Experimental evaluation of azimuth thruster for tanker scale model with dynamic positioning system

The thrust-propeller shaft speed relationship is required to calibrate control parameters in order to perform experimental tests with dynamic positioning system (DPS) installed in the scale model. In general, actuators of a DPS are main propeller, side and azimuth thrusters and their characteristic curves are quite difficult to be obtained theoretically. Therefore, tests in laboratory are necessary to evaluate the performance of those propellers, so tests carried out with azimuth thruster with nozzle are presented. The focuses are twofold: the first one is to evaluate the bollard pull varying the propeller shaft speed and the azimuth angle, as well; the second purpose is to evaluate the thrust while the azimuth is swiveling. In order to do it, the thruster is installed in a captive container and forces and moments in horizontal plane are measured by the load and torque cells connected in a vertical beam. The preliminary bollard pull test results indicate some influence in the thrust due to the relative angle between the azimuth propeller and hull. Swiveling tests results show some thrust reduction in comparison to the bollard pull tests for the some azimuth angle and a difference between clockwise and counterclockwise is observed, albeit not relevant.