A displacement vessel of a given loaded weight has a theoretical optimum length which minimises its total (viscous plus wave) calm-water drag. This length is usually somewhat greater than that of conventional merchant or naval ships but is in an appropriate range for competition boats such as rowing shells. Some simple examples are given to illustrate this property. Genetic algorithm techniques are then used to find optimum dimensions for rowing shells over a wide range of speeds and displacements, with a fixed assumption about the waterline, cross-section, and buttock shapes. Michell's integral is used for the wave resistance, the 1957 ITTC line for the skin friction, and a simple empirical formula for the form drag.
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