The Australian Maritime Safety Authority (AMSA) has issued a notice drawing attention to the International Maritime Organization’s (IMO’s) non-mandatory revised guidelines for the reduction of underwater radiated noise from shipping to address adverse impacts on marine life.
The revised guidelines contain a new section on underwater radiated noise (URN) management planning, which should be considered at the earliest stages of design for new builds, and as far as reasonably practicable for existing ships.
This includes the development of a URN management plan, intended to be a flexible tool that allows a customised approach.
The management plan may include:
- establishing a baseline URN
- setting URN targets
- evaluating various technological, operational, and maintenance approaches to reduce URN.
- Model templates in the revised guidelines help shipowners and designers in this process.
Due to concerns about underwater radiated noise (URN) from commercial shipping affecting marine life, the Marine Environment Protection Committee (MEPC 80) released revised URN reduction guidelines effective 1 October 2023. The guidelines provide updated design, technical, operational, and maintenance advice for shipbuilders, designers, and operators, applicable to new and existing ships. They also include updated measurement standards and classification society rules to evaluate and monitor URN reduction efforts.
Energy efficiency and URN
Recognising efforts to achieve increased energy efficiency in ships may also result in a reduction in URN. A dedicated section of the IMO Guidelines has been included in the revised guidelines on positive synergies with climate policies. This section notes however that URN measures should not come at the expense of efforts to reduce greenhouse gas emissions from ships or other IMO measures associated with ship safety.
Careful consideration should be given to the interrelationships between energy efficiency, GHG and URN reduction while adhering to regulatory obligations and ensuring that the level of URN will meet set targets as established in the URN Management Plan. Many of the energy efficiency improvement options to meet energy efficiency regulations (EEDI, EEXI and CII) may result in an improvement in URN performance and could provide positive synergies with climate policies. Where URN reduction measures are not supportive of energy efficiency, then regulatory obligations pertaining to energy efficiency and emissions must take precedence. URN measures should not come at the expense of IMO requirements on GHG reduction and energy efficiency or other IMO requirements affecting the ship safety as for example manoeuvrability.
Designers, builders, shipowners and operators should investigate and consider the risk of increasing URN with ship design to achieve lower EEDI, EEXI and/or CII.
Scrutiny should be given to the co-design of hull and propeller as a unit, such that a uniform wake flow is created to reduce propeller cavitation, as this will also increase energy efficiency, and reduce emissions.
Reducing propeller cavitation is an effective means of reducing URN. Measures aimed at reducing applied or installed propulsion power and propeller thrust loading, with the appropriate safety caveats,4 are options to improve energy efficiency, reduce emissions, and typically result in URN reduction, e.g. wind assistance, optimized hull design, and regular maintenance and hull cleaning to avoid fouling and reduce hull resistance are all effective measures for reduced emissions and URN.
URN computational methods should integrate optimization methods to include the parameters affecting energy efficiency and other emissions at the same time as underwater noise. This will allow optimization with respect to URN, other emissions and efficiency/performance.
Incentive schemes
Maritime authorities, financial and insurance institutions and others are encouraged to support URN reduction efforts and monitoring by promoting the establishment of incentive schemes. Such schemes could be linked to:
- URN ship class notations
- recognition of URN management plans
- URN reduction targets
- ship and engine technologies and maintenance
- ship speed optimisation programs
- voluntary sustainability certifications, which include evidence of URN reduction.
Examples of incentive schemes include discounts on port dues, fairway fees, extra services, or promotional benefits.
