Inviscid lifting surface techniques are applied to strongly interacting multiple sail configurations. A computer program is developed to solve the resulting non-linear potential flow problem. It is employed to predict the pressure distributions for a number of single and multi-sail rigs. Empirical; tall prediction and correction methods are proposed and implemented.

Catboat rigs are found to be superior to sloop rigs in lift coefficient, while sloop rigs show a lower drag coefficient. A finite optimum mainsail aspect ratio is predicted for masthead and 7/8 rigs, but not for a 3/4 fractional rig. The region of significant perturbation of the onset flow field is shown to extend as much as eight chord lengths ahead of the mainsail of a cat-ketch rig.

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