Underwater noise reduction in focus at IMO

Published: 14 January 2022

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Over the past years concerns have emerged that a significant portion of the underwater ambient noise comes from commercial shipping. BIMCO recognises the importance of the issue which may have both short and long-term effects on marine life.

The subject is however quite complex and many factors must be considered in the quest to take the correct mitigating action. Additionally, careful consideration should be given to avoid implications with other environmental regulations, particularly with regard to the greenhouse gasses reduction (GHG) regulations such as the energy efficiency design index (EEDI) and the like, says Jeppe Skovbakke Juhl, Manager, Maritime Safety & Security at BIMCO.

“A specific example demonstrates that some energy saving measures such as optimising the propeller design (expanding the blade area) may limit the radiated underwater noise but be counter-productive when it comes to GHG reduction,” Juhl says.

BIMCO therefore emphasise that when underwater noise reduction measures are considered, their impact on GHG emissions should be carefully taken into account.

Underwater noise and its impact on the marine environment are currently not covered by IMO regulation. However, in 2008 the IMO agreed to initiate the development of non-mandatory technical guidelines and in 2014, the organisation approved guidelines on reducing underwater noise from commercial shipping to address the adverse impacts on marine life. (MSC.1/Circ.833)

Given the complexities associated with ship design and construction, the guidelines focus on primary sources of underwater noise, namely on propellers, hull form, on-board machinery, and various operational and maintenance recommendations such as hull cleaning.

During development of the regulation the IMO noted significant knowledge gaps and that noise levels in the marine environment and the contribution from various sources was a complex issue. Therefore, the IMO was not able to set future targets for underwater sound levels because research was needed on noise measurement methodologies.

According to Juhl, an important next step should be to focus on common procedures for measuring and determining what criteria should apply to limiting noise emissions, their frequency ranges, and in which geographical areas they should apply. Classification societies have already investigated the alignment of all the various standards of individual societies.

The industry should also aim for global rather than national regulations which should still allow for regional safeguarding in areas that need special protection.

“In accordance with UNCLOS¹, coastal states have limited ability to impose and enforce unilateral environmental and navigation regulations on foreign-flagged ships passing through their waters,” says Juhl.

“If individual states need to establish local thresholds in certain areas to limit the underwater noise, they should do this through the IMO’s Particularly Sensitive Sea Areas (PSSA) regime rather than implementing the special noise-reduction measures unilaterally,” he adds.

Applying restrictions via the PSSA status will allow countries to pin down and protect areas in which animals such as whale populations migrate and avoid imposing those special requirements to parts of the country where they are not needed.

“The aim should be for IMO guidelines on underwater noise to be made mandatory internationally. This would allow everyone to implement special devices when building ships to lower the noise in general while maintaining the option to use those guidelines to apply for special measures where needed,” he says.

¹ United Nations Convention on the Law of the Sea