Fishing vessels rely on a controlled underwater noise emission in order to perform their tasks proficiently and effectively.

DNV has as of 1. January 2010 issued a new voluntary class notation, SILENT. The intention of the notation is to provide owners of acoustically sensitive vessels with concise and realistic criteria to underwater noise emission and also to provide environmental conscious owners with an opportunity to demonstrate a low environmental “footprint”.

Waterborne noise may frighten fish. As such excessive noise emission from fishing vessels involved in any active catch methods is undesirable. In addition, fishing vessels employ advanced hydro-acoustic equipment for fish search and to control and monitor fishing gear. For both modes a low noise level will be an advantage, however, during searching a low noise level may be more important than during catch and at the same time it will be technically more realistic to achieve a low noise level during search than during trawling. Hence, maximum allowable noise levels have been specified for two conditions, one heavy towing condition e.g. trawling, and a light search condition.

DNV has over the years acquired considerable experience on underwater noise control and on underwater noise measurements. This experience has been incorporated in the SILENT criteria, but can also be used for advisory services to clients requiring help in achieving moderate underwater noise levels.

Through the SILENT notation, DNV has taken a proactive approach. SILENT will act as a safeguard against excessive noise radiation and ensure that fishing vessels do not scare fish to take evasive action away from the vessel.