MEPC 84 Advances Underwater Radiated Noise Advice

Last week at MEPC 84, the Committee approved a technical guidance circular on co-optimizing propulsion equipment for energy efficiency and underwater radiated noise at the design and retrofit stage.

The circular seeks to clarify potential trade-offs between noise mitigation and conventional propeller design to promote the co-benefits of quiet ship technologies and energy performance.

Case studies presented at an earlier workshop demonstrated that retrofits, such as propeller upgrades, appendage modifications, and air lubrication systems, can yield underwater radiated noise reductions of 2–10 dB, often alongside energy efficiency improvements.

Effective design optimization requires precise definition of ship operating profiles and related speed ranges rather than relying on a maximum-speed design point. Design optimization should move beyond generic approaches, focusing instead on tailoring strategies to specific ship operational conditions and speed ranges. 

The industry has now progressed beyond simple trade-offs, developing holistic approaches that preserve the ship's core performance characteristics.

Several empirical and semi-empirical methods exist for estimating underwater radiated noise and cavitation, one of its main sources. These methods are increasingly being implemented in onboard systems that can provide real-time data. This allows for adaptive measures including route planning that provide an operational way of reducing both noise and fuel consumption without substantial modifications to existing ships.