Global straight-path tracking control design for underactuated ships with unknown control direction

This paper considers the straight-path tracking problem for underactuated ships with unknown control directions in the presence of external perturbations. By incorporating Nussbaum-gain technique, universal control and the idea of dead zone into adaptive backstepping technique, we propose a new linear course adaptive state-feedback control law based on the output redefinition method. It is shown that the proposed control law makes all signals of closed-loop system bounded, while the system output, which is a combination of the yaw angle and sway displacement, converges to a prescribed arbitrary small neighborhood of the origin after a finite time. Different from the closely rated work, the highlight of the paper is that the controller is relatively easy to implement due to the less number of parameters to be designed.