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L.J.Doctors

University of New South Wales, Australia

In the verbal presentation of the research, you displayed a graph comparing the resistance of a monohull and a catamaran as a function of the speed. Assuming the displacement of the two vessels is the same (implying that the beam of the demihull is one half that of the monohull), then the resistance of the catamaran should asymptotically approach one half that of the monohull at high speeds. However, this feature does not appear on the graph. Could you please clarify this point?

It is true that if you compare a catamaran with an affine monohull of equal length, draft, and displacement, but necessarily, twice the beam, then as the hull separation tends to infinity, which is effectively the case for infinite depth Froude number, the wave resistance of the catamaran in *linear* theory asymptotically approaches one-half that of the monohull. However, following Heuser (1973), we compared the specific resistance of our catamaran with that of a monohull identical to one of the component hulls so that the displacement of the catamaran was twice that of the monohull. In this case, as the depth Froude number and, hence, the effective separation tends to infinity, the specific wave resistance of the catamaran should asymptotically equal exactly that of the monohull, even in nonlinear theory since the interference effects disappear. The same should apply, approximately, also to the specific viscous resistance. Our measurements as well as calculations, as shown, for example, in Fig.7 of Jiang, Sharma, and Chen (1995) are compatible with this requirement. The practical implication is that the theoretical wave resistance reduction achieved for a finite design depth Froude number by exploiting the interference effect between the wave systems of the component hulls of a catamaran does not extend up to arbitrarily high depth Froude numbers.