DYNAMIC INSTABILITY IN QUARTERING SEAS .2. ANALYSIS OF SHIP ROLL AND CAPSIZE FOR BROACHING

In earlier studies we have analyzed the phenomena which can generate l oss of ship controllability in astern seas. In this paper we examine h ow the yaw instability associated with broaching can lead to roll inst ability and ship capsize. The dynamic effects responsible for capsize during the forced turn of broaching do not have their origin in the cu stomary roll equation but are the result of interactions with other mo tions of the ship. Stability studies based solely on the roll equation are thus clearly inappropriate for this case where a multidimensional approach is deemed necessary. After presenting the theoretical backgr ound we set out a multi-degree method of global analysis which is base d on transient maps. We apply this method to clarify how capsize occur s during the escape from surf-riding and also during transients from a rbitrary initial condition of the ship. Our study establishes the conn ection between speed, heading, automatic control parameters and capsiz e. The proposed method can be useful in the context of a design method ology for minimizing the risk of ship capsize in astern seas.