Characteristics of low-frequency propeller noise generated by merchant vessels

Noise radiated by propeller cavitation on merchant vessels is a major contributor to ocean ambient noise in the 2 to 100 Hz frequency regime. This cavitation generates discrete lines at propeller shaft and blade rates and harmonics. In order to understand this acoustic source, an analytical model has been developed to predict the cavitation volume—time histories on a given propeller. This paper reviews this model development, outlining the physical basis for the model, and the acoustic radiation characteristics of this source. The model is exercised for an example merchant vessel. Results are presented showing the variation of the source strength of the propeller-generated lines with ship speed, wind and sea state, vessel ballast condition, propeller design, and hull form variables. It is demonstrated that the propeller source strength is strongly dependent on the vessel design, and on operational characteristics.