Use of Antipitch Hydrofoil to Reduce Added Resistance of a Yacht in Waves

Abstract

The use of a horizontal antipitch hydrofoil for the purpose of reducing the vertical motions and added resistance of a sailing yacht is investigated. The difficulties, limitations and assumptions inherent in studying yachts in waves are discussed. A mathematical model is presented in an attempt to predict the effect of an antipitch foil on the motions and added resistance of the 12-Meter Canada II. Scale model experiments were conducted and the results are presented and compared with the theoretical results. Experimental results show that the antipitch foil is indeed very effective in reducing the motions and added resistance of the model. At resonance, pitch is reduced by 22 percent, heave by 15 percent and added resistance by 40 percent. Theoretical results do not agree quantitatively with experiment. However, they do show good qualitative agreement with respect to the percentage reduction in motions and added resistance that can be expected through the addition of the foil and therefore could be useful as a preliminary design tool.