Autonomous underwater vehicle

Abstract

A waterborne vehicle 300, which may be an autonomous underwater vehicle, comprising a rechargeable energy store 310 and a thermoelectric generator 320 configured to provide power to the energy store.

Description

FIELD The present invention relates to an autonomous underwater vehicle (AUV), and in particular to an AUV comprising a rechargeable energy store and a thermoelectric generator. BACKGROUND Modern autonomous underwater vehicles (AUV), in particular military submersibles, are often required to perform long-duration missions. An AUV must be able to remain submersed for significant timescales to be able to successfully complete a mission. However, current energy source technology limits the range and endurance of such AUVs. Common combustion engines require refuelling regularly, which will require the AUV to resurface periodically, thus placing a strain on the logistics of the AUV’s operator to ensure support ships are always ready to refuel and maintain the AUV. Not only could this jeopardise the success of the mission by virtue of interrupting the AUV’s route, but it also increases the levels greenhouse gas pollution that both the AUV and support ships will produce. Additionally, a combustion engine is relatively loud, further increasing noise pollution to the environment. In contrast, nuclear reactors are much quieter and more environmentally friendly than combustion engines, and have been shown in submarines to provide the desired endurance. However, a nuclear reactor is impractical and overly expensive at the scale of an AUV. Batteries are generally considered a good compromise: they output relatively low noise, do not consume fossil fuels, and are cheap yet effective at powering an AUV. However, the relatively poor energy density of batteries means they are still required to resurface to be recharged to complete missions, once again having to deviate from a mission to find a recharging point, posing a risk or time delay to its success. The present invention seeks to improve the endurance of AUVs, and overcome the limitations of present battery technology. SUMMARY According to an aspect of the present invention, there is provided a waterborne vehicle comprising a rechargeable energy store, and, a thermoelectric generator configured to provide power to the energy store. As such, the waterborne vehicle will produce less noise and pollution emissions, and can recharge without the support of auxiliary ships. The rechargeable energy store may be a rechargeable mechanical energy store, such as for example, a flywheel(s) or a rechargeable electrical energy store, such, as, for example at least one of a rechargeable battery / batteries, a rechargeable capacitor(s), a rechargeable super-capacitor(s), , or a combination thereof. There may be back up or additional power provided by, such as, for example a combustion engine fed by a fuel tank (e.g. diesel), saltwater batteries etc. Preferably the rechargeable energy store is the rechargeable electrical energy store. The waterborne vehicle may be a manned or autonomous surface ship / boat / watercraft, or a manned or autonomous submersible. Preferably, the waterborne vehicle may be an underwater autonomous vehicle (AUV). The AUV may be able to operate underwater for periods of time far exceeding that of conventional AUVs since it can recharge numerous times. Preferably, the thermoelectric generator comprises a “hot” surface and a “cold” surface each formed of a thermoelectric material - while these surfaces are preferably on opposing sides of the thermoelectric generators, any suitable arrangement or geometry is envisaged in the present invention. In one example, the “hot” surface may be facing outwards and the “cold” surface may be facing inwards on opposing sides of a panel that is attached / formed to the body of the waterborne vehicle. In another example, the “hot” surface may be facing downwards and the “cold” surface may be facing upwards. The thermoelectric generator may be integrated into the hull of the waterborne vehicle, or it may be detachable from the hull. In one example, the thermoelectric generator may be arranged on the underside of the waterborne vehicle. As such, the waterborne vehicle can manoeuvre itself to ensure that the thermoelectric generator is directly above a heat source to optimise power generation. In one example, the waterborne vehicle may further comprise an attachment means configured to reversibly fasten the thermoelectric generator to the waterborne vehicle. The attachment means may be controllable to attach and detach the thermoelectric generator. As such, the thermoelectric generator may be easily and quickly fastened and unfastened from the vehicle, permitting rapid deployment. Preferably, the detachment may be achieved without any human intervention, and carried out as part of the autonomous operation of the waterborne vehicle. In one example, the waterborne vehicle may further comprise deployment means for deploying the thermoelectric generator. The ability to deploy and then manoeuvre the thermoelectric generator increases the operational fidelity of the vehicle, and as allows the thermoelectric generator to access areas / depths that the vehicle may not be able to reach directly. Preferably, the deployment means may comprise at least one of a tether, an articulated robotic arm, and / or, an extendable and / or pivotable boom. A first end of the deployment means may be attached to the waterborne vehicle and a second end of the deployment means may be attached to the thermoelectric generator. Alternatively, where the vehicle is an above surface vessel, the deployment means may comprise a crane disposed on the top / upper surface of the vehicle, so as to lift and then release the thermoelectric generator overboard. Preferably, the tether may be configured to be paid-out from, and drawnin to, the waterborne vehicle. The tether may be a cable / wire, multi-cored cable / wire or chain, or any other suitable tether such that it can be paid-out from, and drawn-in to, a storage means in / on the waterborne vehicle. The tether may be stored on a spool or the like, configured to be driven in either direction so as to pay-out and draw-in the tether. The tether prevents the thermoelectric generator from drifting too far from the vehicle while permitting a degree of manoeuvrability. In one example, the waterborne vehicle may further comprise an electrical cable configured to transfer power from the thermoelectric generator to the energy store. The electrical cable may be the tether. Alternatively, the electrical cable may be coupled along its length to the tether. The electrical cable may be coupled along its length to, or disposed within, the body of the robotic arm and / or the boom. The electrical cable may be the tether. In one example, the thermoelectric generator may further comprise an independent propulsion and / or steering means configured to moveably position the thermoelectric generator external to the waterborne vehicle. As such, the propulsion means provides steering functionality to the thermoelectric generator. In one example, the waterborne vehicle may further comprise a memory configured to store location data representing a location of at least one underwater heat source, and, a controller configured to be capable in use to retrieve the location data from the memory. As such, the vehicle is able to identify and transit to suitable underwater heat sources so as to recharge. Preferably, the controller may be further configured to enter a charging mode. In the charging mode, the controller may be configured to navigate the waterborne vehicle towards a location of the at least one underwater heat source, and, deploy the thermoelectric generator so as to charge the rechargeable energy store. In the charging mode and while the thermoelectric generator is deployed to charge, the controller may be configured to monitor the voltage / current generated in the thermoelectric generator. The controller may control the underwater vehicle and / or thermoelectric generator to manoeuvre such that it can find the best position relative to the heat source so as to generate the optimum electrical power for recharging. This may include a feedback loop that considers position and voltage / current. This may also or alternatively include temperature sensors to find the best position for the maximum temperature gradient across the thermoelectric generator. Alternatively, the controller may be configured to navigate the waterborne vehicle according to a route plan, the route plan comprising at least one waypoint for the waterborne vehicle to navigate in a predetermined order. The controller may be further configured to determine the current location of the waterborne vehicle, and, detect the remaining energy in the energy store. The controller may be also configured to calculate whether there is enough remaining energy to complete the route plan from the current location, and, if there is enough remaining energy, navigate the waterborne vehicle to follow the route plan. In this way, the waterborne vehicle is able to complete its mission efficiently, yet is quickly reconfigurable to reroute should the remaining energy is determined to be insufficient. Preferably, if the controller determines that there is not enough remaining energy, the controller may be configured to recalculate the route plan to include at least one underwater heat source as a waypoint such that the waterborne vehicle can charge the energy store and complete the route plan. The controller may also be configured to navigate the waterborne vehicle to follow the recalculated route plan. According to a second aspect of the present invention, there is provided a method of thermoelectrically charging a waterborne vehicle. The method comprises determining the location of a target underwater heat source, and, positioning the waterborne vehicle at a first predetermined distance from the target underwater heat source. The method further comprises deploying a thermoelectric generator such that heat from the target underwater heat source causes the thermoelectric generator to produce power, and, transferring the power from the thermoelectric generator to a rechargeable energy store of the waterborne vehicle so as to charge the rechargeable energy store. This method permits the waterborne vehicle to operate for longer periods and while producing less pollution. In a preferred example, the step of deploying the thermoelectric generator may further comprise controllably detaching the thermoelectric generator from an attachment means on the waterborne vehicle, and, moveably positioning the thermoelectric generator to a second predetermined distance from the target underwater heat source. The second predetermined distance is smaller than the first predetermined distance of the waterborne vehicle. As such, the waterborne vehicle can be kept at a safe distance from the heat source so as to not risk damage (whether from heat, debris, or other chemicals that may be emanating from the heat source) while the thermoelectric generator can generate power to recharge the waterborne vehicle. BRIEF DESCRIPTION OF THE FIGURES Embodiments of the invention will now be described by way of example only with reference to the figures, in which: Figure 1a shows a schematic view of an autonomous underwater vehicle (AUV) with an integral thermoelectric generator arranged on the underside according to the present invention; Figure 1a shows an example AUV with a thermoelectric generator detachably attached on the underside according to the present invention; and Figure 2 shows an example AUV with a thermoelectric generator attached to a tether according to the present invention; Figure 3a shows an example AUV with a thermoelectric generator deployed into a hydrothermal vent according to the present invention; Figure 3b shows an example waterborne vehicle with a thermoelectric generator deployed into a hydrothermal vent according to the present invention; Figure 4a shows an example AUV with a thermoelectric generator deployed with an articulated robotic arm according to the present invention; Figure 4b shows an example AUV with a thermoelectric generator deployed with a boom according to the present invention; Figure 5a shows an example of location data representing the location of hydrothermal vents according to the present invention; and, Figure 5b shows a systematic diagram of an example AUV 500 with a memory 502 and a controller 506; and, Figure 6 shows an example method according to the present invention. DETAILED DESCRIPTION The present invention provides a waterborne vehicle that is capable of operating for extended periods without refuelling or support. Where the waterborne vehicle is submersible, it may remain submersed indefinitely, and is only limited by the life expectancy of the vehicle itself and its constituent parts, and by the availability of underwater heat sources in its mission area. While the examples herein primarily describe an autonomous underwater vehicle (AUV), it will be appreciated by the skilled individual that the present invention may also be suitable for any manned or unmanned vehicles, such as submersible and surface ships. Figure 1a shows an example AUV 100 according to the present invention. The AUV 100 comprises a hull 102 and a propulsion means 104. The AUV 100 further comprises a rechargeable energy store 110, and a thermoelectric generator (TEG) 120 configured to provide power to the energy store 110. In this example, the rechargeable energy store 110 is a rechargeable battery 110. While the subsequent discussion will focus on a single battery and a single TEG, it will be appreciated by the skilled individual that the present invention may be performed with any number of batteries and any number of TEGs (and corresponding supporting devices). The hull 102 may be a pressure hull or the like. In one example, the pressure hull is made of metal, such as steel. As such, the pressure hull can handle the extremely high pressures exerted on the AUV 100 deep under the sea. The hull 102 may also comprise a cylindrical shape, which is known in the art to be particularly suitable for high pressure environments. However, the hull 102 may be any suitable shape or profile. The propulsion means 104 may be any suitable propulsion means for propelling a submersible. In an example, the propulsion means 104 may be a propeller, propulsor or water jet. The propulsion means 104 may also provide steering functionality to the AUV 100. Alternatively or additionally, the AUV 100 may comprise control surfaces, such as planes and / or rudders, for steering the AUV. The AUV 100 may comprise ballast tanks and / or a ballast system to controllably descend and ascend the AUV. The battery 110 may be configured to provide power to the propulsion means 104. Additionally or alternatively, the battery 110 may be configured to provide power to auxiliary devices in the AUV 100, i.e. anything other than the propulsion means 104. For example, the battery 110 may provide power to a ballast system, a controller, a navigation system, etc. The battery 110 may provide power to an electric motor which drives the propulsion means 104. The present invention seeks to improve the range of the AUV 100 by providing it with the ability to recharge the battery 110 while submersed. The operability of the AUV 100 may also be limited by the auxiliary devices, and hence the present invention provides an effective means to extend the AUV’s range by resupplying the battery 110. Therefore resupplying energy to the battery clearly will extend the range and / or endurance of the AUV 100. In the example of figure 1a, the TEG 120 is integrated into the hull 102 such that it is exposed to the water. The TEG 120 may be arranged on the underside of the AUV 100. Alternatively, the TEG 120 may be arranged in any orientation to optimise its ability to extract power from a heat source (discussed in more detail below). Thermoelectric generators - also known as Seebeck generators - operate by converting a temperature gradient across two operating surfaces into an electric voltage. The operating surfaces comprise a “hot” surface and a “cold” surface each formed of a thermoelectric material - while these surfaces are preferably on opposing sides of the TEG 120, any suitable arrangement or geometry is envisaged in the present invention. The resulting heat flow induces a diffusion of charge carriers, and thus creates a voltage difference. The TEG 120 may be any known or suitable thermoelectric generator. In an example, the TEG 120 may comprise a thermocouple or series of thermocouples (i.e. thermopile). The thermocouple / thermopile comprises at least two thermoelectric materials. In an example, the two thermoelectric materials may be any suitable n-doped and p-doped semiconductors. The semiconductors may comprise bismuth telluride, lead telluride, or silicon germanium, or alloys based thereon. As such, the TEG 120 of figure 1a may be deployed relative to a heat source (e.g. hydrothermal vent) so as to receive a temperature gradient thereacross, and subsequently to produce a voltage that is used to charge the battery 110. While figure 1a only shows a TEG 120 arranged on the underside of the AUV 100, it will be appreciated by the skilled individual that the TEG 120 may comprise a “hot” surface arranged on the underside (as drawn) and a “cold” surface arranged elsewhere on the AUV 100 so as to optimise power generation. Preferably the “cold” surface is arranged on the opposing top side of the AUV 100 - however, it is not necessary that either surface of the TEG 120 is arranged as such. Figure 1b shows another example AUV 100 according to the present invention wherein the TEG 120 is attached to the hull 102, as opposed to being integrated into the hull 102. In particular, the AUV 100 comprises an attachment means 130 configured to allow the TEG 120 to be removed and deployed from the AUV 100. The attachment means 130 may integrated into, or itself attached to, the hull 102. The attachment means 130 may be arranged on the underside of the AUV 100. Alternatively, the attachment means 130 may be arranged at any suitable point on the AUV 100 to attach and hold the TEG 120. The attachment means 130 is controllable to attach and detach the TEG 120. As such, during operation of the AUV 100, a user or a controller may initiate the TEG 120 to be released from the attachment means 130, for example upon initiating a charging mode. Additionally, the attachment means 130 may be controlled to attach / reattach the TEG 120 to the AUV 100, for example upon conclusion of a charging mode. The general location of the TEG 120 when attached to the attachment means 130 is henceforth referred to as the stored position. Referring now to figure 2, there is shown an example AUV 200 according to the present invention. The AUV 200 comprises a tether 240. A first end of the tether is attached to the AUV 200 and a second end of the tether is attached to the TEG 220. As such, the tether 240 acts as a safety mechanism to prevent the TEG 220 drifting away or otherwise being lost. In an example, the tether 240 may be maintained at a predetermined length, such that the TEG 220 may be released and then it can lower under its own weight to the predetermined length beneath the AUV 200. Additionally, the AUV 200 may manoeuvre itself to deploy the TEG 220 as desired. The second end of the tether 240 comprises a fastening means 244 fastened to the TEG 220. The fastening means 244 may be releasable, although it is preferable that it is not controllably releasable while operating the AUV 200. Additionally, the fastening means 244 may be arranged to generally support the TEG 220 on its “cold” surface so as to orientate the TEG 220 with its “hot” surface facing downwards when suspended under its own weight. As such, the TEG 220 will generally and favourably be positioned so that additional time- and energyconsuming manoeuvring is not required. In an example, the fastening means 244 may comprise at least two points of attachment to the TEG 220, which converge together at the second end of the tether 240. The two points of attachment may comprise nuts and bolts, screws, clamps, or any other suitable fastening means. Such fastening means may be fastened and undone remotely by mechanical or solenoid actuators. The tether 240 may be configured to be paid-out from, and drawn-in to, the AUV 200. The tether 240 may further comprise a spooling device 242 to pay it out and draw it in. As such, a user or a controller may controllably pay out the tether 240 so as to control the exact distance the TEG 220 is maintained below the AUV 200. The spooling device 242 may, for example upon conclusion of a charging mode, draw in the TEG 220 such that the tether 240 is substantially fully retracted and the TEG 220 is “reattached” to the AUV 200 in the stored position. The AUV 200 may comprise both the attachment means 130 (shown in figure 1 b) and the spooling device 242, or it may comprise only one. For example, a brake or clutch on the spooling device 242 may provide the attachment means 130. The tether 240 may comprise an electrical cable (shown as the tether 240) configured to transfer power from the TEG 220 to the battery 210. Alternatively, the tether 240 may be coupled to an electrical cable along at least a part of its length, the electrical cable configured to transfer power from the TEG 220 to the battery 210. The electrical cable may be arranged so as to not take any tension directly. The electrical cable may be formed within the tether 240, for example concentrically disposed with a tensioned tether. The electrical cable may run adjacent to the tether 240 along its length, and either be attached at points along the length, or both be formed within a sheath or the like to ensure they are held together. Alternatively, the electrical cable may be arranged to take the tension exerted between the AUV 200 and the TEG 220, thus acting both as a power cable and as a tensioned tether. The electrical cable may be any conventional and suitable conducting power cable to transmit electrical power to the battery 210, or a charging device configured to charge the battery 210. The electrical cable may comprise any suitable conductive material. Referring now to figure 3a, there is shown an example AUV 300 in an example environment comprising the sea / ocean floor 10, the sea / ocean 20 and the water surface 30. The AUV 300 is deployed and submersed in the ocean 20. The ocean floor 10 comprises at least one heat source 40 - in this example, hydrothermal vents 40a, 40b are shown. Each hydrothermal vent 40a, 40b is shown emitting heat 42a, 42b respectively. While the following discussion focusses on hydrothermal vents, the present invention is not limited to only this heat source. In a non-limiting example, underwater volcanoes may be suitable heat sources upon eruption. While naturally occurring heat sources are favourable, man-made underwater heat sources will also be suitable. This may be waste heat produced during certain operations or processing. Indeed, it is envisaged that man-made heat sources -potentially controllable to produce heat as desired - may be built into the ocean floor 10 to assist an AUV 300 according to the present invention. The AUV 300 is shown with a tether 340 and spooling device 342; the AUV 300 may have attachment means (not shown) for attaching the TEG 320. While the AUV 300 comprises its own propulsion means 304 for manoeuvring itself, this may not be sufficient to manoeuvre the TEG 320 with sufficient fidelity. This is not least because the ocean 20 - or any other underwater environment - is subject to water currents of varying speeds, turbulence and randomness. Furthermore, heat sources such as hydrothermal vents expel material and create additional turbulence and convection currents. As such, the TEG 320 may comprise an independent TEG propulsion means 350 configured to moveably position the thermoelectric generator external to the AUV 300. Providing the TEG 320 with the independent TEG propulsion means 350 permits the AUV 300 to control the positioning of the TEG 320 more accurately. The independent TEG propulsion means 350 may be any suitable propulsion means for manoeuvring the TEG 320. For example, this may be any of the propulsion means as discussed above in relation to the main propulsion means 304. In the following example scenario for figure 3a: initially, the TEG 320 is attached to the attachment means (not shown) and the AUV 300 is submersed and in transit. Upon detecting that the battery 310 is low on energy, the AUV 300 enters a charging mode (discussed in more detail below) and determines the location of a target underwater heat source, in this example the target hydrothermal vent 40a. The AUV 300 then transits to the target hydrothermal vent 40a, and positions itself substantially above the hydrothermal vent 40a at a first predetermined distance. The AUV 300 subsequently deploys the TEG 320 and positions it in the heat 42a. The TEG 320 may be positioned at a second predetermined distance from the hydrothermal vent 40a, which is closer than the first predetermined distance. First, the TEG 320 is controllably detached from the attachment means. Second, the tether 340 is paid out so that the TEG 320 lowers towards the hydrothermal vent 40a under its own weight. While spooling out the tether 340, the AUV 300 may continually manoeuvre itself to ensure that the TEG 320 is lowered to the desired location. Third, the TEG 320 may, additionally or alternatively, manoeuvre itself using the independent propulsion means 350 to further improve the accuracy of locating it within the heat 42a. The skilled individual will appreciate deploying the TEG 320 to position it relative to the heat 42a from the hydrothermal vent 40a is not trivial, and would likely require a constant feedback control loop to maintain the position. This includes factoring in the environment, currents, convection, etc, and would also require various sensors to coordinate with a controller to control the AUV 300 to perform each of its operations accordingly. While the present inventors have not provided an exhaustive explanation as to the exact control loop for this purpose, it is nonetheless common in the art. Continuing the example scenario, once positioned, the TEG 320 is induced to produce power by the heat 42a. The TEG 320 can thus be controlled to transfer the power to the rechargeable battery 310 so as to charge it. Upon fully recharging the battery 310 - or upon reaching any other predetermined or desired stopping point - the AUV 300 stops charging and can begin retracting the TEG 320. This may include manoeuvring the entire AUV 300 away from the hydrothermal vent 40a. Alternatively or additionally, this may include manoeuvring the TEG 320 itself away from the hydrothermal vent 40a. The spooling device 342 may draw in the tether 340 so as to bring the TEG 320 into proximity with the attachment means. Concluding the example scenario, once the TEG 320 has successfully been positioned proximate to the attachment means on the AUV 300, it is reattached to the attachment means. Thus, the charging mode ceases, and the AUV 300 can continue along its route. Referring now to figure 3b, there is shown there is shown an example waterborne vehicle 300 - in particular, a surface vessel 300 rather than an AUV as shown in figure 3a. The surface vessel 300 is deployed within, and floating on, the ocean 20. The surface vessel 300 comprises a crane 344 disposed on the top / upper surface of the vessel, so as to lift and then release the TEG 320 overboard. In every other aspect, figure 3b is the same as figure 3a. Referring now to figures 4a and 4b, there is shown an AUV 400 according to the present invention. The AUV 400 further comprises deployment means 460. A first, proximal end of the deployment means 460 is attached to the AUV 400 and a second, distal end of the deployment means 460 is attached to the TEG 420. The second end of the deployment means 460 may comprise a distal attachment means 462 - this distal attachment means 462 may be arranged to be controllable to attach and detach the TEG 420. As such, the deployment means 460 may be operated to release and “catch” the TEG 420 with the distal attachment means 462 during use. In an example, the deployment means 460 may be operated to position the TEG 420 at some lateral distance away from the AUV 400, and then release the TEG 420 from the distal attachment means 462 such that the TEG 420 can descend at an offset lateral position. In another example, where the TEG 420 is already released, the deployment means 460 may be operated to position the distal attachment means 462 proximate to the TEG 420, at which point the TEG 420 may be reattached and subsequently moveably positioned at the stored position on the AUV 400. The distal attachment means 462 may be any suitable attachment means. This may be like the fastening means of referred to in figure 2. Alternatively, the attachment means 462 may be a controllable clamp, clip, screw, etc (with corresponding engagement means on the TEG 420). The distal attachment means 462 may be an end effector or the like, such as a gripping device or robotic hand - this provides the deployment means 460 with increased functionality to “grab” the TEG 420 and manoeuvre it accordingly. In the example of figure 4a, the deployment means comprises an articulated robotic arm 460a. The articulated robotic arm 460a may have one or more joints and / or axes of movement. In the example of figure 4b, the deployment means comprises a boom 460b. The boom 460b may be extendable, and may have two or more telescoping sections. Additionally or alternatively, the boom 460b may be pivotable about the first end, in one or two axes. The boom 460b may also be rotatable about a centre axis. In an example, the deployment means 460 may be provided in addition to the attachment means (not shown), the tether 340, the spooling device 342 and the independent propulsion means 350 of the AUV 300 shown in figure 3a - as such, the deployment means 460 supplements these functionalities. In another example, the deployment means 460 may be provided in place of one or some of these features. In yet another example, the deployment means 460 may be provided in place of all of these features, as shown in figures 4a, 4b. In this example, AUV 400 may comprise an electrical cable configured to transfer power to the battery 410. This electrical cable may be coupled to the deployment means 460 along at least a part of its length. Alternatively, the electrical cable may be formed within, or as a part of, the deployment means 460. Referring now to figure 5a, there is shown example location data representing the location of underwater heat sources 40, in this example hydrothermal vents. In particular, figure 5a shows a map of the Atlantic Ocean -including the North and South Atlantic Oceans - in between continental land masses. Above sea level land is referenced as 50; sea / ocean is referenced as 20 (as in figures 3a, 3b). The hydrothermal vents 40 are represented as diamonds. This is not an exhaustive list of hydrothermal vents 40 in the Atlantic Ocean, but rather an illustrative example of the type of location data that may be utilised by the present invention. Additionally, as discussed above, the location data may include heat sources other than hydrothermal vents, and may label them accordingly. Referring now to figure 5b, there is shown an example of an AUV 500 comprising a memory 502 and a controller 506. The memory 506 is configured to store location data 504 representing the location of at least one underwater heat source. The controller 506 is configured to retrieve the location data 504 from the memory 502. When a charging mode is entered, the controller 506 navigates the AUV 500 towards a location of the at least one underwater heat source and deploys the thermoelectric generator so as to charge the rechargeable battery. The controller 506 may be configured to navigate the AUV 500 according to a route plan. The route plan may comprise at least one waypoint for the AUV 500 to navigate in a predetermined order. In an example, prior to setting off on the mission, the route plan may comprise a starting waypoint, a finishing waypoint, and optionally at least one waypoint along the route. As such, the AUV 500 is controlled by the controller 506 follow the route plan according the waypoints and in order. The controller 506 may determine the current location of the AUV 500. The location may be determined by any one of a number of known navigating techniques, such as satellite navigation (at relatively shallow depths), dead reckoning navigation and inertial navigation. The controller 506 may detect the remaining energy in the battery. Any suitable sensor or combination of sensors may be used to determine the remaining energy in the battery, for example current and / or voltage sensors. The controller 506 may calculate whether there is enough remaining energy to complete the route plan from the current location. Based on factors such as remaining distance, state of charge of the battery, state of health of the battery, current discharge rate and more, the effective range of the AUV 500 can be calculated. The calculation could also factor in other extrinsic data, such as water temperatures along the route, tide movement, sea / ocean currents, etc -these may be estimated or received remotely. If there is enough remaining energy, the controller 506 may navigate the AUV 500 to follow the route plan. Since the effective range of the AUV 500 permits it to complete the route plan, a charging mode does not need to be entered, and the AUV 500 can complete its mission. If there is not enough remaining energy, the controller 506 may recalculate the route plan to include at least one underwater heat source as a waypoint such that the AUV 500 can charge the battery and complete the route plan. At this stage, the AUV 500 enters the charging mode. Recalculating the route plan may be designed according to user preference. In one example, the route plan may be recalculated so that the AUV 500 simply diverts to its nearest heat source, before returning back to where it initially diverted, substantially near. Alternatively, the controller 506 may recalculate the route plan so as to optimise at least one of total energy consumption, total mission time, and total distance travelled. As such, the AUV 500 may be controlled to continue along its route (for example for another one or more waypoints) so as to reach a heat source further away but which is optimises at least one of the aforementioned parameters. In another example, the controller 506 may calculate that it requires two or more heat sources as a waypoints to complete the route plan. As above, recalculation of the route plan depends on the desired optimisation. The controller 506 may subsequently navigate the AUV 500 to follow the recalculated route plan. By providing the location data 504 for the heat sources, navigating to thereto is quite simple. However, redundancy may be built into the system by providing various sensors, such as thermal, salinity and chemical sensors. As such, when the AUV 500 is in the vicinity of the target heat source, it can detect characteristics that may be associated with the particular heat source, permitting the controller 506 to more accurately locate the heat source and thus navigate the AUV 500 accordingly. Figure 6 shows an example method 600 of thermoelectrically charging an AUV according to the present invention. Step 602 comprises determining the location of a target underwater heat source. Step 604 comprises positioning the AUV at a first predetermined distance from the target underwater heat source. Step 606 comprises deploying a thermoelectric generator such that heat from the target underwater heat source induces the thermoelectric generator to produce power. Step 608 comprises transferring the power from the thermoelectric generator to a rechargeable battery of the AUV so as to charge the rechargeable battery. Between steps 604 and 606, the method may comprise controllably detaching the thermoelectric generator from an attachment means on the AUV. The method may further comprise moveably positioning the thermoelectric generator at a second predetermined distance from the target underwater heat source. The second predetermined distance may be smaller than the first predetermined distance. The first predetermined distance may be a safe minimum distance for the 5 AUV to operate away from the heat source. While the AUV may be provided with heat panels or the like, it is likely that maintaining the AUV at a safe minimum distance will avoid potential heat damage, and potentially keep the AUV at a safe distance from any corrosive substances ejected from e.g. a hydrothermal vent. 10

Claims

1. A waterborne vehicle comprising:a rechargeable energy store; and, a thermoelectric generator configured to provide power to the energy store.

2. A waterborne vehicle according to claim 1, wherein thethermoelectric generator is arranged on the underside of the waterborne vehicle.

3. A waterborne vehicle according to claim 1 or 2 further comprisingan attachment means configured to reversibly fasten the thermoelectric generator to the waterborne vehicle.

4. A waterborne vehicle according to any preceding claim furthercomprising deployment means for deploying the thermoelectric generator.

5. A waterborne vehicle according to claim 4, wherein the deploymentmeans comprises at least one of:a tether;an articulated robotic arm; and / or, an extendable and / or pivotable boom.

6. A waterborne vehicle according to claim 5, wherein the tether isconfigured to be paid-out from, and drawn-in to, the waterborne vehicle.

7. A waterborne vehicle according to any preceding claim furthercomprising an electrical cable configured to transfer power from the thermoelectric generator to the energy store.

8. A waterborne vehicle according to any of claims 3 to 7, wherein thethermoelectric generator further comprises an independent propulsionmeans configured to moveably position the thermoelectric generator external to the waterborne vehicle.

9. A waterborne vehicle according to any preceding claim furthercomprising:a memory configured to store location data representing a location of at least one underwater heat source; and,a controller configured to be capable in use to retrieve the location data from the memory.

10. A waterborne vehicle according to claim 9, wherein the controller isfurther configured to enter a charging mode,wherein, in the charging mode, the controller is configured to: navigate the waterborne vehicle towards a location of the at least one underwater heat source; and,deploy the thermoelectric generator so as to charge the rechargeable energy store.

11. A waterborne vehicle according to claim 9, wherein the controller isfurther configured to navigate the waterborne vehicle according to a route plan, the route plan comprising at least one waypoint for the waterborne vehicle to navigate in a predetermined order, and,wherein the controller is further configured to:determine the current location of the waterborne vehicle;detect the remaining energy in the energy store;calculate whether there is enough remaining energy to complete the route plan from the current location;if there is enough remaining energy, navigate the waterborne vehicle to follow the route plan.

12. A waterborne vehicle according to claim 11, wherein if the controllerdetermines that there is not enough remaining energy, the controller is configured to:recalculate the route plan to include at least one underwater heat source as a waypoint such that the waterborne vehicle can charge the energy store and complete the route plan; and,navigate the waterborne vehicle to follow the recalculated route plan.

13. A waterborne vehicle according to any preceding claim wherein thevehicle is an underwater autonomous vehicle.

14. A method of thermoelectrically charging a waterborne vehicle, themethod comprising:determining the location of a target underwater heat source;positioning the waterborne vehicle at a first predetermined distance from the target underwater heat source;deploying a thermoelectric generator such that heat from the target underwater heat source causes the thermoelectric generator to produce power; and,transferring the power from the thermoelectric generator to a rechargeable energy store of the waterborne vehicle so as to charge the rechargeable energy store.

15. A method according to claim 14 wherein the step of deploying thethermoelectric generator further comprises:controllably detaching the thermoelectric generator from an attachment means on the waterborne vehicle; and,moveably positioning the thermoelectric generator at a second predetermined distance from the target underwater heat source, and,wherein the second predetermined distance is smaller than the first predetermined distance.

16. A waterborne vehicle according to any preceding claim, wherein therechargeable energy store is a rechargeable electrical energy store.AMENDMENTS TO THE CLAIMS HAVE BEEN FILED AS FOLLOWS:26 06 2521CLAIMS1. A waterborne vehicle comprising:a rechargeable energy store;a thermoelectric generator configured to provide power to the energy store; and,an attachment means configured to reversibly fasten the thermoelectric generator to the waterborne vehicle.

2. A waterborne vehicle according to claim 1 further comprisingdeployment means for deploying the thermoelectric generator.

3. A waterborne vehicle according to claim 2, wherein the deploymentmeans comprises at least one of:a tether;an articulated robotic arm; and / or, an extendable and / or pivotable boom.

4. A waterborne vehicle according to claim 3, wherein the tether isconfigured to be paid-out from, and drawn-in to, the waterborne vehicle.

5. A waterborne vehicle according to any preceding claim furthercomprising an electrical cable configured to transfer power from the thermoelectric generator to the energy store.

6. A waterborne vehicle according to any preceding claim, wherein thethermoelectric generator further comprises an independent propulsion means configured to moveably position the thermoelectric generator external to the waterborne vehicle.

7. A waterborne vehicle according to any preceding claim furthercomprising:a memory configured to store location data representing a location of at least one underwater heat source; and,26 06 25a controller configured to be capable in use to retrieve the location data from the memory.

8. A waterborne vehicle according to claim 7, wherein the controller is5 further configured to enter a charging mode,wherein, in the charging mode, the controller is configured to:navigate the waterborne vehicle towards a location of the at least one underwater heat source; and,deploy the thermoelectric generator so as to charge the 10 rechargeable energy store.

9. A waterborne vehicle according to claim 7, wherein the controller isfurther configured to navigate the waterborne vehicle according to a route plan, the route plan comprising at least one waypoint for the waterborne 15 vehicle to navigate in a predetermined order, and,wherein the controller is further configured to:determine the current location of the waterborne vehicle; detect the remaining energy in the energy store;calculate whether there is enough remaining energy to 20 complete the route plan from the current location;if there is enough remaining energy, navigate the waterborne vehicle to follow the route plan.

10. A waterborne vehicle according to claim 9, wherein if the controller25 determines that there is not enough remaining energy, the controller isconfigured to:recalculate the route plan to include at least one underwater heat source as a waypoint such that the waterborne vehicle can charge the energy store and complete the route plan; and,30 navigate the waterborne vehicle to follow the recalculated routeplan.

11. A waterborne vehicle according to any preceding claim wherein thevehicle is an underwater autonomous vehicle.26 06 2512. A method of thermoelectrically charging a waterborne vehicle, themethod comprising:determining the location of a target underwater heat source;5 positioning the waterborne vehicle at a first predetermineddistance from the target underwater heat source;deploying a thermoelectric generator such that heat from the target underwater heat source causes the thermoelectric generator to produce power; and,10 transferring the power from the thermoelectric generator to arechargeable energy store of the waterborne vehicle so as to charge the rechargeable energy store.

13. A method according to claim 12wherein the step of deploying the15 thermoelectric generator further comprises:controllably detaching the thermoelectric generator from an attachment means on the waterborne vehicle; and,moveably positioning the thermoelectric generator at a second predetermined distance from the target underwater heat20 source, and,wherein the second predetermined distance is smaller than the first predetermined distance.

14. A waterborne vehicle according to any preceding claim, wherein the25 rechargeable energy store is a rechargeable electrical energy store.

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