Application of Advanced Computational Fluid Dynamics in Yacht Design

Nowadays, Computational Fluid Dynamics (CFD) methods are frequently used in sailing yacht design. Mostly these are panel methods calculating the inviscid flow around the hull with free water surface. They can predict the wave pattern and wave making resistance, and, for cases with leeway and heel angle, the side force and induced resistance on the keel and rudder. One of the most advanced codes in this class is the code RAPID, developed by MARIN. It differs from most other codes by taking into account the full nonlinearity of the problem, incorporating the effect of the hull shape above the design waterline, the dynamic trim and sinkage and all effects of the wave steepness. This paper describes the recent extension of the code with modules for lifting surfaces (rudders and keels), asymmetric flows, and other features required for application to sailing yacht computations. The results obtained from calculations with RAPID and with DAWSON, a conventional linearised method, are compared with model tests performed in the Delft Ship Hydromechanics Laboratory for a 3.5 meter model of a 1992 America’s Cup yacht. The nonlinear method is found to produce improved predictions of the bow wave height and the wave profile along the hull. Also, the calculated resistance is in much better agreement with the experiments.