Overview and current state of a new single-handed hydrofoil sailing catamaran

A new, high-speed, recreational hydrofoil dinghy has been developed. The concept of the boat, mathematical model used for design and the one fifth and one third model test results were presented in the previous paper, and first prototype, i.e., real scale model was reported in another paper. This paper shows test results of a revised prototype model, of which main and fore foils are much improved by means of tank tests. Lift to drag ratios approximately become 15% and 30% better than the first ones, respectively. In order to obtain the coefficients of hydrodynamic forces acting on the hydrofoils, we carried out force measurement of the hydrofoils for the first and revised modes in the towing tank, and compared the results with values of Wadlin´s formula 3, which estimate lift force and drag force of a hydrofoil including the effect of free surface. Tank test results gave corrections to the Wadlin´s formula, spray drag´s formula of the strut and the drag formula for the connection of hydrofoil and strut. These test results and comparisons should be useful for the design of fully submerged hydrofoils not only of this sailing boat but also of more general high-speed boats. This revised prototype could be successfully foil-borne in a 50-degree closed-hold wind condition with 50% higher boat speed than wind speed.