1922 Encyclopædia Britannica/Paravane
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PARAVANE, a naval device used in the World War first for attacking submerged submarines and subsequently for protecting vessels against mines and for cutting up hostile minefields. The name of Acting-Comm. C. D. Burney is especially associated with its design and development.
The explosive paravane in its final form consisted of a torpedo-shaped body carrying near its head a large steel plane which was set at a small angle to the centre-line of the body, and was in an approximately vertical position when the paravane was being towed. The thrust of the water on the plane carried the paravane away from the towing vessel, and with two paravanes, one on each side, a spread of sweep of about 200 ft. was obtained, i.e. the two paravanes were that distance apart. Horizontal and vertical fins near the tail increased the stability, and in the tail was fitted a depth-keeping mechanism consisting of a horizontal rudder actuated by a hydrostatic valve which responded to any difference in the water-pressure caused by a change of depth. The paravane carried a heavy charge of high explosive which could be detonated, by means of an electric current passing through the core of the towing-wire, in any one of three ways. If the paravane hit the hull of a submarine, striking-gear on its nose operated a switch which closed the firing circuit. This impact method would not become operative should the towing-line become entangled in the external fittings of a submarine, but in that case an extra load would be put on the line; apparatus was therefore provided such that when the load on the line exceeded a predetermined value a switch was tripped and the circuit closed. Finally a hand-switch on the bridge of the towing vessel enabled the charge to be detonated at will should the presence of a submarine be suspected.
It was soon seen that the explosive paravane could be adapted to protect vessels against moored mines. For this purpose the towing-lines were attached, not at the stern as with the explosive paravanes, but at a point as far forward and as low down as possible. Their outboard ends being kept about 100 ft. away from the central fore and aft line of the ship by the paravanes to which they were attached, they swept a wedge-shaped track in a horizontal plane at the level of the keel or slightly below it, and fouled the mooring-wires of any anchored mines lying in or near the course of the vessel. When this happened the mooring-wire was deflected along the towing-line until it reached the head of the paravane, where it was guided into the jaws of shears or scissors made of special high-grade steel, by which it was severed. The mine then floated to the surface and was exploded by rifle-fire. It was found that with a pull of about 7 cwt. the shears would cut a 1½ in. mooring-wire. The normal length of the towing-lines was 56 yd.; three-strand wire ropes were used, each consisting of 37 galvanized wires, 0.049 in. in diameter, with an ultimate breaking strength of between 100 and 120 tons per sq. in. There were three types of protector paravanes: (1) The merchant-vessel type, known as “otters,” for ships with speeds below 16 knots; (2) the fast-liner type; and (3) the battleship type.
The mine-sweeping paravanes were towed from the stern of high-speed destroyers. As the point of attachment had to be on deck, an arrangement called a “depressor” was used to bring the virtual point of tow down to the required depth at the stern. Wide paths could be swept at speeds of 26 to 30 knots.