An analytical procedure for evaluating the lateral drifting forces on SWATH ship in the beam waves is presented in the paper. By using the previously well developed strip theory and the weak scatterer assumption, the prediction of the nonlinear forces for a single ship in waves was proved to be useful. Therefore the similar way is regarded to be applicable for the estimation of the lateral drifting forces on the SWATH ship if the interaction between two hulls can be treated adequately. In the present paper a SSP model is considered and the results are shown fairly good and the weak scatterer assumption may still be regarded to be valid.
The lateral drifting forces on ship in waves is an important subject for the Naval Architecture. Many analyses for the drifting forces on a single body case have been made by several authors, for example, the farfield method (Maruo, 1960), the near-field method (Kim et al, 1981) and the "weak scatterer" assumption (Salvesen, 1974), etc. The nearfield method was applied in (Fang et al, 1986) while the author (Fang, 1988) used the farfield method to estimate the lateral drifting force and moment on a SWATH ship and the better results than those of (Hong, 1983) were obtained generally. In addition to the nonlinear theory of the far-field method, the reason to reach the better results in (Fang, 1988) may be due to the application of a better strip theory (Kim et al, 1980). In the present paper, the author tries to use the existing nonlinear theory with the weak scatterer assumption (Salvesen, 1974) and the well developed strip theory (Fang, 1988) to estimate the lateral drifting forces on the SWATH ship in the beam waves.