Page 16: of Marine Technology Magazine (November 2024)

OPED UNDERWATER NOISE

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UNDERWATER RADIATED

NOISE AND OCEAN HEALTH

By Chris Waddington, Technical Director at International Chamber of Shipping he maritime industry’s push toward decarboniza- The IMO’s Energy Ef? ciency Existing Ship Index (EEXI), tion brings an unexpected bene? t: the reduction effective from January 2023, limits the power output of ship of underwater radiated noise (URN). While the engines, indirectly contributing to URN reduction. More ad- sector focuses intensively on emissions reduc- vanced technologies, such as wind-assisted propulsion and

T tion and fuel ef? ciency, these same measures are techniques to ensure Just-in Time Arrival, hold promise for quietly contributing to a healthier acoustic environment in further mitigating both emissions and noise pollution.

our oceans. For ship owners and operators already investing in green technologies, addressing URN can be a natural ex- Understanding URN tension of existing environmental initiatives, offering a dual Underwater radiated noise refers to the sound energy emit- bene? t for both emissions and marine life. ted from ships into the ocean. This noise originates from var- ious sources, with cavitation from propellers being the most

Energy Ef? ciency and Noise Reduction signi? cant contributor. Cavitation occurs when water vapor

One of the key insights from recent research is the natural bubbles form and collapse near the propeller blades due to alignment between energy ef? ciency measures and noise re- pressure changes, releasing energy in the form of sound. duction. Most interventions aimed at improving a vessel’s This constant hum of cavitation and other machinery adds to fuel ef? ciency also contribute to reducing its URN output. the ambient noise in the ocean, contributing to a long-term

Speed limitation, a fundamental tactic for lowering fuel con- increase in sound levels.

sumption, simultaneously reduces propeller cavitation and, Since the 1930s, studies have indicated that URN lev- consequently, URN. Technologies like air lubrication sys- els have risen by an average of three decibels per decade, tems, which reduce friction between a ship’s hull and the largely driven by shipping activities. This steady increase water, not only improve energy ef? ciency but also help in disrupts the natural acoustic environment, posing chal- minimizing noise pollution. lenges for marine life that rely on sound for navigation, 16 November/December 2024

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