GB1596275A - Underwater vehicles - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO UNDERWATER VEHICLES (71) We, NATIONAL RESEARCH DE VELOPMENT CORPORATION, a British Corporation established by Statute, a Kingsgate House, 66-74 Victoria Street, London, S.W.1., do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The invention relates to underwater vehicles and in particular but not ex clusively to underwater vehicles designed to be towed behind a surface vessel at any required depth beneath the surface.

Vehicles of this type are in widespread use for such purposes as oceanographic re search, and underwater search operations.

When used for search operations such vehicles are frequently equipped with underwater television, sidescan sonar and other detection devices.

For the use described above it is desir able to maintain as high a towing speed as possible in order to minimize the time taken to cover the area in question. It is also desirable that the vehicle follows a steady course behind and below the towing vessel, in order that its position relative to the vessel will be known at all times.

One problem in the operation of such vehicles is that the inclination of the tow ing cable down to the vehicle will give rise to hydro-dynamic forces tending to lift the cable as well as drag it rearwards. The magnitude of this force will be increased with cable length and with the square of the towing speed as a general approxima tion. It follows that the upforce over the total length of a cable measured in hundreds of metres, as could be required for a seabed search in the deep ocean, will be considerable and all this upforce must be counteracted by an equal downforce on the vehicle if the vehicle is to remain at the depth required.

It can be seen that the downforce that the actual vehicle can provide will con statute a limiting factor in respect of the towing speed and depth. Alternatively it will provide a limitation to the rate at which a given area of seabed in deep water can be covered during a search or survey operation.

Towed underwater vehicles in current use, commonly referred to as "fish", provide the downforce referred to by various methods two of which are as follows.

One such method is to build sufficient weight into the vehicle for the required downforce to be exerted due to gravity.

This method has the advantage of providing a downforce that is consistently acting vertically downwards irrespective of the attitude or inclination of the vehicle. One disadvantage of the method is that the massive weight involved is likely to require powerful deck machinery in order to lift the vehicle from the water, particularly in a heavy sea.

The alternative method in us is to utilise the hydrodynamic forces that are available due to the forward speed of the vehicle through the water. This is achieved by either constructing the body of the vehicle of a suitable shape, to produce a downforce, or attaching to it hydrofoil vanes or inverted "wings", which in themselves provide this downforce. In either application, the principle is that of producing a net force due to pressure variation between the upper and lower surfaces of the body, or the vanes etc., in a manner similar to the operation of an aircraft wing section.

Clearly the force so produced will only act in a downward direction when the vehicle is horizontal and the basic disadvantage of applying this principle to underwater vehicles is that in practice such vehicles will have very little constraint in the roll and pitch planes. Satisfactory compensation for these stability defects may involve considerable development testing, and even then the installation of a gyro stabiliser or similar complication in the form of stabilising or guidance devices is still usually required.

It is an object of the present invention to provide an underwater vehicle in which at least some of the above disadvantages are reduced or avoided.

The invention relies upon the Magnus effect according to which if a fluid flow moves across a spinning cylinder a force is generated normal both to the direction of flow and to the axis of rotation of the cylinder. This force results from the relatively high pressure produced at that side of the cylinder rotating into the flow and the relatively low pressure produced at that side of the cylinder rotating in the same direction as the flow. A cylinder arranged to operate in this way is generally referred to as a Magnus rotor. Although a right circular cylinder is usually the preferred shape for the rotor, any other suitable shape may be used instead if desired, and unless the particular context indicates otherwise references in the Specification to a Magnus rotor or to the "curved surface" of such a rotor are to be understood as embracing these alternative shapes.

According to the invention there is provided an underwater vehicle having a hull to carry a load for underwater operation and including at least one Magnus rotor to impart down forces on the vehicle and exfending from a surface of the vehicle structure, the surface providing a baffle surface at least at one end of the rotor which surface is rotationally decoupled from the rotor and projects beyond the curved surface of the rotor to discourage or prevent fluid flow over the end faces of the rotor.

The effect of the rotational decoupling is of course to allow relative rotation between the rotor and the baffle surfaces.

A rotationally decoupled baffle surface as referred to above may be provided in a variety of ways, for example as a flange on the end of an axial support for the rotor, as a "free-wheeling" plate supported at one end of the rotor, or as a stationary side wall at which one end of the rotor may or may not be supported. One example of this latter method is to have the rotor mounted between the twin hulls of an underwater vehicle of catamaran structure. Experiments indicate that where a plate or flange is used, the diameter of the plate or flange should preferably be between two and three times the diameter of the rotor section adjacent to the said end plate or flange.

Conveniently, the mass and distribution of mass within the rotating members is such as to confer a stabilising effect by means of gyroscopic action as normally defined in engineering texts.

Preferably the speed of rotation of the Magnus rotor(s) can be controlled from the towing vessel in order to permit control of the depth at which the vehicle travels.

In embodiments of the invention where one or more Magnus rotors are associated with each side of the vehicle, means are preferably provided whereby the speeds of rotation of the rotor or rotors on one side of the vehicle can be varied relative to those of the corresponding rotor or rotors on the opposite side, thus providing control of the vehicle attitude about the roll axis.

In embodiments of the invention which incorporate two or more Magnus rotors rotatable about separate axes arranged in tandem, the rotors are suitably spaced from front to rear of the vehicle, and means are provided such that in operation the rotational speed of the or each rotor nearer to the front of the vehicle can be varied relative to that of the or each rotor nearer to the rear of the vehicle, thus provided control of the vehicle attitude about the pitch axis.

Because with the vehicle of the present invention the baffles are rotationally decoupled from the rotor, they add little or nothing to the power requirements for the rotor drive. This means that the baffles can be significantly larger than would be acceptable if they were rigidly connected with the rotor This in turn may allow the use of shorter and fatter rotors than has previously been proposed. Such rotors have a better resitance to bending and this is an important practical consideration in view of the considerable bending loads to which they will be exposed in use.

It will be appreciated that in order to be able to exert a downforce, the vehicles of the present invention must have driving rotors that are horizontal, near horizontal, or at some other substantial angle to the vertical e.g. 300-Si00, In addition to these driving rotors, other Magnus rotors, for example vertical rotors, may also be provided and it is preferable that these additional rotors should also be provided at their ends with decoupled baffle surfaces.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 shows a longitudinal section of one end of a hollow rotor provided with a baffle surface by its axial support; Figures 2 and 3 show similar longitudinal sections of embodiments in which a baffle surface is provided by a free-wheeling disc fitted on the end of the rotor; Figure 4 shows a perspective view of an underwater vehicle using the rotor/baffle arrangements shown in Figures 1 to 3; Figures 5, 6 and 7 show plan, side and perspective views of an underwater vehicle in which baffle surfaces are provided by the inside walls of two interconnected hulls which also provide bearing supports for the rotors; Figure 8 is a detail of a drive mechanism for use in the vehicle shown in Figures 5 to 7;; Figures 9 and 10 show variations of the vehicle shown in Figure 4; Figures 11 to 13 show alternative towing harnesses for use with the vehicle shown in Figures 5 to 7; Figure 14 shows a modification of the vehicle shown in Figures 5 to 7 and the towing harness shown in Figure 13; Figure 15 shows a variation of the embodiment of Figures 5 to 7; and Figures 16 and 17 show perspective views of vehicles according to the present inventtion but with alternative rotor configurations.

The same reference numerals have been used in the different Figures to indicate like parts in the embodiments illustrated in these Figures.

Thus referring first to Figure 1, reference number 10 indicates a rigid non-rotatable support in the form of a bar or beam secured to the body of an underwater vehicle (not shown). The beam carries a bearing 12 to support the free end of a hollow Magnus rotor 14. In accordance with the present invention, the support 10 is provided with an end disc 18 which provides a baffle surface projecting beyond the curved surface of rotor 14 to discourage or prevent fluid flow over the related end face of the rotor. The full diameter of the end disc is not shown by Figures 1 to 3.

In the arrangement shown in Figure 2, the rotor does not need to be hollow and the end disc 18 providing the baffle surface is this time provided with a hollow hub portion 20 mounted on bearings 22, 23.

Hub portion 20 is housed in a recess 25 in the end of the rotor and the bearings 22, 23 are supported on a central spindle 27 screwed or otherwise secured into the rotor to provide a rigid connection. In operation, when rotor 14 rotates, the end disc 18 will be able to "free-wheel" on bearings 22, 23 so as to discourage or prevent fluid uow over the end face of the rotor. It is likely that in practice the rotor will be made hollow for other reasons, in which case spindle 27 will be secured by a suitable bush or insert.

Figure 3 shows a modification of the previous arrangements in which the bearings 22, 23 engage the outside surface of hub portion 20 which is here made solid to form a spindle 27. Obviously in this case a pin or similar device (not shown) must be provided to lock the spindle 27 against axial movement.

Experiments indicate that the optimum diameter of end plates 18 in Figures 1 to 3 is two to three times the diameter of the rotor section adjacent to the said end plate.

Figure 4 shows an underwater vehicle 28 having Magnus rotors fitted with end discs 18 in any of the ways illustrated in Figure 1 and 3. Reference numeral 29 indicates a connector for the towing cable 30. Conveniently, connector 29 will provided one part of a pinned or universal joint the other part of which will be provided by the associated fitting on the towing cable. An alternative arrangement would be to provide a rigid tow staff projecting from the vehicle body, with a pinned or universal joint forming the upper termination of this projecting element.

The main body of the vehicle 28 can be of any suitably streamlined shape but it is preferable that the shape be one that does not generate appreciable forces perpendicularly to the rotor axis (YY) and the vehicle axis (XX) when the vehicle is set at a small angle of incidence to the relative flow (V) over the vehicle body.

The Magnus rotors 14 projecting from either side of the main body may be of slender cylindrical shape, or any alternative shape that will maintain the Magnes effect.

In a variation shown in Figure 9, a second pair of rotors (14) is fitted at the rear of the vehicle to provide a method of increasing the total downforce generated by the vehicle. These additional drive rotors will be provided with end discs fitted in any of the ways shown in Figures 1 to 3. Means are preferably provided for independently driving the two sets of rotors so that the relative speed of rotation of shafts to the front and to the rear of the vehicle can be varied to enable a powerful and highly responsive degree of pitch control to be exercised upon the vehicle with no further requirement for moving parts.

In another variation of the embodiment shown in Figure 10, additional rotors (14") are again provided but this time only for use in making small adjustments to the trim or level attitude of the vehicle body, substantially all the downforce on the vehicle being provided by the driving rotors 14. Although in Figure 10 the "trimming" rotors 14" are shown behind the driving rotor 14 they could if desired equally will be fitted in front of the driving rotors.

Alternatively or additionally, drive means may be provided for rotating the rotors upon opposite sides of the vehicle body with a difference in rotational speed relative to one another. By this means a powerful and highly responsive degree of roll control can be exercised upon the vehicle.

Where differential control of the rotor speeds is to be provided for pitch and/or roll control in the manner described above, then the relative speed control should preferably be fairly precise if the full advantage of the vehicle's inherent stability is to be obtained.

Turning now to Figures 5 to 7 these show an underwater vehicle 28 of catamaran structure comprising twin hulls 32, 33 fitted with vertical tail fins 35, 36 and horizontal stabilizer fins 38, 39. Reference numeral 41 indicates a hollow rotor and numeral 81 indicates connecting bars which are rigidly secured to each hull from which they project towards the rotor centre as shown by Figure 5. They are rigidly interconnected by means of cross struts 43 and a load carrying cylindrical housing 82, thus serv ing to rigidly interconnect the twin hulls of the catamaran structure at that point.

The hollow rotor 41 is mounted on bear ings (not shown) at the connecting bars 81, such that the interconnection structure comprising cross struts 43 and housing 82 are contained within the cylindrical envel ope of the said rotor.

An electrical or hydraulic motor 45 is installed within the cylindrical housing 82.

Drive from this motor is transmitted by means of gear wheels, or a belt drive or both, to an internal ring gear "(53)" formed on the inside surface of the rotor.

The rotor, thus driven, can be rotated to impart a downforce on the vehicle 28.

The ingress of water into the rotor is prevented by suitable rotating shaft seals (not shown) adjacent to the bearings at 83.

This arrangement for mounting the motor within the rotor is chosen to save space within the hull and avoid the need to depart from the preferred narrow width of the hull in order to accommodate the length of a transverse mounted motor. The arrangement shown also permits the bearings, and seals of the rotor to act on a small diameter and thus minimise power losses due to mechanical bearing and seal friction.

A second hollow rotor 47 is mounted between fins 35, 36 on bearings (not shown) supported on a second set of cross struts 49. A second motor 51 is used to rotate rotor 47 in either direction. Rotor 47 is intended principally for use as a trimming rotor which will give a fine control for trimming the vehicle when it is subject to pitch and in this first case rotor 47 will operate in an analogous fashion to rotors 14" in the embodiment of Figure 10. Alternatively, rotor 47 can take the form of a second driving rotor and in this second case it will operate in an analogous fashion to rotors 14' in the embodiment of Figure 9.

The downforce on the twin hull vehicle can thus be provided either solely by the rotor 41 (first case) or by the combined effects of both rotors (second case).

It will be appreciated that in accordance with the present invention, both rotors 41 and 47 have baffle surfaces provided by the inside walls of hulls 32, 33 and fins 35, 36 which will be effective to discourage or prevent fluid flow over the ends of the rotors.

Figure 8, which is section taken on line VIII-VIII of Figure 5, shows three of the cross struts 43 referred to above. A suitable mounting plate (not shown) carries bearings on which is mounted an idler 55.

This engages with an internal ring gear 53 formed on the inside of the rotor and with a pinion 57 of the motor 45. Rotor 47 can be mounted and driven in an identical fashion to rotor 41 so that apart from a change in scale and reference numerals, Figure 8 also represents a cross-section taken across rotor 47 along a continuation of the line VIII-VIII shown in Figure 5.

It will be appreciated that Figure 8 does not show the only mechanical arrangement for mounting or driving the rotors. Gener ally speaking, however, as indicated in Fig ure 8, it will usually be preferable to have the motor and any support beams housed within the envelope of the rotor.

For simplicity, the towing harness for the twin-hull vehicle is indicated only in Figure 7. The harness 59 is of inverted U-shape and is pivotally connected to the twin hulls of the vehicle 28 at 61, 63. A third con nector (29) is provided at the top of the harness for connection with a towing cable 30.

Figures 11 to 13 illustrate alternatives to the harness 59. In these Figures reference numeral 65 indicates a pulley (a fixed connection can be used instead if desired), reference numeral 67 indicates a cross beam and reference numeral 69 indicates an annular attachment plate.

Figure 14 shows a modification of the previous design in which the driving rotor is split into two parts, 14A and 14B. In this case, the attachment place can take the form of a disc 71 e.g. secured to a stationary support structure (not shown) inside the rotors and provision may also be made for driving the rotor halves at different rotational speeds so as to provide roll control for the vehicle.

It will be appreciated that the attachment plates shown in Figures 13 and 14 can also serve as baffles which will avoid any obstruction near the rotor surface that would lead to a disturbance of the smooth flow of the rotor.

Figure 15 shows a variation of the embodiment shown in Figures 7 to 9 in which the rotor 47 of that embodiment is replaced by an aerofoil surface 74.

It will be understood that the embodiment shown in 5 to 7 and 15 and the variations discussed above with reference to Figures 11 to 14 can all be extended to include a plurality of longitudinal bodies, suitably separated, together with a plurality of Magnus rotors which either bridge the spaces between the bodies, or project as cantilever beams from them, or are incorporated in both forms. It would for example be possible to link three hulls together with the rotor or rotors bridging the gap on each side between the central hull and the side hulls e.g. a trimaran structure.

Figure 16 shows an embodiment in which the horizontal driving rotors are supplemented by vertical rotors (76) each provided with a decoupled end plate 18. The purpose of this modification is that a side force can be generated upon the vehicle without the need for the Y-Y axis (see also Figure 4) to depart from the horizontal, as would be the case if the vehicle was rolled or tilted.

The direction of this side force, and its magnitude, can be controlled by variation of the direction and speed of rotation of the vertical rotors. This control is completely independent of the vehicle downforce which is controlled by the horizontal rotors.

The ability to move the vehicle sideways while under tow, without the attendant need to roll or tilt the vehicle, may be of advantage in sidescan sonar operations, since the sonar transducer units can be rigidly mounted within the vehicle and will scan in the same direction, relative to the horizontal, throughout the operation.

In this application the axis of the vertical Magnus rotors would be as near as possible to the axis of the horizontal rotors. This provision would ensure that any sideways force generated by the rotors would tend to move the vehicle bodily sideways without any change in vehicle heading. This mode of action is in contrast with that of a rudder, which is mounted as far to the rear of the vehicle rotational centre as possible, and which generates a sideforce only for the purpose of changing the vehicle heading. Thus the Magnus rotor, when mounted near to the vehicle centre of rotation in yaw, will cause the vehicle to move in the same direction as the force produced. By contrast a rudder (incorporating a Magnus rotor or otherwise) will cause the vehicle to yaw and subsequently move in a direction opposite to that of the force produced.

If desired a series of such vertical rotors can be employed.

Figure 17 shows a four-rotor vehicle in which the rear rotors (80) are downwardly inclined at a small angle to the horizontal to produce what may be termed a reversed dihedral effect, and the front drive rotors 78 remain in the horizontal plane but are inclined at a small angle to the transverse Y-Y axis in order to produce a sweepback effect. Although both the dihedral and the sweepback effects are shown by the inclination of the rotors in Figure 17 by way of illustration, in practice such a vehicle is more likely to adopt a common system for both sets of rotors, or to introduce these inclined rotor variations for one set of rotors only.

In order better to understand the operation of the embodiments so far described, reference should be made in particular to Figures 4, 9 and 10 which show (for the single hull version) the use of one set of driving rotors (Figure 4), the use of a further set (Figure 9) and the use of trimming rotors (Figure 10).

Referring then to these three Figures, the driving rotors 14 (and 14') will be spun in the direction r such that the velocity of the relative flow V passing across them by virtue of the forward speed of the vehicle will produce a downward acting force L which acts upon them and thus depresses the vehicle. Reference letter T indicates the towing force on the vehicle.

For satisfactory stability it is essential that the greater proportion of the hydrodynamic downforce is provided by the driving rotors, and as little as possible by the main body of the vehicle. It is therefore important that the positioning of the driving rotor axis in relation to the towing point should be such that the main downforce generated by the driving rotors during level towing does not exert any turning moment about the towing point. If only one set of driving rotors is used (Figures 4 and 10) to exert a downforce this will mean that the extended line of the towing cable should preferably pass through the rotor spin axis.If two or more driving rotors in tandem are used (Figure 9) so that the total downward force L on the vehicle is split into two separate components (A and B), a centroid between these rotors would be chosen, such that if tension force T acts through point P of the vehicle then Aa = Bb where a and b are the distances of the rotor axes from point P. In all three cases it is also desirable that the main drag force upon the vehicle body and any further appendages should pass through approximately the intersection points of forces T and L. Generally speaking the driving motor(s) (not shown) should be able to rotate the driving rotors such that the periphery of these rotors attains a linear tangential velocity of the order of between 1.5 and 3.0 times the flow velocity V.

Analogous considerations apply to the variations shown in Figures 16 and 17 and to the multi-hull vehicles exemplified in Figures 5 to 7 and Figure 15. These cases have therefore not been separately considered.

Variations of all the embodiments so far described are envisaged in which controlled flow over one or both ends of a Magnus rotor could be deliberately encouraged to vary the efficiency of that rotor or at one of its ends thereby to introduce another method of control into the vehicle.

As indicated earlier in the Specification, the shape of any Magnus rotors referred to in this Specification need not be confined to that of a circular cylinder with constant diameter along its length. The shape of the section at any position, and the profile measured parallel to the axis of rotation can be of any shape or form that will produce the Magnus effect. If a vehicle of particularly high efficiency as required it may in fact prove desirable to select a sectional shape and axial profile that will provide the best compromise between the downforce produced the shaft power absorbed to turn the rotor, and the additional force needed to propel the vehicle due to the rearward acting drag force induced by the Magnus effect.

Some of the advantages of the vehicle of the present invention over currently available alternatives will already be apparent from the Specification. Generally speaking it can be said that the Magnus rotors used in the vehicles of the present invention can generate a greater downforce for a given forward speed of the vehicle and platform area than most single fixed hydrofoil surfaces of known profile. Moreover this downforce can be controlled, eliminated or even reversed by the simple process of controlling the hydraulic flow or current of electricity to the motor(s), a control system introducing no extra moving parts to the vehicle.Most important of all is the fact that the downforce produced by any rotor will act through the axis of rotation of the said rotor, irrespective of any variation in the pitch of the vehicle however great this variation may be, and also irrespective of the magnitude of downforce required. This property will thus eliminate any of the instability in pitch that takes place due to the point of application of downforce or upforce on a fixed hydrofoil being dependent upon its angle of incidence, as referred to previously. The stability of the vehicle in roll may also be improved by the Magnus rotors since they may provide a gyroscopic stabilising effect provided that the rotational speed and moment of inertia of the rotating masses is sufficiently great and for this reason the moment of inertia of the rotors may be made as high as possible.

The bending loads taken by these rotors in transmitting the downforce to the vehicle will make a high moment of inertia necessary for structural reasons alone.

The vehicles of the present invention are essentially simple to design and construct with no requirement for the production of the accurate contours, profile shape, or highly critical dimensions or angles that would be associated with hydrofoil designs.

The small number of moving parts required can be components proved in the field of marine engineering. The problem of providing the electric motor, running it in a submerged vehicle, transmitting power down the cable, and preventing the ingress of water at great depths have all been solved for other applications of submarine technology.

In operation, such a vehicle may permit a higher towing speed at a given depth, or a greater towing depth at a given speed than existing designs, owing to the more powerful downforce that can be generated for a given size and weight of vehicle. In addition to this actual distance covered may be reduced if it is found that the inherent stability of the vehicle can permit more accurate course and depth maintenance behind the towing vessel with less consequent need for overlapping of parallel search lanes. The ability of this vehicle to be brought rapidly to the surface without the need to winch in the towing cable may also prove to be an advantage for efficient operation, in addition to minimizing the power and strength requirements of any deck machinery upon the towing vessel, and thus widening the choice of suitable vessels.

All the factors described can reduce the time taken to search an area underwater, hence reduce the cost of the operation, reduce the risk of bad weather interfering with the operation, and reduce any danger to life and property that may be involved when an object or submarine craft is the subject of an underwater search operation.

Control and stabilising influences other than those described may be provided by the conventional stabilising fins at the rear of the vehicle.

Although only towed vehicles have been discussed in detail in the Specification, it will be appreciated that the Magnus rotor systems used in these vehicles could equally well be used in self-propelled vehicles and the scope of the present invention is to be interpreted as including this possibility. In the case of a self-propelled vehicle, it is of course essential that the drive rotors should be rotatable in either direction so that the vehicle can be driven up or down by the rotors. This ability to be able to rotate the drive rotors in either direction may if desired also be provided in the towed vehicles already described. The propulsion system for a self-propelled vehicle could be of any suitable conventional form currently available and the rotor drives could for example be radio-controlled, as too could any control flaps or vanes present.

Claims (33)

WHAT WE CLAIM IS:

1. An underwater vehicle having a hull to carry a load for underwater operation and including at least one Magnus rotor to impart down forces on the vehicle and extending from a surface of the vehicle structure, the surface providing a baffle surface at least at one end of the rotor which surface is rotationally decoupled from the rotor and projects beyond the curved surface of the rotor to discourage or prevent fluid flow over the end faces of the rotor.

2. A vehicle as claimed in Claim 1 in which another baffle surface is provided as a flange on the end of an axial support for the rotor.

3. A vehicle as claimed in Claim 1 in which another baffle surface is provided by a free-wheeling plate supported at one end of the rotor.

4. A vehicle as claimed in Claim 2 or Claim 3 in which the flange or plate has a diameter of two or three times the diameter of the rotor section adjacent to the said plate.

5. A vehicle as claimed in Claim 1 in which said baffle surface is provided by a side wall of the vehicle hull.

6. A vehicle as claimed in Claim 5 in which there are two baffle surfaces each provided by a respective one of the twin hulls of an underwater vehicle of catamaran structure.

7. A vehicle as claimed in any preceding claim including a plurality of rotors and in which at least two of the rotors are at a significant angle to the vertical.

8. A vehicle as claimed in any preceding claim including a plurality of rotors and in which at least two of the rotors are horizontal or near horizontal.

9. A vehicle as claimed in any preceding claim including a plurality of rotors and in which at least two of the rotors are inclined rearwardly in the horizontal plane to provide a sweepback effect.

10. A vehicle as claimed in Claim 7 or Claim 8 including one or more additional rotors and each provided with rotationally decoupled baffle surfaces projecting beyond the curved surface of the rotor to discourage or prevent fluid flow over the end of the rotor, the or each said additional rotor being vertical or substantially vertical.

11. A vehicle as claimed in any preceding claim in which one or more Magnus rotors are associated with each side of the vehicle and wherein control means are provided whereby the speeds of rotation of the rotor or rotors on one side of the vehicle can be varied relative to those of the corresponding rotor or rotors on the opposite side, thus providing control of the vehicle attitude about the roll axis.

12. A vehicle as claimed in any preceding claim in which two or more Magnus rotors rotatable about separate axes are arranged in tandem and suitably spaced from front to rear of the vehicle, and wherein control means are provided such that in operation the rotational speed of the or each rotor nearer to the front of the vehicle can be varied relative to that of the or each rotor nearer to the rear of the vehicle, thus providing control of the vehicle attitude about the pitch axis.

13. A vehicle as claimed in any preceding claim including means whereby the speed and direction of rotation of the Magnus rotor(s) can be controlled from the towing vessel in order to permit control of the depth at which the vehicle travels.

14. A vehicle as claimed in any preceding claim in which the mass and distribution of mass within the rotor(s) is such as to confer a stabilising effect by means of gyroscopic action.

15. A vehicle as claimed in any preceding claim including control means whereby controlled flow over one or both ends of a Magnus rotor can be deliberately encouraged to vary the efficiency of that rotor or at one of its ends.

16. A vehicle as claimed in any preceding claim in which the rotors have the form of a circular cylinder with constant diameter along the rotor length.

17. A vehicle as claimed in any preceding claim including control means whereby the downforce generated by the rotor(s) can be controlled, eliminated, or reversed.

18. A vehicle as claimed in Claim 1 and substantially as hereinbefore described and illustrated with reference to Figure 1 of the accompanying drawings.

19. A vehicle as claimed in Claim 1 and substantially as hereinbefore described and illustrated with reference to Figure 2 of the accompanying drawings.

20. A vehicle as claimed in Claim 1 and substantially as hereinbefore described and illustrated with reference to Figure 3 of the accompanying drawings.

21. A vehicle as claimed in Claim 1 and substantially as hereinbefore described and illustrated with reference to Figure 4 of the accompanying drawings.

22. A vehicle as claimed in Claim 1 and subsantially as hereinbefore described and illustrated with reference to Figures 5 to 7 of the accompanying drawings.

23. A vehicle as claimed in Claim 1 and substantially as hereinbefore described and illustrated with reference to Figure 8 of the accompanying drawings.

24. A vehicle as claimed in Claim 1 and substantially as hereinbefore described and illustrated with reference to Figure 9 of the accompanying drawings.

25. A vehicle as claimed in Claim 1 and substantially as hereinbefore described and illustrated with reference to Figure 10 of the accompanying drawings.

26. A vehicle as claimed in Claim 1 and substantially as hereinbefore described and illustrated with reference to Figure 11 of the accompanying drawings.

27. A vehicle as claimed in Claim 1 and substantially as hereinbefore described and illustrated with reference to Figure 12 of the accompanying drawings.

28. A vehicle as claimed in Claim 1 and substantially as hereinbefore described and illustrated with reference to Figure 13 of the accompanying drawings.

29. A vehicle as claimed in Claim 1 and substantially as hereinbefore described and illustrated with reference to Figure 14 of the accompanying drawings.

30. A vehicle as claimed in Claim 1 and substantially as hereinbefore described and illustrated with reference to Figure 15 of the accompanying drawings.

31. A vehicle as claimed in Claim 1 and substantially as hereinbefore described and illustrated with reference to Figure 16 of the accompanying drawings.

32. A vehicle as claimed in Claim 1 and substantially as hereinbefore described and illustrated with reference to Figure 17 of the accompanying drawings.

33. A vehicle according to any one of the preceding claims having at least two Magnus rotors one of which can be operated independently of the operation of another of the plurality of rotors.