In this thesis, the numerical computation methods for the resistance in calm water and for the seakeeping performance in waves of multi-hull ships have been developed. In the resistance computation, thin ship theory has been applied since this theory fits quite well to the nature of the slenderness and thinness of the hulls.

The problem is solved by the boundary element method in terms of the Green function. The symmetrical part uses the Havelock source distribution on the center plane of the hull whereas the asymmetrical part is achieved through the doublet distribution on the camber surface. By introducing the tent function, the hull form can be easily expressed by the hull offsets.

Employing the numerical methods developed in this thesis, various configurations of multi-hull ships have been analysed. The wave-making interference characteristics of multi-hull ships and the wave wake influence to the wave-making resistance have been discussed. The numerical results have shown significant influences of hull form, speed and arrangement of individual hulls on the resistance of the multi-hull ships. As one step further, the seakeeping performance of a catamaran has been studied. Motions of a catamaran in waves were computed in the time domain.

The external forces acting on hulls include the linearized radiation and diffraction forces, and nonlinear Froude-Krylov force. The linearized radiation and diffraction forces are obtained from the impulse response functions, which are solved by directly using the time-domain Green function. The nonlinear Froude-Krylov force is computed at the "instantaneous wetted surface" of hulls under the incident wave profile. Computed results have been validated with the published data. Then the computer program were used for general analysis.