1. Computer technology in America’s Cup Yacht Racing
Dr. J. Craig Mudge
Pacific Challenge
ee380 Colloquium
Computer Systems Laboratory
Stanford University
Feb 19, 2003
Goal: present how computer technology is used in the various aspects of an America’s Cup campaign – including the design of the sleek racing yachts, the evaluation of alternate designs, campaign management, and computer help during a race.
This week, New Zealand is defending the America's Cup, the longest-running sports competition in the world, against a challenger selected from nine syndicates by a series of two-boat elimination races beginning in October 2002. 
The would-be challengers came from syndicates based in France, Great Britain, Italy, Sweden, Switzerland, and the United States. Some syndicates have spent $80 million on their campaigns.
Alinghi, the Swiss challenger won the right to challenge for the Cup.
Before we look at some video footage of the racing in the last week off Auckland in NZ, let’s look at the race course

2. Big deal for the economy of the defending nation. Perhaps $300 m in NZ.

3. 6 legs in America’s Cup course
Alinghi Race 2:-
Time
Min:sec
Delta in
seconds
Start 1
26:11 12 2
24:14
-34 3
26:37
-26 4
22:43
-14 5
27:33
finish
25:43 7
Now look at a photo taken at the mark at the top of this diagram.

4. How a sailboat moves ahead
Downwind
Push on sails
Upwind
Lift from sails
Lift from keel
Context
Changes in wind strength and direction
Changes in wave shape, direction, and frequency
The boat on the left has just gone around the floating mark, and the boat on the right is trailing and is about to go around the mark.
<-
Notice the angle of heel is quite different upwind to downwind.
These changes from day to day, and from minute to minute in some cases, add to the complexity of the design and modeling. This weekend, Race 2 was sailed in 10 Knots (approx 10 miles per hour), whereas Race 3 was sailed in winds around 17 knots. Race 1 had extensive little waves of about 18 inches high (?)
Acknowledge corner of white spinnaker

5. Defender vs Challenger
Video clips of last
couple of days racing
- what to watch for
Now turn to some video, and I’ll use this still image to point out some things to look for
Helmsman steering with one of two linked wheels. Steering is with a rudder the way the movable part of the tail provides steering on an aircraft
Tactician looking at his computer display
Orange line (we never use the word rope) is led from the corner of the forward of the two sails to a winch drum controlled by the Jib trimmer
Similarly the yellow line controlled by the Mainsail trimmer
each winch drum is coupled to crank handles powered by the arms of the two grinders working together.
Moving to the top image we’ll see two types of sails. When the boat is heeling over, these two sails are closely aligned with the direction of the hull, and the boat is zig-zagging , or beating, up wind.
Going in the other direction, namely downwind, the sails are roughly at right angles to the boat, and the pressure on the sails is pushing the boat downwind; at this point also the big white parachute sail is at the front of the boat.
So let's roll the video.

7. Elementary theory Lift drag Lift drag (or resistance)
Aerodynamic forces
from sails
Leeway
angle
hydrodynamic
There are two types of forces, each generated by a fluid moving past a curved surface aero and hydro.
For the keel to provide lift we need a non-zero angle of attack – this leeway angle is approx 5 degrees
Lift drag
Lift drag (or resistance)

8. Tacking up wind Zig-zagging up wind towards our destination
Wind direction
Zig-zagging up wind
towards our
destination
The boat that sails
at an angle
“closer to the wind”
gets upwind faster
Now look at moving up wind again.
<-
Obviously the designer of the sails and the hull tries to make the boat sail efficiently at the smallest angle to the wind.

9. Polar representations of boat speed
Radial representation of
Boat speed at different
true wind angles for
one windspeed 5
We represent the upwind and downwind boatspeeds, and points in between, as follows.
<-
Upwind it’s an airplane wing – generating lift
Downwind its both a parachute and lift
Its at this point that boats with very low resistance, such as ice boats, can sail faster than the wind. Another type of boat with low resistance is a catamaran – two narrow floats. Stan Honey, navigator on the catamaran Playstation 2 in likes to say it this way: the boat was fast enough s.t. if released a He balloon, the boat would pass in front of it.
SO how do we use these polars? Given a wind speed, they show the crew what angle is best to sail at, and what the speed should be. 10 20
(Adapted from 12 metre
designed by S Killing)

10. A list of computer uses Area Type Design of hull
Hydrodynamic modeling (to reduce drag)
Hull appendages
Hydrodynamic modeling (lift and drag)
Design of sails
Aerodynamic modeling; photogrammatic
Computational Fluid Dynamics (CFD)
Modeling, analysis, and visualization – sails, hulls, appendages
Two boat testing
Data collection and data management
Navigation/tactics/ strategy
Performance parameters; predictions for next leg
Campaign
Project/financial management, travel, web site
Weather
Forecast wind patterns for each race
Sports media
Visualization of race course from telemetry
Let me complete this introductory section by acknowledging some colleagues

11. Acknowledgements Jim Antrim, naval architect
Richard Burton, sailor and computer scientist
Margot Gerritsen, Computational Fluid Dynamics (CFD) specialist, Stanford Yacht Research
Stan Honey, record-breaking navigator
Olivier Le Diouris, sailor and software engineer
Eric Steinberg, electronics on America True
Brian Tramontana, PARC multimedia
* ESPN for video clips
* americascup.yahoo.com for photos
* Virtual Spectator for screenshots of race course

12. - both canoe body and appendages
Outline
Hull design
- both canoe body and appendages
Sail design
Materials - hull and sails
Two-boat tuning
Winning races
Designers break the floating piece into two parts.
Let’s return to our force diagram, showing both the aerodynamic forces from the sails,
- and the hydrodynamic forces from the keel.

13. Adding heeling/righting moments to two forces
Aerodynamic forces
from sails
Hydro-
mechanical
Righting
moment
Leeway
angle
hydrodynamic
Aerodynamic
Heeling
moment
Here we add the third force due to heeling, shown in green.
The hull shape provides
space for its payload, is shaped to
give low wetted
surface area, and has strength to
hold the appendages underneath
and the rig above. Also the
hull has to withstand
expected sea conditions.
PAUSE
Moreover, by adding the moments as the third force, we have the three balance equations involved in an equilibrium sailing condition
And the solving of these 3 is the basis of modeling by the designer.
Heeling Righting
Lift Drag
Lift Drag (or resistance)

14. Lateral stability Heeling moment from sails
Left hand boat is wide to give form stability
The boat on the right is more like a Cylinder
- biggest evolution since IACC started – use only ballast for stability.
Extreme ballast from
bulb (20 tons of a
24 ton IACC boat)
Lead ballast is placed in the lower portion of the keel.

15. Alternative to lead bulb for righting moment
Even though it’s not contributing to righting, the keel (centerboard) is there to prevent sideways slipping and to generate lift
Hull length = 18
Sandbaggers, an influential American design in the late 1800s
Water ballast is current genre in fast ocean racing yachts.
Sydney Harbour 18 ft skiffs

16. More 18 ft skiffs from Sydney
A very influential design
- on modern racing yachts
- on latest Olympic class (49er)
Yendys 1924
Anecdote: Sydney Harbour racing: as wind drops, crew swim ashore one-by-one, as requested by the captain

17. Newer IACC boats are much narrower
Having looked at sideways stability, lets look at the drag on the hull as it moves through the water.

18. Resistance components - upwind
heeled
Added waves
Induced (from leeway)
Heel
(extra viscous+wave)
upright
Wave
(pushing the water)
Viscous
(friction from
wetted surface)
[describe each one]
Induced -- as water flows form higher pressure (leeward side) to lower pressure and causing eddies.
An important take away from this talk is shown in this diagram-
Each of these components has to be modeled (using empirical data or approximations of theoretical representations of fluid flow).
Then assumptions are made for how the components interact
(Fig 5.4, Larsson, 2000)

19. Appendages: side force and resistance
Side force (also called Lift)
From both keel and rudder
Lift/drag tradeoff
Aspect ratio
Bulb shape
Turbulence
Here we draw on classical wing theory. The aspect ratio is the most important parameter for the lift and drag. This ratio refers to how tall an object is relative to its width.
Ideally we want more depth (or long wings in case of airplane) to give a high aspect ratio but there are limits – on an airplane wing structural or airport rules
- in a boat, the rule, or desire to sail in shallower waters
CLICK
Winglets
Now look at the computer visualization of flow of water passed a bulb on a keel with winglets
Tip vortices if depth is limited
End wall not practical, so Winglets used
Winglets also provide lift when boat heeled

20. Surface pressure and Streamlines around bulb
Just one plane
If showed neighboring planes, one would see interaction between them, which would appear as a spiraling vortex
From M Sawley (2002) at Switzerland’s EPFL,
in Lausanne, an advisor to Alinghi

21. An overview of numerical modeling in yacht design
Fundamental tool is a predictor of performance to compare different designs
Called a VPP (Velocity Prediction Program) -- since early 70s
Given a wind speed and wind angle, a VPP predicts boat speed, heel, and leeway

22. Modeling boat speed - VPP
Go quickly across a few
(Milgram, 1998)

23. An overview of numerical modeling in yacht design
Fundamental tool is a predictor of performance to compare different designs
Called a VPP (Velocity Prediction Program) -- since early 70s
Given a wind speed and wind angle, a VPP predicts boat speed, heel, and leeway
The balance equations are solved
Keel lift and side force
Sails lift and drag
Overturning moment
Modeling these forces in the balance equations is (currently) approximate
Navier Stokes equations (set of differential equations governing the motion of a fluid) are central part
Models are combination of empirically based and approx of N-S equations

24. Overall Hull Design process
Decide range of wind strength, sea state
2. Coarse exploration of shapes by numerical modeling, incl CFD
3. Then tank testing
4. Then build one real thing
5. Refine with two-boat testing
Tank testing very expensive; limited to 2 or 3 models.
Ensure large enough model, say 8 metres, to avoid scaling problems
In 1983, Australia II with its revolutionary winged keel on the Cup, the first time it had been taken away from America. John Bertrand was the skipper, and I later asked him what was different from previous challenges. …
In 2001 there was a America's Cup Jubilee
regatta in Cowes and Australia II was there with many other old Cup boats.
Hugh Treharne, the tactician on Australia II when she won was of course ther too. Later I asked him what it was like – he said the boat was like an old glove – she fitted so well. This emphasizes the enormous amount of time teh sailor spend on the boat in preparation.

25. An overview of numerical modeling in yacht design …contd.
Computational Fluid Dynamics (CFD)
RANS (Reynolds-Averaged Navier-Stokes) is a more
computationally tractable form of the N-S equations.
In RANS, the flow variables are split into
one time-averaged (mean) part,
and one turbulent part. The mean values are solved.
And the turbulent part is expressed in terms of the mean part.
CFD applications
Aerospace -- wing sections, airframe shapes, etc
Automotive -- flow in air intake, right on through engine
Mechanical – pumps
Chemical e.g., separators
Environmental e.g., water borne pollution
Physiological – cardio vascular system

26. An overview of numerical modeling in yacht design …contd.
Typical computer resources are these at EPFL, Lausanne
SGI Origin 3800
128 MIPS R14000 Pc (500Mhz; 64 GB RAM)
Swiss T1
64 DEC Alpha ev6 Pc (500 Mhz; 32GB RAM)
Dell Precision 530
2 Pentium Xeon Pc (1.7 GHz, 2GB RAM)
Largest RANS simulations:
5 million mesh cells: 10 hours on 16 Pc
c.f. AC2000 campaign:
2 million mesh cells: 10 hours on 12 Pc Origin 2000
Transition: so let’s see how it all worked out in the current AC competition

27. Unveiling January 7, 2003 Alinghi Oracle
Cow: Who said Swiss are humorless
Alpine horns, although the cynic might suggest that this bout of Swiss nationalism is to counter the criticism of the multinational nature of their crew. In the 16-person crew, there are just two Swiss.

28. Different winglet configurations and bulb shapes
QUICKLY to normalized view

29. Different winglet configurations and bulb shapes
Oracle
Alinghi
Do they know what they are doing?
Jim Antrim’s comment
Summary of this section hull design:
just how important it is to get the prediction of wind strength right
In higher winds, wave drag higher proportion of total drag
Tradeoff weight sail shape keel weight
PAUSE
When I think about the computers I have designed, I think we had a better handle on things – modeling the workload, modeling the physics, a useful set of layers of abstraction, good simulation and verification tools, and so on.
However, we had a better handle on things, not because we were smarter than naval architects, but because yacht design is a much harder problem.
Team NZ
(based on photos at the unveiling 1/7/03)

30. Universities working in yacht design
University of Auckland
Technical University of Berlin
Chalmers University of Technology
Kiel University
EPFL, Lausanne, Switzerland
MIT
University of Maryland
University of Michigan
University of Southampton
Stanford Yacht Research
Center for Turbulence Research, Stanford
Just give the list

31. Outline Sail design Hull design Materials Two-boat tuning
Winning races
Again we use classic wing theory
Unlike the hull, the camber of the surface can be changed while it’s in operation.

32. Positioning and shaping
Crew positions the sails according to required angle of attack
- from polars
Sailors shape the sail using control lines attached to the edge of a sail
Sailors know how to get a desired shape – with the control lines, so the real issue for a talk like this is what is the right shape?
The shape is to provide max lift/drag and to keep the flow laminar, not separated or turbulent.

33. What is the right shape?
Sailmaker designs each sail for a range of wind strength and wave type. (Sailor selects a sail from the suite, according to expected conditions.)
Want nice laminar flow, without separation and turbulence
Lift vs drag curve; polars again
Both wind tunnels and CFD used
Sail design is challenging.
The hull, sails and rig form an integrated system with many parameters that should be optimized simultaneously.
However, the fluid-structure interaction between the three-dimensional flow around the sail and the hull,
and the effect of the dynamic motion of the boat on the sail flow and hull hydrodynamics are complex.

34. Vertical characteristics of wind
Apparent wind is the wind we feel on the boat,
as opposed to the true wind.
As we go from deck to top of mast,
the wind increases in strength
and apparent direction 8 7 5
Has implications for both sail designers
and sailors (sail trimming)

35. Design of downwind sails

36. Wind tunnels in sail design
University of Auckland
Twisted Flow Wind Tunnel
Sailors spend hours with tunnel.
Trimming and trimming to explore different shapes and angles of attack.
Note: because trimming upwind sails is much finer, this wind tunnel is not used for upwind sails.
In AC2003, only Oracle and TNZ used wind tunnels with twisted flow – Team NZ used this one, and Oracle built their own, very much like this one.
Courtesy U Auckland,
Seahorse magazine

37. Outline Materials - hull, sails, and rig Hull design Sail design
Two-boat tuning
Winning races
Changes in materials, e.g., less stretch in sailcloth or stronger lighter materials in hull construction is requiring more extensive computer modeling, buyt I won’t go into this in any detail.

38. Ocean racers have to be stronger
Courtesy Richard Bennett

39. Forces on rig and hull
Now in this video of One Australia, please pay attention to the detailed explanation that John Bertrand gives after the sinking.

41. Prominent logo of sponsor

42. OneAustralia 1995

43. Older sail material Courtesy: Mariners’ Museum Desirable chars:
Low stretch
Low weight
High strength
Endurance
Resistance to aging in sunlight
Courtesy: Mariners’ Museum

44. Materials and shaping Desired 3D shape in CAD model
Flax Cotton Japara silk various polyesters (with or without film)
(Kevlar is the best known of the aramid fibers) Carbon
Desired 3D shape in CAD model
Panel shape Mold shape
Sew panels Apply layers
(liquid/fiber)

45. Improved sail shape with modern materials
Also note the fat stripes
This time it appears that all syndicates used what they called Sil Scanning
- photogrammatic techniques

46. Lexcen keel Oracle kite Canting keel
Novel designs
Lexcen keel
Oracle kite
Canting keel

47. Ben Lexcen’s winged keel 1983
Start with the first keel with winglets – America’s Cup 1983.
Painted with blue sections to look like a Conventional high-aspect ratio keel with sweep of 30 degrees
Lexcen, a genius designer
experimented in Holland, starting 1981 for several months
with his friend peter van oossanen
24 ft models
Upside down keel (to get weight down and beat draft restriction)
Added wings to cope with horrendous vortexes
Further experiments to get position, overall size, and angle of dihedral
I got info from Peter Joubert, prof of, whom I used to meet annually in the 80s .. .and he published a delightful paper in 1986 jointly with van oossanen.
Joubert was racing his 43 fter in the bad Hobart. He was 74 and had completed many Hobart races in this boat. It rolled sideways and he received broken ribs when a crew member crashed into him down below.. One crew member was washed overboard and picked up by helicopter 40 mins (?) later.
Courtesy: Rosenfeld

48. Oracle kite
Mention kite surfers

49. Canting keel and canard
Wild Oats and Schock 40
Acknowledge Reichel-Puch and Dynayacht
From Dynayacht:
Is it hard to control the boat with two "rudders"?
No. It's so easy, you soon forget you have two steering foils. It steers like a normal sailboat, only better. Both steering foils are controlled by the tiller so steering is intuitive and as simple as any traditional sailboat. The front foil (rudder) turns in an opposite direction to the aft foil (which makes sense since it is forward of the boat's pivot point). Steering control is much more positive than on a boat with a single rudder.
MentionSchock 40
(Reichel-Puch, Dynayacht, 2002)

50. Outline Two-boat tuning Hull design Sail design Materials
Winning races

51. Why two-boat tuning
Shortcomings of numerical modeling and tank testing
Sensors not accurate enough
A two boat lead at end of a 3 mile leg requires boat speed 0.7% accuracy;
Accuracy on wind direction, strength also difficult hard to get accuracy;

52. Instruments and data logging on J/105 Kookaburra
To motivate this section of the talk, we’;; look quickly at the data logging on my 35 foot racing yacht
Data from instruments:- Wind speed (true and apparent); Boat position;
Heading; Boat speed (through water and over the ground); Etc etc

53. A leg of a race selected for further analysis

54. Log of Wind Oscillations during a race
221º
299º
Why wind direction important in a race.
Guys up the mast.
Importance wind shifts very apparent in finals Oracle vs Alinghi

55. Two-boat tuning – Team NZ
Each boat can see the data from the other boat (wireless links)
Range and bearing – laser
Normal instruments plus
rudder angle
deflection sensors on hull
(horizontal and longit flexing)
Load sensors on the rig
Huge data collection and data management exercise
Deciding what’s statistically significant is a challenge.

56. Computer use in America’s Cup races
Outline
Hull design
Sail design
Materials
Two-boat tuning
Computer use in America’s Cup races

57. Performance Performance is a function of Preparation before the race
Start
Boatspeed
Design of hull and appendages
Design of sails
Boat handling by crew
Strategy
Tactics
Helmsman’s skill
Navigation
Navigation must take currents into account.

58. Currents Hauraki Gulf, NZ Feb 19
Time: 1400
Courtesy
David Brayshaw, GoFlow

59. Currents Hauraki Gulf, NZ Feb 19
Time: 1139
Maximum ebb
Courtesy
David Brayshaw, GoFlow

60. The start

61. The start Display of computed parameters time to start time to line
This nice result is helped by
accurately estimating time to the
starting line (Alinghi Race 3)
Display of computed parameters
time to start
time to line
tack+acceleration+ travel time
(for boat speed, index into polars)

62. On each leg Display time to next mark time in each tack remaining
time to layline
target boat speed
etc
Predict next leg
- given assumptions on wind and mark, use polars to display:-
course, wind angles,
Target speeds from polars
Display actual against target - guidance and incentive for helmsman

63. Topics not covered Effect of mast on flow past mainsail
Trim tabs on aft end of keel
Heads-up display in navigator’s sunglasses
Modeling interaction of hull and sails
Modeling of currents
Analysis of materials and structure of hulls
Techniques in rig design and analysis
[JUST QUICKLY READ IT]

64. Bibliography
Joubert, P N. and Oosannen van, P. The Development of the Winged Keel for Twelve Metre Yachts, Rev
Killing, Steve.Yacht Design Explained, Norton, New York, 1998.
Larsson, L and Eliasson, R. Principles of Yacht Design, 2nd ed. International Marine, Camden, 2000.
Milgram, Jerome H. Fluid Mechanics for Sailing Vessel Design, Annual Review of Fluid Mechanics, :
Marchaj, C A. Sail Performance. International Marine, London, 1996.
Sawley, M L. Numerical Flow Simulation for the America’s Cup. EPFL Newsletter,2002.
Whidden, Tom. The art and science of sails, St. Martins Press, New York,1990.
for a copy of this bibliography

65. High performance yachts in the future
Some possibilities
1. Materials
Surfaces
Low drag (MEMS?)
Vortex generators (a la Formula 1 cars) – also slots, porosity
2. Control of sail shape
Auto-adjust (but without stored energy)
3. Rig and masts
4. Better numerical modeling
Downwind sail design
Sail shape optimization, including design in unsteady conditions (waves, …)
Coupling of accurate CFD to structural analysis
Hull-sail interaction
One researcher suggested to me that the Sailing industry is years behind aircraft industry in use of CFD (models, validation, )
This sail shape optimization would use a newer form of performance modeling (ie beyond the VPPs we saw earlier), called PPPs (Performance Prediction Programs). This would include sail design in unsteady conditions.
Of interest to this audience is that all of the possibilities under
Item 4 are focus areas of Stanford Yacht Research over the next 3 years or so.
Rules will have to change in some cases.

66. So computer technology in the America’s Cup, for me is about modeling, design tradeoffs, about simple help with navigation, and helping the sailors think deeply about what makes a boat go fast, and then putting their ideas into the design.
Off Auckland, right this moment, two boats are racing -- we have Team NZ down 3-0 in a best of nine races.
May the best team win.
Thank you very much.

68. Maltese Falcon ideal test case
Design shape flying shape
Square-rigged
Twist onset flow small
Extensive experimental data
160 ft
Prototype testing appealing
280 ft
Stanford Yacht Research
(Gerritsen, Doyle, Perkins) 65 ft

70. Kiwi clip on or hula To extend the waterline; Used to be bustle
It gets more water to the back of the boat and so makes longer waves.
MAYBE don’t show this (LWL arg’t) and have in reserve. However it is the result of computer modeling.

71. 3DL
Contrast with panelled sails

72. Review: computer use Area Type Design of hull
Hydrodynamic modeling (to reduce drag)
Hull appendages
Hydrodynamic modeling (lift and drag)
Design of sails
Aerodynamic modeling; photogrammatic
Computational Fluid Dynamics (CFD)
Modeling, analysis, and visualization – sails, hulls, appendages
Two boat testing
Data collection and data management
Navigation/tactics/ strategy
Performance parameters; predictions for next leg
Campaign
Project/financial management, travel, web site
Weather
Forecast wind patterns for each race
Sports media
Visualization of race course from telemetry