Due to the weathevaning nature of the vessel with a turret mooring system, the vessel may experience large yaw motions. These yaw motions may significantly affect mooring system responses and need to be accounted for in the mooring system analysis. In general, the analysis for a turret mooring system has been focused on the conditions of mean equilibrium heading and low frequency yaw motions. The transient behavior during the weathervaning process has not been well addressed. For the environments that have steady-state directions, such as current, waves, wind, etc. the analysis method may be adequate. However, for squall dominated environment conditions, such as in offshore West Africa, the transient responses of the mooring system could be important considering the dramatic changes of wind speed and direction.
This paper studies the weathervaning process of a turret moored Floating Production, Storage and Offloading system (FPSO) under various environmental conditions. Damping effects on yaw motions are also studied. A number of simulations have been carried for a FPSO with a turret mooring systems. Typical environmental conditions of offshore West Africa are utilized in the simulations. The main focus of the study is to better understand the critical conditions for the responses of a turret mooring system in squalls in terms of the important characteristics of the squalls and the combinations with other environment condition. The recommendations on critical environment conditions for a turret mooring system in squalls are provided.