Amended guidelines on underwater radiated noise planned

By Stela Spiraj, ABS Senior Engineer, Regulatory Affairs

The impact of underwater noise pollution from ships on the marine environment has been a growing concern over recent years. In June 2021, the IMO decided to review the previously approved Guidelines for Reducing Underwater Noise from Commercial Shipping to Address Adverse Impacts on Marine Life (MEPC.1/Circ.833), to identify the next steps to further reduce underwater radiated noise (URN) and encourage stakeholders’ action. At its 9th session, the SDC Sub-Committee finalized the draft Revised Guidelines for the Reduction of Underwater Radiated Noise from Shipping to Address Adverse Impacts on Marine Life, pending final approval in July 2023.

The draft Revised Guidelines provide an overview of methods applicable to designers, shipbuilders, and ship operators for URN reduction of individual ships and support the establishment of mechanisms and programs through which noise reduction efforts can be realized. The Revised Guidelines may be applied to any ship, considering their design, construction, modifications, and operational profile.

New Section on URNMP

A new Section Five on Underwater Radiated Noise Management Planning (URNMP) was added to the Revised Guidelines, covering shipowner actions to reduce URN.

Given the complexities associated with ship design and the various approaches to reducing URN, shipowners and designers should undertake URN Management Planning at the earliest design stages. Similarly, URN Management Planning may be carried out for existing ships as far as practicable.

URN Management Planning is a flexible tool that allows a customized approach and may include establishing a predicted or actual baseline of a ship’s URN, setting specific and quantitative URN targets, and evaluating various technological, operational and maintenance approaches to reduce URN. Model templates are provided to help guide shipowners/designers in this process.

Energy Efficiency Compliance Measures and URN Relationships

The Revised Guidelines include a dedicated section about the relationship between Energy Efficiency Compliance Measures and URN. Many improvement options to meet energy efficiency regulations may result in an improvement in URN performance and could provide positive synergies with climate policies. Designers, builders, shipowners, and operators should investigate any correlated effects on vessel URN because of measures implemented to achieve lower EEDI, EEXI, or CII, as this information could support future vessel operations in protected sea areas.

Incentive Schemes

The Revised Guidelines include a separate section for maritime authorities, financial and insurance institutions, and others, to promote establishing incentive schemes supporting the implementation of noise reduction efforts by suppliers, designers, builders, shipowners, and operators. Coastal and port authorities in protected sea areas may incentivize URN reduction efforts by offering discounts on port dues and fairway fees, or other promotions for ships that have implemented URN monitoring and management.

Design, Technical, Operational and Maintenance Noise Reduction Approaches

The initial ship design and build stages are critical for reducing URN by considering elements such as the hull and propeller design, wake flow improvement, and onboard machinery.

It may be impractical for existing ships to match the URN performance achievable by new designs, although notable URN reduction may be possible through retrofitting and operational changes.

For all vessels, operational and maintenance approaches ranging from optimizing voyage planning, reducing ship speed, and proper maintenance of machinery and hull coatings all help to keep the noise levels low.

The table above summarizes the design, technical, operational and maintenance noise reduction approaches available to new and/ or existing ships.