Yacht research at the Delft Shipbuilding Laboratory

Report No. 382 P

E

L

I

August 1973

LABORATORIUM VOOR

SCHEEPSBOUWKUNDE

TECHNISCHE HOGESCHOOL DELFT

YACHT RESEARCH AT THE DELFT SHIPBUILDING LABORATQRY by J. Gerritsma and G. Moeyes

II

Yacht Research at the Deift Shipbuilding Laboratory

J. Gerritsma G. Ì4oeyes

Summary

In the last few years a substantial amount of sailing yacht research has been

carried out at the Shipbuilding Laboratory of the Delft University of Technology.

In this article the Authors give a short review of these activities, as well as the results of one particular investigation : the determination of the

performance of the Van de Stadt designed "Stormy".

Introduction

The Delft Shipbuilding Laboratory as founded in

₁₉₃₇

was completely renewed

in

1952.

The purpose of this Laboratory is to provide scientists and students

with the experimental facilities for research in the field of ship hydro-mechanics. There are two ship model tanks and a circulating watertunnel for model ship propellers at the disposal of staff and students. The main

particulars and dimensions of the towing tanks are shown in Figure 1.

Extensive electronic measuring instruments arid, a very large central computer are available for data reduction of the experimental results. The Delft

Shipbuilding Laboratory specializes in the dynamic aspects of ship behaviour at sea, such as the seakeeping qualities in waves, steering,maflOeUvrirlg and

stability. The investigations include a large range of ship types and ship

dimensions, covering sailing yachts as well as super tankers and large containerships.'n addition tó model experiments full scale trials at sea

are carried out to check the theoretical and experimental results.

Although already in

1950

yachts had been tested in a previous Deift tank, of

which "eevalk" is for instance a notable example, more interest arose in

the last decenna

and on 30th September

1966 a

Netherlands Yacht Research

Panel was founded to assist the staff of the Laboratory in planning ând

discussing yacht research.

The Panel consists of leading Dutch Yacht designers and staff members of

the Laboratory. In the case of sailing yachts standard performance

measurements for the close hauled and the down wind condition, based on

model experiments in calm water5 form a large part of the activities, but

in addition resistance and motion experiments in waves, aswell as

directional stability and rudder performance tests are carried out.

Sealceeping and steering investigations were carried out for instance for the 12 meters "Columbia" and "Valiant" (of which the lines and particulars were kindly put at our disposal by Sparkman and Stephens)and for "Standfast", a Frans Maas design. For detailed information of such dynamic testing of

yachts the reader is referred to the publications [i] , [2] and [3]

As a further activity,the bi-annual HISWA Yacht Symposia, which started

in 1969, may be mentioned. Lectures and proceedings are in the English language for international circulation and to enable experts of different

natiönalities to give their views on yacht design, yacht building and

related subjects, The technical part of these Symposia is organized by

the Deift Shipbuilding Laboratory. Deift also cooperates in an international comparison of tank test results with scale models of the 5q5 meter

"Antiope", which was tank-tested full scale in the Naval Ship Research and Development Centre in Washington D.C. The coniparison is made to detect

possible scale effects in the prediction of full scale performance from

model test data. An additional model on a - scale will be tested to fill the gap between the small model and the full scale yacht. For the near

future a rather large series of systematically varied aling yacht hull

forms will be tested in the elft Tank to obtain a better insight in the

importance of the various hull form parameters, which influence the

resistance-yachtspeecl. relation. Too much ad hoc work is carried out in

yacht testing and it is anticipated that the results of systematic resistance tests will be an aid for the designer and his adviser to attain optimiun

results in a more direct way.

As an example of our work the results of tank tests with a model of

"Stormy", designed by Van de Stadt, will be given in some detail.

The original keel-rudder arrangement was tested, as well as three modifications, which also include a slightly increased sail area.

3. Model test results with "Stormy".

Racing results with "Stormy" having the original keel and rudder, showed that the performance in the close hauled condition was not always

satisfactory. In order to assist the designer in finding a better solution, three new keel-rudder configurations were tank tested, the huilform itself remaining unaltered.

The four keel-rudder configurations are shown in Figure 2 and the main particulars of the hull form, are given in Table 1.

Table i

Main particulars

Keel I is the original design : a rather thick bulb attached to a

relatively thin keel having a moderate area. There is a long and shallow skeg between keel and rudder and a gap between the upper part of the rudder and the hull.

3. symbol description I configuration II III IV waterline length m 12.91 12.91 12.91 12.85 BDWL waterline breadth m 3.69 3.69 3.69 3.67 BMPLX maximun breadth m 14.16 14.16 14.16 14.16 T draught m 2.51 _2.51 2.68

₂₆₅

displacement ton 11.390 11.390 ,11.390 11.390

LDwL/'

length displacement ratio 5.8I 5.814 5.814 5.86 LCB/LDWL position of centre of

buoyancy behind mid LDWL

0.5 0.5 0.5 0.5

C prismatic coefficient 0.53 0.53 0.53 0.53

z centre of gravity under DWL m 0.141 0.141 _0.25 0.143

ballast ratio 0.141 0.141

_o.14i

0.141

Keel II has a longer and more slender bulb, a slightly larger aspect ratio

and a keel flap. This keel has slightly larger thickness to avôid early

separation effects when heavily loaded

in a seaway. Keel III has no bulb,

a larger area and increased thickness to carry the ballast. The final

version IV has still more thickness at the under side to lower the centre

of gravity and a trim flap of 25% chord length. In the final reconstruction

the mast was lengthened and a corresponding increase in sail area was

obtained as shown in Figure 3.

The speed-resistance relations for the four different configurations are

very similar, as indicated for instance in Figure )4, where the yacht speed

in the down-wind condition (no heeling angle and no leeway) is given as a

function of the true wind speed. A

expected the incrased sail area

increased the speed by approximately 1

to 2%. The speed made good, derived

from model experiments with leeway-. and heeling angles are shown in

Figures 5,

6

and 7.

Keel I and II (figure 5) approximately give the saine result. It should be

remarked that the trimflap of keel II was deflected

respectively 10°,

200

_and

300

_{heeling angle. In Figure}

₆

_{keel III is}

compred with the original one and in this case two conditions are

compared

i) Keel III has the same vertical positiOn of he centre of

gravity as keel I

2) Keel III has the higher centre of gravity which is realistic

for this particular keel form.

With the saine vertical position of the centre of gravity as with keel I,

keel ITI gives a 1.5% to 2% higher speed made good for true wind speeds up

to

urn/s. ForO the more realistic higher centre of gravity keel III is

slightly better below a wind speed of

6m/s

but for higher wind speeds

a

speed loss up to 2% is observed. Thus, the better hydrodynamic quality

of the keel

is lost for a good deal due to decreased stability (higher

centre of gravity). Keel IV, with the larger thickness, gives more

stability and the keel flap, when deflected in

a proper way, reduces the

leeway angle amost by a factor 2 in this case.

o o 6

and

8

at

The same flap deflections as fdr keel II were used and the comparison of the speed made good with the corresponding values for keel I in Figure 7 shows

a marked improvement in a large range of true wind speeds a 3% to 1% increased speed made good is obtained. In the case of keel IV the stability is almost equal to the stability with keel I and therefore the improvement

must be due to the better hydrodynamic quality of fin keel and rudder. 1n

addition the skeg between keel and rudder was completely removed (see Figure 2). The reason for this is, that such a skeg has a low efficiency due to a relatively large induced resistance. The better keel performance is also

shown in Table 2,where the total resistance, the ratio of side force and

total yacht resistance, the leeway angle, the apparent wind angle and the true wind angle are given for a constant heel of 20 degrees, a side force

of 696 kg and a yacht speed of 3,83 in/s. (7.5 knots).

Table 2 Keel Quality

In particular the higher side force-resistance ratio of keel IV should be noted, as well as the lower total resistance. In this Table all of the

keels were assuernd. to give equal stability: The smaller leeway angles are caused by the keel flap; the favourable effect of less leeway upon the sailforces is not taken into account in the analysis and the performance prediction of the yacht with keel IV therefore is conservative.

A more complete picture of the influence of keel flap deflection on the leeway angle is given in Table IV shere the leeway angles of all four

modifications are given for optimum close hauled conditions.

5.

keel I keel II keel III keel IV

total resistance 252 kg 251.4 kg 21.414 kg 237 kg

side force/resistance 2,76 _2,714 2,85 2,914

leeway angle 5,6° 5,30 5,6° 3,1°

apparent wind angle 28,1°

282°

50

27, 27 1°

As already mentioned the flap deflections for keel II and IV were

i°,

6°

and

8°

at heeling angles : 100, 200 and 3O respectively.

Table 3 Leeway Angles

The results of keel II indicate that the flap deflections as used in the experiments were too small for this particular case to have appreciable effect. It should be noted that the area of keel II is approximately 60% smaller than the area of keel IV.

Finally the influence of the increased sail area on the speed made good is shown in Figure 8 for keel IV. For wind speeds lower than 8m/s the speed made

good increases with 3% to 4%. For higher wind speeds the stability is insufficient to carry the increased sail area, and the performance

is

less

than with the original sailpian. Consequently,

in

this particular case, the sail has to be reefed for true wind speeds

higher

than 8

rn/s

or, as an easy indication, when the heeling angle exceeds 20°. Again this emphasizes the importance of the influence of stability on the speed made goocLof a sailing yacht. As a conclusion it may be said that the modified keel, and rudder in

addition to the larger sail area resulted in an appreciable improvement of the yachts performance.

Acknowledgement

The investigation was carried out with the assistance and stimulating

discussions of the designer E.G. van de Stadt, who also provided the model of the yacht.

6..

heeling angle Keel I Keel II Keel II Keel IV

10° 20° 300 3.8° 5.I4 8.3°

350

8.1°

3.9° 5.1° 9.2e 2.1° 3.2°

6.00

References

J. Gerritsma

Course keeping qualities and motions in waves of a sailing yacht Proceedings of the third ALAA Symposium of the Aero/hydrodynamics of

sailing, California

1971.

2 J. Gerritsma and G. Moeyes

The seakeeping performance and steering properties of sailing yachts HISWA Symposium yacht architecture

₁₉₇₃

Amsterdam, Netherlands.

3 J. Gerritsma and G. Moeyes

The seakeeping and steering performance of sailing yachts

Sail, April-May

1973.

Length Breadth Depth

Towing tank I :

t.42m

420m

2.60m

Towing tank]I :

85m

2.75m 1.25 m

Workshops and technical staff

DeLf t

shipbuiLding

Laboratory

tJ6

_{Section AA}

/

Scientific staff

Scientific staff

Ground floor

carriage

Towing tank I

i/carriage

I

I- -II

//

II

A

cay, tunnel

Towing tankL

i il

A

11

II

i-

p

/I

I/Il

Ii, - I!

I

'I'

I'

i i III _I,

I,

-

-

-I I

',,

/I

-:-i.

_'Ip

ii

Ill

_Il

I,

I,

Il

II

t

il.

I'

Fig.1

Ground fLoor

10m

20m

jjUUUU LI

Keel I

L

Keel i!

Keel iii

-j

1.28

1.95

all maurements

in meters.

o

U) U,

o

Figure 2.

Keel

-

rudder conf igurat.ions for

\

\

\

\

original

modified

\

\

\

\

\

\

\

\

\

Figure 3. Original an:d modified sailpian of

o

w8

(n

L-O)

cL7

(n

L.

G)

I

a)

E

G)

C3

w

L.

Keel

I

I original sailpian

I

--

----

KeeL

Keel

saitpLan

-Iv original

sailplan

1V

modified

.

-'7

/

/

1. Knots

-Yacht speed in meters per second

g

$

/.

₅

o

i

2

3

12

11

lo

g

V

.g

_C-)

a)

In

I-.

G)

(n

G)

w

E

w

G)

U)

V

w

I-F1

o

0

1

2

3

Speed made good in meters

per second

Fig.5 Speed made good for keel I and

U.

I

keeL I

-

heeling

flap deflection

(with deflected

'angle

=3O°-=''

§

=

8°..

keel I[

flap)

-

_

=l00

-/

/

2

1. Knots

6

12

11

lo

'DB

g

C-)

w

U)

L.

G)

U)

L.

G)

4-I

w5

E

o

0

1

2

3

Speed made good ¡n meters

per second

Fig.6 Speed made good for keel I and lU

Keel'

I

heeling

ingle

=3O0

---Keelifi.

-

_{(centre of}

with keel I)

gravity as

H

-.-.-.

KeeL

i

_I

1/

/

/

i

/

lO

-/

2

4 Knots

₆

$

g

C

o

C-)

w

U)

.

_o.

U)

t-w

w

E

V

w

w

o-.10

9

5

L

3

i

0

1

2

3

Speed made good in meters per second

Fig.7Speed made good for keeL land Iv

keel

heeLing angLe

_=30°

flap deflection 8=

80

I

1

keeL BL with defLected flap

I

'I

/

+io:

/

/

z

/

7/

¡2

jL Knots_

16

w

2

t-8

7

6

12

11

0

1

2

3

Speed made good in meters per

second.

Fig.8 Speed made good for

original and modified

sait, ptan KeeL

iV

Keel

iVi:

original

deflection

,heeUngang1e

saiLplan

saiLpLan

=O°

Keel ]V: modified

§ =8°

-f Lap

I

/

/

:1

/

/

z

7

I

z

Knots

IN THE last few years a substantial

amount of sailing yacht research has

been carried out at the Shipbtiilding Laboratory of the Deift University of

Technology, tri this. article the Authors, J Gerritsma and G. Moeyes

give review of these activities, _{as well}

as the results of one particular investigation:

_{the détermination of}

the performance of the Van de Stadt

designed Stormy.

The Netherland Yacht Research

Panel consists of leading Dutch Yacht

designers and staff members of the

Laboratory. In _{the case of sailing}

yachts ; standard

performance

measurements for the close hauled

and the down wind condition, based on model experiments in calm water, form a large part of the activities, but

in addition _{resistance and motion}

experiments in Waves, as. well as

directiOnal stability and rudder performance tests are carried: out.

Seakeeping and steering investigations

were. carried out for instance for the.

.12 meters Columbia and Valiant (of

which the lines and: particulars were

kindly put at our disposal by Sparkman and Stephens) and for

Standfast, a Frans Maas design.

As a further activity, the bi-annual

HISWA Yacht Symposia, which

started ¡n 1969, may be mentioned.

Lectures and proceedings are in the

English language for international

circulation and to enable experts of

different nationalities to give their views on yacht design, yacht building

and related _{subjects. The technical}

part of these Symposia is organized

by

the

Deift

Shipbuilding

Laboratory. Delft also co-operates in

an international comparison of tank

test results, with sixth scale models of

the 5.5 meter .Antiope which was

tank-tested full scale in the Naval

Ship Research and Development Centre in Washington

ftC.

The comparison is made to detect possible

scale effects in the prediction of full

scaleperformance from model test

data. An additional model on a third

scale

_{will be tested to fill}

_{the gap}

between the small model and the full

scale yacht:

For the near future

a

rather large series of systematically

18

Keel JIE

varied sailing yacht hull forms will be

tested. in the Deift Tank to obtain a

better insight In the importance of

the various hull form parameters,

which

influence

the

resistance-yachtspeed relation. Too

much ad hoc work is carried out in yacht testing and it is anticipated

that the results of. systematic

resistance tests will be an aid for the designer and his adviser to attain

optimum results in a more direct

Way.

-As an example the results of tank

tests with a model of Stormy,

designed by Van de Stadt, are given.

ail, measurements

in meters.

d

u, 1.95

J

Figure 2.

Keel

- rudder . configurations for

,Stormy"

Racing results with Stormy having the original keel arid rudder, showed that the performance

in the close

hauled condition was not always satisfactory.

_{In order to}

.assist the

designer ¡n finding a better solution, three new keel-rudder configurations were tank tested, the hull form. itself

remaining unaltered.

The four

keel-rudder

configurations are shown in Figure 2

and the main particulars of the hull

forni, are given in. Table 1.

Keel I is the original design:. a rather thick bulb attached to a

relatively thin keel havin'g a

moderate area. There is a long and

shallow skeg between keel and rudder

and a gap between the upper part of the rudder and the hull.

Keel

li

has a longer and more

slender bulb, .a slightly larger aspect

ratio and a keel flap. This keel has

slightly larger thickness to avoid early

separation, effects when heavily

loaded in a seaway. Keel

Ill

has no bulb, a larger area and, increased thickness to carry the .ballast. The

final version IV has still more

thickness at the under side to lower the centre of gravity and a trim flap of 25 per cent chord length. In the

final reconstruction the mast was

lengthened and a corresponding

increase in sail area was Obtained as

shown in Figure 3.

The speed-resistance relations for

the four different configurations aie

very similar, as indicated for instance in Figure 4, where the yacht speed in the down-wind condition (no hee!ing angle and no leeway) is given as a

function of the true wind speed. As

expected the increased sail area

increased the speed by approximatély

1 to 2 per cent. 'lihespeed made good,

derived

from

moael

experiments with . leeway

-

and

heeling angles are show in Figures 5,

6 and; 7.

Table i Keel . I and Il (figure ₅₎ approximately give the same result. It

shôuld be remarked that the trimfia

o o

of keel Il was deflected 4 , 6 and 8

at respectively 100. 20° and 300

heeling angle. 'In figure 6 keel Ill is

'compared with the original one and,

in this case two conditions are

compared:

Keel Ill has the same vertical

position of the centre of gravity as

keel .1

Keel 11.1 has the higher centre

'of gravity 'which is realistic, for this

particular"keel form.

With the same vertical position of

the centre of gravity as with keel: I,

keel III gives a 1.5 per cent to '2 per cent higher speed made good for true

wind speeds up to llm/s. For the

more realistic higher centre of gravity

keel

Ill

is slightly better below a

wind speed of 6m/s but for hi-ier

wind speeds a speed loss up to 2Y2

per, cent is observed.. Thus, the.better

hyd'rodynamic quàlity of the keel is,

lost for a good deal due to decreased

stability (higher centre of gravity). 'Keel IV, with the larger thickness,

gives m'ore stability and the keel flap,

when deflected in a proper way,

reduces the leeway angle almost bya

factor 2 in this case. '

19 j, symbol description 1DWL Waterline length Main particulars configuration

I..

Il.

Ill,

i29t

12.91 12.91.

IV

1285

BDWL waterline breadth m 3.69 3.69 3.69 3.67

UMAX maximum breadth m. 4.16 4.16 4.16 4.16

T draught m 2.51 2.51 2.58 2.65

displacement ton 11.390 .11.390 11390 11.390

Ai _{length displacement ratio.}

5.84 5.84 5.84 5.86 LCB/LDWL position of centre of

buoynocy behind mid LDWL % 0.5 0.5 0.5 0.5

cp prismatic coefficient 0.53 0.53 0.53 0.53

z9 centre of gravity under DWL m 0.41 0.41 0.25 . 0.43

Br ballt ratio 0.41 0.41 0.41 0.41'

S wetted surface 47.60 48.05 46.80 48.1.1

Figure 3. Origiral and

,,Storrny"

The same flap deflectjons as for

keel Il were used and the _comparison

of the speed made good with

the

corresponding values

for keel

i

In

Figure 7 shows a marked

improvement: in a large range of _true

wind speeds a 3 per cent

to 4 per

cent increased speed made good is

obtained. In the case of keelIV the

stability ¡s _{almost equal to the}

stability with keel I and therefore the

improvement must be due

to the

better hydrodynamic quality of fin

keel and rudder. In addition the skeg

between _{keel arid rudder was}

completely removed (see Figure 2). The reason for this ¡s, that such a skeg has a low efficiency due to a

relatively large induced resistance.

The 'better keel' performance, ¡s _also

shown in Table 2, where the total resistance, the ratio of side force and

total yacht

resistance, the leeway angle, the apparent wind angle and the true wind, angle are given for a

constant heel of 20 degrees, a side force of 696 kg and _{a yacht speed of}

3,83m/s. ('T5 knots). U) t-Q'

'E

i

Î

> ,

i

20 O t-.

i

u _{2 3}

Speed rnad

_{good in rnecrs per}

secchd-íig.5Specdnadgood for keel i and ]i

i

i

i

O

u 'I

2'

_3.

Speed made good in meters persecond--..

Fig.6 Speed made. good for keel I and]It

-

I original satiptan original KeeLI Keel

-

-saiLptän

f

et

mofiedsailPlan,,,,d,//

1Knots-6

meters per second.

-\'cht speed iii

¿ keel I

heeling anie

=30tf

flap deflection? § 8°

deflected flap)

I

keeÉ(with

i

-Knrit 6

Keet'I

heeling

Lie

Keel'

Keet' .

(centre of

with

keelI)

'

...

gravity as

¡Ji-Ii

r.

,'

,

-Iii.

-/

=1O.

knots

-I' ₃

Figure _{Yachtspeed in down wind conditIon}

Table 2

KoeIQuality

I.

Keel i Keel Il _{Keel Iii KeetIV}

total resistance _{252kg 254 kg} 244 kg 237 k side force/resjstaiice 2,76 274 2,85 2,94-leeway anglo _{5.60 5,3° 5,6°} 3,1° apparent windangle 28,1o 28,2o 27,5

o

27,1o true wind anglo ..39.1° 39,1°

In particular the higher side force-resistance ratio of keel IV should be noted, as well as the lower total resistance.

In this Table all of

the keels were assumed to give equal

stability. The smaller leeway angles

are caused by the keel flap; the

favourable effect of less leeway upon

the sailforces is not taken into

account in the analysis and the

performance prediction of the yacht

with keel IV therefore is conservative.

A more complete picture of the

influence of keel flap deflection on

the leeway angle is given in Table IV

where the leeway angles of all four modifications are given for optimum

close hauled conditions.

-As already mentioned the flap deflections for keel

Il and IV were:

4°, 6° and 8° at heeling angles: 100, 20° and 30° respectively.

The results of keel Il indicate that the flap deflections as used in the experiments wére too small for this particular case to have appreciable

effect.

It should be noted that the

Heeling anIe loo 200 3Q0 12 11 10 9

i

. Stormy - -:::

-area of keel Il is approximately 60 per cent smaller than the area of keel

lv.

Finally the influence of the increased sail area on the speed made

good is shown in Figure 8 for keel

IV. For wind speeds lower than 8m/s

the speed made good increases with 3

per cent to 4 per cent. For higher

Table 3 Leeway Angles Keel Il 3.5° 490 8.70 Keel Ill 3.9° 5.7° 9.2° 0 1 2 3

Sp2ed rn:de good in metrs per

second--i:7Sp:;d mude good for ieel lanci 1

o o ei (n

w7

Q-4, ei 11

t1

E5

Keel IV 2.10 3.2° 6.00 12 I' ¡

wind

speeds the stability is

insufficient to carry the increased sail

area, and the performance is less than

with

the

original

saliplan.

Consequently, in this particular case,

the sail

has to be reeled for true

wind speeds higher than 8 m/s or, as an easy indication, when the heeling

angle exceeds 20°. Again this

emphasizes

the importance of the

influence of stability on the speed made good of a sailing yacht. As a

conclusion

it may be said that the

modified keel and rudder in addition to the larger sail area resulted ir. an

appreciable improvement of the yachts performance.

0

i

2 3

Speed mcde. good in meters per second

Fiç13Specd macle good icr original and modified

sail ptu

Keel

I

21

-

teetI

heeling angle

=30-.

flap deflection

= 8°

---<eetfl with deflected flap

ii

4=20' Lf

ö= 6'7,

/

10

/

4 KnotsJ6

Keel 12:: original saiplan

modified sailpian

heeling angle

=30'

-- ---- Keel 12.:

flap deflection =8°

4=20'

ö=6°

/

4:1=10° 40

z

4knots

6 Keel I 3.8° 5.4° 8.3°