Propeller cavitation noise and background noise in the sea

Abstract

Background noise in the sea from commercial shipping has increased over the past decades and affects marine life in a variety of ways, mainly masking of vital communication calls of baleen whales.The cause of this low frequency noise is solely attributable to propeller cavitation at frequencies below 300Hz. The noise spectrum features a characteristic maximum at around 50Hz with most ships independent of type, size and speed. This spectrum and its cause are widely unexplained.This paper describes the observations made in full scale ships particularly with respect to the broad band part of the low frequency spectrum. A simple acoustic ship model is presented and procedures to investigate into the physics of noise generation by cavitation are suggested and the possible influence on background noise in the sea be estimated.