Traditional manoeuvring and seakeeping theories do not usually include any study of the interaction of the manoeuvring and seakeeping performances of a ship. A unified mathematical model, which brings together both aspects of ship manoeuvring in a seaway, has been proposed by Bailey, 1999 [9] and a time simulation has been developed on this basis.This study summarises the principles of the unified mathematical model and the verification of software, in which preliminary results for a Mariner vessel are presented. Then it extends the use of the model for another ship, the British Bombardier tanker, in order to further the validation process. The influence of parameters of the model, such as the mesh or the viscous ramp used at low frequencies, is investigated. Then, the predictions of circle manoeuvres and zigzag manoeuvres are compared with full-scale trials results. The comparisons are detailed and it shows that, although non linear effects have to be considered, the software predicts good tendencies in the evolution of ship manoeuvring characteristics, when some parameters such as rudder angle change. The investigation finally includes a preliminary study of the effect of waves on the ship's manoeuvring characteristics, for following and head seas.
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