GB2248587A

GB2248587A - Apparatus for sweeping a body of water

Info

Publication number: GB2248587A
Application number: GB8521417A
Authority: GB
Inventors: Michael Griffins Woollard; Richard John Snow
Original assignee: Baj Ltd
Current assignee: Baj Ltd
Priority date: 1985-08-28
Filing date: 1985-08-28
Publication date: 1992-04-15
Anticipated expiration: 2005-08-28
Also published as: GB2248587B; FR2712559A1

Abstract

Apparatus for sweeping a body of water, for example mine-sweeping, comprises a towing cable 2, a depressor 5 at one end of the cable, a pair of sweep cables 6, 7 extending from adjacent the depressor, and a diverter 11, 12 at the end of each cable, the diverter including controllable hydrodynamic surfaces 25, 26; 36, signal receiving means, and means for adjusting the hydrodynamic surfaces in response to received signals. The apparatus preferably includes depth sensing means so that the diverters may be caused to 'fly' close to but out of contact with the bottom. The diverters may be tailess with swept back wings (32, 33) with elevons 36 or may be of delta wing form with elevators (26) and a fin 24 with a rudder 25. <IMAGE>

Description

APPARATUS FOR SWEEPING A BODY OF WATER.

This invention relates to apparatus for sweeping a body of water with a flexible element, hereinafter called a cable, at levels between the surface and the bottom. The invention is particularly concerned with mine sweeping but it will become apparent that it could be used for other purposes such as surveying, searching and locating.

Mines are often swept by means of a so-called team sweep in which two mine sweepers proceed along parallel but spaced paths towing between them a bight of cable which carries cutters and which is held at a distance below the surface by one or more depressors.

An alternative method of mine sweeping known as Oropesa sweeping employs a single minesweeper from which a single towing cable leads to a depressor which is a passive guide device or kite which, as the minesweeper tows the depressor through the water , is pressed down to hold the end of the cable to which it is connected at a distance below the surface which is dependent on the speed of the minesweeper and the length of cable deployed. Extending laterally from a point on the cable adjacent the depressor, a sweep cable (which, in minesweeping , carries cutters) extends in a generally horizontal curve to a passive diverter which may be of similar construction to the depressor but with its hydrodynamic surfaces extending vertically rather than horizontally.This end of the sweep cable is also attached to the bottom end of a pendant cable to he upper end of which a float is attacked thus maintaining the diverter at a predetermined distance below the surface of the water. Although it is possible toemploy a single lateral sweep cable, the usual arrangement is to have two such cables extending in opposite lateral directions from a central point, so-called double Oropesa sweep. Where reference is made hereafter to only a single sweep cable, it will be appreciated that there may be a second sweep cable to which reference has been omitted.

It has been found that Oropesa sweeping is entirely satisfactory at relatively shallow depths but when an attempt is made to increase the length of the pendant beyond a certain figure the depressor and diverter become unstable.

It is an object of the invention to adapt the apparatus used for Oropesa sweeping so that it may be operated at greater depths.

According to one aspect of the present invention, apparatus for sweeping a body of water comprises a towing cable, depressor means at one end of the towing cable and a sweep cable extending from adjacent the depressor to diverter means and is characterised in that the diverter means includes controllable hydrodynamic surfaces, signal receiving means and motor means for adjusting the hydrodynamic surfaces in response to received signals.

The sweeping apparatus may include depth sensing means coupled to the hdyrodynamic surfaces to control the depth of operation of the diverter means. For example the apparatus may include a depth sensor located adjacent the depressor means, transmission means to transmit a signal from the depth sensor to the diverter means and control means to adjust the hydrodynamic surfaces to maintain the sensed depth at a set value. The diverter means may be arranged to maintain a depth relative to the depressor means such that the sweep cable is substantially horizontal. In the preferred arrangement, the apparatus includes bottom sensing means arranged to adjust the hydrodynamic surfaces to maintain the diverter means at a predetermined distance above the bottom.The sensing means may be mechanical in nature and include a bottom contactor but preferably includes a signal transmitting and reflected signal sensing device such as a sonar.

The bottom sensing means may be located in or adjacent the diverter means or may be located adjacent the depressor means with signal transmission means to the diverter means.

By providing depth sensing means controlling the hydrodynamic surfaces of the diverter means, a bottom following characteristic is provided so that the sweep cable may be maintained close to but out of contact with the bottom. Thus for example it may be possible to sweep mines on short mooring cables located in relatively deep water having an uneven bottom. It may be found desirable for the sweep cable to be provided with an additional depth control device having hydrodynamic surfaces at one or more points intermediate its length and for the depressor means to have controllable hydrodynamic surfaces so that the sweep cable can follow the bottom more closely and adopt different depths at different points along its length where it is being towed over an uneven bottom.

the diverter means may comprise a wing with hydrodynamic control surfaces and arranged when in operation to operate with the plane of the wing approximately vertical so that the lift provided by the wing as it is towed through the water acts to divert the sweep cable generally outwards from the depressor means.

In one possible construction, the depressor means is in the form of a sweep back wing which is tailless and has elevons, i.e. control surfaces (preferably near each wing tip) which perform the functions of both elevators and ailerons providing pitch and roll control respectively. Alternatively the depressor means may be in the form of a delta wing with a rudder control surface on a vertical control fin and elevator control surfaces on each half wing. In the delta wing, roll control is provided either through the secondary effect of yaw on a dihedral led wing or by providing elevators which have some aileron action or by both means.

In the swept back construction, the wings are preferably provided with a positive dihedral angle and may be provided with washout (a term known from aircraft wings) in order to reduce the tendency to stall. The washout (by means of which the stall occurs initially over only a part of the wing, rather than over the whole of the wing simultaneously, and preferably commences adjacent the root of the wing and extends progressively towards the top of the wing) is preferably effected by a change in the cross-sectional form of the wing from the root area to the tip area, for example by a progressive change in section from a region adjacent the root to a region adjacent the tip; this enables the wing section to be produced by a straight-line generatrix extending between a first template section adjacent the root and a second template section adjacent the tip; however, the washout may be produced by twisting of the wing as is usual with aircraft. Preferably the wing tips carry fins extending generally perpendicular to the spanwise axis and in a preferred arrangement such fins extend only downwardly. Such fins reduce the loss of wing lift caused by wing tip effects resulting from flow around each wing tip from beneath to above the foil. The wings also provide some degree of mechanical protection to the wing and control surface during handling and storage out of the water.

In a second possible construction the depressor means is in the form of a delta wing. The wing may have positive dihedral to provide roll stability. The delta shape develops lift through the well known phenomenon of fully separate flow which produces leading edge vortices which are associated with well swept leading edges. The design of the wing and the resulting vortex should be arranged to provide an even undisturbed flow in the region of the control surfaces.

According to a second aspect of the invention, apparatus for sweeping a body of water comprises a sweep cable connected to a submersible vehicle having controllable hydrodynamic surfaces, bottom sensing means and control means for adjusting, in dependence on the sensing, the surfaces to tend to maintain the distance between the vehicle and the bottom at a set value.

According to a third aspect of the invention, a submersible vehicle comprises a wing, anchorage means for a sweep cable, controllable hydrodynamic surfaces and means for receiving signals by which the surfaces are controlled. The signal receiving means may form part of a depth or bottom sensing means. Thus, for example, the vehicle may have means for receiving command signals instructing the vehicle of the sea bed clearance to be maintained, means for sensing the sea bed clearance and means for adjusting the hydrodynamic surfaces to maintain the commanded sea bed clearance.

The adjusting means may comprise a computer.

The invention may be carried into practice in various ways and one mine sweeping arrangement will now be described by way of example together with an alternative construction of diverter described in connection with the apparatus. The apparatus will be described with reference to the accompanying drawings in which:: Figure 1 is a diagrammatic representation of the apparatus as a whole employing diverters each in the form of a delta wing; Figure 2 is a diagrammatic perspective view of one of the diverters of the apparatus shown in Figure 1; Figure 3 is a side view of the diverter shown in Figure 2; Figure 4 is a plan view of the diverter shown in Figures 2 and 3; Figure 5 is an end view of the diverter shown in Figures 2, 3 and 4; Figure 6 is a perspective view similar to Figure 2 of an alternative swept wing form of diverter; Figure 7 is a side view similar to Figure 3 of the alternative form of diverter; Figure 8 is a plan view similar to Figure 4 of the alternative form of diverter; and Figure 9 is a front view of the alternative form of diverter shown in Figures 6 to 8.

Turning now to Figure 1 it will be seen that a minesweeper 1 tows a so-called kite wire 2 which extends to depressor means 3 which in this form is constituted by a kite 4 having a plurality of horizontally arranged passive hydrodynamic surfaces to provide a downward force as the kite is towed through the water and an additional depressor 5 having a construction substantially identical to that of the two diverters to be referred to in greater detail below. The additional depressor 5 has actively controlled hydrodynamic control surfaces and provides secondary depression forces assisting the depression forces provided by the kite 4. The additional depressor 5 has sensing means sensing the distance between the additional depressor 5 and the sea bottom and a means, i.e. a computer, for controlling the control surfaces to maintain the distance constant.

Extending from the additional depressor is a pair of sweep wires 6, 7 each of which carry a plurality of mine cable cutters 8. By means of couplings 9 (see Figures 2 and 6) the sweep wires 6 and 7 are connected to diverters 11 and 12 each of which has actively controlled hydrodynamic control surfaces and is arranged to maintain the outer end of the respective sweep wire laterally diverted from the vertical plane containing the kite wire and at a required distance above the sea bed. Each of the sweep wires carries a plurality of intermediate bodies 13 each of which is constructed in a similar manner to the diverters but is of smaller dimensions.

The intermediate bodies have controlled active hydrodynamic surfaces and depth sensing systems similar to those of the diverters and will not be described in greater detail.

Each of the diverters contains a bottom sensing sonar which may be directed forwardly at an oblique angle to provide an indication of the depth of water beneath and ahead of the diverter and carries a control system by which the hydrodynamic control surfaces may be adjusted continuously to tend to maintain the depth of water beneath the diverter at a predetermined set value. There may also be a depth sensing system by which the depth of the sweep wires beneath the surface of the water is sensed and a signal sent via an acoustic telemetric link to the minesweeper to enable the length of the kite wire to be adjusted to approximate to that which, for the given speed of travel of the minesweeper, will tend to keep the sweep wire at approximately the correct depth to provide the desired clearance above the sea bed.Thus by heaving and veering the kite wires a coarse depth control is achieved while the bottom sensing control system operating the hydrodynamic control surfaces on the diverters provide a fine control system to maintain the sweep wires accurately at the required distances above the bottom. The diverter also provides cable tension control through the elevator action as well as depth control through rudder /aileron action.

One of the diverters is shown in greater detail in Figures 2 to 5 and it will be seen that it consists of a fuselage 21 which is generally of circular but varying cross-section and which carries a pair of wings 22 and 23 and a fin 24. The wings are sharply swept back and have a small positive dihedral angle as can be seen in Figure 5. The fin which is on the underside of the diverter, (treating the point of attachment of the sweep wire as being on the underside) has an adjustable rudder 25 while each of the wings 22 and 23 has an adjustable elevator or elevon control surface 26. The wing when used as a diverter will be flown through the water with the span of the wings generally vertical so that the rudder 25 will provide the main vertical control while the elevators 26 will provide the main lateral control and some additional roll control if required.

The swept back flying wing construction shown in Figures 6 to 9 provides an alternative construction to that of the delta wing shown in Figures 2 to 5. This consists of a fuselage 31 of circular variable cross-section and two swept back wings 32 and 33 with no fin. The wings have positive dihedral and have a cross-section which varies from adjacent the root to adjacent the tip to provide washout, i.e. to provide that in conditions of stall stall will be initiated adjacent the wing root and progress towards the wing tip; however on the occurrence of stall lift will be reduced and the tendency to stall will therefore be reduced and stable conditions will return.

The tips of the wings are turned down to provide wing tip fins 34, these resisting flow around the tips from beneath to above the wing, strengthening the wing at its fragile tip and providing protection to the hydrodynamic control surfaces when the diverter is stored aboard ship or is being handled during deployment and recovery. Each of the wings is provided with an elevon 36 by which the diverter may be controlled.

The adjustable control surfaces of the diverters shown in Figures 2 to 9 are operated by actuators under the control of control systems incorporating computing means and arranged to adjust the control surfaces in dependence upon on board motion sensors and command signals received by the diverter, either from on board sensors or exterior command signals; for example from the sonar or motion sensors. Means may be provided for supplying to the computing means desired values which may be transmitted from the minesweeper for the clearance above the bottom at which the diverter is to fly and possibly controlling the lateral distance at which the diverter flies from the vertical plane containing the kite wire and the minesweeper, and hence the cable tension.

Claims

Claims:

1. Apparatus for sweeping a body of water comprisirg a towing cable, depressor means at one end of the towing cable and a sweep cable extending from adjacent the depressor to divert means, characterised in that the diverter means includes controllable hydrodynamic surfaces, signal receiving means and motor means for adjusting the hydrodynamic surfaces in response to received signals.

2. Apparatus as claimed in claim 1 which includes depth sensing means coupled to the hydrodynamic surfaces to control the depth of operation of the diverter means.

3. Apparatus as claimed in claim 2 in which the depth sensing means includes a depth sensor located adjacent the depressor means, transmission means to transmit a signal from the depth sensor te the diertr means and contrcl means to adjust the hydrodynamic surfaces to maintain the sensed depth at a set value.

4. Apparatus as claimed in claim 1 or claim 2 or claim 3 in which the diverter means is arranged to maintain a depth relative to the depressor means such that the seep cable is substantially horizontal.

5. Apparatus as claimed in claim 1 which includes bottom sensing means arranged to adjust the hydrodynamic surfaces to maintain the diverter means at C redetermined distance above the bottom.

6. Apparatus as claimed in claim 5 in which the sensing means is mechanical and includes a bottom contactor.

7. Apparatus as claimed in claim 5 in which the sensing means includes a signal transmitting and reflected signal sensing device.

8. Apparatus as claimed in claim 7 in which the bottom sensing means is located in or adjacent the diverter means.

9. Apparatus as claimed in claim 7 in which the bottom sensing means is located adjacent the depressor means and includes signal transmission means to the diverter means.

10. Apparatus as claimed in any of claims 2 to 9 in which the sweep cable is provided with an additional depth control device having hydrodynamic surfaces at one or more points intermediate its length and the depressor means has controllable hydrodynamic surfaces.

11. Apparatus as claimed in any of the preceding claims in which the diverter means comprises a wing with hydrodynamic control surfaces and is arranged to operate, when in use, with the plane of the wing approximately vertical so that the lift provided by the wing as it is towed through the water acts to divert the sweep cable generally outwards from the depressor means.

12. Apparatus as claimed in claim 11 in which the diverter means has sweep back wings, is tailess and has elevons.

13. Apparatus as claimed in claim 12 in which the wings are provided with a positive dihedral angle.

14. Apparatus as claimed in claim 13 in which the wings are provided with washout.

15. Apparatus as claimed in claim 14 in which the washout is effected by a change in the cross-sectional form of each wing from the root area to the tip area.

16. Apparatus as claimed in claim 15 in which the washout is provided by a progressive change in section of each wing from a region adjacent the root to a region adjacent the tip.

17. Apparatus as claimed in claim 14 in which the washout is provided by a twist of each wing.

18. Apparatus as claimed in any of claims 12 to 17 in which the wing tips carry fins extending generally perpendicular to the spanwise axis.

19. Apparatus as claimed in claim 18 in which the fins extend only downwardly.

20. Apparatus as claimed in claim 11 in which the diverter means is in the form of a delta wing with a vertical fin having a rudder control surface and having an elevator control surface on each half wing.

21. Apparatus as claimed in claim 20 in which the delta wing has positive dihedral.

22. Apparatus as claimed in claim 21 modified substantially as described herein with reference to Figures 6 to 9 of the accompanying drawings.

22. Apparatus for sweeping a body of water comprising a sweep cable connected to a submersible vehicle having controllable hydrodynamic surfaces, bottom sensing means, and control means for adjusting, in dependence on the sensing, the surfaces to tend to maintain the distance between the vehicle and the bottom at a set value.

23. A submersible vehicle comprising wing means, anchorage means for a sweep cable, controllable hydrodynamic surfaces and means for receiving signals by which the surfaces are controlled.

24. A vehicle as claimed in claim 23 in which the signal receiving means forms part of a depth or bottom sensing means.

25. A vehicle as claimed in claim 23 which has means for receiving command signals instructing the vehicle of the sea bed clearance to be maintained, means for sensing the sea bed clearance and means for adjusting the hydrodynamic surfaces to maintain the commanded sea bed clearance.

26. A vehicle as claimed in claim 25 in which the adjusting means comprises a computer.

27. A vehicle as claimed in any of claims 23 to 26 in which the wing means comprises a pair of sweep back wings, the hydrodynamic surfaces are elevons and the vehicle is tailess.

28. A vehicle as claimed in any of claims 23 to 26 in which the wing means are afforded by a delta wing and which includes a vertical fin and the hydrodynamic surfaces comprise a rudder control surface on the fin and an elevator control surface on each half wing.

29. A submerisble vehicle constructed and arranged to operate substantially as described herein with reference to the accompanying drawings and with specific reference to Figures 2 to 5 thereof.

30. A submersible vehicle constructed and arranged to operate substantially as described herein with reference to the accompanying drawings and with specific reference to Figures 6 to 9 thereof.

31. Apparatus for sweeping a body of water constructed and arranged to operate substantially as described herein with reference to Figures 1 to 5 of the accompanying drawings.

32. Apparatus as claimed in claim 31 modified substantially as described herein with reference to Figures 6 to 9 of the accompanying drawings.

AMENDMENTS TO THE CLAIMS HAVE BEEN FILED AS FOLLOWS.

1. Apparatus for sweeping a body of water comprising a towing cable, depressor means at one end of the towing cable and a sweep cable connected to the depressor and extending to diverter means, comprising a wing which has hydrodynamic control surfaces and is arranged to operate, when in use, with the plane of the wing approximately vertical so that the lift provided by the wing as it is towed through the water acts to divert the sweep cable generally outwards from the depressor means, the diverter means including controllable hydrodynamic surfaces, signal receiving means and motor means for adjusting the hydrodynamic surfaces in response to received signals.

3. Apparatus as claimed in claim 2 in which the depth sensing means includes a depth sensor located adjacent the depressor means, transmission means to transmit a signal from the depth sensor to the diverter means and control means to adjust the hydrodynamic surfaces to maintain the sensed depth at a set value.

4. Apparatus as claimed in claim l-or claim 2 or claim 3 in which the diverter means is arranged to maintain a depth relative to the depressor means such that the sweep cable is substantially horizontal.

5. Apparatus as claimed in claim 1 which includes bottom sensing means arranged to adjust the hydrodynamic surfaces to maintain the diverter means at a predetermined distance above the bottom 6. Apparatus as claimed in claim 5 in which the sensing means is mechanical and includes a bottom contactor.

11. Apparatus as claimed in any of the - preceding claims in which the diverter means has sweep back wings, is tailess and has elevons.

12. Apparatus as claimed in claim 11 in which the wings are provided with a positive dihedral angle.

13. Apparatus as claimed in claim 12 in which the wings are provided with washout.

14. Apparatus as claimed in claim 13 in which the washout is effected by a change in the crosssectional form of each wing from the root area to the tip area.

15. Apparatus as claimed in claim 14 in which the washout is provided by a progressive change in section of each wing from a region adjacent the root to a region adjacent the tip.

16. Apparatus as claimed in claim 13 in which the washout is provided by a twist of each wing.

17. Apparatus as claimed in any of claims 11 to 16 in which the wing tips carry fins extending generally perpendicular to the spanwise axis.

18. Apparatus as claimed in claim ri ln~hich the fins extend only downwardly.

19. Apparatus as claimed in any of claims 1 to 10 in which the diverter means is in the form of a delta wing with a vertical fin having a rudder control surface and having an elevator control surface on each half wing.

20. Apparatus as claimed in claim 19 in which the delta wing has positive dihedral.

21. Apparatus for sweeping a body of water constructed and arranged to operate substantially as described herein with reference to Figures 1 to 5 of the accompanying drawings.