wide light project · 5.1.5 yaw sweeps hull, keel, & rudder ... project prospectus syrf wide...

WIDE - LIGHT PROJECT Final Report – November 2015

Andy Claughton

Land Rover BAR

Sailing Yacht Research Foundation

Warwick, Rhode Island, USA

ii Wide-Light Project

About the Sailing Yacht Research Foundation

The mission of the Sailing Yacht Research Foundation is to develop and catalog the science underlying sailboat

performance, resulting in more accurate sailboat handicapping formulae for the benefit of all racing sailors. The

Foundation serves an international user base of those focused on sailing performance prediction, including naval

architects and handicap rule makers.

The Foundation supports research efforts using scientific and engineering principles, utilizing the best research

facilities and individuals, and reports all findings in public forums. In addition, the Foundation maintains and

continuously updates a free-access library of past research, data and papers relevant to the science of performance

sailing.

The Foundation is sustained through charitable contributions and grants, and its success will be measured by the

widespread use and impact of its research, ultimately resulting in fairer yacht racing, which in turn will stimulate

more participation.

SYRF Board of Directors

Stan Honey, President

Steve Benjamin, Chairman

Scott Weisman, Treasurer

Dina Kowalyshyn

Jay Hansen

Gary Weisman

For more information, contact:

Sailing Yacht Research Foundation

1643 Warwick Avenue, Box 300

Warwick, Rhode Island 02889 USA

www.sailyachtresearch.org

The Wide-Light Project by Sailing Yacht Research Foundation is licensed under a Creative Commons Attribution

4.0 International License.

http://www.sailyachtresearch.org/

https://creativecommons.org/choose/www.sailyachtresearch.org

http://creativecommons.org/licenses/by/4.0/



iii

Contents

Contents .................................................................................................................................................................... iii

Figures ...................................................................................................................................................................... iv

Tables .........................................................................................................................................................................v

Supporting Documents ...............................................................................................................................................v

Acknowledgments .................................................................................................................................................... vi

Abstract ................................................................................................................................................................... vii

1. Introduction & Rationale ....................................................................................................................................1

2. Methodology ......................................................................................................................................................1

2.1 Process ........................................................................................................................................................2

2.2 Test Matrix .................................................................................................................................................2

2.3 Tank Testing ...............................................................................................................................................3

2.3.1 Tank Model ........................................................................................................................................4

2.4 CFD ............................................................................................................................................................4

3. Experimental Results ..........................................................................................................................................5

3.1 Practicalities ...............................................................................................................................................5

3.2 Sailing Yacht Resistance Breakdown .........................................................................................................6

4. Computational Results .......................................................................................................................................9

4.1 Questionnaire ..............................................................................................................................................9

4.2 Star-CCM+ Results ..................................................................................................................................10

4.3 FINE/Marine Results ................................................................................................................................12

4.4 OpenFOAM Results .................................................................................................................................14

4.5 FlowLogic Results ....................................................................................................................................16

4.6 SHIPFLOW Results .................................................................................................................................18

5. Analysis and Discussion ...................................................................................................................................18

5.1 Results and Comparative Charts...............................................................................................................19

5.1.1 Upright Resistance Trim and Heave – Tests CB-1 & HKR-1 ...........................................................19

5.1.2 LCG Variation – Tests CB-2 & 3, HKR-2 & 3 .................................................................................21

5.1.3 Heeled Resistance Tests ...................................................................................................................23

5.1.4 Heel with Yaw – Tests CB-6 &7, HKR-6 & 7 ..................................................................................25

5.1.5 Yaw Sweeps Hull, Keel, & Rudder – Tests HKR-8, 9, 10, & 11 .....................................................28

5.1.6 Yaw Sweeps Twin Rudder – Tests HKr-1 & 2.................................................................................30

5.2 Lift Curve Slope .......................................................................................................................................30

5.3 Discussion.................................................................................................................................................31

6. Conclusions ......................................................................................................................................................32

7. Future Work .....................................................................................................................................................32

References ................................................................................................................................................................34

iv Wide-Light Project

Figures

Figure 1. Typical drag area curve from an upright resistance test ..............................................................................5

Figure 2. Typical heeled and yawed resistance test results. .......................................................................................6

Figure 3. Resistance breakdown for analysis .............................................................................................................7

Figure 4. Typical variation of R0/RU and Te versus speed for a yacht derived from tank tests. ................................8

Figure 5. Star-CCM+ Resistance Curves .................................................................................................................10

Figure 6. Star-CCM+ Yaw Sweep Tests ..................................................................................................................10

Figure 7. Star-CCM+ Yaw Sweeps at 15° and 25° Heel ..........................................................................................11

Figure 8. Star-CCM+ Yaw Sweeps at 15° and 25° Heel, Twin Rudder ...................................................................11

Figure 9. FINE/Marine Resistance Curves ...............................................................................................................12

Figure 10. FINE/Marine Yaw Sweep Tests ..............................................................................................................12

Figure 11. FINE/Marine Yaw Sweep at 15° and 25° Heel .......................................................................................13

Figure 12. FINE/Marine Yaw Sweeps at 15° and 25° Heel, Twin Rudder ..............................................................13

Figure 13. OpenFOAM Resistance Curves ..............................................................................................................14

Figure 14. OpenFOAM Yaw Sweep Tests ...............................................................................................................14

Figure 15. OpenFOAM Yaw Sweep at 15° and 25° Heel ........................................................................................15

Figure 16. OpenFOAM Yaw Sweep at 15° Heel, Twin Rudder ..............................................................................15

Figure 17. FlowLogic Resistance Curves .................................................................................................................16

Figure 18. FlowLogic Yaw Sweep Tests..................................................................................................................16

Figure 19. FlowLogic Yaw Sweep at 15° and 25° Heel ...........................................................................................17

Figure 20. FlowLogic Yaw Sweep at 15° and 25° Heel, Twin Rudder ....................................................................17

Figure 21. SHIPFLOW Resistance Curves ..............................................................................................................18

Figure 22. Trim and Heave Comparison – Zero Heel ..............................................................................................19

Figure 23. Resistance Comparison – Zero Heel .......................................................................................................20

Figure 24. Upright Resistance Data, Ratio to Tank Test Results .............................................................................21

Figure 25. Canoe Body Only Upright LCG Shift, Ratio to Tank Test Results ........................................................22

Figure 26. Hull, Keel, & Rudder Upright LCG Shift, Ratio to Tank Test Results...................................................22

Figure 27. Heeled Resistance Test Data Ratio to Upright Value .............................................................................24

Figure 28. Canoe Body Only Heeled Resistance Test Data, Ratio to Tank Test Results .........................................25

Figure 29. Hull, Keel & Rudder Heeled Resistance Test Data, Ratio to Tank Test Results ....................................25

Figure 30. Canoe Body Only Yaw Sweep Data at 15° and 25° Heel .......................................................................26

Figure 31. Canoe Body Only Yaw Sweep Data, Ratio to Tank Test Results ...........................................................26

Figure 32 Hull Keel & Rudder Yaw Sweep Data at 15° and 25° Heel .....................................................................27

Figure 33. Hull, Keel & Rudder Yaw Sweep Data, Ratio to Tank Test Results ......................................................27

Figure 34. Hull, Keel & Rudder, Summary of Fitted Lines to Yaw Sweep Data ....................................................28

Figure 35. Heeled Resistance Ratio and Effective Draft Comparison .....................................................................29

Figure 36. Comparison of CFD Results for Twin Rudder Configuration ................................................................30

Figure 37. Lift Slope Comparison ............................................................................................................................31

v

Tables

Table 1. Test Matrix, Speed & LCG Indices ..............................................................................................................3

Table 2. Model Dimensions .......................................................................................................................................4

Table 3. List of CFD Codes ........................................................................................................................................4

Table 4. CFD Stakeholder Questionnaire ...................................................................................................................9

Table 5. Comparison Summary – CFD to Model Test .............................................................................................31

Supporting Documents

The defining documents of the project specification and the results from each CFD program are available online

through SYRF’s Technical Resources Library. These documents may be viewed and downloaded from the

following links:

Planning Documents:

Project Plan SYRF Wide Light Project Plan Issue 2.1.pdf [180 KB]

Invitation to CFD Participants SYRF Wide Light Project Invitation to Participate.pdf [274 KB]

Project Prospectus SYRF Wide Light Project Final Prospectus- Rev A.pdf [400 KB]

Project Run Matrix SYRF_-CFD test Program-Rev A.xlsx [1 MB]

3D Model of Project Hull & Appendages SYRF-TH01-CAD for CFD-02-RhinoV4.3dm [2 MB]

Results:

Compiled Results Spreadsheet SYRF-WL Results.xlsx [1 MB]

CFD Participant Questionnaire SYRF-WL CFD-Questionnaire-Compiled.xlsx [97 KB]

Tank Testing Results & Report SYRF-WL Tank Results.zip [9 MB]

Tank Testing Photos SYRF-WL Tank Photos.zip [326 MB]

Star-CCM+ Results Submission SYRF-WL Star-CCM+ Results.zip [236 KB]

FINE/Marine Results Submission SYRF-WL FINEMarine Results.zip [99 MB]

SHIPFLOW Results Submission SYRF-WL SHIPFLOW Results.zip [56 MB]

OpenFOAM Results Submission SYRF-WL OpenFOAM Results.zip [158 MB]

FlowLogic Results Submission SYRF-WL FlowLogic Results.zip [1 MB]

https://drive.google.com/file/d/0B2CUun8QUAMsTWVGazR4R2p4TTA/view?usp=sharing

https://drive.google.com/file/d/0B2CUun8QUAMsX1ROVWpVbXpLdDg/view?usp=sharing

https://drive.google.com/file/d/0B2CUun8QUAMscjBCSjBtd3hUSWc/view?usp=sharing

https://drive.google.com/file/d/0B2CUun8QUAMsM2h1NXFmMTRPOWc/view?usp=sharing

https://drive.google.com/file/d/0B2CUun8QUAMsRlA5U0ZwUVBiVDA/view?usp=sharing

https://drive.google.com/open?id=0B2CUun8QUAMsb0RTd2RfbWlYVnM

https://drive.google.com/file/d/0B2CUun8QUAMsV2prVEF5Wk5ORzA/view?usp=sharing

https://drive.google.com/open?id=0B2CUun8QUAMsb1FRcHdRajdLSjQ

https://drive.google.com/file/d/0B2CUun8QUAMsdHBmWEVaUk5MMTg/view?usp=sharing

https://drive.google.com/file/d/0B2CUun8QUAMseGY0SWJQZDVFOVE/view?usp=sharing

https://drive.google.com/open?id=0B2CUun8QUAMsNURNZ1VYc0NYT3M

https://drive.google.com/file/d/0B2CUun8QUAMsOFV5b2h3dFlENm8/view?usp=sharing

https://drive.google.com/file/d/0B2CUun8QUAMsaFczSGY2TXRQazg/view?usp=sharing

https://drive.google.com/file/d/0B2CUun8QUAMsUGVYNFJxbGEyb3M/view?usp=sharing

vi Wide-Light Project

Acknowledgments

This project was funded by the Sailing Yacht Research Foundation.

The project team would like to thank Judel/Vrolijk & Co. who were kind enough to make available one of their

towing tank models for the project. The availability of this model was one of the main reasons that this project

could proceed.

The project was generously supported by the Wolfson Unit MTIA and the University of Southampton, along with

the Computational Fluid Dynamics (CFD) stakeholders.

Principal Investigator

Andy Claughton, Land Rover BAR

CFD Participants

Benoit Mallol, Numeca

Jason Ker, Ker Yacht Design

David Egan, Ennova Technologies

Sandy Wright, Wolfson Unit MTIA, University of Southampton

Lars Larson, Chalmers University of Technology, FLOWTECH Int. AB

Michal Orych, Chalmers University of Technology, FLOWTECH Int. AB

Rodrigo Azcueta, Cape Horn Engineering

Matteo Lledri, Cape Horn Engineering

Tank Testing Participants

Martyn Prince, Wolfson Unit MTIA, University of Southampton

Etienne Gauvain, Wolfson Unit MTIA, University of Southampton

Project Advisory Committee

Jim Teeters, SYRF Technical Director

Dina Kowalyshyn, CDI Marine Company

Robert Ciesla, The Boeing Company

Stan Honey, SYRF Advisory Council

Steve Benjamin, SYRF Advisory Council

SYRF Project Management

Myles Cornwell, SYRF Executive Director

McKenzie Wilson, SYRF Research Analyst

vii

Abstract

The modern era of high performance sailing has ushered in a new design paradigm for modern race boats.

Compared to past hull shapes, the current in-favor design is both wide and light – it is in this description that the

Wide-Light’s project’s name originates.

This project provides insight into the accuracy of existing modelling methods in predicting performance of Wide-

Light designs. It is intended for this information to better inform and equip handicapping systems and box rules to

address Wide-Light designs.

Five different CFD stakeholders carried out “blind” CFD analysis on an identical test matrix using different

computational codes and approaches. The same test matrix was run as a tank test for both canoe body only and

appended (heel, keel, rudder) configurations as a control for the hull geometry. The CFD results were compared

with the tank test control results to determine CFD model accuracy. This project illustrated the accuracy of

commercial CFD codes in predicting the forces on a Wide-Light sailing yacht. Additionally, this project provides

a comprehensive set of data against which researchers may develop and validate their own numerical tools.

viii Wide-Light Project

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1

WIDE - LIGHT PROJECT

1. Introduction & Rationale

The report that follows describes the Wide-Light Project, a project conceived and sponsored by the Sailing Yacht

Research Foundation (SYRF). Following its 2013 annual meeting, SYRF solicited a program proposal from Andy

Claughton who was then engaged to manage the project.

The “Wide-Light” label is meant to describe the design of the modern high performance sailboats. These so-called

Wide-Light boats present many of the hydro-dynamic effects that are a challenge to predict: semi-planing hull

forms, immersed transom effects, spray creation, keels operating close to the water surface, rudders, dagger-

boards and canting keels that generate vertical force, the list goes on. The complexity of these interacting effects

is challenging for the designer and a minefield for yacht handicappers who are obligated to handicap all boats

equitably, both new and old.

It is therefore the goal of this project to provide data and conclusions of what might be seen as best practice or

state-of-the-art modelling methods so as to better inform and equip handicapping systems and box rules to address

Wide-Light designs. Projects such as the Delft Systematic Yacht Hull Series and the nine model series performed

at the Canadian National Research Council (NRC) have established the current database of hydrodynamics, but

they are no longer representative of today’s racing fleets. This project is the first step toward expanding the public

database to include modern yachts.

The Wide-Light project aligns with the SYRF mission to develop and catalogue the science underlying sailing

performance and handicapping, by:

a) Publishing an assessment of alternative methodologies to specify and analyze sailing yacht hydrodynamic

resistance using computational tools,

b) Making the data available for researchers, and students as an accessible experimental data set for a

contemporary sailing yacht, and

c) Demonstrating how this type of study can be used to inform the handicapping process.

It is expected that the project will also be particularly valuable for academics as it will allow students, researchers

and lecturers to frame new research projects most effectively.

2. Methodology

This project’s methodology draws upon well established procedures in ship hydrodynamics for comparing CFD

data with experimental tank data (Reference 1). Unlike in typical commercial and military studies where there are

2 Wide-Light Project

numerous tight controls on the process, for the Wide-Light project the methods were accelerated to more quickly

generate results.

A “test matrix” was developed to reflect a typical evaluation program for a sailing yacht, including tests of the

bare canoe body and the appended hull over a range of speeds, heel and leeway angles. This matrix was

distributed to the CFD stakeholders who used their usual procedures to generate data for each point in the matrix.

The analysis was performed at model scale to avoid conflating the uncertainties of the scaling procedure with the

CFD comparison. The stakeholders completed a “CFD Questionnaire” documenting the methodologies used to

perform their CFD analysis.

The CFD calculations were delivered to the project leader before the tank testing was performed, therefore

ensuring a blind test of the CFD codes. However, due to misinterpretations of the original test matrix, some CFD

points were re-worked to correct for mistakes. The towing tank test was performed using the same test matrix as

the CFD stakeholders, unfortunately due to limited tank availability two of the twenty planned test sequences

were omitted. It is the intent of SYRF to complete these missing tank runs when the opportunity arises, but the

timing on this is currently unknown.

2.1 Process

The project process was as follows;

1. Procure a contemporary racing yacht tank test model.

2. Prepare a test matrix appropriate to this model that could be used in a physical model test and a CFD

study.

3. Agree terms with a working group of leading CFD practitioners who were prepared to engage in a blind

comparison of data whilst sharing their methodologies.

4. CFD practitioners perform analysis and submit results.

5. Conduct towing tank tests using a state of art facility and methodology.

6. Prepare comparative data of CFD and model tests.

7. Prepare a summary report of the work for publication by SYRF, including not only the technical

conclusions but also a discussion on how the data generated by the project can best serve the research and

educational aims of SYRF.

8. Summarize the way that the methodologies developed can be applied to yacht handicapping.

2.2 Test Matrix

The full test matrix is shown in the Project Prospectus PDF file and is summarized in Table 1. In the test matrix,

there is no mention of “sail trimming moment” or sail plan center of effort height; traditionally, towing tank tests

have been conducted using an assumed sail center of effort height so that an appropriate bow down trimming

moment from the sail thrust can be applied to the model. To take this approach, an estimate of the hull resistance

is required. In this study, each test run had a predetermined longitudinal center of gravity (LCG) to avoid each

contributor applying a slightly different sail trim moment. The specified LCG position for each test broadly

simulates the effect of the sail trim moment based on an assumed hull resistance curve and appropriate sail plan.

3

Table 1. Test Matrix, Speed & LCG Indices

ID Configuration TEST Heel Fn Description

CB-1

Canoe Body Only

Upright Resistance 0 0.10-0.80 Basic resistance test on the unappended hull.

CB-2 LCG Variation 0 0.35 Effect of shifting the Longitudinal Centre of Gravity, i.e. changing fore and aft trim. CB-3 LCG Variation 0 0.5

CB-4 Heel at zero yaw 15 0.25-0.45 Resistance test with the hull heeled.

CB-5 Heel at zero yaw 25 0.25-0.45

CB-6 Heel with yaw 15 0.35 Change of leeway with rudder on centerline, +ve and –ve leeway. CB-7 Heel with yaw 25 0.5

HKR-1

Hull Keel & Single Rudder

Upright Resistance 0 0.10-0.80 Basic resistance test on the unappended hull.

HKR-2 LCG Variation 0 0.35 Effect of shifting the Longitudinal Centre of Gravity, i.e. changing fore and aft trim. HKR-3 LCG Variation 0 0.5

HKR-4 Heel at zero yaw 15 0.25-0.45 Resistance test with the hull heeled.

HKR-5 Heel at zero yaw 25 0.25-0.45

HKR-6 Heel with yaw 15 0.35 Change of leeway with rudder on centerline, +ve and –ve leeway. HKR-7 Heel with yaw 25 0.5

HKR-8 Yaw Sweep 15 0.35

Leeway Sweeps and Rudder Variations at fixed speed and heel angle.




HKr-1 Hull Keel & Twin Rudders

Yaw Sweep 15 0.35 Leeway Sweeps and Rudder Variations at fixed speed and heel angle. HKr-2 Yaw Sweep 25 0.5

2.3 Tank Testing

The tank testing was carried out by the Wolfson Unit for Marine Technology and Industrial Aerodynamics

(WUMTIA) in the QinetiQ #2 towing tank at the Haslar Technology Park, Gosport England.

Standard WUMTIA test and analysis procedures were performed. The report describing the tests is presented in

the PDF Portfolio.

LCG Index

LCG m

LCG_001 -2.488

LCG_002 -2.476

LCG_003 -2.469

LCG_004 -2.459

LCG_005 -2.447

LCG_006 -2.431

LCG_007 -2.403

LCG_008 -2.367

LCG_009 -2.330

LCG_010 -2.294

LCG_011 -2.262

LCG_012 -2.235

LCG_013 -2.206

LCG_014 -2.172

LCG_015 -2.127

LCG_016 -2.784

LCG_017 -2.634

LCG_018 -2.484

LCG_019 -2.334

LCG_020 -2.184

Speed Index

Fn Vs m/s

V_001 0.1 0.681

V_002 0.15 1.022

V_003 0.2 1.363

V_004 0.25 1.703

V_005 0.3 2.044

V_006 0.35 2.385

V_007 0.4 2.725

V_008 0.45 3.066

V_009 0.5 3.407

V_010 0.55 3.747

V_011 0.6 4.088

V_012 0.65 4.429

V_013 0.7 4.769

V_014 0.75 5.110

V_015 0.8 5.451


2.3.1 Tank Model

A previously tested model canoe body was donated to the project. To protect the intellectual property of the

designer and the owner, the hull was modified to lines supplied by SYRF, re-faired, painted and marked up. The

model was re-commissioned for testing and fitted with a previously used keel fin, bulb and movable single rudder.

The principal dimensions for this model, designated as model number M1108 by the Wolfson Unit, are presented

below.

Table 2. Model Dimensions

2.4 CFD

An invitation was extended to practitioners who were active in the racing yacht field. Those who felt able to

support the project were allowed to participate. In total, five individuals were designated as CFD stakeholders.

Fortunately, this list represents a large segment of the CFD community, from commercial and open source RANS

codes to computationally less intensive panel codes.

Table 3. List of CFD Codes

Software Contributor Affiliation Type

FINETM/Marine Benoit Mallol, Jason Ker

Numeca, Ker Yacht Design

RANS

FlowLogic David Egan Panel Code

OpenFOAM Sandy Wright Wolfson Unit MTIA, University of Southampton

Open Source RANS

SHIPFLOW Lars Larsson, Michal Orych

Chalmers University of Technology, FLOWTECH Int. AB

Combination Panel Code & RANS

Star-CCM+ Rodrigo Azcueta, Matteo Lledri

Cape Horn Engineering RANS

M1108 Metric Imperial

Overall length 4.88 m 16.0 ft

Design waterline length 4.60 m 15.1 ft

Displacement (appended) 215 kg 474 lbs

Displacement (canoe body) 197 kg 434 lbs

Maximum beam 1.28 m 4.2 ft

Draft to datum 1.15 m 3.8 ft

5

3. Experimental Results

The experimental results and procedure are presented in Report No. 2546D from the Wolfson Unit MTIA. The

report, spreadsheets, and tank photos are available for download from the SYRF Technical Resources Library.1

3.1 Practicalities

The test matrix for the project was developed with the computational (CFD) work in mind. In comparison to the

computational process, the experimental (tank test) process is more complex and requires additional processing

steps to allow for the comparison between the experimental and computational data. The rationale behind the

processing of the experimental data follows.

A typical upright resistance curve, expressed as a drag area (AD = drag/q), is shown in Figure 1. The first few runs

of the upright resistance curve are used to align the model to produce a minimum amount of sideforce and yaw

moment. It is impossible to set the model up so accurately that it runs with no sideforce or yaw moment, but the

data is corrected for the presence of these forces and moments.

Figure 1. Typical drag area curve from an upright resistance test

For the heeled and yawed tests, a series of runs over a range of yaw angles, are carried out at each speed and heel

angle combination. These tests are conducted on both port and starboard tacks.2 The yaw angles should be chosen

so that the sailing sideforce for the heel angle is spanned. Using a predetermined leeway angle sequence that

remains the same for all speeds and heel angles will produce a substantial number of test points that are far

1 Link to results and photos: SYRF-WL Tank Results.zip [9 MB], SYRF-WL Tank Photos.zip [326 MB] 2 The Wolfson Unit is unique in that the experimental set up allows testing on both tacks, giving the ability to determine the

forces from a mean value from both tacks. This approach delivers a more reliable test data set.

0.2

0.3

0.4

0.5

0.6

0.7

4 6 8 10 12 14 16 18

Speed kts

Dra

g A

rea

Upright

Resistance

https://drive.google.com/open?id=0B2CUun8QUAMsb1FRcHdRajdLSjQ

https://drive.google.com/file/d/0B2CUun8QUAMsdHBmWEVaUk5MMTg/view?usp=sharing


removed from the ‘sailing’ condition. Also, for the heeled tests, it is convenient to determine the down thrust of

the sails (SF tanφ) based on estimated sailing sideforce for the yacht. This may be applied regardless of the

leeway angle set as it is not only easier from a practical view point but also avoids fluctuations in displacement

affecting the determination and interpretation of induced drag.

Typical test data is shown in Figure 2. There is usually some difference in the sideforce for a given leeway on the

two tacks and at higher speeds and heel angles a difference of drag tack to tack at the same sideforce, not the same

leeway, of 1–2% is acceptable. Greater differences than this indicate a misalignment of the center planes between

the hull, keel and rudder.

Figure 2. Typical heeled and yawed resistance test results.

Typically 3-4 tests per tack are done at each speed. It should be noted that although it is tempting, from an

analysis perspective, to make one of these a zero yaw point, there is often some non-linearity close to zero

sideforce that makes it more useful to begin the tests at some low leeway angle. This process is repeated for all

the speed/heel angle combinations in the test matrix.

As part of the tank analysis, the data from both tacks was analyzed to determine the mean line through the data

from both tacks and to average out the sideforce differences at the same nominal leeway on each tack.3

3.2 Sailing Yacht Resistance Breakdown

The total hydrodynamic drag of the yacht is assumed to be the sum of the following components:

𝑅𝑇𝑂𝑇 = 𝑅𝑈 + 𝑅0 + 𝑅𝐼

Upright Resistance (RU) comprising:

Wave resistance (RW)

Appendage viscous drag (RVapp)

Canoe body viscous drag (RVcb)

3 This data is presented in Table 4 of the towing tank report.

0.20

0.25

0.30

0.35

0.40

0.45

0.50

0.55

0 200 400 600 800 1000 1200

Sideforce2

Dra

g A

rea 11 knots

Leew

ay

2 d

eg

10 knots

9 knots

Leew

ay 3

deg

Filled Symbols = Port tack

Open Symbols = Stbd. tack

7

R0 (R zero) the increase in drag above RU at zero sideforce from the fitted line to the test data,

RI the Induced drag.

Because this study is not extrapolating the data to full scale it is not necessary to consider the de-construction of

the resistance into viscous and gravitational components.

The combination of the aforementioned drag components is shown graphically in Figure 3. At a speed VS and

heel angle φ the resistance value can be determined by the intersection of the resistance against sideforce squared

line with the equilibrium sailing sideforce line (shown as a dotted vertical line in Figure 3). The requirement of a

typical Velocity Prediction Program (VPP) hydrodynamic force model is to determine these three resistance

components — this approach must be adopted to assist with the comparison of the experimental and computed

data.

Figure 3. Resistance breakdown for analysis

The first step is to fit a cubic spline curve to the upright resistance results using a least squares fit. This allows the

upright resistance to be determined at any speed. Looking at the heeled and yawed results, unless stall is

occurring, a straight line can usually be fitted to the drag versus SF2 data points at each speed and heel angle. The

slope of the line is determined by the induced drag characteristics of the keel and rudder combined with the

wavemaking effects. The slope of the line may be expressed as an effective draft (Te) derived from the formula:

𝑇𝑒 = √1

(𝑑𝑅

𝑑𝑆𝐹2) 𝜌𝜋𝑉2𝑐𝑜𝑠2𝜙

dR/dSF2 = slope of resistance versus sideforce2 line

ρ = density

V = velocity

ϕ = heel angle

Dra

g

R U

V S Sailing SF2

R0

R I

Resistance vs. SF 2 line. Speed = V S

Heel =

R TOT

Dra

g


The intercept of the straight line with the zero sideforce axis (R0) determines the drag due to heel, and may be

expressed as a ratio to the upright resistance RU. Thus, for each tested speed and heel angle, the hydrodynamic

behavior can be expressed as an effective draft (Te) and a heel drag ratio (RH/RU), where RH = RU + R0.

Figure 4 illustrates this approach and shows the results from tests HKR 8-11 expressed as effective draft and heel

drag ratio.

Figure 4. Typical variation of R0/RU and Te versus speed for a yacht derived from tank tests.

These plots show typical behavior — heel drag increases both with heel angle and speed while effective draft

reduces with increasing speed and heel angle as the keel root comes closer to the water surface.

2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.00.90

0.95

1.00

1.05

2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.00.0

0.2

0.4

0.6

0.8

1.0

Solid Line 15 deg heelDashed Line 25 Deg

SPEED m/s

HE

EL

- D

RA

G R

atio

SPEED m/s

EF

FE

CT

IVE

DR

AF

T m

9

Presenting the data in this form gives a much clearer insight into the quality of the results than simply comparing

on a point by point basis. It allows us to see if the computational results actually match the trends of the physical

test results, even if the “absolute” values are somewhat different.

4. Computational Results

Each participant submitted computational results for his specific CFD program. In addition to submitting results

via spreadsheet, each participant provided a brief summary of his methodology and results. The submitted files

from each participant are available via the SYRF Research Library links included in the section footers. The CFD

results are presented in the graphs that follow.

4.1 Questionnaire

Each CFD stakeholder was asked to complete a questionnaire detailing the software and methods used to generate

the results.4

Table 4. CFD Stakeholder Questionnaire

CFD Questionnaire

CFD package?

Mesh Generation Software?

Solver?

Post process and visualization software?

Towing point?

Free surface tracking/capturing method?

Turbulence model?

Numerical Ventilation/Streaking

Ventilation observed?

Correction/Type?

Mesh type?

Computational Domain Size?

Local refinement?

Speed treatment?

Cell resolutions (in mm)?

Mesh sizes (in million cells)?

Time to prepare meshing?

Time to mesh each case?

CPU requirements?

Computer?

MeshSize/meshing/Solving/cores?

Cost effectiveness?

4 Link to compiled questionnaire: SYRF-WL CFD-Questionnaire-Compiled.xlsx [97 KB]

https://drive.google.com/file/d/0B2CUun8QUAMsV2prVEF5Wk5ORzA/view?usp=sharing


0

50

100

150

200

250

300

350

0.0 1.0 2.0 3.0 4.0 5.0 6.0

Dra

g (N

)

Speed (m/s)

Star-CCM+ CB-1, 4 & 5, HKR-1, 4 & 5

CB1 Heel 0° Yaw 0° HKR1 Heel 0° Yaw 0°CB4 Heel 15° Yaw 0° HKR4 Heel 15° Yaw 0°CB5 Heel 25° Yaw 0° HKR5 Heel 25° Yaw 0°

20

40

60

80

100

120

140

160

-2.8 -2.7 -2.6 -2.5 -2.4 -2.3 -2.2 -2.1

Dra

g (N

)

LCG (m)

Star-CCM+ CB-2 & 3, HKR-2 & 3

CB2 Fn 0.35 Heel 0° Yaw 0° CB3 Fn 0.5 Heel 0° Yaw 0°

HKR2 Fn 0.35 Heel 0° Yaw 0° HKR3 Fn 0.5 Heel 0° Yaw 0°

20

40

60

80

100

120

140

160

180

-2 -1 0 1 2 3

Dra

g (N

)

Yaw (deg)


CB6 Fn 0.35 Heel 15° CB7 Fn 0.5 Heel 25°

HKR6 Fn 0.35 Heel 15° HKR7 Fn 0.5 Heel 25°

-300

-200

-100

0

100

200

300

400

-2 -1 0 1 2 3

Sid

efo

rce

(N

)

Yaw (deg)




4.2 Star-CCM+ Results

The results and all associated files which were submitted can be downloaded from the SYRF Technical Resources

Library.5

Figure 5. Star-CCM+ Resistance Curves

Figure 6. Star-CCM+ Yaw Sweep Tests

5 Link to results: SYRF-WL Star-CCM+ Results.zip [236 KB]

https://drive.google.com/file/d/0B2CUun8QUAMseGY0SWJQZDVFOVE/view?usp=sharing

11

40

60

80

100

120

140

160

180

0 50000 100000 150000 200000 250000 300000 350000 400000

Dra

g (N

)

Sideforce2 (N2)

Star-CCM+ HKR-8 & HKR-9

HKR8 Fn 0.35 Heel 15° Yaw var Rudder 2


ZeroPoint = 146.40Slope = 6.51E-05


40

60

80

100

120

140

160

180

0 50000 100000 150000 200000 250000 300000

Dra

g (N

)

Sideforce2 (N2)

Star-CCM+ HKR-10 & HKR-11





40

60

80

100

120

140

160

180

0 50000 100000 150000 200000 250000 300000

Dra

g (N

)

Sideforce2 (N2)

Star-CCM+ HKr-1 & HKr-2

HKr-1 Fn 0.35 Heel 15° Yaw var Twin Rudder 2




Figure 7. Star-CCM+ Yaw Sweeps at 15° and 25° Heel

Figure 8. Star-CCM+ Yaw Sweeps at 15° and 25° Heel, Twin Rudder


20

40

60

80

100

120

140

160

-2.8 -2.7 -2.6 -2.5 -2.4 -2.3 -2.2 -2.1

Dra

g (N

)

LCG (m)

FINE/Marine CB-2 & 3, HKR-2 & 3



20

40

60

80

100

120

140

160

180

-2 -1 0 1 2 3

Dra

g (N

)

Yaw (deg)




-300

-200

-100

0

100

200

300

400

-2 -1 0 1 2 3

Sid

efo

rce

(N

)

Yaw (deg)




0

50

100

150

200

250

300

350

0.0 1.0 2.0 3.0 4.0 5.0 6.0

Dra

g (N

)

Speed (m/s)

FINE/Marine CB-1, 4 & 5, HKR-1, 4, & 5


4.3 FINE/Marine Results


Library.6

Figure 9. FINE/Marine Resistance Curves

Figure 10. FINE/Marine Yaw Sweep Tests

6 Link to results: SYRF-WL FINEMarine Results.zip [99 MB]

https://drive.google.com/open?id=0B2CUun8QUAMsNURNZ1VYc0NYT3M

13

40

60

80

100

120

140

160

180

0 50000 100000 150000 200000 250000 300000 350000 400000

Dra

g (N

)

Sideforce2 (N2)

FINE/Marine HKR-8 & HKR-9





40

60

80

100

120

140

160

180

0 50000 100000 150000 200000 250000 300000

Dra

g (N

)

Sideforce2 (N2)

FINE/Marine HKR-10 & HKR-11





40

60

80

100

120

140

160

180

0 50000 100000 150000 200000 250000 300000

Dra

g (N

)

Sideforce2 (N2)

FINE/Marine HKr-1 & HKr-2





Figure 11. FINE/Marine Yaw Sweep at 15° and 25° Heel

Figure 12. FINE/Marine Yaw Sweeps at 15° and 25° Heel, Twin Rudder


0

50

100

150

200

250

300

350

400

450

0.0 1.0 2.0 3.0 4.0 5.0 6.0

Dra

g (N

)

Speed (m/s)

OpenFOAM CB-1, 4 & 5, HKR-1, 4 & 5

CB1 Heel 0° Yaw 0° HKR1 Heel 0° Yaw 0°CB4 Heel 15° Yaw 0° HRK4 Heel 15° Yaw 0°CB5 Heel 25° Yaw 0° HKR5 Heel 25° Yaw 0°

20

40

60

80

100

120

140

160

180

200

-2.8 -2.7 -2.6 -2.5 -2.4 -2.3 -2.2 -2.1

Dra

g (N

)

LCG (m)

OpenFOAM CB-2 & 3, HKR-2 & 3



20

40

60

80

100

120

140

160

180

200

-2 -1 0 1 2 3

Dra

g (N

)

Yaw (deg)




-300

-200

-100

0

100

200

300

400

-2 -1 0 1 2 3

Sid

efo

rce

(N

)

Yaw (deg)




4.4 OpenFOAM Results


Library.7

Figure 13. OpenFOAM Resistance Curves

Figure 14. OpenFOAM Yaw Sweep Tests

7 Link to results: SYRF-WL OpenFOAM Results.zip [158 MB]

https://drive.google.com/file/d/0B2CUun8QUAMsaFczSGY2TXRQazg/view?usp=sharing

15

40

60

80

100

120

140

160

0 50000 100000 150000 200000

Dra

g (N

)

Sideforce2 (N2)

OpenFOAM HKR-10 & HKR-11 (no data)



40

60

80

100

120

140

160

180

0 50000 100000 150000 200000 250000 300000

Dra

g (N

)

Sideforce2 (N2)

OpenFOAM HKr-1 & HKr-2 (no data)



50

100

150

200

250

0 50000 100000 150000 200000 250000 300000 350000

Dra

g (N

)

Sideforce2 (N2)

OpenFOAM HKR-8 & HKR-9





Figure 15. OpenFOAM Yaw Sweep at 15° and 25° Heel

Figure 16. OpenFOAM Yaw Sweep at 15° Heel, Twin Rudder


0

50

100

150

200

250

300

350

0.0 1.0 2.0 3.0 4.0 5.0 6.0

Dra

g (N

)

Speed (m/s)

FlowLogic CB-1, 4 & 5, HKR-1, 4 & 5


20

40

60

80

100

120

140

160

-2.8 -2.7 -2.6 -2.5 -2.4 -2.3 -2.2 -2.1

Dra

g (N

)

LCG (m)

FlowLogic CB-2 & 3, HKR-2 & 3



20

40

60

80

100

120

140

160

180

-2 -1 0 1 2 3

Dra

g (N

)

Yaw (deg)




-300

-200

-100

0

100

200

300

400

-2 -1 0 1 2 3

Sid

efo

rce

(N

)

Yaw (deg)




4.5 FlowLogic Results


Library.8

Figure 17. FlowLogic Resistance Curves

Figure 18. FlowLogic Yaw Sweep Tests

8 Link to results: SYRF-WL FlowLogic Results.zip [1 MB]

https://drive.google.com/file/d/0B2CUun8QUAMsUGVYNFJxbGEyb3M/view?usp=sharing

17

40

60

80

100

120

140

160

180

0 75000 150000 225000 300000 375000 450000

Dra

g (N

)

Sideforce2 (N2)

FlowLogic HKR-8 & HKR-9





40

60

80

100

120

140

160

180

0 50000 100000 150000 200000 250000 300000

Dra

g (N

)

Sideforce2 (N2)

FlowLogic HKR-10 & HKR-11





40

60

80

100

120

140

160

180

0 50000 100000 150000 200000 250000 300000 350000

Dra

g (N

)

Sideforce2 (N2)

FlowLogic HKr-1 & HKr-2





Figure 19. FlowLogic Yaw Sweep at 15° and 25° Heel

Figure 20. FlowLogic Yaw Sweep at 15° and 25° Heel, Twin Rudder


0

50

100

150

200

0.0 1.0 2.0 3.0 4.0 5.0 6.0

Dra

g (N

)

Speed (m/s)

SHIPFLOW CB-1

CB1-Pot & BL method-Trim v1 CB1-Pot & BL Method-Trim v2

CB1-RANS-Trim v1 CB1-RANS-Trim v2

34

36

38

40

42

44

46

-2.8 -2.7 -2.6 -2.5 -2.4 -2.3 -2.2 -2.1

Dra

g (N

)

LCG (m)

SHIPFLOW CB-2 & 3

CB2 Fn 0.35-Pot & BL mthd-Trim v1CB2 Fn 0.35-Pot & BL mthd-Trim v2CB2 Fn 0.35-RANS-Trim v1CB2 Fn 0.35-RANS-Trim v2

4.6 SHIPFLOW Results


Library.9

Figure 21. SHIPFLOW Resistance Curves

5. Analysis and Discussion

Section 3 describes an approach to viewing the hydrodynamic behavior of a yacht hull that can be applied to any

sailing vessel. Applied to Wide-Light designs, three fundamental features are apparent: the upright resistance

increases with speed, the appendages represent a significant proportion of the total resistance, and the effective

draft of the hull and keel reduce as speed and heel angle increase. The model tank test results can be compared

with the CFD results with regards to the two following questions:

a) Do the computational results capture the general behavior?

b) Do the absolute values of the data points agree?

Although CFD results are acknowledged to differ point by point with the experimental data, their relative

differences can still be used as a reliable comparator. This approach can still be adopted for this study even though

there is only a data set for one hull.

9 Link to results: SYRF-WL SHIPFLOW Results.zip [56 MB]

https://drive.google.com/file/d/0B2CUun8QUAMsOFV5b2h3dFlENm8/view?usp=sharing

19

-0.5

0.0

0.5

1.0

1.5

2.0

0.5 1.5 2.5 3.5 4.5 5.5

Trim

(d

eg)

Speed (m/s)

CB-1

-0.04

-0.03

-0.02

-0.01

0.00

0.01

0.02

0.5 1.5 2.5 3.5 4.5 5.5

He

ave

(m

)

Speed (m/s)

Tank Star-CCM+ OpenFOAM

FlowLogic FINE/Marine

-0.5

0.0

0.5

1.0

1.5

2.0

0.5 1.5 2.5 3.5 4.5 5.5

Trim

(d

eg)

Speed (m/s)

HKR-1

-0.04

-0.03

-0.02

-0.01

0.00

0.01

0.02

0.5 1.5 2.5 3.5 4.5 5.5

He

ave

(m

)

Speed (m/s)



5.1 Results and Comparative Charts

The experimental and computational results are available in a combined spreadsheet from the SYRF Technical

Resources Library.10

5.1.1 Upright Resistance Trim and Heave – Tests CB-1 & HKR-1

The trim and heave curves for the tank test and CFD calculations are summarized in Figure 22 for the bare canoe

body and the appended model.

Figure 22. Trim and Heave Comparison – Zero Heel

10 Link to Results Spreadsheet: SYRF-WL Results.xlsx [1 MB]

https://drive.google.com/open?id=0B2CUun8QUAMsb0RTd2RfbWlYVnM


0

50

100

150

200

250

300

350

400

0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5

Dra

g (N

)

Speed (m/s)

Resistance Curve CB-1 & HKR-1

Tank CB1 Tank HKR1Star-CCM+ CB1 Star-CCM+ HKR1OpenFOAM CB1 OpenFOAM HKR1FlowLogic CB1 FlowLogic HKR1FINE/Marine CB1 FINE/Marine HKR1

0.010

0.015

0.020

0.025

0.030

0.035

0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5

Dra

g A

rea

(m2 )

Speed (m/s)

Speed vs. Drag Area CB-1 & HKR-1

Tank CB1 Tank HKR1Star-CCM+ CB1 Star-CCM+ HKR1OpenFOAM CB1 OpenFOAM HKR1FlowLogic CB1 FlowLogic HKR1FINE/Marine CB1 FINE/Marine HKR1

The Upright Resistance curves from the tank results and the computed results are shown in Figure 23. The left

hand plot is the force comparison, and the right hand plot is presented as a drag area, where:

𝐷𝑟𝑎𝑔 𝐴𝑟𝑒𝑎 =𝑅𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒

12⁄ 𝜌𝑉2

Resistance is in N,

ρ = water density (1000 kg/m3)

V = speed (m/s)

In the Drag Area plot, it is important to note the suppressed zero — the resistance at low speed is due to surface

friction resistance, and the increase in drag above that is due to residuary (wave making) resistance. For the canoe

body, only the friction and residuary resistance are of similar magnitude. For the appended model, the friction

resistance is nearly always greater than the residuary resistance. The friction resistance can be calculated from

published data using the wetted area and waterline length, while only the residuary resistance requires model tests

or CFD to predict.

Figure 23. Resistance Comparison – Zero Heel

A “ratio plot” approach is used to more clearly evaluate the magnitude of the differences between the results. The

results are expressed as the ratio of

𝐷𝑟𝑎𝑔 𝐶𝑜𝑚𝑝𝑎𝑟𝑎𝑡𝑜𝑟

𝐷𝑟𝑎𝑔 𝐵𝑎𝑠𝑒𝑙𝑖𝑛𝑒

21

0.6

0.7

0.8

0.9

1.0

1.1

1.2

1.3

1.4

0.5 1.5 2.5 3.5 4.5 5.5

Dra

g R

atio

(-)

Speed (m/s)

CB-1 Upright Ratio



0.6

0.7

0.8

0.9

1.0

1.1

1.2

1.3

1.4

0.5 1.5 2.5 3.5 4.5 5.5D

rag

Rat

io (

-)Speed (m/s)

HKR-1 Upright Ratio



for each test point. Where tank test data is available, the tank drag is used as the baseline and therefore the tank

test drag ratio is constant at 1.00. The results for the upright resistance tests are shown in Figure 24.

Figure 24. Upright Resistance Data, Ratio to Tank Test Results

In summary, Figure 22 shows that in broad terms the CFD prediction of the body motions agree well with the

towing tank values. Figure 24 for the CB-1 (canoe body only) case shows that most CFD points, for resistance

prediction, lie within 7-8 % of the tank value. However, Figure 24 also reveals that the agreement for OpenFOAM

and FlowLogic is less in the HKR-1 (appended) configuration. The lack of agreement for OpenFOAM is largely

because the computational scheme inherent in OpenFOAM meant that the computational time needed to

accurately capture the drag of the keel and rudder was far beyond that which could be devoted to this project. As

such, a simplified mesh was employed that reduced the accuracy of the appendage resistance predictions, but

which did not affect the prediction of heeled resistance ratio and effective draft.

5.1.2 LCG Variation – Tests CB-2 & 3, HKR-2 & 3

The ratio plots for the LCG shift tests on the hull alone (CB-2 & 3) are shown in Figure 25.


0.6

0.7

0.8

0.9

1.0

1.1

1.2

1.3

1.4

-2.8 -2.7 -2.6 -2.5 -2.4 -2.3 -2.2 -2.1

Dra

g R

atio

(-)

LCG (m)

CB-2 Fn 0.35 Heel 0° Yaw 0° Ratio



0.6

0.7

0.8

0.9

1.0

1.1

1.2

1.3

1.4

-2.8 -2.7 -2.6 -2.5 -2.4 -2.3 -2.2 -2.1

Dra

g R

atio

(-)

LCG (m)

CB-3 Fn 0.5 Heel 0° Yaw 0° Ratio



0.6

0.7

0.8

0.9

1.0

1.1

1.2

1.3

1.4

-2.8 -2.7 -2.6 -2.5 -2.4 -2.3 -2.2 -2.1

Dra

g R

atio

(-)

LCG (m)

HKR-2 Fn 0.35 Heel 0° Yaw 0° Ratio



0.6

0.7

0.8

0.9

1.0

1.1

1.2

1.3

1.4

-2.8 -2.7 -2.6 -2.5 -2.4 -2.3 -2.2 -2.1

Dra

g R

atio

(-)

LCG (m)

HKR-3 Fn 0.5 Heel 0° Yaw 0° Ratio



Figure 25. Canoe Body Only Upright LCG Shift, Ratio to Tank Test Results

The ratio plots for the LCG shift tests on the appended hull (HKR-2 & 3) are shown in Figure 26.

Figure 26. Hull, Keel, & Rudder Upright LCG Shift, Ratio to Tank Test Results

23

Figure 3 from the tank report below shows typical behavior for a change of LCG – there is a discernible resistance

minimum for each speed at a given LCG position.

The CFD results mirror the tank behavior, although the rate of change of resistance moving away from the

minimum varies slightly as shown by the ratio plots, Figure 25 for the hull only results and Figure 26 for the hull

keel and rudder results.

5.1.3 Heeled Resistance Tests

The results of the heeled resistance tests are best expressed as a ratio of 𝑅𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑎𝑡 𝐻𝑒𝑒𝑙

𝑈𝑝𝑟𝑖𝑔ℎ𝑡 𝑅𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒 at each test speed. This

“Heel drag ratio” for the tests is summarised in Figure 27. For example, for the canoe body tests at 15 degrees

heel the Heel drag ratio for the Star-CCM+ result at 1.7 m/s is 0.947; in other words, when heeled, the drag of the

hull is 5.3% less than with the hull upright.


0.85

0.90

0.95

1.00

1.05

1.5 2.0 2.5 3.0 3.5

He

el-

Dra

g R

atio

(-)

Speed (m/s)

15° Heel, HKR-4

0.85

0.90

0.95

1.00

1.05

1.5 2.0 2.5 3.0 3.5

He

el-

Dra

g R

atio

(-)

Speed (m/s)

25° Heel, HKR-5



0.85

0.90

0.95

1.00

1.05

1.5 2.0 2.5 3.0 3.5

He

el-

Dra

g R

atio

(-)

Speed (m/s)

15° Heel, CB-4

0.85

0.90

0.95

1.00

1.05

1.5 2.0 2.5 3.0 3.5

He

el-

Dra

g R

atio

(-)

Speed (m/s)

25° Heel, CB-5



Figure 27. Heeled Resistance Test Data Ratio to Upright Value

The data from Figure 27 is re-cast as a ratio plot in Figure 28 for the canoe body tests, and Figure 29 for the hull

keel & rudder tests.

Although it is not a condition that the yacht can ever sail in, the resistance of the yacht when heeled at zero yaw

angle provides a reliable indicator of the hull’s characteristics. With this understanding, Figure 27, which only

illustrates CFD results for the canoe body, shows consistent hull behavior, with the heeled hull consistently

having less resistance than the upright hull because the wetted area reduces as heel angle increases. A similar

behavior is shown for the appended hull, but the resistance reduction is somewhat reduced because the keel and

rudder wetted surface do not change with heel. The towing tank results also show a trend of heeled resistance

increasing as speed increases, and this is generally captured by the CFD results. Again, the ratio plots show that

the trends are captured, but the absolute values differ to the same degree as the upright resistance results.

25

0.6

0.7

0.8

0.9

1.0

1.1

1.2

1.3

1.4

1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2

Dra

g R

atio

(-)

Speed (m/s)

CB-4 Heel 15° Yaw 0° Ratio



0.6

0.7

0.8

0.9

1.0

1.1

1.2

1.3

1.4

1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2

Dra

g R

atio

(-)

Speed (m/s)

CB-5 Heel 25° Yaw 0° Ratio



0.6

0.7

0.8

0.9

1.0

1.1

1.2

1.3

1.4

1.5

1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2

Dra

g R

atio

(-)

Speed (m/s)

HKR-4 Heel 15° Yaw 0° Ratio



0.6

0.7

0.8

0.9

1.0

1.1

1.2

1.3

1.4

1.5

1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2

Dra

g R

atio

(-)

Speed (m/s)

HKR-5 Heel 25° Yaw 0° Ratio



Figure 28. Canoe Body Only Heeled Resistance Test Data, Ratio to Tank Test Results

Figure 29. Hull, Keel & Rudder Heeled Resistance Test Data, Ratio to Tank Test Results

5.1.4 Heel with Yaw – Tests CB-6 &7, HKR-6 & 7

The results of the yaw sweeps on the bare canoe (CB-6 & CB-7) are presented in Figure 30 as plots of Drag vs.

yaw angle and Sideforce vs. yaw angle. Because the model is heeled these do not show a discernible minimum at

zero yaw. In fact the drag minimum is at a negative yaw angle because this aligns the centerline of the heeled

waterplane more nearly with the hulls direction of travel through the water.


0.6

0.7

0.8

0.9

1.0

1.1

1.2

1.3

1.4

-2 -1 0 1 2 3

Dra

g R

atio

(-)

Yaw (deg)

CB-6 Fn 0.35 Heel 15° Ratio



0.6

0.7

0.8

0.9

1.0

1.1

1.2

1.3

1.4

-2 -1 0 1 2 3

Dra

g R

atio

(-)

Yaw (deg)

CB-7 Fn 0.5 Heel 25° Ratio



20

40

60

80

100

120

140

-2.0 -1.0 0.0 1.0 2.0 3.0

Dra

g (N

)

Yaw (deg)

CB-6 Fn 0.35 Heel 15°, CB-7 Fn 0.5 Heel 25°

15° - Tank 25° - Tank15° - Star-CCM+ 25° - Star-CCM+15° - OpenFOAM 25° - OpenFOAM15° - FlowLogic 25° - FlowLogic15° - FINE/Marine 25° - FINE/Marine

-10

0

10

20

30

40

50

60

70

80

90

-2.0 -1.0 0.0 1.0 2.0 3.0Si

de

forc

e (

N)

Yaw (deg)

CB-6 Fn 0.35 Heel 15°, CB-7 Fn 0.5 Heel 25°


The yaw sweep results are presented as ratio plots to the tank data in Figure 31.

Figure 30. Canoe Body Only Yaw Sweep Data at 15° and 25° Heel

Figure 31. Canoe Body Only Yaw Sweep Data, Ratio to Tank Test Results

The results of the yaw sweeps with the keel and rudder (at zero rudder angle) fitted (HKR-6 & HKR-7) are

presented in Figure 32 as plots of Drag vs. yaw angle and Sideforce vs. yaw angle. Here the drag minimum is

27

0.6

0.7

0.8

0.9

1.0

1.1

1.2

1.3

1.4

1.5

-2 -1 0 1 2 3

Dra

g R

atio

(-)

Yaw (deg)

HKR-6 Fn 0.35 Heel 15° Ratio



0.6

0.7

0.8

0.9

1.0

1.1

1.2

1.3

1.4

1.5

-2 -1 0 1 2 3

Dra

g R

atio

(-)

Yaw (deg)

HKR-7 Fn 0.5 Heel 25° Ratio



20

40

60

80

100

120

140

160

180

200

-2.0 -1.0 0.0 1.0 2.0 3.0

Dra

g (N

)

Yaw (deg)

HKR-6 Fn 0.35 Heel 15°, HKR-7 Fn 0.5 Heel 25°


-300

-200

-100

0

100

200

300

400

-2.0 -1.0 0.0 1.0 2.0 3.0

Sid

efo

rce

(N

)

Yaw (deg)

HKR-6 Fn 0.35 Heel 15°, HKR-7 Fn 0.5 Heel 25°


closer to zero yaw because this corresponds to the minimum Sideforce from the appendages. The yaw sweep

results are presented as ratio plots to the tank data in Figure 33.

Figure 32 Hull Keel & Rudder Yaw Sweep Data at 15° and 25° Heel

Figure 33. Hull, Keel & Rudder Yaw Sweep Data, Ratio to Tank Test Results


0

50

100

150

200

250

0 50000 100000 150000 200000 250000 300000

Dra

g (N

)

Sideforce2 (N2)

HKR-8 Fn 0.35 & HKR-9 Fn 0.5 Heel 15°

Tank HKR8 Tank HKR9Star-CCM+ HKR8 Star-CCM+ HKR9OpenFOAM HKR8 OpenFOAM HKR9FlowLogic HKR8 FlowLogic HKR9FINE/Marine HKR8 FINE/Marine HKR9

0

50

100

150

200

250

0 50000 100000 150000 200000 250000 300000

Dra

g (N

)

Sideforce2 (N2)

HKR-10 Fn 0.35 & HKR-11 Fn 0.5 Heel 25°

Tank HKR10 Tank HKR11Star-CCM+ HKR10 Star-CCM+ HKR11OpenFOAM HKR10 OpenFOAM HKR11FlowLogic HKR10 FlowLogic HKR11FINE/Marine HKR10 FINE/Marine HKR11

Just as with the previous figures, the ratio plots in Figures 31 and 33 show that the CFD results capture the trends

shown by the tank test results, with similar divergence of absolute results that are seen consistently throughout the

tests.

5.1.5 Yaw Sweeps Hull, Keel, & Rudder – Tests HKR-8, 9, 10, & 11

As shown in Figure 2 of Section 3, the results of the yaw sweep tests can be captured in a single straight line on a

resistance vs Sideforce2 plot. The yaw sweep data are presented in Figure 34.

Figure 34. Hull, Keel & Rudder, Summary of Fitted Lines to Yaw Sweep Data

As described in Section 3.2, the character of the Resistance vs Sideforce2 plots can be expressed as a heeled drag

ratio RH/RU and an effective draft, expressed in meters. Figure 35 shows the data expressed in this way.

29

0.90

0.92

0.94

0.96

0.98

1.00

1.02

1.04

2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0

He

el-

Dra

g R

atio

(-)

Speed (m/s)

HKR-8 & 9 Heel 15°

0.0

0.2

0.4

0.6

0.8

1.0

2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0

Effe

ctiv

e D

raft

(m

)

Speed (m/s)



0.90

0.92

0.94

0.96

0.98

1.00

1.02

1.04

2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0

He

el-

Dra

g R

atio

(-)

Speed (m/s)

HKR-10 & 11 Heel 25°

0.0

0.2

0.4

0.6

0.8

1.0

2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0

Effe

ctiv

e D

raft

(m

)

Speed (m/s)



Figure 35. Heeled Resistance Ratio and Effective Draft Comparison

In broad terms, the Star-CCM+ and FINE/Marine codes are closest to the towing tank results in both absolute

terms and capturing the slope of the Drag vs. Sideforce2 line. The FlowLogic results capture the slope, but the

OpenFOAM results are at some variance to the experimental result for the reasons discussed in 5.1.1.

While no tank tests were carried out on the twin rudder configuration, a similar summary of the Resistance vs.

Sideforce2 results for the twin rudder configuration are shown in Figure 35.


0

50

100

150

200

250

0 50000 100000 150000 200000 250000 300000

Dra

g (N

)

Sideforce2 (N2)

HKr-1 Fn 0.35 Heel 15°, HKr-2 Fn 0.5 Heel 25°

Star-CCM+ HKr-1 Star-CCM+ HKr-2

OpenFOAM HKr-1 OpenFOAM HKr-2

FlowLogic HKr-1 FlowLogic HKr-2

FINE/Marine HKr-1 FINE/Marine HKr-2

5.1.6 Yaw Sweeps Twin Rudder – Tests HKr-1 & 2

Figure 36 shows the Resistance Sideforce2 plots for the twin rudder results derived from the CFD calculations. No

tank tests were made with the model in this configuration.

Figure 36. Comparison of CFD Results for Twin Rudder Configuration

5.2 Lift Curve Slope

This report has focused on the comparison of resistance and side force with speed and heel angle, as these are the

main drivers of performance. However, the data was also analyzed to determine a simple lift slope from the HKR-

8, 9, 10, & 11 tests. These results are presented in the Table below.

The value was determined from the slope of the line 𝑆𝐹/𝑉2 versus yaw angle where Sideforce (SF) is in N and

Speed (V) in m/s.

The results are presented in Figure 37 and reflect a satisfactory degree of consistency – the trend of lift slope

reducing as heel angle increases is captured by CFD. However, these results reveal that the reduction of lift slope

as speed increases is not captured.

31

Figure 37. Lift Slope Comparison

5.3 Discussion

The fundamental aim of this project was to explore how computational methods might be employed to inform

force models used in VPP based handicap rules. The fundamental components of a sailing yacht’s resistance are

described in Section 3.2.

𝑅𝑇𝑂𝑇 = 𝑅𝑈 + 𝑅0 + 𝑅𝐼

Upright Resistance (RU) comprising:

Wave resistance (RW)

Appendage viscous drag (RVapp)

Canoe body viscous drag (RVcb)

R0 (R zero) the increase in drag above RU at zero sideforce from the fitted line to the test data, and,

RI the Induced drag.

The table below describes how the computational results compared with the physical model test.

Table 5. Comparison Summary – CFD to Model Test

Component

Upright Resistance Figure 24 shows that the computational methods are tolerably capable

of predicting the upright resistance of both the bare canoe body and the

appended hull. Generally there is an offset of a few % across the speed

range, and the CFD generally under predicts the resistance. As

discussed in Section 5.1.1, for these wide, light hull forms nearly 50%

of the resistance is skin friction drag that can be calculated simply from

published data and hull wetted surface area.

The computational methods are also sensitive to the effects of shifting

the center of gravity fore and aft.

Heeled Resistance Figure 29 shows that the advanced RANS codes (Star-CCM+ &

FINE/Marine) are able to accurately predict the effects of heel on

resistance.

Fn 0.35, Heel 15° Fn 0.5, Heel 15° Fn 0.35, Heel 25° Fn 0.5, Heel 25°

Tank 13.4 12.3 9.5 8.8

Star-CCM+ 10.7 11.5 8.2 9.1

OpenFOAM 9.8 10.8 8.0

FlowLogic 11.5 12.5 9.2 10.3

FINE/Marine 10.5 11.2 8.1 8.9

0.0

5.0

10.0

15.0


Resistance due to yaw angle Figures 31 and 33 show that the computational methods are all able to

predict the effect on sideforce of changing yaw angle.

Heel Drag Ratio The upper plots in Figure 35 show that the computational methods are

all able to predict the increase of drag at zero sideforce as speed

increases, although of course the “offset” found in the upright

resistance curves is carried through into the results.

Induced Resistance The lower plots in Figure 35 show that the tank test derived effective

draft reduces as speed increases, this trend is not well captured by the

computational codes. For handicapping work it is crucial that the force

models capture this effect because it is where designers can seek to find

a performance advantage by optimizing the hull and keel volume

distributions.

6. Conclusions

This first phase of the Wide-Light project brought together several respected CFD technicians with experience in

evaluating the hydrodynamics of sailing yachts. They were able to collaborate on setting up the tank test program

for an existing model of a boat fitting the parameters of Wide and Light design. Using the geometry of the boat

and the design of the tank test program they performed pre-test evaluations of that model. CFD results were

compared with the tank test results.

The study described in this report is the most comprehensive ever undertaken for publication in the public

domain, and has met the goals that were set. The following broad conclusions may be drawn.

A body of physical test data relating to a defined geometry has been published and is available for

validation of other data.

Commercial CFD codes may be used to confidently predict the variation of the forces on a sailing yacht

hull as speed heel and leeway change. These studies do not need prohibitively large mesh density to

achieve valid results.

Less computationally heavy codes, e.g. FlowLogic can produce data to capture the typical global behavior

of a sailing yacht hull.

Yacht Handicapping organizations can rely on correctly configured CFD studies to generate data for a

wide variety of yacht hull shapes. (Reference 2)

7. Future Work

A second phase of the Wide-Light project is planned to build upon the lessons from Phase 1. Specifically, Phase 2

is intended to take one or two of the promising CFD programs of Phase 1, provide their contributors with the

geometry of a small fleet of designs and let them evaluate those designs and the combinations of

speed/heel/leeway that are of interest to handicap rule-makers. The fleet of boats included in Phase 2 will

represent realistic variations from a baseline design in the critical parameters that drive performance:

displacement and beam for a fixed length are an obvious choice of variations.

33

The proposed Phase 2 program will build upon the success of an earlier study conducted in the 1990s: the nine

model tank test program conducted at the National Research Council (NRC) in Canada. The NRC's program has

been immensely useful in providing the differences in hydrodynamics for a range of beam and displacement

variations that bracketed the fleet of boats racing worldwide in the 1990s. Since the NRC study, there has been

rapid growth in the number of new Wide-Light designs with significantly wider beam and lighter displacement

than the designs included in the NRC’s nine-model series. With these new Wide-Light designs represented at

every major big boat regatta, it is paramount that handicap rules treat them fairly. To equitably rate them against

the existing fleet of heavier and narrower designs, it is imperative that the developers of those rules have a

database of hydrodynamics of these Wide-Light designs.

To build the most accurate and informative database requires understanding the nuances of existing CFD

programs. Wide-Light Phase 2 intends to continue refining our understanding of CFD programs so as to better

inform handicappers in fairly rating these new and popular designs. As Phase 1 has demonstrated the value of

CFD analysis in predicting differences in hydrodynamics between designs, and because a multiple model tank

series is prohibitively expensive, Phase 2 will not use tank testing. Instead, Phase 2 will focus solely on the use of

the most accurate CFD programs to develop a database of the hydrodynamics of Wide-Light designs. Upon

completion, Phase 2 will produce the first publicly available database of Wide-Light hydrodynamics.


References

1. Lars Larsson, Frederick Stern, Michael Visonneau, “Numerical Ship Hydrodynamics, an assessment of

the Gothenburg 2010 Workshop.” ISBN 978‐94‐007‐7188‐8

2. ORC Technical Committee, ORCi Documentation.

<http://www.orc.org/rules/ORC%20VPP%20Documentation%202015.pdf>.

3. Keuning, J.A., Sonnenberg, U.B., Developments in the Velocity Prediction based on the Delft Systematic.

Yacht Hull Series, The Modern Yacht Conference March 1998.