A ship noise rating system for underwater vessel noise reduction targets

To support Canada's efforts in addressing underwater radiated noise (URN), a novel ship noise rating system was developed using the distribution of Radiated Noise Levels (RNL) measurements from over 49,000 transits of 5947 different ships. The system sets category-specific URN targets for nine ship categories and allows for URN evaluations using semi-controlled measurements made during routine ship operations. The approach extends the framework recommended by the national Underwater Vessel Noise Reduction Targets (UVNRT) Working Group, by using scaled RNL measurements to account for operating condition differences during measurements, and vessel dimensional differences within the same ship category. Ships are rated according to their URN quartile, allowing for future refinements as vessel RNL distributions evolve. Integration into automated monitoring tools, including the Boundary Pass Underwater Listening Station, facilitates cost-effective ratings of large numbers of ships and allows for data-driven refinements. The rating system contributes to Canada's development of ship URN management methods and target setting approaches and provides information to support the country's continued engagement at the International Maritime Organization (IMO) as international policy frameworks evolve.