon,

O

rig

259

moment 40 89

Institute of

Technology 138

rudder aspect ratio and area 220, 221

249,

NACA

thickness 229, 232, 249

sections 116-21

forces 220-22, 256

Navier Stokes equations 287 Nordic Boat Standard (NBS) 183 Netherlands Ship Model Basin

wet 232, 233 Larsson, L 2 lead 155. 161-62

(MARIN)

Leather. J 2

Length between perpendiculars 16 of waterline 16 of waterline/canoe body draft 92-3 of waterline/draft 92 overall 16

overall/length of waterline 94

overall/max

upright 58 viscous 58, 60-1 viscous pressure 59, 64-6 wave 58. 69-73, 287-88

153

1.

59. 66-8, 125-27. 145.

total 59

Moment

I

1.

section 26

metacentric height 40 metacentric radius 40 midship section 26 Milgram. J H 134-37

bolts 257, 258

Knkman. K L

27

7,

metacentre, transverse 40

2

82, 165, 287

heel 59, 83, 287

198, 199

longitudinal stiffness 184, 195. 196

maximum

keel

61^,

frictional 59,

general 57

fractional top 195, 197

master curves

Kav.

Resistance

location of foot 184, 185

61. 136. 153

International

301

K

Sandwich

ABS

157-59

calculations 257, 259 bending 239, 241, 244, 245

nose radius 115-18, 125

buckling 240, 241

Oossanen van, P 53 orbital motion 50 Osaka University 157

core 239, 242, 243, 261 critical

load 238

general 237

normal

osmosis 228

beam 91-2

stress 241,

242

shear strength 241, 242, 244 scale factor 20, 32

perpendicular, aft 16

rated 16

forward 16

length/beam 82 length/displacement 78. 79, lift^lOO. 148-52, 289

221, 222, 256

stock 256, 257

sagging 49

171

neutral axis 204. 209. 210

Nomoto.

moments

93^

Phillips-Birt,

D

Scheel keel 114

pitch 46, 84, 89, 90, 169, 174-75

lifting line

planform

Load

planimeter 24, 25 polar plot 284 Poor, C L 53 potential flow 287 prismatic coefficient

theory 100, 111 lines drawing 20 Lloyd's Register 8 global 203. 205-11. 225 keelbolt 216. 217 local 203, 211-22. 224. 225

slamming 212. 213 Maas. F 73 mainsheet system 274, 275 Marchaj, C A 1. 125. 137, 139 Marshall, R 276

sea berths 266, 272

I

99, 107, 134

seakeeping 84 seaworthiness 53 Section

max

area

1

midship 17

1

Modulus 17,

18, 65, 66,

204. 210. 260

sectional area 34

separation 61, 65, 122-24, 142-45

78-80 profile 26

sheer 19

profile plan 20

sheet load 275, 276

propeller characteristics 169-70, 176

SHIPFLOW shroud, angle

ratios,

dimensionless 50

reef factor

1

13,

90-5, 281

63. 288, I

forces 185, 187-89

SI system 4

290

88, 189

302

Principles of Yacht Design

SI system 4

taper ratio 99

Simpson's rule 31 Simpson's multiplier 31. 34 Skene,

N

Teti,

100, 103

5,

ballast ratio 95

108 9

R 230

centre of buoyancy 37

thrust 169, 170

computer aided design 27-9

shape 105 7 torque 169. 170

deck layout 273 79 Dellenbaugh angle 52 dynamic stability 53-5 freeboard 94-5 frictional resistance 64 grounding forces 218, 219

tip

1

skin friction 63

slammmg212,

213, 225

SNAME/AIAA

transition 61. 62, 63. 118

symposium

1

Southampton University 143 speed length ratio 73 spline 22, 24 spreaders

transom 26 trim tab 109, 123-24 Troost propellers 171-76, 180 tumble home 19 turbulent 60, 62, 63

heel resistance 83 hull girder

twist 107 8

angle 184, 197, 198

64

scantlings 261

accommodation layout 267 73 added resistance in waves 167-68

1

wave height 88

significant

ABS

sway 46 sweep angle 99 100, 103-5 tandem keel 13

shroud, angle continual forces 1«5. 187-89

numbers of 184

210

and rudder

keel

130, 131, 220,

221, 256. 257

requirements 195, 198. 199 Consulting 286-87

USA

keel forces 216. 217

111

SSPA Maritime

length displacement ratio 94

van de Stadt

stability

&

Partners 74

Velocity Prediction Program (VPP)

dynamic 30 form 41

length of waterline/draft 92 6,

length of wl/canoe

body

draft 93

w

282-87 ventilation 277, 278

length overall/length of

range 44, 52 weight 41 stagnation point 96, 97 stall 102, 122

venturi effect 134

lines

drawing 20

moment

viscosity 60

long long

viscous sublayer 61

mast 143

statistics

vortex 48, 59, 84, 98-112

preliminary design 12-15 propeller calculations 171-81

waterline. length of 16

resist

Whitbread Race 280, 281 winch placement of 275, 276 size 276 wind

168

114, 147, 280,

general 30

vertex

hull

90

keel

and rudder area 130

stability 52

stay

forces 189-91 fore-

and

aft-

190

fore- curve 193

steering wheel stiffness

and

tiller

222, 274

204

stove fuels 270. 271 strain 204, 233, 235 stress,

general 204

7,

stability,

of inertia 38 small angles 42

calm and rough weather

rig 199-201 rudder forces 220, 221. 256 sail

area 154

sail coefficients 151

sectional area 34

velocity triangle 57, 284

total resistance 59. 168

windage 166 wing section

yaw 46

YD-40

static stability

trans

15-30 winglet, keel wing 107-10 1

194

beam 92

apparent 57 true 57

normal and shear 241, 242 Sunshine i(y-l surge 46

27

length overall/max

moment

curve 44, 45 of inertia 39

trans stability, large angles

42^

trans stability, small angles 40, 41

volume displacement 35 waterplane area 38^0 wetted surface 33

Lars Larsson,

a naval architect,

Hydrodynamics

at

He

and was a

from 1971-89.

A

is

in

President of Flowtech

scientist at

SSPA Mantime

Consulting

compu-

has wntten over 50 papers on

dynamics applied to ship hydrodynamics, and has

tational fluid

taught

He

Professor of

Chalmers University of Technology

Gothenburg, Sweden. International

is

many academic and

1

in

yacht design.

Larsson was instructor

sailor since birth, Lars

hydrodynamics to the

public courses

984 Swedish Olympic

aero and

in

sailing

team,

was design consultant to the Swedish Amenca's Cup team from

1

Italian

US

975-80, the //

Moro

di

America

II

team from

Venezia team from

Rolf E Eliasson, structures, runs his

1

1

984-87, and the

989-92.

a construction engineer specialising

own

design

company

in

for both production

and one-off yachts. More than 3000 yachts have been

from 1

his

designs over the past 20 years.

yacht

Between

1

built

976 and

982 he won three intemational design competitions and was

runner up

in

a fourth.

Rolf Eliasson has

EEC and

been

a

since 1990, setting scantlings.

wood and

He

member

ISO standards

has built

using different

forerunners

in

six

for yacht safety, stability

yachts himself-

GRP methods

- and

computer techniques

using

for the evaluation of

new

designs.

International Marine

Camden,

of working groups within the

h'^.^.\,

in steel,

is

one of the

for yacht design

and

CONTENTS DESIGN

METHODOLOGY

DESIGN CONSIDERATIONS

THE YACHT'S SPECIFICATIONS

HULL GEOMETRY, INCLUDING LINES PLANS DESIGN

AND COMPUTER AIDED

HYDROSTATICS AND STABILITY IN

CALM WATER AND WAVES

HULL DESIGN KEEL

AND RUDDER

SAIL

AND

DESIGN

RIG DESIGN

BALANCE PROPELLER

AND ENGINE

CHARACTERISTICS

HULL CONSTRUCTION CONSIDERATIONS RIG

CALCULATIONS

COCKPIT, DECK

AND

CABIN LAYOUT

WEIGHT CALCULATIONS DESIGN EVALUATION, PERFORMANCE PREDICTION TESTING

AND TANK

ISBN 0-07-036492-3

780070"36A929