The CFD tool used to estimate the wave drag is based on the zeroth-order slender ship approximation. It is applied to the design of optimal hull forms and optimal arrangement of hulls for a wave cancellation multihull ship. The hull surface is represented by a triangulation, and almost every grid point on the surface can be used as a design variable. A smooth surface is obtained via a simplified pseudoshell problem. The optimal design process consists of two steps. The optimal center and outer hull forms are determined independently in the first step, where each hull keeps the same displacement as the original design, while the wave drag is minimized. The optimal outer-hull arrangement is determined in the second step for the optimal center and outer hull forms obtained in the first step. During the optimization process, each hull keeps the same displacement as the original design while the wave drag is minimized. There are 76 design variables for the center hull and 64 for the outer hull. Four design cycles are required for each hull form optimization. Results indicate that the new design can achieve a fairly large wave drag reduction in comparison to the original design configuration.