Engineering modelling and the Americas Cup
by
Peter Jackson
Yacht Research Unit, Dept of Mechanical Engineering, University of Auckland

While modelling of various kinds is now used extensively in the Americas Cup, both during the design stage and during racing, little of this is made known. This is not so much for reasons of secrecy as that either the media or the public find these methods to be incomprehensible, with the result that the engineers and other modellers who are responsible for it do not get the credit they deserve. This talk will therefore explain some of the interesting modelling problems which arise, the methods used to solve them and the areas in which further refinement is needed.

Various kinds of modelling, both physical and computational, are used at different stages of a campaign. The talk will briefly outline modern methods used to predict the speed of yachts before they are built, as embodied in so-called velocity prediction programs (or VPP's). These require descriptions of the coefficients of various hydrodynamic and aerodynamic forces and moments, expressed as functions of the pertinent angles (of leeway, heel and apparent wind), the relevant non-dimensional numbers which control the fluid dynamics (Reynolds and Froude numbers) and the shape of the sails, hull and appendages. The talk will show the kinds of physical modelling used in wind tunnels and towing tanks, and the more recent attempts to replace or complement them using CFD. A problem of particular interest to the speaker is that of modelling the changes in shape of the sails while sailing, enabling the VPP is to choose the best trim for any sailing condition. The design must be carried out subject to the constraints of the AC class rule, which also raises the possibility of using optimisation methods to find the best part of the allowable design space.

The resulting balance of forces obviously changes with wind speed, which means that the optimum design also depends upon speed. Syndicates therefore expend considerable effort in trying to anticipate the wind speeds they will encounter. Wind speeds also vary during races, making the selection of the optimum boat even more difficult. The talk will therefore also cover some of the techniques developed to maximise the chance of winning using a match-racing simulator.

If time permits, the implications of the external forces on the yacht for its internal structure will also be discussed, both to illustrate the particular problems faced by the designers of the various components and to explain the significance of the improvements in materials over the last century.

Date received: October 27, 2000

Copyright © 2000 by the author(s). The author(s) of this document and the organizers of the conference have granted their consent to include this abstract in Atlas Conferences Inc. Document # caek-77.