Underwater Radiated Noise (URN)
In-service vessels emit a range of noises and vibrations when sailing, which can adversely affect underwater life. Excessive levels of underwater noise can be especially dangerous for sea creatures like whales and dolphins, hindering their ability to communicate, hunt, migrate and echolocate.
Bureau Veritas’ Underwater Radiated Noise (URN) notation enables ship operators and managers to demonstrate the actions taken to minimize URN. In addition to protecting the marine ecosystem, managing onboard sources of noise and vibration can enhance passenger experience and crew wellbeing. Addressing URN can also further help ship owners prepare for an evolving regulatory landscape.
Bureau Veritas’ URN notation is applicable to all types of self-propelled vessels, and covers ships operating in both shallow and deep water conditions. The notation applies to continuous noise from general shipping activities, vessels with specific noise reduction needs, and ships with high expectations for sustainable operations.
An acoustic specialist can take URN measurements during sea trials for newbuilds and surveys for in-service vessels. Measurements are conducted onboard, and account for engine and propeller noise, onboard machinery and equipment, and other types of flow noise.
Propellers and engines are the primary producers of onboard noise and vibrations. Ship managers can reduce URN from engines by adding acoustic enclosures, affixing damping plates, widening engine stiffeners and adding dampers when possible. For propellers, experts can optimize blade design, conducting hydrodynamics simulations and tests to reduce propeller cavitation.
Passengers and crew can be negatively affected by onboard noise and vibrations, with crew health being particularly impacted, as their quarters are often close to ship engines. By identifying onboard sources of noise and vibrations, and limiting energy transmitted underwater, ship operators can minimize disturbances for personnel and passengers. Ships that significantly reduce URN can take the first steps toward earning a Comfort Class notation from Bureau Veritas.