This report presents the results of a review of means of mitigating and predicting the underwater radiated noise (URN) from ships. This noise can have significant environmental impacts, with damaging effects on marine animals of many types.
The main outcome of the work undertaken is a matrix of URN mitigation measures. Measures are categorized in four main areas, covering propeller noise reduction; machinery noise reduction; flow noise reduction; and other, where the first three categories are not easily applied.
Each measure is described, and then defined in a standardized approach that aims to define the advantages and benefits to the ship’s design and operations; disadvantages and challenges; technology readiness; cost impacts for implementation and operation; applicability to different ship types; and effectiveness; in terms of frequency ranges and reduction in sound levels. A final section of the matrix provides a summary of prediction methods for URN.
A wide range of mitigation measures are available to address different types of noise at varying levels of effectiveness. All will incur some level of cost, but in some cases there are co-benefits such as efficiency enhancements that may offset some or all of this disadvantage.