Extreme manoeuvres for America's Cup catamarans

This paper explores the manoeuvring aspects of the 34th International Americas Cup catamarans as the current rule draft allows [1] using the Futureship GmbH developed program FS_Equilibrium. With the results of this analysis the implications of implementing other manoeuvring solutions including varying the size of the rudder and the implementation of a pure drag rudder are investigated. The effectiveness of varying the rudder size was tested by specifying different lateral areas with a consistent chord length and profile shape. It was concluded that increasing the rudder size allowed the vessel to turn sharper but reduced overall speed due to the increased drag. In addition it was shown that the optimum rudder size for the manoeuvre specified, had a lateral area of 1 m2 and a wetted surface area of 2m2. This rudder size was then tested against a new proposed design, here termed the pure drag rudder in order to determine any possible performance gains. It was concluded that the addition of the pure drag rudder caused the vessel to turn with a much smaller radius at the expense of forward speed. It was determined however that this loss in forward speed was outweighed by the smaller radius of the turn and the potential tactical gains to be had from sailing further to windward and as such the pure drag rudder is a viable method of turning the vessel.