the Paravane

PARAVANE, THE, is a type of underwater kite which was developed by Lieutenant (now Lieut.-Commander, retired) C. D. Burney, R.N., during the World War as an anti-submarine and anti-mine weapon. It consists essentially of a torpedo-shaped buoyant body towed by a wire from a ship and carrying a plane which from the motion of the ship through the water gives the necessary thrust to cause the paravane to stand out a considerable lateral distance from the ship's side. It is fitted with a rudder to keep it at a pre-arranged depth below the surface, the rudder being governed by a hydrostatic valve and an oscillator.

The paravane is divided into three parts, namely: (I) head; (2) body; (3) tail. The head carries a tow anchorage, plane and (a) in anti-mine paravanes, the cutter, which requires no setting and can cut successive parts of a mine mooring of wire in rapid succession, (b) in anti-submarine paravanes the striking device, and the gear for transmitting the effect of the impact to the striker-switch.

The body is watertight and is made of welded steel plate. (a) In the anti-submarine paravane the body carries within it the charge of T.N.T., the primer tin and the detonating gear. Whilst the paravane is on board or in close proximity to the ship the detonators are withdrawn from the primer and two safety shut ters form an effective fire screen between the two. At a speed greater than about ro knots, a water flap, which projects from the under side of the paravane, is forced aft by the water pressure upon it. This movement is transmitted to the detonator carriage, which moves aft, forcing the safety shutters to one side and plac ing the detonators in position in the primer ready for firing. The body also carries the striker-switch and depth-recording gear. The depth-recording gear registers on the attacking vessel the depth at which the paravane is running. (b) In the case of the anti mine paravane the body contains the oscillator. The depth-keeping mechanism in the paravane is composed of two distinct portions, the hydrostatic valve and the mercury oscillator. The hydrostatic valve depends, for its action, on a change of depth above or below the normal depth. It therefore causes the paravane to follow a sinusoidal path through the water. At high speeds this motion

becomes excessive and a device is required which will return the paravane to its correct position as soon as it is inclined to move from its set depth. This function is performed by the oscillator. When a paravane is fitted with this gear, the depth at which it runs does not vary more than 4f t. on either side of the set depth.

The tail of the paravane carries the two rudders, the hydrostatic valve which actuates them, and the horizontal and vertical fins. The paravane being required to run at a certain depth, a compres sion corresponding to this depth is put upon the hydrostatic valve spring. The load due to this compression forces the rudders "down"; the water pressure acting on the hydrostatic valve tends to force the rudders "up"; when the two balance, the rudders return to the amidships position.

Protector Paravanes.

Paravanes for anti-mine use are known as Protector paravanes. The installation is designed to pro tect ships from moored mines. A paravane is towed on either side of the vessel, by means of a length of special wire. Due to the position taken up by the paravanes, the wires form a wedge on either side of the ship, and sweep through a broad path. If they foul the mooring wire of a mine, the mine is deflected away from the path of the vessel, and the mooring wire slips along the paravane wire until it reaches the paravane. There it is severed by the cutter fitted on the head and the mine rises to the surface, where it can be seen and destroyed. The towing wire is attached to the vessel by a specially designed fitting situated at the point of intersection of the stem and keel. When the towing wire fouls a mine mooring wire, a minimum outward thrust must be imparted to the mine and sinker in order to deflect them from the path of the vessel. If a paravane be designed to give this minimum thrust whilst moving at a moderate speed through the water, its total thrust when moving at a high speed would be very great, and an excessive load might be thrown upon the towing wire. Broadly speaking, a paravane is designed to protect a vessel at all speeds from about one-third her maximum upwards.