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Protecting Marine Cables

Nature volume 142, page 640 (08 October 1938) | Download Citation



ONE of the most prolific sources of damage to ocean cables is the heavy drags, called otterboards, which are attached to the nets of steam trawlers and dragged along the ocean bottom. In the Nickel Bulletin of September, it is estimated that the damage caused to cables by the steel runners of otterboards averages about £100,000 a year. To get rid of this source of loss, the Western Union Telegraph Co. has, for some time, been experimenting with a submarine plough which will automatically make a furrow in the bottom of the ocean, feed the cable into it and cover it up. The cable will then be buried at a depth sufficient to ensure that the otterboards cannot come into contact with it. Encouraging results have been obtained from experiments made so far, but many difficulties have had to be faced. A new series of experiments has now been started off the Irish coast. The plough is towed by the cable-ship Lord Kelvin. In handling the equipment a very flexible towing line had to be provided able to withstand a load of 29 tons. The ordinary equipment necessitates that the line must be neither too light nor too rigid. It must be capable of being paid out gradually from the ship while ploughing under full load. After careful investigation and a series of tests it Was found that 'di-lok', a special chain made of 3½ per cent nickel-steel, was quite suitable. In order to get continuously smooth operation a very minute tolerance on the size and shape of each individual link was imposed. The requirements were about five times as severe as those imposed by the U.S. Navy in their specifications. There are eleven Western Union trans-Atlantic cables and eight of these pass through fishing areas off the Irish coast where most of the ploughing work will be carried out.

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