Vibration control by propeller design

•The paper focusses on the design method of NPT propeller which enables to achieve not only high propeller efficiency but also preferably low vibration and noise level.•Numerical predictions of pressure impulses for the NPT propellers are also presented to demonstrate the correlation between calculated values and data obtained from model experiments.

Propeller research has generally been focussed on improving the open water efficiency, and by considering the various energy losses associated with the marine screw propeller, it can be seen that for a design brief with given main engine power and RPM input, plus a thrust requirement defined by the specified ship speed, the most fruitful area for improvement in efficiency by propeller design is a reduction in energy losses. The simple way to increase the efficiency is reduction of blade area, increasing load near the tip and adopting a larger diameter with low RPM. However, vibration and noise will be the first issues when a designer tries to increase the efficiency of the propeller by these ways. This paper will present a simple prediction method of pressure fluctuations induced by thickness, propeller loading and unsteady cavitation taking not only propeller dimensions but also stern shape into account at the beginning of the propeller design.