Underwater radiated noise from small vessels

The Impact of Small Vessel Noise on Marine Life and Ecosystems

Underwater radiated noise from marine vessels is a growing problem, with a large body of evidence showing the negative impacts it can have on a variety of marine life. Much of the focus in recent years has been on large commercial ships but, in many shallow and coastal waters, small vessels can dominate the soundscape. Small vessels often operate in areas where marine life is very sensitive to noise, such as on coral reefs and marine safari tours with very high biodiversity. As a result, there is a clear need to better understand the origins of small boat noise and to develop solutions to reduce it.

Noise from marine vessels comes from the engines and machinery onboard, as well as from the propeller and flow over the hull. Propeller cavitation, where vapour bubbles form around the propeller and then collapse, can be a particular problem leading to a large increase in noise levels.

Our Efforts to Reduce Small Vessel Noise and Protect Marine Life

Dr Tom Smith and the team within UCL Mechanical Engineering are exploring ways of reducing this noise. Working in partnership with BMT, the team are gaining a better understanding of radiated noise from smaller vessels including what the acoustic sources are and how they change with speed and from one vessel to another. Using hydrophones and underwater cameras, they have shown that the propellers on small boats can start cavitating at speeds as low as 5 knots, leading to a sharp increase in noise levels. They have also shown that small boat noise does not always increase with speed, as is commonly assumed for large ships. Recently published research has shown that small amounts of roughness applied to a propeller can actually reduce noise levels in some instances, and work is now underway to determine if this can be done without compromising efficiency. The team are now working to develop and test technologies that can reduce radiated noise levels to help minimise the impact we have on the marine environment.

Further links

• Dr Tom Smith's UCL profile
• An experimental study of underwater radiated noise from a small vessel with damaged and fouled propellers (JASA Volume 4, Issue 12)