[001] The present invention concerns a kite deployment system for deploying and retracting a kite and, in particular, an aerofoil kite.

[002] In this connection, there is increasing interest in utilising kites to harness wind power. Kites are of particular interest because they are able to extract greater amounts of energy compared to conventional sails or wind turbines. One reason for this is that kites are able to harness higher altitude winds, which have higher speeds and are more consistent. In addition, kites are able to operate over a much greater area, and therefore they are less restricted by the Betz limit associated with conventional wind turbines.

[003] In this connection, companies such as SkySails and KiteShips have utilised large kite systems on large water vessels, such as tanker ships, to assist with the vessel's propulsion. Such systems have been shown to provide up to a 25% reduction in fuel consumption. Another area of recent interest has been the use of large kites in land based wind power generation systems. Such systems are at the prototype stage and are being developed by companies such as Kite Gen. These systems typically involve a kite being attached to a variable length tether. The kite is then controlled to produce periods of high and low tension in the tether, with the periods of high tension being used to drive a generator as the tether is reeled out.

[004] A particular problem hindering the widespread adoption of kite technology relates to deployment and retraction of the kite. Close to the ground, wind speeds are generally lower and more erratic. Furthermore, changes in landscape and the presence of obstructions, such as buildings and trees, can cause turbulence in the wind. This makes launching large kites extremely difficult because such kites will often require a continuous minimum wind speed in order to generate sufficient lift to hold the kite open and begin to fly. Consequently, it is common for kites to fold under their own weight during launch, particularly if lateral gusts of winds disrupt the kite. Furthermore, if the kite is provided with a rigid frame to help it to retain its shape, it becomes more susceptible to lateral winds during launch, which can often cause the kite to crash. Moreover, the additional weight of the frame may necessitate higher minimum wind speeds in order to launch the kite.

[005] The above problems are exacerbated because a commercially viable kite system would need to also allow for the kite to be easily retracted and redeployed. The difficulty with this is that in instances where the wind speed drops, it becomes extremely difficult to retract the kite in a controlled manner, again because the wind speed may be insufficient or too turbulent to keep the kite's shape. The result of this is that the kite becomes unstable, and may stall or fold. The kite's tethers may become tangled, which would require a manual operation to untangle the tethers and prepare the kite for redeployment.

[006] One method proposed for deploying large kites involves the use of an aerostat (zeppelin) or balloon to carry the kite to higher altitudes. Such methods rely on the buoyancy of the aerostat to lift the kite to an altitude where the wind is sufficient to support it. However, such a system is impractical in many instances. Firstly, the size of the aerostat or balloon makes it particularly sensitive to turbulent gusts of wind or higher wind speeds. This can result in the aerostat or balloon becoming entangled with the kite or being unable to position the kite suitably for sustained flight. Furthermore, the deployment of the aerostat or balloon adds additional complexity to the system and makes deployment slow. Moreover, deployment, retraction and redeployment would all require manual operations with such a system, which renders it unsuitable for large scale, commercially viable, kite deployment.

[007] Accordingly, it is an object of the present invention to seek to address the above problems.

[008] According to a first aspect of the present invention there is provided a kite deployment system for launching a kite, said system comprising: two spaced supports between which a portion of the kite can be suspended, wherein said supports are moveable for positioning the portion of the kite between the supports into the oncoming wind for generating lift there across.

[009] In this way, the supports act to support a proportion of the kite's weight, whilst a free portion of the kite can be positioned into the wind. As a result, relatively low wind speeds are required in order to lift the free section of kite material suspended between the supports. As this portion of the kite is lifted, the kite's shape begins to form, which in turn generates further lift from the wind, which can be used to lift an ever larger portion of the kite's material. This allows the kite to be progressively deployed by feeding the kite material out between the supports to gradually increase the size of the portion being lifted by the wind. Furthermore, the moveable supports allow the position of the kite to be adjusted during the launch operation so as to react to the changing wind conditions and control the flight of the unreeled sections of the kite as the kite is progressively deployed. This allows the position of the kite relative to the oncoming wind to be maintained and therefore maximum lift can be generated. These actions provide time during the launch operation for the kite's shape to gradually form before it is required to support its own weight in full. Advantageously, this allows the kite to be launched even in relatively low speed or turbulent winds.

[0010] Conveniently, the supports are moveable to increase their pitch for tilting the kite's leading edge upwardly. In this way, the kite can be tilted up so as to increase the exposure of the under surface of the suspended portion, between the kite's leading and trailing edges, to the oncoming wind. This helps the wind to lift the underside of the kite during the initial stages of launch. That is, the oncoming wind will act to inflate the kite and allow its shape to form. In the case of an aerofoil kite, this allows the aerofoil shape to form, which generates further lift as the wind passes over the kite's profile.

[0011] Conveniently, said supports are moveable about the vertical axis for controlling the kite's yaw. This allows the kite to be positioned and repositioned during launch to maximise the lift generated by the oncoming wind.

[0012] Preferably, the two spaced supports are moveable independently. This allows the kite's shape to be modified during launch in order to maximise the lift generated by the oncoming wind.

[0013] Preferably, the kite deployment system further comprises: a wind direction sensor system for sensing the direction of oncoming wind; and a support control system for controlling the movement of the supports in response to the direction of oncoming wind. In this way, the deployment system can automatically position and reposition the kite for generating the maximum lift during the launch process to optimise the chances of successful launch.

[0014] Conveniently, each of said supports is supported by an articulated joint.

[0015] Conveniently, wherein at least one of said supports comprises a kite pay out mechanism for feeding out the kite between the supports. In this way, the kite can be fed or spooled out from one or both supports as the free section of the kite between the supports is lifted by the wind. This allows the size of the free portion of kite to be gradually increased by feeding out more of the kite.

[0016] Conveniently, the kite pay out mechanism comprises a roller for spooling out the kite between the supports.

[0017] Conveniently, in use during launch, said kite pay out mechanism is operable for progressively feeding out the kite as the portion of the kite between the supports is lifted by the wind. In this way, the kite is gradually fed out as it takes shape and generates lift. This avoids premature stalling of the kite during launch.

[0018] Conveniently, both said supports comprise a kite pay out mechanism, each for feeding out one side of the kite. This allows the kite to be uniformly spooled out, from the middle outwardly, which provides for maximum lift during launch .

[0019] Conveniently, each of said supports comprises a tether attachment for connecting the supports to the kite's tethers .

[0020] Conveniently, the kite deployment system further comprises a tether pay out mechanism for progressively feeding out the kite's tethers through said tether attachments as the kite rises in altitude. In this way, once the kite is launched, it's tethers may be reeled out as it generates lift. This allows the kite to be flown up to higher altitudes where wind speeds are higher and more consistent .

[0021] Conveniently, said tether pay out mechanism comprises a winch system for reeling in the kite's tethers for retracting the kite.

[0022] Conveniently, each of said tether attachments comprises a pulley system.

[0023] Conveniently, the pulley systems are moveable axially along said supports for altering the positions of the tether attachments on the supports. This allows the axial position of the kite's attachment point to be adjusted for altering the trimming of a water going vessel fitted with the kite deployment system.

[0024] Conveniently, the kite deployment system further comprises a tether for connecting the supports to the kite.

[0025] Conveniently, the kite deployment system further comprises a locking mechanism for locking the movement of said supports about the pitch and yaw axes. In this way, once the kite is in flight, the position of the supports can be locked in order to more evenly distribute the forces delivered to the supports from the kite and avoid premature component failure.

[0026] Conveniently, the kite deployment system further comprises an aerofoil kite. [0027] Conveniently, the kite comprises an inflatable frame for forming the aerofoil shape.

[0028] Conveniently, the supports are moveable laterally apart for increasing the space between the supports. This allows the area of kite suspended between the supports to be increased during launch. This can help to launch the kite if the supports are based on a narrow platform which may otherwise mean that the supports are too close together.

[0029] According to a second aspect of the present invention there is provided a water going vessel comprising the kite deployment system described above.

[0030] Conveniently, the water going vessel further comprises a submersible turbine for generating electricity as the water based vessel is pulled through the water.

[0031] Conveniently, the water going vessel further comprises a wind tracking unit for steering the kite into regions of optimal wind conditions.

[0032] Illustrative embodiments of the present invention will now be described with reference to the accompanying drawings in which:

Figure 1 shows the kite deployment system according to a first embodiment of the present invention;

Figure 2 shows the kite deployment system with the kite retained in the stored position;

Figure 3 shows a front perspective view of the kite deployment system in a launch position;

Figure 4 shows a rear perspective view of the kite deployment system in a launch position; Figure 5 shows a rear perspective view of the kite deployment system as the kite is deployed;

Figure 6 shows the interior of one of the kite deployment system's rollers and the reeling mechanism contained therein; Figure 7 shows the deployed kite tethered to the kite deployment system;

Figure 8 shows a side view of the aerofoil kite; Figure 9 shows a water going vessel for power generation incorporating the kite deployment system according to a second embodiment of the present invention;

Figure 10 shows the second embodiment during launch of the kite;

Figure 11 shows the second embodiment once the kite is deployed.

[0033] Figure 1 shows the kite deployment system according to a first embodiment of the present invention. In this figure, the kite and its tether lines have been omitted for clarity. The kite deployment system comprises two rollers 1 which are each rotatable about their longitudinal axes for reeling and un-reeling the kite during launch and recovery. The rotation of each roller is driven by means of a motor/drum-drive (not shown) , which can hold the drum in a fixed position or rotate it in either direction.

[0034] Each of the rollers 1 are independently connected to the floor platform through an articulated joint 2 and 3 which allows the rollers 1 to be tilted vertically upwards (i.e. rotated about the horizontal axis) for adjusting their pitch and rotated about the vertical axis for adjusting their yaw. In this way, the articulated joints 2 and 3 form universal joints for permitting multi-axis movement of the rollers 1. The articulated joints 2 and 3 are shown as simple lines in the figures for clarity. The articulated joints 2 and 3 can be driven in unison or independently for changing the angles between the two rollers, as conditions require.

[0035] Each of the rollers 1 contains within it a tether reeling mechanism for paying out and reeling in the tether connected to the kite. This mechanism is discussed in further detail below in reference to Figure 6.

[0036] Figure 2 shows the kite deployment system with the kite 4 attached and retained in the stored position. Here, the rollers 1 are held horizontally with the two sides of the kite 4 wound around them. A free portion of the kite 4 is suspended between the two rollers 1, which act as supports for supporting the spooled up side sections of the kite 4 wound there around. The side edges of the kite 4 are held in position on the rollers 1 at the base of the spool by their attachment to the tether (not shown) , which is held by the tether reeling mechanism within each roller 1. In this position, the suspended portion of the kite 4 between the rollers 1 may be held under tension to prevent it being caught prematurely by the wind.

[0037] The kite 4 is of an inflatable aerofoil construction. In the stored position, the inflatable sections of the kite remain under low pressure to allow spooling. During launch, an inlet/valve system (not shown) is provided to intake oncoming air and inflate the inflatable sections of the kite 4 as it is launched.

[0038] Figures 3 and 4 shows the kite deployment system in a launch position. The rollers 1 are tilted upwardly by articulated joint 2 to present the under surface of the kite

4 into oncoming wind. In this position, each of the rollers

1 supports across the kite 4, from its higher leading edge to its lower trailing edge. In the example shown in the figures an aft wind is shown and therefore each of the rollers is simply tilted upwardly. However, in instances where the wind has a lateral vector component, the pitch and yaw of the rollers 1 may be independently modified to optimise the presentation of the kite to the oncoming wind. Furthermore, the control system (not shown) can actively modify the position of the rollers 1 in response to changing wind conditions during the launch process.

[0039] As is shown in Figure 3, the small section of the kite 4 which is suspended between the rollers 1 is presented to the wind. As the remainder of the kite's weight is supported by the rollers 1, only relatively low levels of wind are required at this stage in order to lift the free section of kite. As the suspended section of the kite lifts, its aerofoil shape begins to form, which generates further lift forces.

[0040] Figure 4 shows the continuation of the launch process. As the wind continues to provide uplift to the kite 4, the rollers 1 rotate to spool out further kite material and increase the portion of the kite 4 suspended between the rollers. This acts to progressively deploy the kite 4 between the two rollers 1, the speed of which is controlled, depending on the prevailing wind conditions, to ensure the kite 4 has sufficient time to inflate and develop sufficient uplift over its surface to maintain its shape and support further kite material.

[0041] As this process continues, the pitch of the rollers 1 is reduced, thereby increasing the lift forces generated by the aerofoil shape of the kite 4 and preventing the kite

4 from collapsing. Importantly, by actively adjusting the pitch-axis and yaw of each of the rollers 1, the shape and position of the half-unreeled kite can be controlled. This allows the present invention to react to changing wind conditions during the kite's launch and thereby ensure a successful launch operation, i.e. by controlling the flight of the partially un-reeled kite. Furthermore, in instances where the wind suddenly drops, the rollers may be quickly reversed to retract a portion of the unreeled kite material back onto the spools in order to generate apparent wind.

[0042] Figure 5 shows the kite 4 as it reaches a position in which it is nearly entirely deployed. The lift forces being generated by the kite's aerofoil shape act to promote the further uncoiling of the kite. The process of kite deployment continues until the kite 4 is entirely deployed and its aerofoil shape is fully formed. As mentioned above, the kite 4 is secured at each of its side edges to tether ropes, which connect the kite 4 to reeling mechanism within each of the rollers 1.

[0043] Figure 6 shows the interior of one of the rollers 1 and the reeling mechanism contained therein. The reeling mechanism comprises a pulley system 8 located within the roller 1 and which is axially rotatable therewith. The pulley system 8 acts as the attachment point for the tether 5 connecting between kite 4 and the rollers 1. The pulley system allows the tether 5 to be fed from an external winch 7 out through a slot 6 provided in the surface of the roller 1. Linear actuation system 9, such as a hydraulic piston, is provided for moving the pulley system 8 along the longitudinal axis of the roller 1, which enables the position of axial attachment point of the kite's tether 5 to be adjusted.

[0044] When the kite 4 is wound around the rollers 1 in storage, the external winch 7 locks the tether 5, thereby holding the edges of the kite relative to the slots 6 on the rollers 1. During the initial stages of kite deployment, the rollers 1 rotate to unreel the kite 1, and each pulley system 8 rotates with its roller 1 in order to keep the tether 5 in line with slot 6. Once the kite 1 is fully deployed from the rollers 1, and the rollers 1 are rotated into a position where their slots 6 are pointing upwardly, the external winches 7 associated with each roller 1 are able to reel out the tether rope 5 as the uplift generated by the kite 4 causes the kite to climb. Once the kite 4 has reached a sufficient altitude, the winches 7 can be locked so as to transfer the kite's pull forces fully to the rollers 1.

[0045] Figure 7 shows the deployed kite 4 tethered to the kite deployment system. The tethers 5 connect the kite 4 at its side edges to the rollers 1. Once the kite has reached a sufficient altitude after launch, the rollers 1 are able to return to a substantially horizontal position and a locking mechanism may be provided to lock them in this position. Such a locking mechanism helps to spread the pull forces transferred to the rollers 1 and hence reduce the forces applied through the articulated joints 2 and 3.

[0046] During flight, the radial angle of the rollers 1 may be adjusted, either actively or passively, so that their slots 6 follow the lateral angle of the tether ropes 5. Furthermore, the length of each of the tether ropes 5 can be adjusted to maintain the kite's shape where the kite is flying laterally to the tether point.

[0047] Figure 8 shows a side view of the kite 4 and shuttle kite control system. The kite 4 comprises an inflatable frame

12 which provides the kite's aerofoil shape for generating the kite's lift. In the present embodiment, the tether ropes

5 are connected to shuttles 11 located on a track 10 formed on the side edges of the kite 4. The shuttles 11 can be moved along the track 10 under the control of an actuator and control system (not shown) . This adjusts the attachment point of the tether 5 to the kite 4, which alters the angle at which the kite's aerofoil profile is presented. This allows the kite 4 to be steered and provides responsive control of the kite's flight path. As this steering system only requires two tether ropes 5, it minimises the drag placed on the kite and hence improves efficiency.

[0048] In alternative embodiments, steering can be achieved by providing multiple control ropes 5 tethered to the kite 4 and controlling their lengths. However, such a system suffers from increased drag and slower kite speeds.

[0049] To retract the kite 4, the external winches 7 are activated to reel in the tethers 5. The control system may be used to steer the kite 4 into a neutral position vertically above the vessel so as to maintain a stable flight pattern and reduce the pull force generated by the kite 4.

That said, it is preferred if the kite 4 is not forced to stall, as this may result in the kite 4 and its tethers 5 crashing in an uncontrollable manner. Instead, a stable flight pattern is desired, which allows the kite 4 to gradually decrease in altitude as the tethers 5 are reeled in by the winches 7. Although the forces required to reel in a large kite are relatively high, this reeling action is archived via winches 7, which can have a small reel diameter and may include additional reel drums. As such, the torque power required by these winches can be minimised.

[0050] Once the kite 4 is reeled in so that it is adjacent to the rollers 1, the external winches 7 are locked to hold the tethers 5 in position and the rollers 1 are rotated to further draw in the kite 4 and wind it back on to the rollers 1. At this stage, the kite 4 is low in the air and therefore the uplift generated is minimised, meaning that the torque forces required for rotating rollers 1 is not excessively high. This allows the kite to be easily returned to the position shown in Figure 2, ready for relaunch.

[0051] During flight, in the event that wind speed drops and the kite 4 becomes unstable, the external winches 7 may be activated to rapidly pull on the kite to recover it from the unstable flight conditions by generating apparent wind. In water based applications, this rapid pull technique may also be used to re-launch the kite 4 after a water landing. If this action fails to return the kite 4 to stable flight, the winch 7 may simply fully retract the tethers 5 so the kite 4 can be wound back onto the rollers 1. This returns the kite 4 to the launch position, ready for relaunch when conditions permit.

[0052] Accordingly, it will be understood that the present invention provides a simple and effective kite deployment system which allows for automated or largely automated deployment and retraction of large aerofoil kites. This makes it commercially viable to use such large aerofoil kites in a variety of applications, such as:

i. Land based kite driven power generation; ii. Water based kite driven power generation; iii. Water based kite driven propulsion or assisted propulsion of water vessels.

[0053] Figures 9 to 11 show an embodiment of the present invention which provides a water going vessel 13 incorporating the kite deployment system discussed above in reference to Figures 1 to 8. In this embodiment, the water going vessel 13 is used for kite driven power generation and therefore incorporates a generator 15 which is connected to a water turbine 16 which sits beneath the waterline. It will be understood that although in this embodiment one turbine is used, multiple water turbines could alternatively be fitted.

[0054] Rotation of the water turbine 16 results in the generator 15 generating electricity, which in turn is transmitted to an electrolysis unit (not shown) which electrolyses water to produce hydrogen. Produced hydrogen can then be fed to the storage containers 14. A cryogenic unit may be provided for converting the hydrogen to liquid form before it is stored.

[0055] In unsuitable weather conditions, or when approaching a harbour for discharge, the kite 4 can be held in its stored position on the rollers 1, as shown in Figure 9. At this stage, it may also be necessary to fold the water turbine 16 and generator 15 into an elevated position at its mounting to the vessel's hull to provide clearance. When the kite 4 is to be launched, the rollers 1 are pitched upwards and positioned so that the suspended section of the kite 4 is held up by the oncoming wind, as shown in Figure 10. The kite 4 proceeds to launch, as is described above in reference to Figures 1 to 8.

[0056] Figure 11 shows the water going vessel 13 once the kite 1 has been fully deployed and is in flight. As can be seen, the rollers 1 have been tilted back and locked in their horizontal position, although they are able to rotate radially as the kite moves laterally with respect to the vessel 13. As the kite 4 generates lift, the force is transferred to the vessel 13 through tethers 5. This force acts to pull the vessel 13 forwards through the water, thereby causing the turbine's rotor blades 16 to rotate, and in turn the generator 15 to generate electricity for forming hydrogen. Alternatively, the electricity could be stored in a battery or by other means. Once the hydrogen containers 14 are filled, the vessel can then be steered to a harbour and the filled containers removed and replaced for the process to be repeated. The containers can be provided in the form of standard shipping container sizes in order to make use of conventional harbour infrastructure. One of the advantages of such a water based power generation system compared to a land based system is that it is able to access high and consistent off-shore winds. At the same time, such a water based system could be utilised, for example, in the far northern and southern regions of the Pacific and Atlantic oceans, which have high winds and are outside of the main shipping lanes. In this way, the vessels would not disturb shipping traffic, would not affect any environmental aesthetics, and do not occupy land area, as land based power generation systems.

[0057] As discussed above, the kite 4 is steered by a control system (not shown) to maintain its flight and hence the forward propulsion of vessel. For this purpose, the control system incorporates navigational and wind tracking systems (based on wether forecasts) which are able to direct the kite 4 and the vessel 13 towards areas of sufficient wind speeds which can be used to generate almost continuous energy at the designed nominal power of the system. As such, the system does not suffer from stalling winds, as do stationary wind power systems. This can improve the yield of the system up to three fold compared to stationary systems. In practice, it is not necessarily a requirement for the kite to remain permanently in the location of the highest winds because, provided the kite is prevented from stalling, moderate wind speeds are still able to generate useful levels of propulsion and hence power generation. Wind forecasts may be also used to avoid storms, high waves, sea ice, or icing of the kite, and as such prevent damage or inoperability of the kite or the vessel.

[0058] During travel, the trimming of the vessel 13 may also be adjusted when the kite 4 flies port or starboard. As the vessel 13 travels through the water, the lateral forces from the kite's pull need to be counterbalanced. The vessel's hull can be used to achieve this counter balance, thereby reducing the forces placed on the vessel's rudder (not shown) which may otherwise cause drag. This is achieved by controlling the hull's angle of attack (i.e. the vessel's stern-fore axis with respect to the travelling direction) . In this respect, the kite's attachment point to the vessel 13 can be shifted either towards fore or stern by using the linear actuation device 9 to move the pulley system 8 within the roller 1 (see Figure 6) . This acts to shift the kite's pull force moment around the vessel's axis to bring this into balance with the vessel's angle of attack. As a result, the lateral force components can be balanced, leaving the vessel's rudder to merely deal with course changes and minor fluctuations in the kite's pull force and direction. In an alternative embodiment, the shifting of the attachment point may be achieved, for example, by providing the rollers 1 on axially moveable platforms which can be moved along the vessel.

[0059] As will be understood from the above, the present invention therefore provides a simple and effective kite deployment system which allows for automated or largely automated deployment and retraction of large aerofoil kites from low altitudes.

[0060] It will be understood that the embodiments illustrated above show applications of the invention only for the purposes of illustration. In practice the invention may be applied to many different configurations, the detailed embodiments being straightforward for those skilled in the art to implement.

[0061] For example, it will be understood that the ability of the above embodiments to control the pitch and yaw of the rollers during launch and retraction of the kite allow the kite to be launched in a great variety of wind conditions. However, mechanically more simple arrangements are also possible, albeit this may compromise the system's ability to account for changing wind conditions. For example, on water based deployment systems, the vessel itself could be rotated in order to orientate the kite into the wind. Alternatively, for both land and water based systems, the rollers could be located on a rotatable platform able to rotate the kite into the wind during launch and retraction. Furthermore, the rollers could be tilted upwards in unison, which may be achieved, for example, by mounting both rollers on a single frame .

[0062] It is also envisaged that the rollers could be moved laterally relative to one another. During launch, this could be used to increase the area of the suspended kite exposed to the wind. This may be required in water going applications if the vessel is very narrow. Once launched, the drums could then be moved closer together to narrow the distance between the attachment points of the two kite tether ropes. This can be helpful to avoid distortion of the kite's shape when the kite flies in an off angle.

[0063] The rollers could also be moved independently in a number of directions. For instance, by shifting the rollers independently, the launch and recovery procedure may be further improved by avoiding shearing of the kite. As an example, in water based applications, vessel roll could be compensated by moving the rollers up and down independently of one another. Another use of the vertical shifting of the rollers would be to allow their height to be increased for launch or to generate clearance to allow greater movement of the rollers. For example, such an operation could be used in the embodiment shown in Figures 9 to 11 to provide clearance between the rollers 1 and the containers 14.

[0064] Various additional components could also be used in conjunction with the above mechanisms to improve their operations. For example, the rollers may be provided with tensioning wheels for tensioning the kite as it is wound on the rollers. These may be useful during launch, for example, to prevent the wound kite material from slipping on the spools as the as rollers are inclined. Additionally, eyes could be provided for controlling the feeding of the tethers onto the rollers and the winch.

[0065] It is also envisaged that instead of utilising external winches to reel in the tethers, the rollers themselves could be used for this purpose. For this, a shuttled eye could be used to control the laying of the tether rope on the rollers. However, the difficulty with such an arrangement is that the rollers would need to apply very high torque to be able to reel in a kite after use, and therefore such an arrangement is not preferred.

[0066] Furthermore, although in the above embodiments, the rollers have been described as cylindrical drums, it will be understood that alternative arrangements are possible. For instance, the roller may have a rounded "V" cross-section, where the above described pulley system is located in the valley of the "V". Moreover, more than two rollers may be provided. For instance, two main rollers could be used to store the kite, and two further drum rollers could be used to guide the kite during deployment and recovery. [0067] It will also be understood that although in the above example shown in Figures 9 to 11 the present invention is described in reference to a boat type vessel, the present invention could also be used to propel submersible vessels. For example, a submersible vessel could surface for deployment of the kite, and then submerge once the kite is airborne. In the application of power generation, this would allow a better stabilisation of the vessel by minimising wave influence and, as such, reducing mechanical loading on, for example, the water turbine (i.e. gyroscopic effect) .

[0068] Furthermore, although in the above examples, two rollers have been provided, it is feasible that a single roller may be provided onto which the kite is wound, with the other roller being substituted for a simple tether reeling system (pulley and winch system) . The kite could then be spooled from the single roller and, during launch, suspended between this and the tether reeling system. Once the kite has been inflated, the tethers could be reeled out from the roller and the tether reeling system in the same way as discussed above. The difficulty with such a system is that the kite would need to be deployed from one side, and hence may be uneven during its initial flight stages if the kite has an variable camber. This would make these initial stages difficult and therefore much less consistent than embodiments including two or more rollers.

[0069] Moreover, in the above embodiments the kite has been described as including an inflatable frame which is inflated by means of a valve which draws in oncoming air. It is, however, also envisaged that an inflation mechanism could be used to inflate the inflatable sections during launch and deflate the kite during recovery. For instance, a wind powered generator could be used to drive a compressor mounted on the kite for inflating the kite. Alternatively, the kite may simply include open inlets for feeding air into the inflatable sections from the airstream. In another example, the kite may include some permanent elastic structural elements which allow the kite to be wound around the rollers, but help its shape to form once the kite is deployed.

[0070] In embodiments where an inflation mechanism is provided for inflating the kite's frame, the inflation mechanism may be used during launch to actively inflate the suspended sections of the kite between the rollers. This acts to actively form the aerofoil shape in these un-reeled portions of the kite during the launch process and thereby helps to generate lift therein.

[0071] It may also be useful to be able to wind the kite onto a single roller 1 for longer term storage so that the entire of the kite material is retained on a single spool and therefore protected from damage. To ready the kite for launch, the kite material could then be re-spooled back onto both rollers to return it back to the position shown in Figure 2.

[0072] It will be understood that the multi-axis movement of the rollers may also allow them to be moved into a storage position. For example, the rollers could be retracted into a recess and moved adjacent to one another to reduce the space occupied by the deployment system when the kite is not in use.

[0073] It will also be understood that in instances where a strong wind is blowing, the kite may be launched by positioning the rollers so as to present the underside of the kite into the oncoming wind and utilising the kite's traction to achieve rapid launch, without making use of the kite's aerofoil characteristics. [0074] In very strong winds it is also feasible that the stored kite may be used as a sail by moving the rollers into a vertical or near vertical position and utilising the traction generated by the portion of the kite suspended between the rollers.

[0075] Finally, the rollers may be adjustable for accommodating different kite configurations. Moreover, the rollers may also be provided as detachable units to allow different kites to be rapidly fitted to the deployment system.