The use of Velocity Prediction Programs (VPP’s) in sailing yacht design has been standard practice for years. VPP fidelity, however, continues to be limited by the accuracy of aero and hydro force data used to represent a particular yacht. Even the most advanced America’s Cup VPP’s usually derive sail forces from panel or vortexlattice models, and hull forces from potential flow codes or experiment. Real world effects attributed to viscosity are added using simplified theoretical or empirical models that cannot resolve all the complexity of sailboat physics.

This paper describes a new approach for performance prediction and design optimization that relies solely on high-resolution Reynolds-Averaged NavierStokes (RANS) computational fluid dynamics. All aero and hydro forces and moments are generated by RANS, and therefore include the real-world flow features of boundary layers, separation, shed vorticity, and turbulence. RANS software and grid model requirements suitable for VPP applications are discussed, and sample aero and hydro solutions included. Examples from America’s Cup design are used to demonstrate the technique’s practicality and accuracy. Finally, since VPP’s require forces from a large number of sailing conditions, the extensive development effort (undertaken through three America’s Cup cycles) to transition state-of-the-art RANS into the practical realm is summarized.

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