A Method of Performance Analysis for Sailing Vessels

Citation

Denison, Frank G. (1944) A Method of Performance Analysis for Sailing Vessels. Engineer's thesis, California Institute of Technology. doi:10.7907/3697-3Y49. https://resolver.caltech.edu/CaltechETD:etd-11252008-092219

Abstract

A general method for calculating the performance of all types of wind driven vessels has been developed. The method is of such a nature that it may be used, without specific experimental assistance, as a qualitative guide in preliminary design. To this same procedure, data from a few simple tests of the model in question may be applied to obtain good quantitative performance information. As a result, existing yacht model testing procedure {Reference (4)} can be considerably simplified while at the same time obtaining information of much broader applicability. The use of the principles of this method, if not the letter, should tend to rationalize the arbitrary and extremely restrictive handicapping rules for ocean racing now in existence. Further, the owner, in possession of a performance analysis of his vessel, can be guided in his choice of course and sail setting as these are fundamental parameters of the general performance equation. The optimum sail setting for any wind speed and boat direction is of a necessity obtained in the process of the solution of this equation. The method provides several rather surprising general conclusions. It is indicated that angle of heel, contrary to Reference (4) is not a fundamental variable, and therefore stability only enters the picture in so far as the designer has a "gentlemen's agreement" not to provide more sail than will heel the vessel to a certain angle in a given wind. It is found that only draft is a monotonic parameter in performance; all other form and sail variables exhibit optimums, some perhaps outside of the practical range. Also, it is found from the experimental data of Reference (5) that yacht underbodies, despite their extremely low aspect ratio, exhibit a polar of lateral force and induced resistance with a character in agreement with the simple Prandtl theory. The interference effect of the surface, however, is found to be at variance with the result obtained from a lifting line vortex arranged to satisfy the water boundary condition. It is found that the usual triangular yacht sail does not have as bad a downwash distribution as one might first suspect on considering the plan form and twist. The presence of the water surface has the effect of providing a corrective upwash distribution. It is found that simple static stability calculations with the water surface assumed undisturbed, at the boat, lead to surprisingly good agreement with the righting moments obtained experimentally under dynamic conditions.

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