Computer technology in America’s Cup Yacht Racing

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 www.pacific-challenge.com

3. 6 legs in America’s Cup course Alinghi Race 2:-

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

5. Defender vs Challenger Video clips of last couple of days racing - what to watch for

7. Aerodynamic forces from sails Leeway angle hydrodynamic Elementary theory Lift drag Lift drag (or resistance)

8. Tacking up wind Wind direction Zig-zagging up wind towards our destination The boat that sails at an angle “closer to the wind” gets upwind faster

9. Polar representations of boat speed Radial representation of Boat speed at different true wind angles for one windspeed 5 10 20 (Adapted from 12 metre designed by S Killing)

10. A list of computer uses

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. Outline Hull design - both canoe body and appendages Sail design Materials - hull and sails Two-boat tuning Winning races

13. Aerodynamic forces from sails Leeway angle hydrodynamic Adding heeling/righting moments to two forces Hydro- mechanical Righting moment Aerodynamic Heeling moment Heeling Righting Lift Drag Lift Drag (or resistance)

14. Lateral stability Heeling moment from sails 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 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

17. Newer IACC boats are much narrower

18. Added waves heeled Induced (from leeway) Heel (extra viscous+wave) Wave (pushing the water) Viscous (friction from wetted surface) upright Resistance components - upwind (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 • 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 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 (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

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.

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

27. Unveiling January 7, 2003 Alinghi Oracle

28. Different winglet configurations and bulb shapes

29. Different winglet configurations and bulb shapes Oracle Alinghi 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

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

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

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

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 Courtesy U Auckland, Seahorse magazine

37. Outline Hull design Sail design Materials - hull, sails, and rig Two-boat tuning Winning races

38. Ocean racers have to be stronger Courtesy Richard Bennett

39. Forces on rig and hull

41. Prominent logo of sponsor

42. OneAustralia 1995

43. Older sail material Courtesy: Mariners’ Museum

44. Materials and shaping 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

46. Novel designs Lexcen keel Oracle kite Canting keel

47. Ben Lexcen’s winged keel 1983 Courtesy: Rosenfeld

48. Oracle kite

49. Canting keel and canard Wild Oats and Schock 40 (Reichel-Puch, Dynayacht, 2002)

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