PREDICTING THE SPEED OF SAILING YACHTS

In this paper an overview is given of the state-of-the-art of predicting the speed of sailing yachts. After explaining the importance of this topic in the design and racing of sailing yachts, the basic hydrodynamic and aerodynamic forces and their inter- dependence, which ultimately determine the speed potential at the various points of sail, are described. The different possibilities of determining these forces, together with their centres of effort, is the principal subject of this paper. The use of model testing techniques and associated data reduction methods for the determination of the various hydrodynamic forces are first of all dealt with. Details of how these model tests are best carried out are given. A method is defined with which it is possible to divide the total measured hydrodynamic resistance into its six basic components. Extrapolation of model test results to arrive at full-scale values, and their use for speed prediction, are described. A major part of the paper is associated with the state-of-the-art of calculating sailing yacht performance as this is performed in semi-empirical models for so-called velocity prediction programs (VPP's). Each of the elements involved are considered, e.g. the side forces on hull and appendages, induced resistance, viscous and wave resistance, the resistance due to heel, the added resistance due to waves, etc. The recent availability of computation fluid dynamics programs and their present and future impact on sailing yacht performance prediction is addressed in the final part of the paper.