Control of Ship Motion at Low Speed: Experiments With a Physical Tanker Model

The paper presents a system controlling ship motion at low speed. The control system makes use of three fuzzy logic controllers. They are: course keeping controller, longitudinal position keeping controller and transverse position keeping controller. Three controllers work independently to keep the ship hull centre at the reference point with the set course. The ship motion is controlled by tracing and following coordinates of the reference point. They change according to the assumed ship motion trajectory and speed. The ship control system use three propellers: bow thruster, stern thruster and the main propeller of the ship. The control signals (propellers powers) have the form of pulses with relevant amplitude and time duration. The pulsatory nature of the control signals was obtained by proper selection of the shape of the member functions in Mamdani-type controllers and the use of the bisector defuzzyfication method. The magnitude of the signal is changed in steps and plays the role of rough control while its duration is adjusted continuously and plays the role of fine control The control system was worked out in Matlab-Simulink with RTW, xPC-target toolboxes and tested on a scaled physical model of a tanker in the real lake environment. The system installed on model contain two PC computers and as the measured devices use DGPS RTK Leica system, ST20 Anschutz gyrocompass and Gill-windobserver. The paper discuss the controlling algorithm, along with the results of control system tests.