Seakeeping performance of high speed catamaran vessels in head and oblique waves

Assessment of the performance of high speed catamaran vessels in waves from all directions is particularly important in the determination of operating envelopes for such craft and in the evaluation of design alternatives. Such procedures are more readily undertaken if theoretical techniques can be used to perform calculations of vessel response with confidence. These theoretical techniques not only reduce reliance on experimental testing but also provide information on design loads experienced by such craft, which are often more critical for oblique waves than head waves. In this paper the performance of a catamaran based on the Series 64 hull form, with two alternative hull separations, is investigated in head and oblique waves at one forward speed. Predictions of the rigid body response of the vessel in heave, pitch and roll are obtained through application of three-dimensional potential flow theory. These predictions are compared to experimental results measured through tests of a free-running model in regular waves. The theoretical techniques adopted require representation of the mean wetted surface of the vessel by panels, each containing a source at its centre. Two alternative forms of source distribution are employed; a pulsating source distribution satisfying the zero speed linearised free surface boundary condition and a translating pulsating source distribution which satisfies the forward speed dependent linearised free surface boundary condition. Comparisons between the theoretically derived responses and experimental data, for both hull separations, indicate that the translating pulsating source method provides more accurate predictions than the pulsating source method for head waves and oblique wave headings. The variation of vessel response with heading angle to the waves is predicted accurately by the translating pulsating source method