Robust tracking control of underactuated surface vessels is an important issue in marine control engineering all along. This study intends to enhance the robustness of the motion control system which associates with unknown dynamics and time-varying disturbances. A practical adaptive backstepping control scheme is developed to keep a surface ship along the desired course that generated by a virtual ship. This control scheme can guarantee the error dynamic system to be globally uniformly asymptotically stable by the Lyapunov stability theorem. Furthermore, this algorithm can be implemented without the exact information of the non-linear hydrodynamics and random ocean disturbances. The employed pre-filter can provide a smooth transition of the desired course angle and its derivatives that based on the line-of-sight guidance method when the desired path is a non-smooth curve. The proposed controller can steer the underactuated vessel and follow the reference course accurately whether the desired course is smooth or non-smooth. In addition, this method can effectively reduce the fluctuation of the control moment when the desired path is a non-smooth curve. Two simulation cases are drawn to illustrate the validity of the proposed control strategy.


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