Model for the radiated noise source spectra of merchant ships

Abstract

Ocean ambient noise in the frequency range 20–300 Hz is, in many cases, dominated by the radiated noise from merchant ships [G. M. Wenz, J. Acoust. Soc. Am. 34, 1936 (1962)]. Predictions of noise in this frequency regime have usually been based on a ship spectrum of a highly simplified type. A study of the sources of merchant ship radiated noise leads to the conclusions that (1) the radiated spectrum of a typical merchant ship includes two cavitation related sources—continuous and narrow band; (2) the lowest frequency noise attributed to distant shipping is the sum of narrow-band components; and (3) the higher frequency noise is due to the sum of continuous components. In this paper, expressions relating the source spectrum of each component to ship engineering parameters (e.g., propeller diameter) are presented. The shape of the ambient noise spectrum is determined by evaluating these expressions for the distributions of engineering parameters appropriate to the ensemble of ships in the world's merchant fleet. This shape is shown to be characteristic of observed deep-ocean ambient noise.