Rubber is being used on ships to reduce noise, after a report revealed excess noise in the ocean was causing problems for whales and dolphins.
The noise of passing ships is disturbing marine animals, such as killer whales and dolphins, by adversely affecting their ability to communicate and find prey. Researchers have been saying for some time that the low rumble caused by ships is disturbing large whales.
New research carried out in the United States has revealed persistent noises at medium and high frequencies are also taking their toll, as killer whales (known as orcas) hear best at 20,000Hz – the frequency of much of the noise from ships.
Endangered species threatened
The orcas use a process called echolocating to identify prey and pinpoint where it is. This involves bouncing sound off objects, but the noise from ships is preventing them from doing so effectively. Scientists say dolphins and porpoises may be suffering from the same problem. They fear the phenomenon could affect the endangered killer whale species living near shipping lanes. There is a population of around 80 killer whales foraging along the United States’ west coast and along the Puget Sound.
Even slightly increased noise can make echolocation more difficult for whales, according to Beamreach, the body carrying out the research. This is of particular concern, since the whales eat chinook salmon, which is a species that’s quite rare anyway.
The killer whale listens for the “click” of the salmon before it pounces – a challenging activity because the sound is so subtle anyway, so the noise from a ship could completely stop the whale from recognising that its prey is in the vicinity.
Using underwater microphones, the study measured the noise created by around 1,600 individual ships passing through Haro Strait, in Washington. The two-year study measured the noise made by 12 types of ship including cruise liners, military vessels and container ships.
Some vessels were quieter than others, although the average noise was 173 underwater decibels – similar to the sound of a loud rock concert. As the whales won’t be swimming right next to the ships, it’s estimated the noise they experience is around 60 to 90 decibels. This is still loud enough to have a detrimental effect on their well-being.
To combat the problems of noise pollution in the ocean, rubber is being used on ships to reduce the noise of their machinery. It has been a common practice on mega-yachts when the owner doesn’t want a lot of noise, or on warships where stealth is of the essence due to submarines listening. Research vessels need soft mountings too, as noise from the hull can mask the sonar.
To quieten noise from the engine, which can be transmitted to the hull, the engine is placed on a raft, which rests on acoustic absorbent mounts. The base is bolted to the frame, with the engine secured on top and a rubber “sandwich” in between.
There can be variations of the design, but in all cases, both the raft and the engine are usually absorbent-mounted. This is particularly important on minesweepers, as it avoids the risk of accidentally detonating an acoustic mine.
Pump and piping
Ships’ pumps can also cause excess noise. So can any other rotating machinery. In the case of the pump, the baseplate is mounted on acoustic mounts, in the same way as the engine, with “compensators” installed on the suction and discharge flanges. Once these have been fitted, the problem of vibrations from the pump being transferred to the piping via the flanges is minimised.
The piping will have bellows pieces fitted to further reduce the noise. Piping can transfer noise throughout the whole ship, as the lengths of pipe span all over the interior of the vessel. They are usually clipped on to the ship’s structure.
Pipe mounts are attached flexibly to the ship and feature a rubber pad on each clamp, which absorbs any vibrations from the working fluid. The pipes from the exhaust on diesel engines are also mounted flexibly with bellows pieces. This effectively stops the exhaust noise from being transmitted to the hull.
Insulation is also applied to dampen any airborne noise and vibrations. Experts say that any ship which has all of this kit added should be able to operate quietly, causing as little disruption as possible to the surrounding marine life.
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