Experimental Studies on the Effectiveness of the Side Thruster

Abstract

With regard to the effectiveness of the bow thruster, there exist a number of theoretical and experimental investigations. Especially, it is well known that the forward speed of a ship has a great influence upon the effectiveness of the bow thruster: the hydrodynamic forces which are generated by operating the bow thruster and act on the ship's hull, decrease remarkably with increase of the forward speed of a ship. On the other hand, there seems exist little knowledge of the effccts of several factors, i.e.ship speed, water depth, etc., on the effectiveness of the stern thruster. Therefore, the authors decided to investigate into the influences of the ship speed and the water depth upon the effectiveness of the stern thruster by the model experiments. As the result of the experiments, it is clarified that the ship speed has a great influence on the effectiveness of the stern thruster, which is quite different from the influence of the ship speed on the bow thruster. Namely, even in deep water, the hydrodynamic forces generated by operating the stern thruster do not decrease so much as in case of the bow thruster.In particular, it should be kept in mind that in shallow water, the lateral force due to the stern thruster increases with increase of the ship speed, and it may amount to several times the lateral force at zero forward speed. In this paper, the authors try to explain the increase of the lateral force by an analogy between the stern thruster and the jet-flap wings.