Abstract
A nonlinear time domain method is presented to calculate the vertical responses of fast ships. The extended 2.5D theory is used to evaluate nonlinear fluid radiation and diffraction forces which can take into account both the effects of the change of the underwater wet surface and the forward speed of a fast ship at free surface. A matched boundary integration equations algorithm is applied to solve the 2.5D theory in order to avoid numerical divergence observed when ships have large flare. The hydrostatic and Froude–Krylov forces are calculated below the incident wave elevation. The comparison of numerical results with model test data shows that the numerical method can capture the main nonlinear effects and is valid for the calculation of vertical motions and wave loads of high speed ships.