Study on the effect of layout on navigation characteristics of trimaran in stern quartering seas

As one of the high-performance ships, the performance of trimaran is significantly affected by the side hull position. The influence of side-hull positioning on the resistance and seakeeping of trimaran has been widely studied, but the effect on the sailing performance and broaching susceptibility is still not clear enough. In this paper, the autopilot of a trimaran model in waves is simulated by a hybrid method coupling Fully-nonlinear-potential-flow-theory (FNPT) and computational fluid dynamics (CFD), and the effect of the side hull position on the course keeping and broaching susceptibility is studied. The effect of the grid on the computed results is tested first. Then, the autopilot of the trimaran model with different layouts in quartering stern waves is simulated at a relatively high speed that could lead to broaching. By changing the wave steepness, the effect of the layout on the sailing performance and broaching of trimaran is studied. The research results indicate that the arrangement of the side hulls has a significant impact on the vessel's broaching phenomenon and course-keeping performance. Under steep wave conditions, a forward side-hull arrangement increases the vessel's susceptibility to broaching and weakens its course-keeping ability, while a rear side-hull arrangement with a larger transverse spacing demonstrates better directional stability and can effectively reduce the probability of broaching. The systematic analysis in this paper provides new insights for optimizing the stability of trimarans in following quartering seas.