Listening in: Stolt Tankers gains a better understanding of underwater radiated noise

Stolt Tankers is continuing to take a proactive approach to supporting the UN’s Sustainable Development Goal (SDG) 14 - Life Below Water by investigating the impact that ships could be having below the surface of our seas and oceans.

New regulations on underwater radiated noise (URN) levels from the commercial shipping industry are expected soon, but in general, there are not many guidelines for tackling this issue. So, with the help of Richard Thill, an energy conservation department intern from the Webb Institute, the Stolt Tankers team conducted a comprehensive review of URN sources, current and potential future regulations, measurement methods, and mitigation techniques. 

What lies beneath

URN within the range of 1-10kHz has been shown to harm marine life such as fish, dolphins, and whales. This is the exact band in which most commercial vessels operate. In addition, noise travels four-to-five-times faster underwater and for much longer distances, meaning large areas of marine wildlife habitat can be affected by a single, distant ship. 

Richard (left) explained: “Within the comprehensive review, we explored several avenues for URN mitigation for both newbuilds and the retrofitting of the current fleet. Because most ship noise comes from propeller operations and/or cavitation and machinery vibrations/noise, our focus was on these two sources.”

Stolt Tankers has already applied various technologies that reduce underwater noise from its ships, including Propeller Boss Cap Fins (PBCF) (main photo). These energy-saving devices are attached to the propellers of ships and break up the hub vortex, resulting in less noise-producing bubbles (cavitation). The primary purpose of PBCFs is to reduce fuel consumption which results in lower emissions of greenhouse gases (GHGs). 

To reduce biofouling, another cause of underwater noise, Stolt Tankers is applying advanced graphene coatings as standard to propellers and has planned a trial for hull coating. Both technologies are eligible for environmental credentials and offer shipowners a reduction in port charges at some locations. 

What lies ahead

URN has not historically been a major concern for the shipping industry, but Stolt Tankers supports the industry’s increasing focus on reducing its environmental impact and is committed to understanding its own impact and where it can improve. 

The project team made several recommendations for mitigating URN including the introduction of new technologies, innovative ship design for newbuildings and more accurate measurement of URN so that shipowners can monitor noise levels more closely. 

Following Richard’s findings, Stolt Tankers is waiting to hear more about the upcoming regulations on URN and is well-prepared to meet them. Energy and Conservation Manager at Stolt Tankers, Jose Gonzalez Celis said: “The research team made several recommendations, and it is reassuring that we are already implementing some of these measures, including PBCFs and graphene coatings.

"Following on from this project, we are looking at ways to inform and educate our fleet and operations team on how they can contribute to reducing underwater radiated noise and help support Stolt Tankers’ sustainability ambitions for the future.”

Stolt Tankers recently announced that its ships traveling south of Sri Lanka, the north-west of the Mediterranean Sea, the waters around Vancouver Island and the east coast of the US will modify their routes and reduce their speed by 20% to minimise the negative impact of shipping on the whale populations in these areas.