Underactuated ships follow smooth paths with Integral actions and without velocity measurements for feedback: theory and experiments

Steering a ship along a desired path with a prescribed forward speed is a vitally important issue in many offshore applications. This paper presents a global controller that forces a ship without a sway actuator to follow a reference path and without velocity measurements for feedback. Nonlinear damping terms are also included to cover both low- and high-speed applications. Integral actions are added to the controller to compensate for a constant bias of environmental disturbances. Experimental results on a model ship illustrate the effectiveness of the proposed method.