New Research Looks At Noise Reduction From Ships That Have Been Retrofitted

For many years, researchers at UC San Diego’s Scripps Institution of Oceanography have used High-frequency Acoustic Recording Packages (HARPs) and hydrophones to study the marine life and the threats they face in the Santa Barbara Channel, a heavily trafficked area off the coast of Southern California.

This single instrument has recorded a wide range of sounds, from dolphin clicks and whale songs to military sonars and vessels, for over a decade.

This region is home to the endangered northeastern Pacific blue whale and intersects with the Channel Islands National Marine Sanctuary.

Retrofitted ship
Image for representation purposes only

To gain insight into the effects of shipping on marine life, the Whale Acoustics Lab at Scripps, Maersk, a major container shipping company, and the National Resource Defense Council have partnered to study the behaviour of Maersk ships before and after an extensive modernisation project.

According to Vanessa ZoBell, Scripps doctoral student and lead author of the survey, it is clear that human-generated noise underwater can detrimentally affect marine creatures that rely on sound for communication, navigating, and finding food.

Maersk’s Radical Retrofit was instigated to improve fuel efficiency, but it also had the additional benefit of lowering noise levels.

Lee Kindberg, Maersk North America’s director of environment and sustainability, commented that with the International Maritime Organization’s increased attention to underwater noise levels, there is a need to reduce greenhouse gas emissions and decrease noise levels – “we need more information” to do this.

They conducted 111 moves from 12 sister ships to observe blue whales, humpback whales, fin whales, and dolphins between the ports of Los Angeles and Long Beach before and after the upgrade.

An examination of 177 voyages between 2008-2018 showed that 66 of them were discounted because of whale song or sound interference from other vessels or snapped underwater phone cables.

Results of the study exposed a noteworthy decrease in monopole force levels in the low-frequency range following retrofitting – likely caused by alterations to the propeller and arc.

Furthermore, due to the added mass of the containers, an increase in the voice emission from the ships after retrofitting was also recognised.

This could result in a decreased level of movement and thus sound if global demand remains the same. However, John Hildebrand, the Principal Investigator from the Scripps Whale Sound Laboratory, has concluded.

This has altered the outlook on sound levels in correlation with the number of transported containers. At slower velocities, the level of the monopole originator is most affected by equalisation.

The International Maritime Organization (IMO) has recommended analysing particular design modifications to the propeller and hull to lower underwater noise.

The authors, however, could not determine which of the alterations were the most successful due to the various changes being implemented simultaneously. As a result, further investigations are demanded on a global scale to determine which methods are the most effective for reducing noise.

For this purpose, ZoBell expressed his hope that the IMO document will be utilised for initiating discussions on noise abatement. He added that the study’s co-authors are Sean Wiggins, Kaitlin Frasier, Martin Gassman, and himself of Scripps Oceanography, who initiated the project.

Hildebrand noted that such collaborative efforts are anticipated when ships are designed to have lower carbon emissions and, hopefully, less underwater noise.

Source: Scripps, UC San Diego Today

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