Cork

The strong, silent type: rubber mountings mean that the Celtic Explorer won't frighten fish.

The world's quietest research vessel set sail last month on its first scientific mission. By using low-noise electric engines and mounting equipment on rubber, Ireland's €32-million (US$35-million) Celtic Explorer should be able to approach fish more closely, improving the accuracy of fishery surveys.

Noise from ships is recognized as a major source of bias in such surveys, according to a 1995 report by the International Council for the Exploration of the Sea (ICES). Low-frequency sounds from vessels cause fish to stay 100–200 metres from some ships, and up to 400 metres from noisier ones.

Only two other vessels — the Scotia and the Corystes, both based in Britain — meet targets cited in the ICES report for reducing the sound from ships, and the Celtic Explorer outperforms them both. “Its performance is better than any fisheries research vessel measured to date,” says the report's author, Ron Mitson of Acoustec in Lowestoft, UK, a company that advises ICES on underwater noise levels.

Most noise from ships is caused by pumps, engines and the propeller, or by protrusions on the hull that generate bubbles in the water. On the Celtic Explorer, all of the equipment is rubber-mounted onto the hull. The propeller mounting also reduces noise, by fixing the propeller in a set position, rather than allowing its angle to be adjusted as on some other vessels.

The ship's project manager, Michael Gillooly of the Marine Institute in Galway, Ireland, adds that the resulting low noise levels reduce interference in the sonar systems that are used to survey fish.

Celtic Explorer, which can accommodate 19 scientists, will conduct a seabed survey around Ireland until October, with the aim of producing maps for telecommunications applications, management of underwater hazards, and the protection of areas of scientific interest. In November, it will carry out a survey of fish such as cod and plaice that live on or near the bottom of the ocean.

Other countries outside Europe are also developing vessels that can fulfil the ICES guidelines. “We are currently in the middle of constructing the first of four new vessels designed and contracted to meet the ICES noise standards,” says John Hotaling of the US National Marine Fisheries Service in Silver Spring, Maryland. “The first ship, Oscar Dyson, is expected to be launched in September and be in service by late 2004.”