This paper compares performance predictions from a Reynolds Averaged Navier Stokes (RANS) based Velocity Prediction Program (VPP) to on the water testing of a J70. The J70 has been outfitted with a system to determine sail flying shapes, apparent wind conditions and performance data. The on the water testing is conducted in both racing and controlled sailing conditions. Data taken during racing conditions is analyzed to determine optimal performance envelopes while data taken in controlled conditions is used to match exact sailing and VPP states. The data acquisition system combines a number of standard marine sensors including a sonic anemometer, a GPS, a digital compass, an accelerometer and a gyroscope with custom sensors that measure rudder and boom angles as well as a custom sail shape acquisition system. The RANS based VPP developed by Doyle CFD has three main components; an aerodynamic force model, a hydrodynamic force model and an algorithm to balance the forces. The force balance routine uses four degrees of freedom; boat speed, yaw, heel and rudder angle to balance the aerodynamic and hydrodynamic forces for a given true wind speed and angle. The force models are derived from RANS CFD data calculated using OpenFOAM. The aerodynamic forces are calculated using steady state RANS as a function of apparent wind angle, apparent wind speed and sail flying shape. The VPP force model is derived by fitting response surfaces to this data. The aerodynamic CFD is run with sail flying shapes recorded from on the water testing. Using accurate flying shapes is critical for picking out slight aerodynamic differences in sail and rig setup. The hydrodynamic CFD data points are calculated using RANS Volume of Fluid CFD (VOF) as a function of boat speed, rudder angle, yaw angle, heel angle and displacement. Response surfaces are generated from a 128 data point array of RANS VOF simulations.

In order to create capability for analyzing course instabilities of sailing yachts in waves, the authors are at an advanced stage of development of a mathematical model comprised of two major components: an aerodynamic, focused on the calculation of the forces on the sails, taking into account the variation of their shape under wind flow; and a hydrodynamic one, handling the motion of the hull with its appendages in water. Regarding the first part, sails provide the aerodynamic force necessary for propulsion. But being very thin, they have their shape adapted according to the locally developing pressures. Thus, the flying shape of a sail in real sailing conditions differs from its design shape and it is basically unknown. The authors have tackled the fluidstructure interaction problem of the sails using a 3d approach where the aerodynamic component of the model involves the application of the steady form of the Lifting Surface Theory, in order to obtain the force and moment coefficients, while the deformed shape of each sail is obtained using a relatively simple Shell Finite Element formulation. The hydrodynamic part consists of modeling hull reaction, hydrostatic and wave forces. A Potential Flow Boundary Element Method is used to calculate the Side Forces and Added Mass of the hull and its appendages. The Side Forces are then incorporated into an approximation method to calculate Hull Reaction terms. The calculation of resistance is performed using a formulation available in the literature. The wave excitation is limited to the calculation of Froude - Krylov forces.

Recent breakthroughs in the America's Cup have put hydrofoil technology in the focus of high-performance sailing. This paper describes the performance assessment of two different centreboard hydrofoils designed for a C-class catamaran. Regarding the numerous design criteria resulting from sailing on hydrofoils, a reliable performance assessment tool helps to find the best compromise [1]. A Velocity Prediction Program (VPP) has been developed in order to facilitate the analysis of numerical simulation results obtained for appendages and the wing-sail in terms of speed potential of the C-Cat. The approach used to model the hydroand aerodynamic forces on the catamaran is described, along with the challenges peculiar to a VPP model for sailing on hydrofoils. Different optimization schemes for trimming the wing-sail and hydrofoil configurations are tested to obtain the theoretically most efficient trim settings and to evaluate the different hydrofoil designs. Using the developed VPP model, realistic velocity prediction can be carried out. The catamaran flying on hydrofoils sails at up to 2.8 times the true wind speed in many conditions. Records and observations made during the International C Class Cup (ICCC) of 2013 confirm the predicted performance of the modelled C-Cat. Some remaining challenges in velocity prediction of vessels equipped with hydrofoils are highlighted.