Wing-Body Interaction on a Sailing Yacht

Wing-Body Interaction on a Sailing Yacht.

J.A. Keuning and G.K. Kapsenberg

Chesapeake Sailing Yacht Symposium, 1995

Report No. 1019-P

1995

TU Deift

Faculty of Mechanical Engineering and Marine Technology Ship Hydromechanics Laboratory

THE TWELFTH

CHESAPEAKE

SAILING

YA C H T

SYMPOSIUM

JANUARY 28, 1995

THE CHESAPEAKE SECTION OF

THE SOCIETY OF NAVAL ARCHITECTS

AND MARINE ENGINEERS

U.S. NAVAL ACADEMY

THE TWELFTH CHESAPEAKE SAILING YACHT SYMPOSIUM

TABLE OF CONTENTS

Papers Presented on Saturday, January 28,. 1995

Scoriñg IMS Regattas - An Empirical Study

f Alterñative Methods

John W. Cane, ENW International, Ltd., St. Michaels, Maryland, USA ...i

Drawing with Performance Prediction

Peter Schwenn, Velocity, University Park, Maryland, USA

GeorgeHazen, gShell, Inc., Annapolis, Maryland, USA

15

Design Criteria, for Composite Masts

PaulMiler, Dept. of Naval Arch. & QffshoreEng., U. C., Berkeley, CA, USA

29

The Development of the B&R Rig, Structural Space Frame

and Tripod Süpport System with Integrated Boom

Lars Bergstrom, B & R Mast and 'Rigging Designs, Sarasota, Florida, USA

Sven Olof'Ridder, B & R Mast and Rigging Designs, Sarasota, Florida, USA

45

The Alexandria Class Dinghy - A Design For Change

William H. Hunley,. The Alexandria 'Seaport Foundation, Alexandria, Virginia, USA

53

Design, Construction, and Performance of a 27' MORC Boat

Brian A. Jones, Annapolis, Maryland, USA

,

63

Imagine - an Open Class 60 BOC Racer

-Design and Program Management

- Lessons

Learned

Kenneth E. Court, P.E., Kaufman Design, Inc., Annapolis, Maryland, USA

F. Michael Kaufman II'!, Kaufman Design, Inc., Annapolis, Maryland,'USA

Harold M. Whitacre HI, Kaufman Design, Inc., Annapolis, Maryland, USA

69

Note: A presentation titled "Progress Report on the Schooner Sail Coefficient

Program Utilizing the Yacht Brilliant as a Dynamometer" was given by

Walter Stubner, Olin J. Stephens, II, and' Paul Spens

Moderators 'for the 12th CSYS

Leif Eareckson

Roger H. Compton

THE TWELFTH CHESAPEAKE SAILING YACHT SYMPOSIUM

TABLE OF. CONTENTS

Papers Presented on Friday, January 27,

1995

.át the SNAME SC-2 "Sailing Craft" Panel Meeting

The Design of Yacht Sailpians for Maximal Upwind

Speed

Dr. Sandy Day, University of Strathclyde; Scotland

97

Tacking Simülation of Sailing Yachts - Numerical

Integration of

Equations of Motion and Application of Neural Network Technique

Yutaka Masayuma, Kanazawa Institute of Technology, Ishikawa,

Japan

Toichi Fukasawa, Kanazawa Institute of Technology, Ishikawa,

Japan

Hiroshi Sasagawa, Dengyousha Machine Works, Ltd., Shizuoka, Japan

1.17

Wing- Body interaction on a Sailing

Yacht

. .

Prof ir J A Keuning, Ship Hydromecharncs Lab , Deift Univ

of Tech

,

Deift, The Netherlands

Ir. G. K. Kapsenberg; MARIN, Wageningen, The

Netherlands

133

Improvement of Sailing Yacht Performance Prediction by Including

Force-Moment Equilibrium for the Calculation of Helm Angle

in a Velocity Prediction Program

Dr. Peter van Oossanen, Van O,ossanen & Associates,

Wageningen, The Netherlands...45

YACHT97: A Fully Viscous Nonlinear Free-Surface

Analysis Tool for L CC Yacht Design

J. Farmer, Dept. of Mech. and Aerospace Eng.,

PrincetOn Univ., Princeton, NJ, USA

L. Martinelli, Dèpt. of Mech. and Aerospace Eng., Princeton

Univ., Princeton, NJ, USA

A. Jameson, Dept. of Mech. and Aerospace Eng., Princeton

Univ., Princeton, NJ, USA

. .

157

THE TWELFTH CHESAPEAKE SA1LIÑG YACHT SYMPOSIUM

12th CSYS Committee Members

Steering Committee

Joseph O Salsich

General Chariman

John J. Zseleczky

_{Papers Committee Chairman}

Volker Stamninitz

Publicity

Sarah L. 'Gretzky

_Arrangements

Howard A. Chatterton

Treasurer

Jacqueline C. Diggs

_{Assistant Treasurer}

Gregory Buley

_Secretary

LCcIr. Stephen R. Judson, USCG

_{SNAMIE Representative}

Bruce Johnson.

_{CBYRA Representative}

Robert E. Carruthers

NASS Representative

Richards T.. Miller

.

Advisor

Robert W. Peach

.

AdvIsor

C. Gaither Scott

. . .

Advisor

Ronald L. Ward

Advisor

Papers Committee

Diane Burton

David A. Helgerson

LCdr. Stephen R. Judson, USCG

Andrew R. Kondracki

Gregory J. Opas

J. Otto Scherer

John J. Slager

THE TWELFTH CHESAPEAKE SAILING YACHT SYMPOSIUM

The Twelfth Chesapeake Sailing Yacht Symposium was co-sponsored by:

The Society of Naval Architects and Marine Engineers, 601 Pavonia Avenue, Jersey City, NJ 07306

The Chesapeake Bay Yacht Racing Association, 612: Third Street, Annapolis, MD 21403

The U.S. Naval Academy Sailing Squadron, The Robert Crown Sailing Center, U.S.N.A., Annapolis, MD 21402

The Twelfth CSYS was held in the Francis Scott Key Auditorium

on the campus of St. John's College in Annapolis4 Maryland, USA.

The SNAME SC-2 "Sailing Craft" Panel meeting was open to all CSYS attendees and was held

in conference room 103, Rickover Hall, U.S. Naval Academy, Annapolis, Maryland, USA.

LIST OF SYMBOLS

A rôference area C = chord lengih

CI = lift coefficient

Cdi = induced drag coefficient

Cf = frictional coefficient

Ct = total resistance coefficient

g = gravity 9.81 m/sec2 H = hull K = keel k = form factor R = rudder Re = Reynolds number ni = Induced Resistance nf = Frictional Resistance Rr Residuary Resistance Rt = Total Resistance

DePt University of Technology, Ship Hydromechanics

Laboratory, DePt. The Netherlands 2MARIN Wageningen, The Netherländs

WING BODY INTERACTION ON A SAILING YACHT

J.A. Keuning,1 and G.K. Kapsenberg2

ABSTRACT

Model testshave been carriedout in the Delft Shiphydromechanics Laboratory with a 3.5 meter ¡mdcl of an l992 America Cup yacht. Tliekeel (withoùt the bùlb)and the rudder have been islolated from the hull and connected to seperate force transducers placed inside the hull in order to be able to measure the lift the drag and the moment

around a horizontal axis on these appendages while being in their regular position underneath the model, as well as on the model as a whole. The experiment consisied of the regular 'upright" and "under leeway and heel" tests ascústomairaly performed

in the standard testing routine for sailing yachts of the Delli Shiphydromechanics

Laboratory. The model tests have been carried out with four different configurations of (lie model, i.e.:

- hull with keel andrudder

- hull with keel alOne

- hull with rudder alone

- bare hull

Dy combining the results of all these tests it became possible to evaluate thedrag- and lilt-interaction of the appendages on the hull and from the hull on the appendages under all conditions of sailing The results of this analysis of the measurements will be

presented in the paper.

lii addition these results will be compared with the results obtained from calculations using (lie CFI) panel methods DAWSON and RAPII).

i

V = forward speed

p = specific densiy of water

p leeway angle

«I = heeling angle

1. INTRODUCTION

The drag and lift of the appendages of a sailing yacht have since long been a area of extensive research. The development In the design of sailing yachts has toa considerable extendtaken place In

this area. In particular durIng the last decade an enormous impetus to the development of these appendages has come from the area of IACC

Wlthbread 60's and ROC designs.

On the other hand the development of Velocity

Prediction Programs based on the use of the Delft

Systematic Yacht Hull Series originally predicted the resistance of the hulls with a standard keel and hull configuration only. The need was felt to

chango this approach because of' the hugh variety of keel designs present on the market nowadays.

Therefore a total of 25 models out of the DSYHS

was retested Without appendages and the results of these tests are now used to predict the

residu-ary resistance of the bare huilsonly. This

introdu-cod however the necessity to formulate

expressi-ons that take account of the

resistance of the

keel and ruddor, I.e. the frictional- the form- and

the residuary-drag of

these appendages. This procedure is momentarily adopted by the IMS. Strict formulations for this residuary drag of the

appendages however are not available yet.

Another important aspect in the appendage drag

can also not be taken into account yet diJe to lack of relevant (experimental), data i.e. the interferen ce drag between hull and appendage. Apart from

viscous effects arising from the connection of the

two bodies1 there Is also a possible interference in

the wavemaking drag, in particular under leeway and heel as was already demonstrated a.o. by Beukelman and Keuningin 1975 [11.

A similar situation with respect to interference

occurs when the side force production and the

Induced drag' of the yacht as a whole and the

ndividual componenets is concerned. The pros-sence of the hull affects the pressure distribution

over the keel and rudder of the yacht sailing under leeway 'and heel. The -pressence of the keel and rudder on their turn affects the pressure distributi-on over the hull.

In the VPP's these effects are generalily

accoun-ted for by introducing the "equivalent keel" or

"extended keel' method, when dealing with the sideforce production and the "effective aspect,

ratio concept" when dealing with the induced

drag. These approximations however remain rat-her coarse and do not take into account sorne specific parameters known to' influence the inter-ference between the wings and the 'body both in

lift and drag.

To investigate these interference effects it was decided to carry out a series of experiments In

the towing tank of the Delit Shiphydromechanics

Laboratory. The aim of these experiments was to

measure the lift and drag of the three different

components of a yacht hull, i.e. the hull, the keel and the rudder, seperately under different

combi-nations and conditions in order to be able to deter mino their mutual interaction.

The tests were to be conducted in 'a similar man-ner as the well known experiments carried out by

DeSaIx with a model of a 5.5 meter hull. These

results

clearly showed the

mutual interaction between the hull and the keel: but the model was considered to be not 'representative for, the mo

dorn day designs anymore. So the results presen

tod in this paper are derived from a series of

experiments with a hull resembling an IACC

de-sign of 1992 vintage with its nowadays more

fashionable high aspect ratio appendages.

The presented Information Is not sufficient to'

develop generally applicable formulations for

ap-pendage residuary drag and interference effects

yet. An extension of the presented' type of

experi-ments with a larger variety of sailing yachts is

foreseen in the near future. Combination of these

results with those obtained by DeSaix may ylold a method to accôunt, atleast in a qualitative

sen-se, for the interference effects.

To facilitate the analysis of the results and to

check to which extend modern Computational

Fluid Dynamiques techniques can be used to

determine some of these Interaction effects,

cor-responding calculations to match the model expe-riments have been carrried out using the EAW-SON and RAPIDcodes.as developped by MARIN

at Wageningen The results of those calculations

are shown together with the experimental resUlts.

Once the validity of the uso of these calculation

techniques could be demonstrated they 'could be

used to asses the influence of' a number of the parameters supposedly influencing atleast a part

of the interaction effects under consideration.

2. SETUP OF THE EXPERIMENT

The aim of the experimeñt described hereafter

was to measure the drag and lift on the' keel, the

rudder and the hull of a sailing yacht seperately.

By measuring these on the seperate components

'in different combinations it was possible to de termine how much the lift and drag of one com-ponent was influenced 'by the presence 'of anot-her. This has been done with the model both in the upright condition as well as with leeway and

heel because interference in lift but also in wave-making and induced drag was sought for.

2.1 The model

The model used in thoexperiment was made more

or less along the IinesofanIACC hull of the1992

vintage.

A bodyplan of the model is presented 'in Figure 1.

As' may be seen from this figure it represents a

typical modern day racing boat design. The main dimensions of the model are depicted in Table 1.

In addition In Figure 2 the planvorm 'and profile of the keel and the rudder as used In the experiemnt

are presented. lt shoúld be mentioned that the

TABLE i

has been taken away from the lower end of the keel, because it was felt that its presence did not

contribute to the issues under consideration in this research project.

The main particulars of both the keel and the

rudder are prosented in Table 2. TABLE 2 keel rudder span chord-length tip chord-length root thickness tip thickness root section profile volume position 1/4 chordline

with respect to ord 10 -0.46 m

2.2 Measurement set-up

The model has been tested in the #1 towing tank

of the Deilt Shiphydromechanics Laboratory. The

dimensions of this tank are: length 142 meter,

width 4.2 meter and max. waterdepth 2.5 meter.

The model was connected to the towing carriage by the standard equipement of the Laboratory,

consisting of two balanced connecting rods which leave the model free to heave , pitch and roll but keep the model restrained in surge, sway and

yaw. The resistance, the side force and the

yawing moment on the model as a whole were

measured at the connections between the balanc-od rbalanc-ods and the mbalanc-odel, by using strain gauge type dynamometers.

iThe keel was connected to the model by means of a rod which protruded through the bottom of

the model. This rd was connected to a set of

dynamometers which measured the sideforce,

the resistance and the vertical bending moment on NACA 63-010

0.456 0.110m3

the keolin a body fixed coordinate system. These

forces were translated to the lift and drag forces

in a earth fixed coordinate system as customarry. The dynamometer output was also compensated

for errors introduced by the heeling angle of the

hUll.

The watertight sealing of the rod passing through the hull was made very flexible and any significant

force transdUction through this seal côuld not be

measured during callibration. Great emphasis has

also been put on the minimising. the "gap"

be-tween the hull and keel. The puipose was to

make this gap so small that no pressure leakage could occur and yet without any significant force transduction from the keel on the hull. This was finally achieved by a combination of very flexible and thin sealant and a labyrinth shaped, cross

section through the upper surface of the keel.

in a similar way the rudder was connected to the model. Due to the limited space available inside the model the force on the rudder could be

mea-sured in one direction at the time only. For those

conditions in which both the lift and the drag of

the rudder were to be determined the tests had to be carried out twice.

2.3 Measurement scheme.

The experiment consisted of a series of runs with the model in (he upright condition and a series of runs with the model under leeway and heel.

In the upright condition only the resistance of the model and the appendages was measured. The resistance of the model in all the combinations

was measured using atleast 1 2 different forward

velocities in the Froude number range from Fn=

0.10 to Fn 0.60. For each combination exactly the same towing speeds of the carriage have been

used for the sake of exact. comparison of the

results. All the tests have been carried out with carborundúm stripes as turbulence stimulators.

Three stripes on the canoe body have been used with approximate positions at ord 19 /2, ord 16 '/2 and ord 13 (ordinate 20 is the forward perpendic-ular). On the appendages the carborundum stripes were located at a distance of approximately 10% of the chord ionght 'aft from the loading edge. To be able to correct the measured resistance for the additional resistance introduced by thU presence

of these carborundum stripes themselfes all the

resistance tests were carried' eut twice: once

with single and once with double width of the

carborundum stripes. Twice the difference be-tweôn these two measurements was subtracted

from the raw measurement data to obtain the

corrected reslstance 2.618 2.250m 1.386

0.0 m

1.841

0.82 m

10

10%

10

10%

Length waterline 19.1B0 m Length over all 24.360 m

Beam waterline 4.242 m

Maximum beam 5.075 ni Depth canoe body 0.854 m Displacement canoe body 24.254 m3 Piismatic coefficient 0.569.

Longitudinal position Centre

of :Bouyancy LCB -5.0 % Lwl Wetted area hull 60662 m2

1:ho tests under leeway and heel were carried out

at three

heeling angles, i.e. 0, 15 and 30

de-grees. The speeds used during these tests were considered to cover the speed range of interest

under upwind sailing and reaching conditions, i.e. 1.4, 1.8 and 2.0 meter/second for the modeL For each speed at least three different leeway angles

were tested using the standard measurement

technique of the Delft Shiphydromechanics

Labo-ratory. In this technique the stability of the model is changed by shifting weighths in the artwarth ship direction to enable different combinations of

leeway angle and forward speed at one particular heeling angle.

All these tests indicated above were carried out with four different configurations of the model,

i.e.:

- hull with keel and rudder

- hull with only the keel (no rudder)

- hu!l with only the rudder (no keel) bare hull without keel and rudder

3. THE CALCULATIONS

The CFD calculations of the wavemaking

resistan-ce of the model have been carried out with both

the DAWSON and the RAPID code as developped

by MARIN at Wageningen The Netherlands. The calculations under leeway and heel have been

carried out using the DAWSON code only.

DAWSON'is amore conventional type of program.

lt calculates the potential flow around the hull

including the effect of the free surface An invis-cid flow is 'assumed for this program, so only the generated waves have been calculated and the associated pressures on the pane!s representing

the hUll surface. Intergration of these pressures in the X direction yields the wave making resistance

and in the Z direction the vertical force and

trim-ming moment due to the forward speed.

Lift generating surfaces like the keel and rudder have been added to the hull. By forcing the flow seperation point on the trailing edge of the keel and the rudder profile, the lift and the lift distribu-tion over the span of the keel and the rudder can

be established. The inflUence of the pressure

distribution on the keel and rudder on the free

surface, in particular manifest when under heel, can also be taken into account. The DAWSON.

code can quantify this additional wave making'

program. This effect gives rises to socalted In-duced resistance. The DAWSON program is dis-creibed in full detail by Raven in 1988 1 2 J. The program RAPID is a non-linear development of

DAWSON. lt uses an iterative approach to caIcu

late the pressures on the panels of the hull. The

result of the first iteration is similar to the result of

DAWSON but for the second iteration the actual

wetted surface of 'the hull due to the wave crests

and throughs is taken into account and also the

panels on the water surface now follow the shape

of the waves around the ship. The program may be used In two ways: fixed draughts of the ship

can be entered and only the non linearitíes In the wetted surface of the hull and the free surface as

discrebed above are taken into account. The

se-cond application of the program is to use the

calculated vertical force and moment to calculate

the actual trim and sinkage of the 'ship under

speed. This makes the RAPID' code in particular applicable for sailing yachts were the effects of

long overhangs on the .effeötive..length of the ship at higher speeds may be of importance.

An early version of the DAWSON code without

the free surface effects has been used to calcula

te the effects of the well known winglets of

Aus-tralia Ii's keel. Later on the program has 'been used for a variety of commercial projects for

de-termining wave making resistance and side force

production of sailing yachts A first application of

the RAPID code' to saIling yathts includinga

com-parison with DAWSON results was presented by Raven In 1994 1 3 J. iTher results calculated for

Australia II showed a good agreement for

resistan-ce and side Forresistan-ce production to speeds upto 9 knots. Application of both codes on a IOR maxi

yacht showed far more realistic bow wave shapes.

when calculated using RAPID although the diIfe-rence between RAPID and DAWSON on the

re-suits of the wavemaking resistance was only

marginal.

4. RESULTS

The results of the measurements and the calcula-tions are presented 'in the FigUrés 3 to i

For the sake of clarity only a limited amount of all the datá obtained from the measurements will be presented In this paper.

All the data'presented in these Figures are based

presentad in the figures are derived by dividing

the sideforce and Induced drag by: Y2 rho speed

squared and a typical reference area for each

"lifting" surface or combinútions thereof, com-posed by:

the keel 0.0864 m2

the rudder 0.0331 m2

the htill 0.3343 m2

In Figure 3 the upright resistance of the bare hull is presented together with the frictional resistan-ce. In the calculation procedure of the frictional resistance the ITTC-57 friction line is used. The Reynolds number of the canoe body is based on

90% of the Lwl. The wetted aroa used ln the

calculations is the wetted area at zero forward

speed. The residuary resistance of the bare hull is shown also as obtained from the tests with the

bare hull alone and as obtained from substraction -of the resistance of the keel as measûred

underne-ath the hull from the resistance of the hull with

keel together.

In Figure 4 the resistance of the model in the four

different conditioñs tested is presented, i.e. the hull with keel and rudder, the hull with keel, the

hull with rudder and the bare hull.

In Figure 5 the socalled "Prohaska plots" are

pre-sented of the model with keel and rudder, of the

bare hull, of the keel and the rudder. For the

determination of the frictional resistance of the

appendages the Reynolds number is basúd on 100 % of the mean chord length In all conditions In Figure. 6 the resistance or the keel is presented as measured directly on the keel itself In the

con-dition of the hull With keel añd the concon-dition of the hull with keel and rudder Also the resistance of the keel is presented as determIned from the

substraction of the bare hull resistance from the resistance of the "hull + keel" combination. The

results are presented as model scale resistance In Newtons, as total resistance coefficient divided by

the frictional resistance coefficient and as

residu-ary resistance divided by the weight of

displace-ment of the keel.

In Figure 7 the same data is presented for the

resistance of the rudder. The rudder resistance is

presented as measured directly on the rudder in the "hull + rudder" condition and as difference of,

the "hull + rudder" minUs the "bare hUll"

resistan-ce and noW also as the "hull + keel + rudder"

minus the "hull + keel" resistance.

In Figure 8 the lift coefficient of the "hull + keel"

combination is presented for the three heeling

angles and the forward speeds tested on a basis of leeway angle as well as the induced drag

coef-fiôient on a basis of the -lift coefficient squared.

These resUlts are presented for comparison with the similar results of the keel measured directly on the keel underneath the hull: and the bare hUll se-peratly, which are presented In Figures 9 and 10.

6. DISCUSSION 0F THE RESULTS

First of all the- resistance measurements on the hul -and appendages seporatoly lend themselfs to an

evaluation of the respective form factors

The Prohaska plots of the hull with appendages show value of the form factor k of approximately 0.09 Considering the fàirness -of the linear

fit

presumably the flow around-the hull rehiains tut

bulent to Froude numbersas low as Fn = 0.15.

When considering the Prohaska plots for the ap-pendages seperatly it

is obvious that the form

factor of the keel is much higher, i.e. 0.18. This corresponds quite reasonable with the values formulated by Hoerner L 4 1

for foils with this

sectional thickness. In the case of the rudder a strong deviation from the straight line In the Pro-haska plot is observed which could possibly be

attributed te surface wave generation by the

rudder in the low speed regime when: the rudder is

- piercing the free surface.

-One of the intúrfererice effects is between the

appendages: Le, the wake of the keel over the rudder. This effect, is quite noticable as may be seen from the- Figure presenting the resistance

measured directly on the rudder in the "hull +

rudder"- condition and the similar resistance found by subtraction of the 'hull + koel" resistance from -the "hull keel + rudder" resistance. The

esti-mated wake reduction factor for the water

veloci-ty over the rudder from these measurements is

approximately 08 at a Froudenumbar of 0.40. In the upright condition, without leeway and heel,

the residuary resistance per ton of displacement

of the barO hull Is smaller than the--residuary

resis-tance per ton of displacement of the hull with

keel. At the highest Froude number- the-- difference is approximately 4 % increasing at lower speds. A close look at the residUary resistance of the keel

-per ton displacement of the keel itself reveals

values that are more than twice: or at the highest speeds even three times as large -as for the bare húll alone at corresponding forward speeds. This seems to indicate that the procedure used a.o. in some of the VPP's in which the- residuary

is-multiplied with the displacement of hull including appendages to yield the residuary resistance of

the combination may be Justifiable. The volume of

the keel should be taken twice t three times iñtú

tho hull volume to account for the interference lt

should be noted however that for the present

model the volume of, the keel ¡s only 1.9 % of the

volume of the hull, I.e rather small. Also viscous interference effects will be present which are not

accounted for. Whether the multiplication factor 'is dependend on keel volume and some hull

parame-ters is topic for futureresearch.

Beukelman and Keuning L '1 F found ¡n their study

on the influence, of sweep back of the keel on the sailing yacht performance a sudden increase of

roughly 8% In the upright resistance on the 0

degrees swept back keel when compared with the

20 'and 40 degrees swept keel. They atrributed

this increase to the interference between hull- and keelvolume In the wave making resistance which was considered as to originate from a

discontinui-ty in the curve of cross sectional areas which

resulted from the use of the zero sweep angle of

the keel. In yacht design it was known as "the

area ruling to prevent this by a smooth introduc

tion" of the keel volume in the cross sectional

area curve. In the present situation such a effect may also be apparent because the sweep back angleof thekeol investigated is alsozorodegrees. The sum of the resistanceof the bare

hullcom-bined with the resistance of the keel, as measured

directly on the keel' when fixed underneath the

hull, isblgger.than'.therosistance measured on the

combination of 'hulI + keel" when the speed is

higher than Fn = 0.40 and smaller for speeds

with Froude numbers smaller than that. This trend

is consistent throughoutall the results. This.impii

cates a defiñite interference between the two

albeit for the present case rather small. A similar experiment with a high.volume keel 'is presently

been carried out and this should throw some light

on the possible dependency of this interference

effect on the "keel volume - hull volume" ratio. In Figure 11 the frictional resistance and residuary

resistance of the hull and the keel as seperate bodies are presented as percentages of the total resistance of the hull + keel combination as

func-tion of the forward speed. The interference

ef-fects' ¡n the upright resistance are demonstrated as function of forward speed. Due to the

interfe-rence effects there is a underprediction in the low

speed range and a over prediction in the high

speed range ÑhAn considering the resistance of

the seperate components;

for the resistance are, compared with the

measu-red data for the bare húlI and the hull with keel

and rudder. The difference between 'the DAWSON and RAPID calculations in the wavemaking

resis-tance is marginal. The' difference in wave profile and the effect of the stern wave obviously does not 'affect the outcome of the resistance

calcula-tions too much; Generally spoken the agreement between the calculated and measured resistance

is good. For the appended keel with keel and

rudder It is even excellent.

From the figures presenting the lift coefficient of the keel as function of the leeway angle it Is ob-vious that the lift of the keel Is increased by the presence of the hull. The positive Interference Is

larger at O and 15 degrees of heel than at 30

degrees. The results are presented for ohe for-ward speed only but results for the other speeds

show similar trends;

This positive interaction

Is even more evident

when the sideforce production of the hull with

and without the presenôe of the keel is

conside-red; For the hull alone4t became apparent that the side force per degree leeway angle Increase with heel, althoUgh the difference between 15 and 30 degrees of heel Is smaller than between O and 15 degrees. With the keel present this trend ¡s re-versed:' there is hardly any difference between O

and 15 degrees of heel and at 30 degrees the

sideforce production per degree leeway Is consi-derably smaller.

:TheInduced resistance In the results presented is the additional resistance due to side force

produc-tion only. To determino this addiproduc-tional resistance

the resistance of the combination under

considera-tionata given leeway andheel has been

corn-paredwith the resistance of the same

combina-tien under the same heeling angle without

sido-force production.

The induced resistance coefficient of the bare hull

is hardly influenced by the heeling angle of the hull. The derivative of the Cdl curve on basis of lift coefficient Cl squared however is very steep. With the keel present the Induced resistance of

the hull seems much lower for 0' and 1 5 degrees of heel. and in particular at zero, heel some positive interference seems to occur;

The induced resistance 'measured directy on the keel is considerably higher than when obtained from the comparison of the "hUll + keel"

combi-nation and the bare hull. In the later condition the Induced resistance increases with increasing heeling angle. When, measured on the kel directly

co of the hull and keel ¡s higher than the induced resistance of the "hull + keel" combination.

To visualise some of these effects the plots of

Figure 13 have been prepared. In Figure 12a the contribution of the hull and the keel to the lift of

the hull + keel combination is presented as

func-tion of, the heeling angle and at a onstant Ci for

the hull + keel combination. As may be seen from this plot the contribution of the hull increases with

Increasing heeling angle and the contribution of

the keel decreases. At all heeling angles there is a

significant interaction between the two not

ac-counted for by the summation of the seperate

components.

in Figure 12b and c the induced resistance

is

presented on a similar basis for a constant leeway

angle in 12 b and for a constant lift coefficient for the hull + keel combination in 12c. None of the

two represents a real life condition which will

presumably be somewhat different, in particular the combination of zero heel and considerable

sideforce is not a realistic condition. Nevertheluss these conditions are useful for the sake of

cornpa-rison. What these plots show however is that the

induced resistance at large heeling angles is

domi-nated by the hull, in particular at constant leeway angle. The interference due to surface wave ele-vation seems to influence the hull more than the

keel itself.

The measured values compare reasonably weil

with computed results obtained from the

"ex-tended keel" and "eFfective aspect ratio" method

as presented a.o. by Gerritsma 1 5 J 1 6 1. This

corresponds with earlier experiences with similar, shallow draft and beamy hulls. More problems in

this respect may be expected with deep draft

hulls with short span keels and keels with high

taper ratio's.

The calculations of the lift and induced drag of all

combinations using the CFD codes required

con-siderable more time and effort than

originally foreseen. In particular the calculations for the bare

hull under leeway demand more attention than

was possible within the scope of the present

study. Since the both the resistance and the side

forces on the bare hull are an essential part in the

determination of the interaction effects,

it was

decided to deal with these topics in more detail in

a new research project in which also the towing tank results of similar exeriments carried out with a model with an additional high volume and an additional low aspect ratio keel will be usôd.

7. CONCLUSSION

The results presented from the experiments with a

hull, keel and rudder of a sailing yacht In different

combinations reveal considerable interaction

be-tween' the hull and Its appendages both in resis-tance as ¡n sideforce production. The results lack

sufficient generality in order to be able to derive

approximation methods for a wide variety of

con-figurations of these wing - body interaction

ef-fects yet. Moro future research ¡s needed (and foreseen) to deal with this in more detail.

REFERENCES

Li]

BEUKELMAN, W. and KEUNING, J.A. Influence of keel sweep back on sailing yacht performance

HISWA Symposium 1975 Amsterdam

12]

RAVEN, H.C.

Variations òn a theme by Dawson 17 th Symposium on Naval Hydrodyna-mics 1988

I 3]

RAVEN, H.C.

A practical non-linear method for calcu-lating ship wavemaking and wave resis-tance

19 th Symposium on Naval Hydrodyna-mics 1992

14J RAVEN, H.C.

Inviscid CFD codes applied in sailing yacht design

Ship Techn. Research, Vol 41, 1994

1 5] HOERNER

Fluid Dynamic Drag

1 6 J GERRITSMA, J., ONNINK, R. and

VERSLUIS, A.,

Geometry Resistance and Stability of the Delft Systematic Yacht Hull Series

International Shipbuilding Progress Volume 28, No 328, 1981

1 7] GERRITSMA, J. KEUNING, J. A. and

VERSLUES, A.

Sailing yacht performance in calm water and waves

i ith Chesapeake Sailing Yacht Sympo-sium, Jan 1993, Annapolis

Figure la. Bodyplan of model

Figure lb. Position of keel and rudder ön the

hull

Figure ic. Keel ànd rudder pian form 60' 20 o w

I

loo 8 60 4°

Figure 2b. Upright Resistance of four different combinations I.0 1.4 1.2. I.0 o 0 408 0 lilI y' lin ,H ? 0 speed Im/si 3 F/C

Figure 3a.

'Prohaska plots of the hull,

keel,

and rudder 0.45 .20 .25 F, -35 3

:,1iiF';

i

iiT:i

- .... _-

___;._

. spood (nì/s(

Figure 2a. Barb Hull Resistance in upright

condition Figure 3b.. Prohaskaplots of the hüll

1.6

1.4

F,/CF

Figure 3c. Prohaska plots of the keel

l.a . . . 1.6 1.4 1.2 I.0 1.4 1.0 lID 60 20 015 .20 ).10 .25 .30 IS .10 .20 o 11,11 n V fl,,II 4 II,,IIxnIIfl o 11,,II0II FICF

Figure 3d. Prohaska plots of the rudder

F, - .40

3

speed lull/SI

Figure 4. Bare Hull upright resistance as

obtained from different combina-tions 5 .00 w .1 le 8 6 Figure 6a. o speed Ini/si

Resistance of the keel measured directly and obtained as differential In upright condition o iian o lic V X. Il

I,

/

.7, + o II11611 speed Im/si

Figure 5. Non dimensional residuary

resistan-ce of the

hull in four different

combinations

o 2 3

speed Im/si

Figure 6b. Resistance of the keel measured directly and obtained as differential in upright condition o 2 o 1.2 tr ir .04 .02 w

I

40 u. o

IL Figure 6c. o Figure 7a. 3 O .Ilfl.II O 1041.111'. s n n, O n V Intl O lIKfl.11I'. speed tin/si

Resistance of the keel measured directly and obtained as differential in upright condition

3,

speed in/si

Resistance of the rudder measured directly and obtained as differential in the upright condition

'.4 o o .0 .0 .2 Figure 7c. Figure 8a. spend (rn/si

Resistance of the rudder measured directly and obtained as differeñtial In the upright condition

4 0

I (dogi

Lift and induced drag of

keel combination the hull O till_H O Hnn.HK

JH

speed tin/si c. i O

Figure lb. Resistance of the rudder measured

directly and obtained as differential Figure Sb.

Lift and Induced drag of the hull

in the upright condition keel combination

.3 u' o. n: a: o o o 2 o' 3 loo 200 300

N_Q -. 40 o 60, 60 20 o o Figure 9a. N_Q o N o o -j o O 060e1 £ o o

-°'

.0 -I5 O -3° 40 10(11 . £ 2000 O

c io4

Figure 9b. Litt and induced drag of the keel

o oui O I5 O 30 rI0(K I5 I Ideol 4000 6000

Figure lOa. Lift and induced drag of the bare

hull

1.

o o z w 1.0 .5

Figure lOb. Lift and induced drag f the bare

hull lo 75 Figure 11. 60 40

cib4

20 o V0( (10j

Contribution of hull and keel on the combined upright resistance

speud rn/s

Figure 1 2a. Results of CFD calculations for the

bare and the appended hull

O O O 4.OH .l0( $-30 $-0 10(5 s - IO. --. ---£ lion! '1 lucho keI

fl5 ins. issislorco hull

ludion IuuO : + no o n, O..no,i u u o 12 3 o 12 4 6 1 [deg

Lift and induced drag of the keel

20 15

lo

z

ISO 20 25 o 25 O loo 75 5O 25 O mil koisl

u-

hufl 7 V, IO 5 0' I 45' 0005 iool IO IS' 50" 0005 1.0 30" 7.0' 0.005 P 0inw Cim 1.0 0' 5" 2.4 0056 IO IS' 5" 0 0.005 1.0 30' 5' 2.4 OaSI huh ligol O IO 20 3° speed in/s

Figure 12b. _{Results of CFD calculations for the}

bare and the appended hull _{Figure 1 3c. Contribution to Induced drag}

Io 20 30

+ 1dgJ

ligure 13a. _{Contribution to total lilt}

O lo 20 30

Figure 1 3b. Contribution to indUced drag

loo

75

.J Sn

loo