Increase in the Propulsive Efficiency of a Ship by a Nozzle Installed just in front of a Propeller

Abstract

By installing a nozzle just in front of a propeller, the propulsive efficiency and other performance of a ship can be improved. In this paper, effects of the nozzle are discussed by the use of experimental results and theoretical calculations. The effect of the nozzle on the propulsive efficiency is firstly illustrated with results of the propeller load test conducted by making use of an axi-symmetrical body. Secondly, nozzle's effects ascertained in towing tank tests of a ship model are shown. A theoretical calculation is applied in order to investigate into hydrodynamical characteristics of the nozzle in the non-uniform flow behind the ship model. Thirdly, sea trial results of actual ships, which confirm the effectiveness of the nozzle, are described. Other effects of the nozzle are lastly shown. The cavitation of a propeller is reduced and the maneuverability of a ship is improved by the nozzle.