Underactuated dynamic positioning of a ship-experimental results

The paper considers the dynamic positioning problem for a ship having only two independent controls, namely surge force and yaw moment. A time-varying feedback control law including integral action is developed and proved to exponentially stabilize both the North and East positions and the orientation of the ship. Experimental results are presented were the controller is implemented on a model ship, scale 1:70, of an offshore supply vessel. The experiments show that the ship converge to a neighborhood of the desired position and orientation, oscillating about stationary errors, and that with integral action in the control law these stationary errors are reduced.