Practical Performance Prediction of Foil-Configured Monohull Yachts

Interest in foil-assisted monohulls continues to increase. Indicative of this trend is the success of the current IMOCA60 class, the proliferation of new or modified foil-assisted dinghies, performance luxury yachts, as well as race boats, including the novel America’s Cup Class (AC75). Is there a more practical, design-oriented, and sufficiently accurate approach – than existing ones – generally available to the design community to evaluate the total performance of the foil-configured yacht and its appendages? This paper describes recently developed and incorporated methods in a new VPP program for yacht designers and analysts. New methods are discussed to calculate the foil forces within the VPP solution loop for fully- or partly-immersed foils. A variety of non-trivial hydrodynamic issues are addressed, including dynamic hull forces and moments when wetted. A practical approach to surface-piercing foil hydrodynamics with the potential for ventilation and stalling is presented. Calculations for quickly varying forces and moments must be incorporated in a multi-degree of freedom and multi-state solution, for all the state variables (velocities, position, orientation, etc.) as well as control variables, such as rake, dihedral, and elevator. The methods and design-oriented computer programs described in this paper have been used for various successful projects. The procedures are illustrated for various non-planar foils, including DSS, so-called “Dali”, L, C-Foils, as well as planar configurations such as a T-Foil rudder.