Influence of propellers and operating conditions on underwater radiated noise from coastal ferry vessels
McIntyre, D., W. Lee, H. Frouin-Mouy, D. Hannay, and P. Oshkai
Ocean Engineering 232: 109075 (2021)
Underwater radiated noise from marine ships represents the largest source of anthropogenic noise in oceans the world over, representing a substantial and persistent stressor to the health of marine ecosystems. The radiated noise from vessels can often be related to their velocity, and slowing vessels in critical habitat areas has been shown to reduce the average level of ambient noise in those regions; however, universal speed limits ignore the significant variation in speed-noise behaviour between vessels. We investigated the underwater radiated noise signatures and levels from eight coastal ferry vessels each operating at a range of speeds in order to examine the underlying causes of the atypical speed-noise correlations. The analysis revealed discrete patterns associated with speed ranges, suggesting that the increase in noise radiated at low velocities that was observed from some vessels was the result of a change in the regime of the physical mechanism generating the sound. Propeller-induced cavitation is the strongest possible explanation for noise of this type. The present results suggest that controllable-pitch propellers may be susceptible to changes in cavitation regimes resulting in increased radiated noise when operated under reduced loads, a finding that corroborates previous model-scale experimental evidence of the same behaviour.
