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Ships must cut underwater noise or face mandatory regulation

Published: 07 February 2024

The focus on underwater radiated noise (URN) from shipping has significantly increased over the past few years. As a result, the International Maritime Organization (IMO) has decided to raise awareness of the issue by drawing on lessons learned from the recently updated, non-mandatory IMO Guidelines. These aim to monitor the impact of URN from shipping and assess the efficacy of different mitigation solutions.

On 22-26 January, the Sub-Committee on Ship Design and Construction (SDC) convened its 10th session at the IMO in London. High on the agenda was underwater radiated noise (URN), which is increasingly attracting attention and demanding action due to negative its effects on marine life and the environment.  

As a result, the IMO recently updated its (non-mandatory) guidelines and uses lessons learned to monitor the impact of URN from ships and the efficiency of different mitigation solutions. In addition, the subcommittee discussed a paper showing a clear connection with ships adopting energy efficiency measures and reducing their level of URN in the process. The benefit is clear: as our industry cuts greenhouse gas emissions, the level of underwater radiated noise will reduce as well. 


An opportunity for shipping to show commitment 

The IMO has acknowledged the growing problems relating to underwater noise pollution caused by ships, primarily commercial ships, and has revised its guidelines in order to address the adverse effects on marine life (2023 IMO Guidelines on URN, IMO MEPC.1/Circ.906).  

The revised guidelines, which encompass a ship's design, construction, modifications, and operation, can be applied to any ship. Due to the complexities of ship design, and the multiple approaches to reducing URN, the revised guidelines recommend that shipowners and designers plan for URN management at the early design stage. For existing ships, the guidelines recommend implementing management plans to the extent that is feasible and practical.  

Such planning can help improve the understanding and management of underwater noise, boosting operational efficiency and reducing fuel costs. In addition, the implementation of the guidelines from the IMO offers an opportunity for shipowners and the shipping industry to demonstrate a commitment to environmental sustainability. 

The IMO released URN guidelines back in 2014 which were, however, not widely adopted. A revised version of the guidelines has therefore been developed to both increase uptake in the industry and monitor effectiveness. The IMO also approved an experience-building phase (EBP) starting already in 2023 to collect information on best practices and lessons learned from the application of the guidelines.

The EBP is anticipated to run until 2026, with a possible two-year extension depending on the outcomes and lessons learned. The IMO will not be revising the guidelines further until the EBP is complete to allow enough time to gather valuable experience before further changes are proposed.


Energy efficient ships are quiet ships

At the recent SDC 10 meeting, BIMCO co-sponsored a paper along with ICS, INTERTANKO, and IPTA which highlighted insights from a new study conducted by the University of Southampton. The study explored the interrelationship between ship energy efficiency measures and the reduction of URN. Download here the IMO submission, SDC 10/5/1.
The industry paper was very positively received by the sub-committee although the synergies still had to be identified and documented. The Southampton study, however, underscores a long-standing concern that global URN has been steadily increasing for decades, with an average increase of about 3 dB (decibels) per decade. Shipping has been identified as a major contributor to this trend, which is particularly noticeable in the Arctic. However, the study also notes that this trend is not consistent globally, with some regions experiencing static or even decreasing URN levels. Notably, the study identifies energy efficiency measures as a potential factor in reducing URN levels. Nearly 28% of the global fleet is now fitted with energy-saving or propulsion- improving devices, which may also significantly reduce URN. The study estimates that by 2050, energy efficiency measures will contribute to about 32% of the total decarbonisation effort and suggests that decarbonisation will also lead to a significant reduction in underwater noise levels. 

This emphasises that, as the shipping industry moves towards decarbonisation, we could also see a significant reduction in underwater noise levels.

BIMCO has repeatedly highlighted the synergies between energy efficiency and URN reduction. For most energy-saving measures considered or installed by ship owners, there is a clear URN benefit. Many measures yield around a 5-decibel URN reduction, with some even reaching potential reductions of around 10 decibels.
The study reflects the targets proposed by the Okeanos Foundation which advocates for a 3-decibel reduction in URN within 10 years and a 10-decibel reduction within 30 years. It also concludes that achieving a 3 dB reduction in shipping’s contribution to ambient noise within a decade is a feasible goal, given the synergies between energy efficiency and URN reduction.


Shipping must adopt the guidelines or face mandatory measures

As a consequence of the discussion at SDC 10, BIMCO is committed to raising awareness of the new guidelines, particularly with regards to the strong synergies between energy efficiency and URN which was highlighted in the Southampton study. As part of this, and to accompany the EBP, BIMCO and other industry associations plan to launch a survey to track and log the number of ships that have adopted the revised URN guidelines and/or applied any quiet ship class notations to their certificates.

The survey will help the shipping industry show progress in adapting to mitigating measures, even without mandatory IMO requirements on URN.
It is in the shipping industry’s collective interests to collect information on URN and submit the information to the IMO. Unless the shipping industry can demonstrate an increased uptake of the guidelines, mandatory measures may be imposed after the EBP in 2026. Ship noise is a loss in energy. Vibrating propellers, appendages and cavities are a structural risk. There are many incentives for the shipping industry to reduce noise.
One thing is certain: the focus on underwater radiated noise levels from commercial shipping is increasing, not only at the IMO but also in the EU and the Americas. As ship noise continues to impact marine mammals, better technology, increased data availability, and advanced analytics are providing much-needed context for impact assessments.

The recently revised IMO Guidelines are a positive step in ensuring that relevant parties have the best available information to guide URN reduction efforts and to take account of linkages with energy efficiency compliance measures.  


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Jeppe Skovbakke Juhl


Jeppe Skovbakke Juhl

Manager, Maritime Safety & Security

Copenhagen, Denmark