Motions of Catamarans in Oblique Seas at Speed

Motions, particularly roll, may have significant implications for passenger comfort when operating a catamaran in oblique seas. Designers of high-speed catamarans therefore need tools for predicting a vessel's seakeeping performance. This work presents three numerical methods for predicting vessel motions in oblique seas: a boundary-element method combined with a strip-theory approach modified for multihulls, a two-dimensional Green function time-domain strip-theory and a modified strip-theory method. Experiments to measure the motion response of a catamaran in oblique seas were conducted using an NPL 5b model at three speeds (Fn = 0.203, 0.406 and 0.508). The experiments showed that all motions tended to increase with increasing speed. Generally the boundary-element method and modified strip-theory method correctly predicted responses in all of the experimental configurations. The two-dimensional Green function time-domain strip-theory was used to predict the motions at the two higher speeds only and was also found, in general, to predict the motions satisfactorily.