WO1990001001A1

WO1990001001A1 - A depressor

Info

Publication number: WO1990001001A1
Application number: PCT/GB1989/001123
Authority: WO
Inventors: Gerald Frederick Jepson
Original assignee: The Secretary Of State For Defence In Her Britannic Majesty's Government Of The United Kingdom Of Great Britain And Northern Ireland
Priority date: 1988-07-22
Filing date: 1989-07-15
Publication date: 1990-02-08
Also published as: ES2016705A6; GB2244251A; GB8817546D0; GB9102387D0

Abstract

A depression kite for taking towed bodies down to a certain depth and maintaining them at that depth. Previous kites have been very large and heavy, with very high drag. The kite of the invention comprises a hull plate (1), a deflector (2) attached to the hull plate, a keel (3) extending below the hull plate to which is attached a stabilising fin (4) and a stabilising fin (5) or fins (8a) and (8b) which have a variable position tail plane (9), is attached to the upper surface of the hull plate. This kite allows high towing speeds whilst being light weight and possessing low drag and may be used to maintain towed cables at a predetermined depht.

Description

A DEPRESSOR

The invention relates to depressors for towed cables.

When an object (payload) is towed behind a vessel by means of a cable problems can occur in maintaining the payload at a predetermined depth. As the speed of the towing vessel rises the cable and its attached payload tend to be lifted due to hydrodynamic forces. To overcome this effect depressors are suspended from the cable to induce a downward force and keep the cable at a predetermined depth. Various different types of depressor are used, such as hydrodynamically shaped delta wings, angled vanes held in a frame, or "bomb'' shaped bodies with tail fins. In order to be effective these are usually large and have very high drags. For example, certain delta wing depressors can have a drag of 40 tonnes or more. The "bomb" shaped types of depressors have smaller drag effects but are difficult to maintain at depth as they tend to rise with increasing towing speed. When small payloads are being towed, high drag depressors are wasteful of the energy required for towing. They also restrict the speed of towing and it may be impossible to use small craft to tow them.

The object of the invention is to provide a low drag, stable depressor for towed cables that can be used by smaller towing craft and/or at higher speeds than conventional depressors; while still maintaining the cable at a desired depth.

The invention provides a depressor for towed cables and the like having a body and means to attach the body to the cable wherein the body comprises:

a) a hull plate; and

b) a deflector attached to the upper surface of the hull plate and positioned towards the forward end of the hull plate.

The hull plate may be any convenient shape but is advantageously narrower at the forward end than at the aftward end.

The deflector may be a single plate perpendicular to the fore/aft axis of the hull plate and angled back towards the rear of the plate at an angle of less than 90°, preferably about 45°. Preferably the deflector comprises two plates arranged symmetrically about the fore/aft axis, joined at their forward edges and at an angle of less than 90° to the fore/aft axis. Preferably the plates slope inwards and rearwards. In this arrangement the enclosed volume behind the plates could be used to carry a small payload.

Preferably the body further comprises one or more keels extending below the hull plate, the keels providing lateral stability for the depressor. Preferably it further comprises a stabilisingplate attached to the bottomof at least one of the keels. A stabilising plate of an appropriate size and mass will lower the centre of gravity of the depressor below the hull plate and thus enable the depressor to have self-righting control. The stabilising wing also increases the depression effects. Advantageously the body has a single keel along the fore/aft axis of the hull plate. Alternatively two, or more, keels may be used if desired. The stabilising plate is preferably delta wing shaped, with its narrow end pointing forward. The keel is conveniently formed from a single plate. Advantageously this keel plate may have one or more holes in it to reduce the keel area and thus reduce lift on the depressor when it is in yawl whilst still enabling the centre of gravity of the depressor to be lower than the hull plate.

Advantageously the body further comprises one or more stabilising fins on the upper surface of the hull plate. Conveniently a single fin is used, preferably of approximately the same area as the keel. Additionally, an adjustable tail fin may be added to the stabilising fin to enable the attitude of the body when towed to be altered. Such a fin provides stability and self-righting from a yawing motion. The moment of the fin shouldbe greater than the moment of the keel to provide maximum stability. For optimum performance, the centre of gravity is preferably below the mid point of the keel.

Themeans to attach the body to the cable is preferably attached to the body at a towing point well forward of the hydrodynamic centre of the body.

The invention will now be described, by way of example only, with reference to the drawings, of which: Figure 1 shows, in plan view, a depressor according to the invention;

Figure 2 shows, in side view, a depressor as shown in Figure 1; Figure 3 shows, in front view, an alternative stabilising fin arrangement; and

Figure 4 shows the stabilising fin arrangement of Figure 4 in the direction X-X.

As shown in Figures 1 and 2, a depressor for a towed cable comprises a hull plate 1 which is pointed at its forward end. Attached to the topof the hull plate 1 is a deflector 2 formed from two plates 2a and 2b. Extending below the hull plate 1 is a keel 3 to which is attached a stabilising plate 4. The plate 4 is delta shaped with its narrow end pointing forwards. The keel 3 has a hole through it to decrease its area and thus reduce the lift created when the depressor is inyaw . In thisway the keel 3 extends belcw the hull, such that the stabilising plate 4 lowers the centre of gravity of the depressor below the hull to give self-righting control, whilst also providing lateral stability yet not creating excessive lift if the depressor yaws.

A stabilising fin 5 is attached to the upper surface of the hull plate 1. This provides stability and self-righting from a yawing motion.

The depressor is attached to the cable to be depressed (not shown) via a towing point 6 at the front of the hull plate 1. A towing point 7 can be used to attach a cable and payload or a drogue (none shown) behind the depressor.

Figures 3 and 4 show an alternative stabilising fin arrangement in place of the fin 5 of Figures 1 and 2. Twin fins 8a and 8b are attached to the hull plate 1 in place of the fin 5. A tail plane 9 is adjustaoly fitted between the two fins 8a,b such that it can be positioned to provide varying depression, for example between the positions of its forward edge raised 15° and its forward edge lowered 15° such that different degrees of lift can be provided depending on the desired depth or the payload being towed.

The depressor can be made in a variety of different shapes and arrangements while continuing to have the stated advantages over the prior art.

Claims

1. A depressor for towed cables and the like having a body and means to attach the body to the cable wherein the body comprises:

a) a hull plate; and

2. A depressor according to claim 1wherein the hull plate is narrower at the forward end than at the aftward end.

3. A depressor according to claim 1 or claim 2 wherein the deflector is a single plate perpendicular to the fore/aft axis of the hull plate and angled back towards the rear of the plate at an angle of less than 90°, preferably about 45°.

4. A depressor according to claim 1 or claim 2 wherein the deflector comprises two plates arranged symmetrically about the fore/aft axis, joined at their forward edges and at an angle of less than 90° to the fore/aft axis.

5. A depressor according to claim 4 wherein the plates slope inwards and rearwards.

6. Adepressor according to any one of thepreceding claims wherein thebody further comprises one or more keels extending below the hull plate.

7. A depressor according to claim6 wherein thebody has a single keel along the fore/aft axis of the hull plate.

8. A depressor according to claim 6 or claim 7 wherein the body further comprises a stabilising plate attached to the bottom of at least one of the keels.

9. A depressor according to claim 8 wherein the stabilising plate is delta wing shaped, with its narrow end pointing forward.

10. Adepressor according to any one of claims 6 to 9 wherein the one or more keel plates have one or more holes to reduce the keel area.

11. A depressor according to any one of the preceding claims wherein the body further comprises one or more stabilising fins on the upper surface of the hull plate.

12. A depressor according to claim 11 wherein a single fin is used of approximately the same area as the keel.

13. A depressor according to claim 11 or claim 12 wherein an adjustable tail fin is added to the one or more stabilising fins to enable the attitude of the body when towed to be altered.

14. A depressor as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.

15. A depressor as hereinbefore described having stabilising fins as described with reference to Figures 3 and 4 of the accompanying drawings.