MODELING THE AERODYNAMICS OF UPWIND SAILS

This paper discusses the formulation of models for sail forces and mom ents as needed for the prediction of performance of a given yacht. It is shown that the effects of heel angle may be accounted for accuratel y using a simple geometric construction, with excellent agreement with wind-tunnel tests. With the aid of lifting-line theory the usual Kerw in model for accounting for the effects of sail trim is extended to in clude both sail twist and the effects of nonuniformity in the incident flow. The penalty in increased induced drag resulting from a constrai nt on heel moment is derived. Some earlier results regarding optimum l oading are generalised for nonuniform flow, in which it is shown that optimum loading requires the induced downwash to vary linearly with he ight.