WO2009077778A1

WO2009077778A1 - Waterwheel

Info

Publication number: WO2009077778A1
Application number: PCT/GB2008/051147
Authority: WO
Inventors: Simon James Chance Rushbrook Williams
Original assignee: Hydreau Limited
Priority date: 2007-12-18
Filing date: 2008-12-03
Publication date: 2009-06-25
Also published as: CN201972830U; GB0724579D0; CN201818425U

Abstract

A watercraft having two hulls and a waterwheel mounted between the two hulls is disclosed. The watercraft also has a transverse member, which connects the bows of the hulls together and which is shaped to direct water passing between the bows upwards towards the waterwheel. Further embodiments are also disclosed, including watercrafts with a non- linear hull separation, and watercrafts able to regulate their pitch and/or roll. An undershot waterwheel having paddles, each of which comprise a plurality of curved guide members and a blade formed from a flexible sheet is also disclosed. A method of making a waterwheel paddle is also disclosed. Applications of this technology for energy generation and water filtration in the third world are discussed.

Description

"Waterwheel"

The present invention relates to a waterwheel. More particularly, the invention relates to an undershot and/or a "breastshot" waterwheel, which can be used to extract energy from a water flow.

It is known to use a waterwheel to perform mechanical work. The waterwheel is typically located on land, next to a river. The waterwheel is rotated by water flowing in the river. The waterwheel is connected mechanically to grinding apparatus, e.g. to grind corn. An "overshot" waterwheel is a waterwheel in which incoming water is fed to the top of the waterwheel and is carried "over" the top of the waterwheel in buckets. An undershot waterwheel has paddles and is rotated by a current passing past and underneath the waterwheel, impacting on paddles at the bottom of the waterwheel. A "breastshot" waterwheel is a waterwheel in which the incoming water is direct onto the periphery of the waterwheel, below the top of the waterwheel.

According to a first aspect of the present invention there is provided a watercraft having: two hulls, each hull having a bow and a stern; a waterwheel mounted between the two hulls; and a transverse member, which connects the bows of the hulls together and which is shaped to direct water passing between the bows upwards towards the waterwheel.

The transverse member helps to direct more incoming water onto the waterwheel than would otherwise be the case, thereby increasing the power output of the waterwheel. The transverse member also causes an increase in height of the water as it arrives at the waterwheel. Preferably, the upstream end of the transverse member is lower than the downstream end of the transverse member, with respect to the hulls.

In use, the transverse member tends to be inclined with respect to the direction of flow at a negative angle of attack.

Preferably, an upper surface of the transverse member is curved upwards in the direction of flow, to direct incoming water up the transverse member and onto the waterwheel.

Typically, the transverse member is attached to the bottoms of the hulls.

Typically, the transverse member comprises a planar member.

Preferably, the downstream end of the transverse member is located substantially at the waterwheel. It is preferable if the transverse member extends up to the blade tips of the waterwheel.

Optionally, the watercraft includes a stabilizing means to regulate at least one of the pitch and the roll of the watercraft. Hence, the watercraft is more stable, and can keep itself upright in most situations, preferably without any human intervention.

Optionally, the stabilizing means comprises a horizontal level control to regulate the pitch of the watercraft.

Optionally, the horizontal level control includes: a horizontal level sensor; computing means, which receives information from the horizontal level sensor; and a feedback system which is controlled by the computing means and adjusts the orientation of the watercraft so as to regulate the pitch of the watercraft.

Additionally or alternatively, the stabilizing means may comprise the shape of the hulls, which increase in width with increasing upwards height out of the water. Hence, if the watercraft starts to pitch or roll, a larger portion of the hull in the direction of pitching/rolling becomes submerged in the water, creating a large buoyancy force which counters the pitching or rolling motion, and acts to push the watercraft upright again.

Preferably, at the bows of the hulls, the separation of the inwardly-facing sidewalls of the hulls is greater at the tips of the bows than at the waterwheel and the inwardly-facing sidewalls at the bows are curved, such that the separation of the hulls varies non-linearly with distance towards the waterwheel.

This reduces the turbulence of the water when it enters the space between the hulls.

Preferably, the curvature of the inwardly-facing sidewalls of the bows is convex near the tips of the bows, and concave downstream of the convex region, between the convex region and the waterwheel.

This convex-concave shape causes the water that flows into the space between the bows first to accelerate, and then to pile up to form a wave. This causes an increase in the height of the water impacting on the waterwheel. The wave might break on the waterwheel or just in front of it, which means the energy of the breaking wave is directly used to turn the waterwheel and is not wasted.

The smooth curves at the bow tips and in the convex regions minimizes any wave breakage too far in front of the waterwheel, e.g. on/at the bow tips. Preventing waves from breaking on the bow tips conserves energy in the incoming water - the less wave breakage, the more energy remains in the water when it reaches the waterwheel. Another advantage of preventing waves from breaking at the bow tips is such breakage tends to cause turbulence which could destabilize the watercraft.

The overall shape of the bows provides a smaller amount of turbulence for a given flow of incoming water.

According to a second aspect of the invention there is provided a watercraft having: two hulls, each hull having a bow and a stern; and a waterwheel mounted between the two hulls; wherein, at the bows of the hulls, the separation of the inwardly- facing sidewalls of the hulls is greater at the tips of the bows than at the waterwheel, with the inwardly-facing sidewalls at the bows being curved, such that the separation of the hulls varies non-linearly with distance towards the waterwheel.

Hence, not all embodiments include a transverse member.

Preferably, the curvature of the inwardly-facing sidewalls of the bows is convex near the tips of the bows, and concave downstream of the convex region, between the convex region and the waterwheel. According to a third aspect of the present invention there is provided a watercraft having: two hulls, each hull having a bow and a stern; a waterwheel mounted between the two hulls; and a stabilizing means to regulate at least one of the pitch and roll of the watercraft.

Hence, not all embodiments of the invention have a transverse member or a non-linearly varying separation of the hulls.

This allows for the effect of the transverse member to be compensated for, as the water velocity changes and its effect alters. Also, it reduces the effect of the torsional bow dip caused by a blade of the waterwheel leaving the water, and keeps the blade in the water longer, thereby increasing the energy extraction. Such a system also reduces the required hull length for stability and reduces the overall weight and cost of the watercraft.

Optionally, the horizontal level control includes: a horizontal level sensor; computing means, which receives information from the horizontal level sensor; and a feedback system which is controlled by the computing means and adjusts the orientation of the watercraft so as to regulate the pitch of the watercraft. Optionally, the watercraft includes two adjustable hydroplanes, one on each hull, and the feedback system adjusts the orientation of the watercraft by adjusting the orientation of the hydroplanes.

Alternatively or additionally, the stabilizing means comprises the shape of the hulls, which increase in width with increasing upwards height out of the water.

Optionally, a portion of each hull is wedge-shaped, the thickness of the wedge increasing with increasing height out of the water, and the buoyancy of the watercraft is selected such that the water level is between the upper and lower ends of the wedge. Hence, if the watercraft starts to roll in one direction, a larger part of the hull will become more submerged, creating a large buoyancy, counter-balancing, upth rust force. Simultaneously, on the other side of the watercraft, the hull has risen relative to the water, leaving a smaller part of the hull in the water to reduce the upthrust on that opposite side.

Optionally, each hull has a hydroplane on its outside edge. The hydroplanes are typically provided on the bows.

By "hydroplane", we mean a winglike structure, attached to the hull of the watercraft.

Preferably, the hydroplanes have a lower surface that is angled with respect to the hulls, the lower surface sloping downwards in the direction of flow.

In use, the hydroplanes tend to be inclined with respect to the direction of flow, at a positive angle of attack. Water travelling past the transverse member tends to provide a downwards thrust to the bows of the watercraft. The hydroplanes can provide an upwards thrust to counter this downwards thrust.

Typically, the hydroplanes each have a fixed body and a moveable flap, and the angle of the flap can be adjusted with respect to the fixed body, to provide a thrust force.

Typically, the moveable flaps of the hydroplanes are provided at downstream ends of the hydroplanes.

Hence, the moveable flaps can be adjusted, like aeroplane wings, to provide upwards and downwards thrust forces, as required. The amount and direction of thrust can be controlled, by varying the moveable flaps. If the flaps are moved downwards, this creates an upthrust. If the flaps are moved upwards, this creates a downthrust. In some embodiments, the size of the flaps and their range of movement means that the maximum downthrust generatable by the flaps can more than balance the upthrust created by the positive angle of attack of the hydroplanes. However, this is not essential.

The combined effect of the transverse member and the hydroplanes is to cause an increase in height of the water as it arrives at the waterwheel. This tends to create a "breastshot" waterwheel, as opposed to a purely "undershot" waterwheel. This leads to a higher extraction of water energy, as well as increasing the volume of water through the waterwheel.

Optionally, the watercraft includes a hydraulic pump arranged to be driven by the waterwheel, the hydraulic pump being connected to a hydraulic system via hydraulic flowpaths, such that energy from the waterwheel is converted into a hydraulic output which can be used to power the hydraulic system.

The hydraulic system could be a motor, for example, which can be used to power e.g. a refrigerator.

Preferably, the waterwheel is connected to a hydraulic accumulator and a cut-off regulator.

Optionally, when the available power produced by the waterwheel is less than the power demand of the hydraulic system, the cut-off regulator cuts off power output from the waterwheel to the hydraulic system, and the waterwheel is arranged to charge the accumulator instead, the accumulator being arranged to deliver power to the hydraulic system after being charged.

Hence, if the supply is less than the demand, the power reaching the hydraulic system is always sufficiently high (e.g. 50 Hz at 240 Volts when converted into electric power), instead of the power decreasing with any decrease in water current.

Optionally, when the available power produced by the waterwheel is greater than the power demand of the hydraulic system, the waterwheel is arranged to charge the accumulator with the excess power not required by the hydraulic system, the accumulator being arranged to deliver power to the hydraulic system in the case of the available power produced by the waterwheel becoming less than the power demand of the hydraulic system. Hence, if the supply is generally greater than the demand, having power stored in the accumulator enables there to be no drop in delivered output due to sudden wind shear or passing boat wake disrupting the waterwheel.

Optionally, the hydraulic pump is incorporated into the centre of the waterwheel hub. Optionally, the waterwheel is mounted on the watercraft by a support, part of which also provides a flowpath for the hydraulic fluid.

Alternatively, a respective hydraulic pump is provided in each hull.

These arrangements allow a balanced weight distribution of the pump on the watercraft.

Alternatively, the watercraft may include a water pump arranged to be driven by the waterwheel, the water pump being connected to a conduit system, arranged to pump water from a body of water on which the watercraft is floating to shore.

Optionally, the conduit system is connected to a filtration system, e.g. for providing drinking water. Optionally, the conduit system may also provide water for irrigation and/or any other desired use.

The above uses may be particularly beneficial for energy generation in the third world, in converting energy from a river to either drive a hydraulic system or for providing fresh drinking water. The watercraft may be left tethered and has no running costs, since it is providing energy from a renewable source. Optionally, the watercraft includes a flow sensor on each hull and a wheel rotation sensor, and the outputs from these sensors are monitored by a computing means.

The flow sensors may be located, e.g. on the bows.

Typically, the watercraft includes a stern rudder, provided on the stern of one of the hulls. Optionally, a respective stern rudder is provided on the stern of each hull.

Optionally, the stern rudder is hydraulically powered and is controllable by the computing means, in response to signals from the flow and wheel rotation sensors.

Preferably, the watercraft includes lifting apparatus adapted to raise and lower the waterwheel, such that the extent of submersion of the waterwheel can be varied.

Optionally, the lifting apparatus is controllable by the computing means in response to signals from the flow and wheel rotation sensors.

Typically, the waterwheel has paddles, each paddle comprising a respective blade.

Preferably, at least one paddle is curved when viewed parallel to the rotational axis.

The curvature of the blade reduces the amount of water lifted by the paddle on leaving the water. Hence, the waterwheel is energy efficient. Typically, all paddles comprise curved blades. Optionally: the paddles are rotatable about the rotational axis of the waterwheel; each blade is formed from a flexible sheet; each paddle also includes a plurality of guide members that are curved when viewed parallel to the rotational axis; and the guide members are located in two rows adjacent to the front and rear surfaces of the blade respectively, the guide members causing the blade to adopt a curved shape corresponding to the curved guide members.

Typically, the guide members are spines. By spine, we mean a pin-like, elongate member.

Such embodiments have two advantages. Firstly, the paddles can be very light, which improves the energy efficiency of the waterwheel. Secondly, the paddles can be flat-packed for transportation more efficiently.

Optionally, the curvature is a parabola.

Alternatively, the curvature becomes steeper towards the tip of the blade.

Optionally, at least one blade is curved when viewed along the radial direction.

This increases the volume of water which the blade can hold, thus increasing the effective cross-sectional area presented to the water, and the energy extracted. Preferably, the hulls are shaped such that the flowpath along the outwardly-facing sidewall of each hull is greater than the flowpath along the inwardly-facing sidewall.

Thus, the hulls act as aerofoils, and the watercraft will tend to move towards the fastest flowing current, keeping the watercraft in an optimum position to obtain a large amount of power from the current, within the limits of any tethered restraint.

Typically, at the rear of the watercraft, the hulls are shaped such that the separation of the inwardly-facing sidewalls of the hulls increases with distance away from the waterwheel.

Preferably, the bows are connected to the rest of the hulls at a hinged connection, the bows being pivotable upwards about the hinged connection, relative to the rest of the hulls.

Preferably, the watercraft includes lifting apparatus, adapted to pivot the bows about the hinged connection, to lift the bow tips and the transverse member out of the water.

This allows the transverse member to be lifted clear of the water, e.g. to help clear an obstruction, e.g. debris, which could have become stuck between the hulls, impeding the current flow between the hulls and/or the turning of the waterwheel.

Typically, the hydroplanes are also located on the bows, and so would also be lifted clear of the water when the bows are pivoted upwards. Optionally, the hulls are inflatable. The hulls are typically formed from a waterproof, flexible material, such as a rubber or a plastic material. When inflated, the hulls take on the desired hull shape. Optionally, the hulls are made of Butile^(TM), which is polychlorinated vinyl, a type of UV stable, flexible plastic. The hulls may be attached to a space frame, e.g. of light aluminium or carbon fibre, which supports the waterwheel, etc. An advantage of inflatable hulls is that they are light and can be efficiently packed, for example, if the watercraft is being fabricated in one country and then transported into another country for use.

The hulls do not necessarily comprise rubber or plastic; other materials could be used, for example, metal.

Optionally, the watercraft includes a deflector grill attached to the bows of the hulls, the deflector grill including a series of deflector bars for deflecting any floating debris away from the area between the two hulls, thereby protecting the waterwheel.

Optionally, the deflector grill is mounted on the bows of the hulls.

Alternatively, the deflector grill is tethered to the hulls.

According to a fourth aspect of the present invention there is provided an undershot waterwheel having a rotational axis and paddles rotatable about the rotational axis; wherein each paddle comprises a blade formed from a flexible sheet and a plurality of guide members that are curved when viewed parallel to the rotational axis, wherein the guide members are located in two rows adjacent to the front and rear surfaces of the blade respectively, the guide members causing the blade to adopt a curved shape corresponding to the curved guide members.

Optionally, the curvature is a parabola.

According to a fifth aspect of the present invention there is provided a method of making a paddle for a waterwheel, comprising: attaching a plurality of curved guide members in two rows to a mounting plate, aligning the curved guide members such that the curvature is when viewed parallel to the rotational axis of the waterwheel; and inserting a blade formed from a flexible sheet between the two rows of guide members and fixing the blade in position relative to the guide members, whereby the guide members cause the blade to adopt a corresponding curved shape.

Optionally, all aspects of any of the above inventions may be combined with any other aspects of any of the above inventions, whether these relate to essential or optional features.

An embodiment of the invention will now be described, by way of example only, and with reference to the following drawings (not to scale), in which :-

Fig 1 shows a plan view of a watercraft;

Fig 2 shows a front view of the watercraft of Fig 1 ;

Fig 3 shows a side view of a part of the watercraft of Fig 1 ; Fig 4 shows a side view of a further part of the watercraft of Fig 1 , with interior detail of the waterwheel;

Fig 5 shows a side view of the watercraft of Fig 1 ;

Fig 6 shows a perspective view of a paddle of Fig 5;

Fig 7 shows a sectional view of the paddle of Fig 6;

Fig 8 shows a side view of the paddle of Fig 6;

Fig 9 shows a perspective view of a nose of the paddle of Fig 6;

Fig 10 shows a schematic view of the watercraft of Fig 1 being used to power a hydraulic system;

Fig 11 shows a schematic side view of the watercraft of Fig 1 , with the bows in a raised (pivoted) position relative to the rest of the hulls;

Fig 12 shows a perspective view of an alternative embodiment of a paddle;

Fig 13 shows a perspective view of a blade of the paddle of Fig 12;

Fig 14 shows a front view of an alternative embodiment of a watercraft in an upright position;

Fig 15 shows a front view of the watercraft of Fig 14, undergoing a roll motion; Fig 16 shows a perspective view of an alternative embodiment of a waterwheel paddle;

Fig 17 shows a side cross-sectional view of the paddle of Fig 16;

Fig 18 shows a plan view of an alternative embodiment of a watercraft, including a deflector grill attached to its bows;

Fig 19 shows a side view of the watercraft of Fig 18;

Fig 20 shows a perspective view of a further alternative embodiment of a watercraft, including a deflector grill tethered to its bows; and

Fig 21 shows a schematic diagram of an alternative use for the watercrafts of the present invention, being used to pump and filter water.

Referring now to Figs 1 to 5, a watercraft 10 has two elongate hulls 12 and a waterwheel 14 mounted between the hulls 12 on a support 16. The hulls 12 are typically made from a modern composite material (optionally a reinforced material). The material is optionally carbon fibre.

The support 16 includes support arms 17, which mount the waterwheel 14 on the watercraft 10, and lifting apparatus L (hydraulic lifting cylinders). The lifting apparatus L can be activated to raise and lower the waterwheel 14 with respect to the watercraft 10, to vary the extent of submersion of the waterwheel 14.

Each of the hulls 12 has a bow B and a stern S. A respective stern rudder 18 is mounted to each stern S. Although perhaps not obvious from Fig 1 (which is not drawn to scale), the hulls 12 are shaped such that the flowpath along the outwardly-facing sidewall of each hull 12 is greater than the flowpath along the inwardly- facing sidewalk Thus, the hulls 12 act as aerofoils, and the watercraft 10 will tend to move towards the fastest flowing current, keeping the watercraft 10 in an optimum position to obtain a large amount of power from the current, within the limits of any tethered restraint. The greater (longer) flowpath along the outwardly-facing sidewalls ensures that the watercraft 10 will align itself with the current (and realign itself if necessary). The watercraft 10 is typically tethered to an anchor at the bows end, such that the bows B are at the upstream end of the watercraft 10.

A transverse member 20 is mounted between the bows B, and connects the bows B together. The transverse member 20 is shaped to direct water passing between the bows B upwards towards the waterwheel 14. In particular, the transverse member 20 is a substantially planar member, made of carbon fibre. The transverse member 20 has an upstream end 22 at the tips of the bows B, and a downstream end 24, which is located substantially at the waterwheel 14. The downstream end 24 extends up to the blade tips of the waterwheel 14, as close as possible without obstructing the blades.

The upstream end 22 of the transverse member 20 is lower than the downstream end 24 of the transverse member 20, with respect to the hulls 12. Thus, in use, the transverse member 20 is generally inclined with respect to the direction of flow at a negative angle of attack.

The transverse member 20 curves upwardly in the flow direction, from a starting position of substantially horizontal at the upstream end 22, so that incoming water is directed up the curved surface of the transverse member 20 to arrive at the waterwheel 14.

In this embodiment, both of the upper and lower surfaces of the transverse member 20 are curved upwards. The transverse member 20 is attached to the bottoms of the hulls 12, and forms an underwater "mouth" between the hulls 12 (see Fig 2).

Each hull 12 has a hydroplane 26 (a winglike structure) attached to its outside edge, near the bows end of the watercraft 10. The hydroplanes 26 are upstream of the waterwheel 14.

Referring to Figs 1 and 3, each hydroplane 26 includes a fixed body 28 and a moveable flap 30 at the downstream end of the body 28.

The body 28 of each hydroplane 26 is relatively thin and straight, and is mounted on its respective hull 12 at an angle thereto. Specifically, the body 28 is inclined downwards relative to the hull 12, in the direction of flow. Hence, the lower surface of each hydroplane 26 is angled with respect to the hulls 12, the lower surface sloping downwards in the direction of flow. In use, the hydroplanes 26 tend to be inclined with respect to the direction of flow, at a positive angle of attack.

Water travelling past the transverse member 20 tends to provide a downwards thrust to the bows B (i.e. the bows B are pushed downwards into the water by the weight of water travelling up the transverse member 20 towards the waterwheel 14).

The bodies 28 of the hydroplanes 26 being mounted at a positive angle of attack tends to provide an upwards thrust to counter the downwards thrust caused by the transverse member 20. This helps to stabilise the watercraft 10 and to reduce any downwards dip of the bows B with respect to the sterns S.

The hydroplanes 26 function similarly to aeroplane wings. The moveable flaps 30 can be adjusted to provide upwards and downwards thrust forces, as required. The amount and direction of thrust can be controlled, by varying the angle of the flaps 30. If the flaps 30 are moved downwards, with respect to the axis of inclination of the bodies 28, this creates an upthrust. If the flaps 30 are moved upwards, this creates a downthrust. In some embodiments, the size of the flaps 30 and their range of movement means that the maximum downthrust generatable by the flaps can more than balance the upthrust created by the positive angle of attack of the hydroplane bodies 28.

Referring now to Fig 11 , the bows B are connected to the rest of the hulls 12 at a hinged connection H. The bows B are pivotable upwards about the hinged connection H, relative to the rest of the hulls 12. The hinged connection H is typically located on an upper part of the hulls 12, at approximately a quarter of the way along the hulls 12, starting from the tips of the bows B.

Fig 11 shows the bows B in a raised position, such that the tips of the bows B are out of the water. Since, the transverse member 20 and the hydroplanes 26 are attached to the bows B, these are also pivoted upwards. It is preferable that, as shown in Fig 11 , the pivoting can be sufficient to raise the transverse member 20 (part of which extends below the level of the bows B) completely out of the water. The pivoting action is achieved by lifting apparatus (not shown), typically hydraulic lifting apparatus.

Lifting the transverse member 20 out of the water can be useful to help clear an obstruction, e.g. debris which has got trapped between the bows B of the hulls 12. Such debris could impede the current flow between the hulls 12 and/or the turning of the waterwheel 14. Also, lifting the hydroplanes 26 out of the water can help to clear any obstructing material which has got caught on the hydroplanes 26. Mounting both the transverse member 20 and the hydroplanes 26 on the bows B means that both the transverse member 20 and the hydroplanes 26 can be lifted out of the water by the same lifting action.

Referring now back to Fig 1 , at the sterns S, the separation of the inwardly-facing sidewalls of the hulls 12 increases with distance away from the waterwheel 14.

At the bows B, the separation of the inwardly-facing sidewalls of the hulls is greater at the tips of the bows B than at the waterwheel 14. The inwardly-facing sidewalls at the bows B are curved, such that the separation of the hulls 12 varies non-linearly with distance towards the waterwheel 14.

The curvature of the inwardly-facing sidewalls of the bows is convex near the tips of the bows B, and concave downstream of the concave region, between the convex region and the waterwheel 14. The convex region turns into the concave region at a saddle point X, with the convex region being upstream of X, and the concave region being downstream of X. Upstream of the saddle points X, the narrowing of the channel between the bows B causes the speed of the water to increase. Downstream of the saddle points X, the channel broadens again, which causes the height of the water to pile upwards, causing a wave of water to be formed in this region. The wave might break on the waterwheel 14 or in front of it. This causes an increase in the height of the water impacting on the waterwheel 14.

Fig 5 shows a side view of the watercraft 10, which includes an exemplary form of the waterwheel 14. The waterwheel 14 has a plurality of paddles 32 which are mounted on arms 34 about the hub of the waterwheel 14.

One such paddle 32 is shown in Figs 6 to 9. The paddle 32 includes a blade 36, which has a leading face LF and a trailing face TF. The blade 36 is curved when viewed parallel to the axis of rotation of the waterwheel 14. The curvature of the blade 36 reduces the amount of water lifted by the paddle 32 on leaving the water. Hence, the waterwheel 14 is energy efficient. Typically, all paddles 32 comprise curved blades 36.

The curve is optionally a parabola. However, in alternative embodiments, the equation of curvature of the "chord" of the blade changes with position along the chord. Advantageously, the curvature becomes steeper towards the tip of the blade, in the last quarter of the radial chord. This further reduces the amount of water lifted by the blade.

The paddle 32 also includes a cover plate 38 that extends from the trailing face TF of the blade 36. The cover plate 38 partly encloses the top of the blade 36 radially, to reduce spillage of water over the top of the blade 36. In use, when the paddle 32 enters the water, the current impacts the trailing face TF of the blade 36, and is hindered from travelling further over the top of the blade 36 by the cover plate 38. Hence, water pressure builds up between the trailing face TF of the blade 36 and the cover plate 38. The pressure causes the waterwheel 14 to rotate to allow the current past the blade 36. Maximum power is produced when, on submergence of the blade 36, the surface of the water reaches the cover plate 38 of the blade 36.

The cover plate 38 has vent holes 40, to vent any air enclosed beneath the cover plate 38, preventing a vacuum forming as the paddle 32 rises from the water.

The paddle 32 also includes side panels 42 that extend from the trailing face TF of the blade 36, between the cover plate 38 and the blade 36.

The side panels 42 reduce passage of water past the sides of the paddles 32, on entry to the water, and as the paddles 32 travel through the water. The side panels 42 are substantially triangular. In embodiments where the blade 36 is curved when viewed in the radial direction, the side panels 42 might be redundant or alternatively might be formed integrally with the blade 36, to form the extended curved sides of the blade 36.

The blade 36 has a radially outer tip T, and the lower part of the blade 36 is shaped such that h α A³, where h = distance from the blade tip, and where A = the surface area of the blade 36 between the tip and that distance. The power generated by a paddle 32 is proportional to the cube of the submerged area of the paddle 32, i.e. Power α area³. Thus, since h α area³, and Power α area³, therefore h α power; i.e. the power generated by the waterwheel 14 is directly proportional to the submerged depth of the paddles 32. This greatly simplifies power regulation, as no complex calculations are needed. For example, if twice as much power is required, the vertical submersion distance of the paddles 32 must be doubled.

A nose 43 is provided on the leading face LF of the blade 36, at the tip T. The nose 43 extends from the blade 36. The nose 43 smoothes the entry of the blade 36 into the water, reducing the energy loss on entry. The nose 43 is substantially pyramidal, with slightly concave outer faces; see Fig 9.

The blade 36 has two flap valves 44, mounted on (e.g. hinged to) the trailing face TF of the blade 36.

The flap valves 44 are a means to vary the effective surface area of the blade 36 and tend to be open until water pushes against the blade 36. On entry of the blade 36 into the water, the flap valves 44 are open, and the effective surface area of the blade 36 is reduced. Hence, water resistance to the blade 36 is low on entry, reducing energy losses. When the waterwheel 14 rotates, the blade 36 moves into a position where the current pushes on the blade 36 and shuts the flap valves 44. Thus, the current impacts the entire blade area. Hence, the flap valves 44 increase the efficiency of the waterwheel 14.

The paddle blade could also/instead be curved when viewed along the radial direction. A paddle 32' having one such paddle blade 36' is shown in Figs 12 and 13. Like parts have the same reference numbers, primed. Fig 12 shows the entire paddle 32' whilst the blade 36' alone is shown in Fig 13. In Fig 12, a longitudinal axis Y is shown in dotted lines, along which a longitudinal spine of the blade 36' lies. The blade 36' "bulges" along its longitudinal spine such that the leading part of the leading face LF' is the longitudinal spine of the blade, with the more outward regions of the blade 36' trailing this longitudinal spine. Curvature when viewed along the radial direction reduces energy loss on entry to the water, and increases the volume of water which the blade 36' can hold, thus increasing the effective cross-sectional area presented to the water, and the energy extracted.

The paddle 32' may also have any of the other features of the paddle 32 of Figs 6 to 9.

As shown, the cover plate 38' curves smoothly and continuously to become the side panels 42', which in turn curve smoothly and continuously to become the blade 36'. Optionally, the cover plate 38' and side panels 42' are formed integrally. Optionally, the blade 36' can be formed separately from the cover plate 38' and side panels 42' and then be attached thereto. Alternatively, the entire paddle 32' can be formed integrally, as a single-piece.

The watercraft 10 also has a stabilizing means comprising a horizontal level control (not shown), to regulate the pitch of the watercraft 10. By "pitch", we mean dipping and lifting of the watercraft 10 along the bow-to- stern axis. This relates to the configuration of the watercraft 10 when the bows B are not upwardly pivoted at the hinged connection H but instead the watercraft 10 is in the configuration of Fig 1.

The horizontal level control includes: a horizontal level sensor; computing means, which receives information from the horizontal level sensor; and a feedback system which is controlled by the computing means and adjusts the hydroplanes 26 such that they act to regulate (and typically minimize) the pitch of the watercraft 10. The computing means could be any electronic equipment which can perform these functions, e.g. a microprocessor.

Specifically, if the computing means deduces, from the information provided by the horizontal level sensor, that the bows B are too high, it causes the flaps 30 of the hydroplanes 26 to rise upwards, to create a downwards thrust at the bows B, to lower the bows B. Conversely, if the computing means deduces that the bows are too low, it causes the flaps 30 to lower, to create an upwards thrust at the bows B, to raise the bows B. The computing means can keep reacting in this way, over time, to regulate (typically reduce and/or minimize) the pitch of the watercraft 10, as the paddles 32 enter and leave the water, and throughout any changes of current strength and direction. The horizontal level control also reduces the required hull length for stability and reduces the overall weight and cost of the watercraft 10.

Fig 10 illustrates the watercraft 10 in one possible system of use. The watercraft 10 is floating in a river, aligned with the current and with the bows B upstream of the rest of the watercraft 10. A hydraulic pump (not shown) is located on the watercraft 10 in the centre of the waterwheel hub, and is arranged to be driven by the waterwheel 14. Two flowpaths connect the hydraulic pump to a submersible 360° free rotation coupling 48. The flowpaths comprise hydraulic transmission conduits 46 (only one shown). The support arms 17 are hollow and fluidly connect the hydraulic pump to the transmission conduits 46. Hence, the support arms 17 have the dual functions of supporting the waterwheel 14 on the watercraft 10 and providing flow channels for the hydraulic fluid. Hence, parts of the support 16 also provide flowpaths for the hydraulic fluid. The hydraulic pump being located in the centre of the waterwheel hub allows a balanced weight distribution of the pump on the watercraft.

The coupling 48 is also connected to further hydraulic transmission conduits 50 (only one shown) that are connected to a motor M provided on the land. Hence, the hydraulic circuit between the hydraulic pump and the motor M is complete. The motor M drives a system S, which could be any system, for example, a heating system, a fridge, an air conditioner, a corn grinder, etc. The hydraulic circuit comprises weak link hydraulics. Biodegradable hydraulic oil is used to safeguard the environment.

The motor M and the pump can both be any suitable high pressure motor/pump, for example, a standard commercially-available agricultural high pressure hydraulic motor/pump. Alternatively, an aeronautical pump/motor could be used.

The 360° coupling 48 allows the watercraft 10 and waterwheel 14 to be used, self-sufficiently and unattended, in tidal rivers or other rivers with reversing flow. By locating the hydraulic coupling 48 and the transmission conduits 46, 50 underwater, wind resistance is reduced. A pulley 52 is located between an anchor 54 and the coupling 48. A buoy B is tethered to the pulley 52 and acts as a release to the pulley 52, so that the coupling 48 can be raised, e.g. for servicing. The buoy B also acts to caution approaching vessels.

A feedback arrangement acts to control the extent of submersion of the waterwheel 14 as a function of the power demanded by the system S. The feedback arrangement uses the pressure of the fluid returned from the motor M to determine the required extent of submergence of the waterwheel 14, and the lifting apparatus L is controlled accordingly. The deeper the submerged area of the blades 36, the greater the power produced. Hence, the power obtained from the waterwheel 14 can be matched to the power demanded from the system S. Controlling the extent of submersion of the waterwheel 14 can also reduce deployment drag, and can limit stress on the arrangement in times of flood or low demand. A bypass valve ensures this is also true if the self-sealing hydraulics break. Optionally, the feedback arrangement can be arranged to raise the waterwheel 14 completely out of the water when the system S is not connected.

The waterwheel 14 is connected to a hydraulic accumulator and a cut-off regulator (not shown).

When the available power produced by the waterwheel 14 is less than the power demand of the hydraulic system S, the cut-off regulator cuts off power output from the waterwheel 14 to the hydraulic system S, and the waterwheel 14 is arranged to charge the accumulator instead. The accumulator is arranged to deliver power to the hydraulic system S after being sufficiently charged (e.g. sufficiently to be able to deliver 60 seconds of power). Power is then delivered to the hydraulic system S until the accumulator charge is exhausted. The accumulator is then recharged with power from the waterwheel 14 and the cycle is repeated.

Hence, if the supply is less than the demand, the power reaching the hydraulic system S is always sufficiently high (e.g. 50 Hz at 240 Volts when converted to electrical output), instead of the power decreasing with any decrease in water current. This ensures no adverse effect on the load except that the supply is intermittent. When the available power produced by the waterwheel 14 is greater than the power demand of the hydraulic system S, the waterwheel 14 is arranged to charge the accumulator with the excess power not required by the hydraulic system S, the accumulator being arranged to deliver power to the hydraulic system S in the case of the available power produced by the waterwheel 14 becoming less than the power demand of the hydraulic system S. The accumulator typically delivers power to the hydraulic system S until its power is used up. After the power from the accumulator has been used up, if the available power produced by the waterwheel 14 continues to be less than the power demand, the accumulator is recharged with power from the waterwheel 14, as described above in the case where the available power is less than the demand.

However, if the power produced by the waterwheel 14 has only decreased temporarily, and then returns to its previous level of more than that required by the hydraulic system S, once the power from the accumulator has been used up, the waterwheel 14 begins to power the hydraulic system S once again, with any excess power being used to recharge the accumulator. Hence, if the supply is generally greater than the demand, and is only interrupted for short periods, having power stored in the accumulator enables there to be no drop in delivered output due to sudden wind shear or passing boat wake disrupting the waterwheel 14.

The watercraft 10 also includes a flow sensor (not shown) on each of the bows B, and a wheel rotation sensor (not shown), and the outputs from these sensors are monitored by a computing means (not shown). This may, or may not, be the same computing means as described above with reference to the horizontal level control. The stern rudders 18 are hydraulically powered and are controllable by the computing means, in response to signals from the flow and wheel rotation sensors. The lifting apparatus L is also controllable by the computing means in response to signals from the flow and wheel rotation sensors.

The flow and rotation sensors can be used in the following ways.

a) if there is water flow on either flow sensor, but no wheel rotation, than the waterwheel 14 can be lifted out of the water, held in place for a pre-set time, then lowered. This aids in the clearing of obstructions. The raising and lowering action can be powered by power stored in the accumulator, and can be repeated until exhaustion of accumulated pressure.

In addition to, or instead of the step of lifting the waterwheel 14 out of the water, the bows B can optionally be pivoted about the hinged connection H (see Fig 11 ), such that the transverse member 20 and the hydroplanes 26 are lifted out of the water. This also could aid in the clearing of any obstruction.

b) if there is uneven water flow around both of the hull sensors, the stern rudder(s) 18, can be driven by hydraulic pressure, to steer the watercraft to a new position in which the water flow on each side is balanced. This generally maximises the flow through the waterwheel 14, if there is little or no cross-wind (wind that is not in the direction of the current, but is at an angle thereto).

If there is a cross-wind, there are two forces acting on the watercraft 10 - the current and the wind. In such situations, the flow sensors on the bows B might both be registering an even (balanced) water flow on both sides of the watercraft 10, even if the watercraft 10 is lying in a location of weak current, instead of in a location of maximum current. In such situations, the computing means and the wheel speed sensor can be used to override the signals from the flow sensors. The computing means can have a programmed expected threshold wheel speed. If the sensed wheel speed falls below this expected threshold, this might mean the current is genuinely very low, and the watercraft is in a good position, or it might mean the watercraft 10 is not lying in the location of maximum current.

If the sensed wheel speed does fall below the threshold, the computing means activates the stern rudders 18, to change the position of the watercraft 10. The wheel speed can then be checked at watercraft positions corresponding to different stern rudder positions. If no higher wheel speed can be achieved, this indicates the current is simply low at that time. If a higher wheel speed can be achieved at a different position, the computing means and stern rudders 18 act together to hold the watercraft 10 in that position. So, essentially, the hydraulic output of the waterwheel 14 can be temporarily diverted from the system S and used instead to change the positions of the stern rudders 18 to try to gain more energy from the water flow.

Hence, using the stern rudder(s) 18 and computing means, the watercraft 10 can position itself for maximum wheel rotation rate, whatever the angle of the watercraft 10 to the current, and whatever the windage against any tethered restraint.

c) if an obstruction is detected, a combination of steps (a) - wheel lifting and/or bows lifting and (b) - hull orientation adjustment by rudder action, can be used. The transverse member 20 helps to direct more incoming water onto the waterwheel 14 than would otherwise be the case, thereby increasing the power output of the waterwheel 14. The transverse member 20 also causes an increase in height of the water as it arrives at the waterwheel 14.

The combined effect of the transverse member 20 and the hydroplanes 26 is to cause an increase in height of the water as it arrives at the waterwheel 14. This tends to create a "breastshot" waterwheel, as opposed to a purely "undershot" waterwheel. This leads to a higher extraction of water energy, as well as increasing the volume of water through the waterwheel 14.

The moveable flaps 30 can be adjusted, to provide upwards and downwards thrust forces, as required, e.g. to compensate for any pitch of the watercraft 10. Hence, the watercraft 10 can be shorter in length, for a given stability.

The convex and concave curvature of the inwardly-facing sidewalls of the bows reduces unwanted turbulence at the tips of the bows B, speeds up the incoming water and piles up the incoming water into a wave which breaks on the waterwheel 14. This increases the height of the water impacting on the waterwheel 14, and therefore the amount of power extracted by the waterwheel 14.

Fig 14 shows a partial view of an alternative embodiment of a watercraft 100, which is the same as the watercraft 10 except it has hulls 112a, 112b which have a different shape to the hulls 12 of Figs 1 and 2. The hulls 112a, 112b each have a lower portion 114, which is cuboid, and an upper portion 116, which is wedge-shaped, the thickness of the wedge increasing with increasing height out of the water. The inner walls of the hulls 112a, 112b are vertical, and the wedge is provided by an increasing width of the outer walls of the hulls 112a, 112b. The buoyancy of the watercraft 100 is arranged so that the waterline lies between the lower and the upper ends of the wedge. Also shown is a paddle 118 of a waterwheel 120.

As shown in Fig 15, if the watercraft 100 starts to roll in one direction, a larger part of the hull in the direction of the roll (hull 112a in this example) will become submerged, creating a large buoyancy, counter-balancing, upthrust force. Simultaneously, on the other side of the watercraft 100, the hull 112b has risen relative to the water, leaving a smaller part of the hull 112b in the water, to reduce the upthrust on that opposite side.

Hence, in this embodiment, the shape of the hulls 112a, 112b provides a stabilizing means for the watercraft 100. The shape of the hulls 112a, 112b regulates the roll of the watercraft 100 (as shown in Fig 15) and also regulates the pitch (fore-aft motion) of the watercraft 100, for a similar reason. Any pitch submerges more of the wedge shaped portion in that direction, causing a counter-balancing buoyancy force which acts to push the watercraft 110 upright again. Hence, the watercraft 100 is able to keep itself upright in most situations, without human intervention.

Also, as shown in Figs 14 and 15, the lower portions of the hulls 114 extend downwards beyond the paddle 118. Hence, if the watercraft 100 is used on a river in conditions of drought, and the water level of the river goes down, the lower portions of the hulls 114 may end up sitting on the river bed, but without damaging the paddles 118/the waterwheel 120. Figs 16 and 17 show an alternative embodiment of a paddle 130. The paddle 130 includes a blade 132, a plurality of guide members in the form of spines 134 and a cover plate/mounting plate 136. The cover plate 136 is mounted to a waterwheel spoke 138.

The blade 132 is formed from a flexible sheet of material, typically a very thin, light sheet of aluminium of approximate thickness 1 mm. Prior to assembly of the paddle 130, the blade 132 is flat.

The spines 134 are long, thin, pin-like members which are curved in the direction viewed parallel to the rotational axis of the waterwheel. The spines 134 are formed from gravity-cast aluminium, and have a triangular cross-section (not shown).

As shown in Fig 17, the cover plate 136 comprises upper and lower plate members 138, 140, held together by bolts 142. The spines 134 extend through apertures in the lower plate member 140. The spines 134 have enlarged heads 135, which are larger than the apertures in the lower plate member 140, so the heads 135 are retained within the cover plate 136.

The spines 134 are located in two rows adjacent to the front and rear surfaces of the blade 132 respectively. Four spines 134 are in the front row, and three spines 134 are in the rear row. The spines 134 are staggered along the width of the paddle 130, such that the rear spines 134 are located intermediate two front spines 134.

To assemble the paddle 130, the spines 134 are attached in their two rows to the cover plate 136, and are aligned so that the curvature is when viewed parallel to the rotational axis of the waterwheel (as shown). This is done by inserting the spines 134 through the apertures in the lower plate member 140 in the correct orientation, and by bolting the lower plate member 140 and the upper plate member 138 together by bolts 142. The blade 132 is inserted between the two rows of spines 134 and is fixed in position relative to the spines 134. This may be done by fixing the blade 134 to the cover plate 136 and/or fixing the blade 134 directly to the spines 134, e.g. by bolts 144 located at one or more positions along each spine 134.

Since the blade 132 is flexible, the spines 134 cause the blade 132 to adopt a corresponding curved shape, as shown in Figs 16 and 17.

Such embodiments have two advantages. Firstly, the paddles 130 can be very light. The spines 134 provide the strength for the paddles 130, so the blades 132 themselves can be very thin. When any waterwheel turns, in addition to extracting energy from the water, the waterwheel also delivers some energy back to the water on re-entry of the paddles. Angular momentum = mass x radius x angular velocity, so the larger the mass of the paddles, the more angular momentum is transferred from the waterwheel to the water on re-entry of the paddles into the water. Hence, lightweight paddles increase the efficiency of the waterwheel.

Secondly, it is only the spines 134 that are curved originally, and the blades 132 are flat. Flat blades 132 and a set of curved guide members (e.g. spines) can be flat-packed more efficiently than a set of curved paddles. So, in transportation, this arrangement saves both space and weight.

Figs 18 and 19 show a further embodiment of a watercraft 150, which is the same as the watercraft 10 except for the following modifications. The watercraft 150 has two hulls 152 which have extension portions 154 at their bows. The extension portions 154 extend the length and the width of the bows and effectively enlarge the watercraft's "mouth" which feeds water onto the waterwheel (the area between the two hulls 152 at the bows). The extension portions 154 feed smoothly into the remainder of the hulls 152. Enlarging the mouth increases the velocity of the water impacting the waterwheel. Since energy is proportional to the cube of the water velocity (energy α v³), increasing the width of the mouth makes a significant difference to the energy efficiency of the waterwheel.

Also shown is the waterwheel 156, which has a hub 157; and the transverse member 158, which has a front end 158f and a rear end 158r. The transverse member 158 is attached to the base of the extension portions 154. The front end 158f of the transverse member 158 extends as far forward as the tips of the extension portions 154, and to the full width of the extension portions 154 (see Fig 18). The rear end 158r of the transverse member 158 terminates just before the entry point of the blades of the waterwheel 156.

The extension portions 154 comprise floatation vessels, which counteract the downwards force of the transverse member 158.

The watercraft 150 also includes a deflector grill 160 attached to the bows of the hulls.

The deflector grill 160 is shaped like an arrow head, with a tip 168 that forms the very front of the watercraft 150, and two backwards extending arms 170, which terminate at ends 172. The ends 172 are attached to the front tips of the extension portions 154 and have an identical separation. The tip 168 of the deflector grill 160 is attached to a primary tether 174 of the watercraft 150. Each arm 170 comprises an upper rail 164, a lower rail 166 and an array of deflector bars 162 spanning therebetween. The deflector bars 162 deflect any floating debris away from the area between the two hulls 152, thereby protecting the waterwheel 156. The deflector bars 162 slope diagonally downwards in the direction of the rear of the watercraft 150. The deflector bars 162 are narrow in the fore-aft direction (which is the direction of water flow), to minimize flow disruption.

The upper rail 164, lower rail 166 and the deflector bars 162 form a sealed, air filled structure. This provides additional buoyancy forces to counteract the downwards force of the transverse member 158.

The deflector grill 160 is designed to deflect floating, and below water floating objects away from the area between the hulls 152. To this end, the width between the ends 172 of the deflector grill (and the distance between the ends of the extension portions) is considerably wider than the distance between the hulls 152 at the level of the waterwheel 156. Hence, any debris is pushed clear of the mouth of the watercraft 150.

Hence, in the embodiment of Figs 18 and 19, the deflector grill 160 is mounted on the bows of the hulls 152.

In contrast, Fig 20 shows a further embodiment of a watercraft 180, which has hulls 182 and a deflector grill 184, which is tethered in a river by a primary tether 186. However, the deflector grill 184 is not mounted on the bows of the hulls 182 and is instead tethered to the hulls 182 by two secondary tethers 188, of approximate length 2 metres. Should the deflector grill 184 become clogged up by floating debris, this decelerates the flow of water heading towards the waterwheel. However, the secondary tethers 188 provide sufficient room between the deflector grill 184 and the waterwheel for the water to accelerate again, before hitting the waterwheel. Hence, this arrangement reduces any energy loss in the water due to a clogged up deflector grill 184. Furthermore, any large debris (e.g. a log) impacting the deflector grill 184 with sufficient momentum causes the deflector grill 184 to pivot, altering the tension in the secondary tethers 188 and causing the watercraft 180 to pivot such that the mouth of the watercraft 180 is deflected away from the debris as it continues to float downstream.

Fig 21 shows an alternative use for any and all watercrafts of the present invention. It has already been described with reference to Fig 10 how a watercraft and waterwheel of the invention can be used to drive a hydraulic system. Fig 21 illustrates how energy from the waterwheel could be used to drive a pump which pumps water up from the body of water

(e.g. river) in which the watercraft is sitting and to shore. Fig 21 shows the watercraft 100 afloat on a river R, adjacent to land L. The waterwheel 120 drives a pump P (located on the watercraft 100). A first water conduit 200 leads from the pump P into the river R. A second water conduit 202 leads from the pump P to a water processing system 204 located on the land L. The water processing system 204 includes solenoid valves 206, 208, a control unit 210 and a filtration system 212. River water is pumped through these components in that order. The filtration system 212 produces a first output 214 comprising filtered, drinking water. Optionally, the filtration system 212 (or another part of the water processing system) may also produce a second output 216 comprising irrigation water.

Optionally, the waterwheel 120 could drive both this water pumping system and a hydraulic system (e.g. see Fig 10) such that the waterwheel also provides the energy to run the water processing system 212, as well as pumping the river water therethrough. Optionally, some or all of the hydraulic energy can be converted into electrical energy (e.g. by a dynamo) to run computers of the water processing system 212.

The above uses may be particularly beneficial for energy generation in the third world, in converting energy from a river to either drive a hydraulic system or for providing fresh drinking water. The watercraft may be left tethered and has no running costs, since it is providing energy from a renewable source.

Modifications and improvements may be incorporated without departing from the scope of the invention. For example, in an alternative embodiment, the transverse member 20 might not be planar. For example, the transverse member 20 could be wedge shaped, with only the upper surface being upwardly curved.

The specific embodiment of waterwheel shown in Figs 5 to 9 was included for purposes of describing one embodiment, but that exact form of waterwheel is not essential, and other forms could be used. E.g. the paddles could be any shape, the blades could be curved/straight, there could be more or fewer paddles, the vent holes and/or nose and/or flaps could be omitted, the blades could be curved in one or more planes, or they could be flat, and the side panels could be omitted altogether, or they could be formed integrally with the blade (e.g. in a smooth curved shape).

Instead of a central hub location of a single hydraulic pump, a respective hydraulic pump could alternatively be provided in each hull 12. Rotation transmission to each pump could be provided along an outer part of the hulls 12, allowing a static hydraulic line and bearing axle to connect the two hulls 12. The materials given above for the hulls, the transverse member, the extension portions, the deflector grill and the paddles are given by way of example only, and these materials are not limiting on the invention. Furthermore, none of the exemplary dimensions given above are limiting on the invention.

Although the aforementioned embodiments are depicted as separate embodiments, any features of one embodiment may be combined with any features of any of the other embodiments in a single watercraft. For example, the deflector grills of Figs 18 to 20 may be used with any of the watercraft embodiments. Likewise, the shaped hulls of Figs 14 and 15 may be provided as part of any embodiment, etc.

Claims

1. A watercraft having: two hulls, each hull having a bow and a stern; a waterwheel mounted between the two hulls; and a transverse member, which connects the bows of the hulls together and which is shaped to direct water passing between the bows upwards towards the waterwheel.

2. A watercraft as claimed in claim 1 , wherein the upstream end of the transverse member is lower than the downstream end of the transverse member, with respect to the hulls.

3. A watercraft as claimed in claim 1 or claim 2, wherein an upper surface of the transverse member is curved upwards in the direction of flow, to direct incoming water up the transverse member and onto the waterwheel.

4. A watercraft as claimed in any preceding claim, wherein the downstream end of the transverse member is located substantially at the waterwheel.

5. A watercraft as claimed in any preceding claim, wherein the waterwheel has paddles, each paddle comprising a respective blade.

6. A watercraft as claimed in claim 5, wherein at least one paddle is curved when viewed parallel to the rotational axis.

7. A watercraft as claimed in claim 6, wherein: the paddles are rotatable about the rotational axis of the waterwheel; each blade is formed from a flexible sheet; each paddle also includes a plurality of guide members that are curved when viewed parallel to the rotational axis; and the guide members are located in two rows adjacent to the front and rear surfaces of the blade respectively, the guide members causing the blade to adopt a curved shape corresponding to the curved guide members.

8. A watercraft as claimed in claim 6 or claim 7, wherein the curvature is a parabola.

9. A watercraft as claimed in any preceding claim, wherein, at the bows of the hulls, the separation of the inwardly-facing sidewalls of the hulls is greater at the tips of the bows than at the waterwheel and wherein the inwardly-facing sidewalls at the bows are curved, such that the separation of the hulls varies non-linearly with distance towards the waterwheel.

10. A watercraft as claimed in claim 9, wherein the curvature of the inwardly-facing sidewalls of the bows is convex near the tips of the bows, and concave downstream of the convex region, between the convex region and the waterwheel.

11. A watercraft as claimed in any preceding claim, including a stabilizing means to regulate at least one of the pitch and the roll of the watercraft.

12. A watercraft as claimed in claim 11 , wherein the stabilizing means comprises a horizontal level control to regulate the pitch of the watercraft.

13. A watercraft as claimed in claim 12, wherein the horizontal level control includes: a horizontal level sensor; computing means, which receives information from the horizontal level sensor; and a feedback system which is controlled by the computing means and adjusts the orientation of the watercraft so as to regulate the pitch of the watercraft.

14. A watercraft as claimed in any of claims 11 to 13, wherein the stabilizing means comprises the shape of the hulls, which increase in width with increasing upwards height out of the water.

15. A watercraft having: two hulls, each hull having a bow and a stern; and a waterwheel mounted between the two hulls; wherein, at the bows of the hulls, the separation of the inwardly- facing sidewalls of the hulls is greater at the tips of the bows than at the waterwheel, with the inwardly-facing sidewalls at the bows being curved, such that the separation of the hulls varies non-linearly with distance towards the waterwheel.

16. A watercraft as claimed in claim 15, wherein the curvature of the inwardly-facing sidewalls of the bows is convex near the tips of the bows, and concave downstream of the convex region, between the convex region and the waterwheel.

17. A watercraft having: two hulls, each hull having a bow and a stern; a waterwheel mounted between the two hulls; and a stabilizing means to regulate at least one of the pitch and roll of the watercraft.

18. A watercraft as claimed in claim 17, wherein the stabilizing means comprises a horizontal level control to regulate the pitch of the watercraft.

19. A watercraft as claimed in claim 18, wherein the horizontal level control includes: a horizontal level sensor; computing means, which receives information from the horizontal level sensor; and a feedback system which is controlled by the computing means and adjusts the orientation of the watercraft so as to regulate the pitch of the watercraft.

20. A watercraft as claimed in claim 19, including two adjustable hydroplanes, one on each hull, and wherein the feedback system adjusts the orientation of the watercraft by adjusting the orientation of the hydroplanes.

21. A watercraft as claimed in any of claims 17 to 20, wherein the stabilizing means comprises the shape of the hulls, which increase in width with increasing upwards height out of the water.

22. A watercraft as claimed in claim 21 , wherein a portion of each hull is wedge-shaped, the thickness of the wedge increasing with increasing height out of the water, and wherein the buoyancy of the watercraft is selected such that the water level is between the upper and lower ends of the wedge.

23. A watercraft as claimed in any preceding claim, wherein each hull has a hydroplane on its outside edge.

24. A watercraft as claimed in claim 23, wherein the hydroplanes have a lower surface that is angled with respect to the hulls, the lower surface sloping downwards in the direction of flow.

25. A watercraft as claimed in claim 23 or claim 24, wherein the hydroplanes each have a fixed body and a moveable flap, and wherein the angle of the flap can be adjusted with respect to the fixed body, to provide a thrust force.

26. A watercraft as claimed in any preceding claim, including a hydraulic pump arranged to be driven by the waterwheel, the hydraulic pump being connected to a hydraulic system via hydraulic flowpaths, such that energy from the waterwheel is converted into a hydraulic output which can be used to power the hydraulic system.

27. A watercraft as claimed in claim 26, wherein the waterwheel is connected to a hydraulic accumulator and a cut-off regulator.

28. A watercraft as claimed in claim 27, wherein, when the available power produced by the waterwheel is less than the power demand of the hydraulic system, the cut-off regulator cuts off power output from the waterwheel to the hydraulic system, and the waterwheel is arranged to charge the accumulator instead, the accumulator being arranged to deliver power to the hydraulic system after being charged.

29. A watercraft as claimed in claim 27 or claim 28, wherein, when the available power produced by the waterwheel is greater than the power demand of the hydraulic system, the waterwheel is arranged to charge the accumulator with the excess power not required by the hydraulic system, the accumulator being arranged to deliver power to the hydraulic system in the case of the available power produced by the waterwheel becoming less than the power demand of the hydraulic system.

30. A watercraft as claimed in any preceding claim, including a water pump arranged to be driven by the waterwheel, the water pump being connected to a conduit system, arranged to pump water from a body of water on which the watercraft is floating to shore.

31. A watercraft as claimed in claim 30, wherein the conduit system is connected to a filtration system.

32. A watercraft as claimed in any preceding claim, wherein the watercraft includes a flow sensor on each hull and a wheel rotation sensor, and wherein the outputs from these sensors are monitored by a computing means.

33. A watercraft as claimed in any preceding claim, wherein the watercraft includes a stern rudder, provided on the stern of one of the hulls.

34. A watercraft as claimed in claim 33 when dependent on claim 32, wherein the stern rudder is hydraulically powered and is controllable by the computing means, in response to signals from the flow and wheel rotation sensors.

35. A watercraft as claimed in any preceding claim, including lifting apparatus adapted to raise and lower the waterwheel, such that the extent of submersion of the waterwheel can be varied.

36. A watercraft as claimed in claim 35 when dependent on claim 32, wherein the lifting apparatus is controllable by the computing means in response to signals from the flow and wheel rotation sensors.

37. A watercraft as claimed in any preceding claim, wherein the waterwheel has paddles, each paddle comprising a respective blade.

38. A watercraft as claimed in claim 37, wherein at least one paddle is curved when viewed parallel to the rotational axis.

39. A watercraft as claimed in claim 38, wherein: the paddles are rotatable about the rotational axis of the waterwheel; each blade is formed from a flexible sheet; each paddle also includes a plurality of guide members that are curved when viewed parallel to the rotational axis; and the guide members are located in two rows adjacent to the front and rear surfaces of the blade respectively, the guide members causing the blade to adopt a curved shape corresponding to the curved guide members.

40. A watercraft as claimed in claim 38 or claim 39, wherein the curvature is a parabola.

41. A watercraft as claimed in any preceding claim, wherein the hulls are shaped such that the flowpath along the outwardly-facing sidewall of each hull is greater than the flowpath along the inwardly-facing sidewall.

42. A watercraft as claimed in any preceding claim, wherein the bows are connected to the rest of the hulls at a hinged connection, the bows being pivotable upwards about the hinged connection, relative to the rest of the hulls.

43. A watercraft as claimed in any preceding claim, wherein the hulls are inflatable.

44. A watercraft as claimed in any preceding claim, including a deflector grill attached to the bows of the hulls, the deflector grill including a series of deflector bars for deflecting any floating debris away from the area between the two hulls, thereby protecting the waterwheel.

45. A watercraft as claimed in claim 44, wherein the deflector grill is mounted on the bows of the hulls.

46. A watercraft as claimed in claim 44, wherein the deflector grill is tethered to the hulls.

47. An undershot waterwheel having a rotational axis and paddles rotatable about the rotational axis; wherein each paddle comprises a blade formed from a flexible sheet and a plurality of guide members that are curved when viewed parallel to the rotational axis, wherein the guide members are located in two rows adjacent to the front and rear surfaces of the blade respectively, the guide members causing the blade to adopt a curved shape corresponding to the curved guide members.

48. An undershot waterwheel as claimed in claim 47, wherein the curvature is a parabola.

49. A method of making a paddle for a waterwheel, comprising: attaching a plurality of curved guide members in two rows to a mounting plate, aligning the curved guide members such that the curvature is when viewed parallel to the rotational axis of the waterwheel; and inserting a blade formed from a flexible sheet between the two rows of guide members and fixing the blade in position relative to the guide members, whereby the guide members cause the blade to adopt a corresponding curved shape.