Studies on Propulsive Performance of Semi-Submerged Ship and its Model Testing Method

A semi-submerged ship with small water-plane area will easily change its trim and dipping by small disturbances unless it is controlled by fins. This character of semi-submerged ships is unfavourable for the propulsive performance test, because it is difficult to make coincidence of the both running conditions in the resistance and self-propulsion tests. To avoid the above mentioned difficulty in the propulsive performance test, the authors adopted the locked model testing system as the first step for completion of the free running system with fin control.In this study, a new propulsive performance test, tentatively named “Self-propulsion test in thrust shifting”, was proposed. In this method, the resistances of a model ship can be determined from the relation between thrusts and towing forces obtained by the self-propulsion test in thrust shifting. The new self-propulsion test was performed for a locked model and the attempts were successful.According to the results of the experiments, the shallow draft semi-submerged ships will contribute to saving energy. Furthermore, the authors found out that the surface force and the bearing force generated by the propeller operations behind hulls played an important role in the ship behaviour in calm water.