A report commissioned by the International Fund for Animal Welfare (IFAW), and submitted in July to the International Maritime Organization’s Marine Environmental Protection Committee, provides a detailed assessment of the prospects for using ship-quieting technologies to reduce the level of background noise in the world’s oceans. According to the report, which cites a wide array of recent research, similar types of ships can vary in their sound emissions by 30-40dB; some engineering experts suggest that the noisiest of these could reduce the primary source of noise (propellor cavitation) by 10dB. The report, Reducing Underwater Noise Pollution from Large Commercial Vessels, by Dr. Marin Retilson, is available for download on the IFAW website. “The noisiest 10% of ships account for between 50% and 90% of the noise pollution and it is these vessels that are most likely to benefit from relatively minor modifications to reduce propeller noise,” said Russell Leaper, an IFAW scientist. The report summarizes technical approaches to reducing ship noise, with an emphasis on utilizing modern propeller design, along with fins and ducts to improve wake flow, which could reduce noise output from the noisiest ships and be cost effective. There is a relatively poor understanding of noise output from large commercial vessels and the next step is to do more wide-reaching assessments of individual ship noise, in order to identify the vessels that could make the most difference in reducing ocean noise levels.
A target of a 3dB reduction (i.e. halving the acoustic energy) in 10 years in ocean noise was suggested at an International Workshop on Shipping Noise and Marine Mammals held in Hamburg in April 2008. This target has been endorsed by the Scientific Committee of the International Whaling Commission. You can download the Hamburg workshop report here.