Ship Motions and Capsizing in Astern Seas

An analytical and experimental study of ship motions and capsizing in extreme seas has been conducted. The analysis of linear and quasi-linear one- dimensional roll models has revealed motion anomalies not apparent from the usual linearized ship motion theory. Extensive tests have been conducted using two radio-controlled models in the wind generated seas of San Francisco Bay. Directional spectra were computed, using a variety of techniques, from the wave measurements by an array of wave gages. Comparisons of the experimentally determined motions and a linear strip theory prediction are presented. A time domain numerical simulation program for motions and capsizing has been used to investigate motions in a variety of wave group configurations. The results show good agreement with observed capsizing phenomena and have revealed a number of important characteristics associated with large geometry changes in waves.