Wednesday, March 7, 2012

Shipboard Noise

Michael Zucker, et al., Classification of Ship Radiated Noise from
Recordings Made in the Hudson River
I lived half my life in eight by five room, just cruisin' to the sound of the big diesel boom-- Jimmy Buffet, "Landfall"
My boss was angrier than I'd ever heard him. "The noise level on our vessels is within Coast Guard standards," he told me. My second mate had been walking around with a decibel meter, measuring the noise level in various parts of the ship. But the main office wanted that stopped. We were in compliance with the law: stop trying to prove we weren't.


Among the many health, safety, and environmental regulations that modern ships are subject to are those controlling how much noise a ship can make, both in its interior, and how much it can expose the outside world to.


Sources. Most of the noise a ship generates is mechanical. The two most common sources are propeller cavitation, in which the turning of the propeller creates bubbles that than burst, and crankshaft vibration, produced by the internal workings of engines. On a large, modern, steel ship these noises are carried through the ship's structure, and their vibrations often cause other objects to vibrate, creating further noise. Other noise may be created by pumps, electrical equipment, and even waves slapping against the hull.


Problems. The most immediate concerns about noise come from its effect on human beings. On a ship, too much noise makes it difficult to get proper rest, leading to reduced alertness and more chance of an injury or watchkeeping error. Exposure to high noise levels may lead to hearing loss, also a safety concern in the short run, but a medical expense and quality-of-life issue later.


Beyond the human effects, noise and the vibrations causing it also increases wear and tear on equipment and structures. Equipment constantly subject to vibrations wears out quicker, fails sooner, and needs to be replaced more often. Propeller cavitation decreases the efficiency of the propellers, and thus increases fuel costs


Noise also affects the marine environment. A recent study of North Atlantic Right Whales found that the whales' ability to communicate was reduced by 85-percent when a ship passes near them. The low frequency sounds emitted by propeller cavitation in particular interfere with communication needed for feeding, mating, and social behaviors like gathering into a pod.


Sonar. For a decade, experts have debated how much sonar from Navy ships affects the behavior of whales and other marine life. On one side are claims that sonar, at the very least, leads to increased beaching behavior in some species of whale. Others dismiss the claims as unproven or at least that the effects are not as widespread as claimed. The issue reached the US Supreme Court in 2008, but the court did not look at the science so much as the authority of the president to ignore environmental regulations. More recently, whale watching captains in Puget Sound reported audible sonar pings from a Navy ship several miles away.


Related Posts
Marine Mammal Protection Act
Monday Morning Mariner: If You Really Miss Going To Sea


Related Articles
DieselShip.com: IMO Noise Limits
MarineLog: Give Your Ship The Silent Treatment
KING5-TV: People Report Hearing Navy Sonar Tests Near Everett

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