An analytical and experimental study on dynamic stability of a vessel

Many researchers have studied the roll stability of ships since it is the most critical case of capsizing for conventional vessels. In this study external exerted forces from waves or winds on a vessel are modeled as a step exciting moment. Calculation of dynamic angle of stability Φdy, which is the first overshoot angle of vessel response to exciting moment, is the main objective of this paper. For this purpose two methods are used. The first one, so-called traditional method, determines Φdy by equalizing the external heeling moment energy and righting moment energy; while the other solves the rolling equation assuming step exciting moment and linear damping.Additionally, a model experiment is carried out with a step exciting moment then model rolling responses are registered. The results of both theoretical methods are compared with experimental results. The comparison shows that for large rolling amplitude such as 35 degrees, inclusion of linear damping does not have any considerable effect dynamic angle of stability. It means that the traditional method is reliable.