Assessment of the effectiveness of ship machinery noise reduction measures using a test platform in a water basin

Abstract

Underwater radiated noise (URN) from commercial shipping is partly responsible for increased ocean ambient noise levels in the last decades. To preserve marine wildlife, there is a need to reduce it. Machinery noise is the dominant URN source at lower speeds. Mitigation technologies exist to reduce it, but a lack of quantitative data regarding their effectiveness results in limited practical ship applications since the cost-to-benefit ratio is imprecise. A small ship-like structure (test platform) representative of a ship section is designed and constructed to conduct measurements in a controlled environment and at a lower cost than actual on-ship testing. The platform is deployed in a water basin whose acoustic response is first characterized by reverberation measurements. Vibroacoustic sources simulate structure-borne and airborne noise, while hydrophones and sensors measure the response in the water basin and of the platform. Measurements with and without standard mitigation technologies installed in the platform are conducted to quantify the insertion loss. Up to 37 and 20 dB URN reductions are obtained with elastic mounts and mineral wool, respectively. The results obtained with the platform and the developed methodology can support and guide the implementation of mitigation measures in current and future ship constructions.