On an Estimation Method of Propeller Exciting Force and Its Application : Development of Four Bladed Propeller with Unequal Angle

Abstract

In order to reduce vibration of ship hull which resonates with the second unbalanced moment of a main engine, four bladed propeller with unequal blade angle, which induces the even order component of bearing force, was designed. When this propeller is installed with appropriate phase lag for exciting effect of main engine, the second components of propeller and main engine are counterbalanced and vibration of ship hull is reduced. First in this paper, a simple estimation method of bearing force in effective wake is proposed. This method, which uses the data of self-propulsion test and nominal wake pattern, is applied to a tanker and a cargo ship, and thrust variation is compared with results of model experiment and Kumai's method. Next, bearing force of four bladed propellers with unequal blade angle is obtained from this method and experiment. And besides it is discussed based on the result of sea trial and the bearing force obtained from this method that the second order component of hull vibration of a 10,000 DWT cargo ship at resonance frequency reduces to a half, if four bladed propeller with unequal blade angle is applied to this vessel.