The contribution from propeller cavitation to the airborne noise in after spaces on high speed marine vessels

Abstract

Propeller cavitation is often overlooked as a source of airborne noise on ships, because it is unusual to have manned spaces in the vicinity of the propellers. However, when design considerations require that berthing spaces be located over the propellers, cavitation can produce severe airborne and structureborne noise problems. These problems are especially severe in high speed or high power craft, where the propellers are heavily cavitating and the vessel structure is fairly light. This paper presents the results of measurements aboard a high speed (35 knots) research vessel which identifies the contribution to structural vibration and airborne noise from propeller cavitation. Predictions of the airborne noise existing in a proposed crew living space on a similar vessel show airborne noise levels to be 25 dB in excess of compartment specs at a similar speed. The mechanism of propeller cavitation and procedures to estimate source strength are reviewed. Relationships are presented to describe the power input to the hull structure from this source, and to describe the airborne sound power resulting from this hull vibration. Procedures for the control of propeller generated airborne noise are outlined, along with some of the unsolved technical problems associated with each of these noise control procedures.