Towards realistic estimation of ship excessive motions in heavy weather. A case study of a containership in the Pacific Ocean

Synchronous roll and parametric roll resonance are critical phenomena that lead a ship, under certain conditions, to quickly develop large roll amplitudes. This will result in excessive accelerations that can be dangerous for a ship and her cargo. Ships with large bow and stern flare (i.e. container carriers and RoPax) are especially prone to this type of hazards. Therefore, it is of utmost importance for ship operators to be aware of a set of conditions under which these two unwanted phenomena happen. This will help implementing necessary counter measures, either operational (speed or course alterations) or tactical (route finding). In this context, the development of a fast and reliable method for screening the conditions leading to excessive accelerations would improve ship safety. Therefore, in this study, we propose a method detecting critical scenarios for a container ship in heavy weather conditions. The method utilizes an original, six-degree numerical model of ship motions, called LaiDyn, to investigate large amplitude motions and the associated longitudinal and transverse accelerations that a ship is experiencing. Finally, the accelerations that are calculated for a set of operational conditions are checked against their predefined threshold values associated with the cargo lashing system. The proposed method can be used for operational purposes, at the stage of route planning, where the expected accelerations could be considered as another objective function in the route-finding algorithm.