Speed loss due to seakeeping and maneuvering in zigzag motion

Abstract Ships are prone to experience a slight zigzag motion due to the interaction between steering, waves and other external disturbances. The zigzag motion will induce an added resistance and hence speed loss. This paper aims at addressing an effective tool to predict a ship's zigzag motion and azimuth propulsion system behavior in calm water and different sea conditions, and the resulting speed loss. Both model tests and numerical simulations have been carried out. Model tests with a freely running model were done in MARINTEK, Trondheim, Norway. The propulsion system was composed of two azipull thrusters, with autopilot control system to keep the power constant during the test process. Model speeds and the propulsion system behavior were recorded as time series when the models were freely running in calm water and regular head sea waves. Numerical simulations with simplified modular maneuvering model were conducted to verify the model test data. Good agreement between simulations and experimental results was found. The results also showed that when wave added resistance reach its peak value, the vessel has the most severe speed loss.