Lyapunov design for global tracking of underactuated ships

It is well-known that ship control is a hard problem. In this paper, we consider the global tracking problem for a simplified chip model with only two propellers. By application of Lyapunov's direct method and exploitation of the inherent cascade-interconnected structure of the ship dynamics, two constructive tracking designs are presented. In contrast to the existing cascade approach, our approach produces an explicit Lyapunov function which can be used for robustness analysis and robustification. Unmeasured thruster dynamics is addressed for the first time. Computer simulations demonstrate the efficiency of the proposed tracking method.