the Paravane

The protection afforded by the paravanes depends, amongst other things, upon the distance between the fore and aft line of the ship and the paravane when running. This distance, or spread, in turn depends upon three things :—(i) the length of the towing wire; (2) the size of the paravane ; (3) the size of the towing wire. Also the paravanes must be attached to the ship as far forward and as low down as practicable. If the point of attachment were above the level of the keel, mines could pass under the towing wire and hit the ship. Further, the paravanes should not tow at any considerable depth below the keel. They are usually set to run at a depth about 5ft. in excess of the deepest draught of the vessel. Any mine within the sweep of the paravanes, which lies between the line of keel and the surface of the sea, will then be deflected by the towing wire. If a mine be moored so deeply that it passes under the towing wire, it cannot, under ordinary circum stances, strike the ship in calm water.

As already described, an effective paravane will deflect any mine from the path of a vessel which is on a straight course, but it is conceivable that, whilst a vessel is turning, a mine may be missed by the paravane and yet hit the ship near the stern. For relatively small ships, up to 400ft. in length, one pair of paravanes gives practically complete immunity from moored mines as long as the ship is not in a heavy sea. With larger ships, the distance swept out by the vessel when turning under full helm may be so great that one pair of paravanes does not give adequate protection.

Explosive Paravanes.

A considerable amount of auxiliary apparatus is required in connection with explosive paravanes, the whole installation being called the "high speed submarine sweep." It enables a vessel to attack a submerged hostile submarine whose position is only approximately known. The sweep consists essen tially of a paravane, towed astern of the attacking vessel, and con taining an explosive charge fired electrically by means of a dynamo fitted in the vessel. It is towed from a winch, by armoured elec tric cables led over a fairlead in the stern of the attacking vessel. When the towing wire fouls a submerged submarine it will slip over her smooth surface until the submarine is struck by the para vane. The striking gear which is fitted to the nose of the paravane is moved inwards by the impact, actuates a firing switch and de tonates the charge. Alternatively, if the nose of the paravane does not strike the submarine, the wire may be caught or nipped over some part of the submarine, thus increasing the load on the wire. This increased load trips a dynamometer switch which again de tonates the charge. A third method of firing, by a hand switch.on the attacking vessel, is fitted in case it is desired to get rid of the paravane in an emergency. The principal advantages of this type of sweep are that it can be towed at high speeds and it leaves un affected the manoeuvring powers of attacking vessels.

(A. H. W.)