Underwater vehicle launch and recovery cradle

Abstract

A cradle (100) for underwater launching and recovery of an underwater vehicle (200) from a marine body (400). The cradle (100) comprises a receptacle (102) for receiving the underwater vehicle (200), a tether attachment (107) for connecting the cradle (200) to the marine body (400) via a tether (106), and a propulsion means (104) for manoeuvring the receptacle (102) in water (404) relative to the marine body (400).

Description

UNDERWATER VEHICLE LAUNCH AND RECOVERY CRADLE ,SYSTEM AND METHOD

[0001] The present application concerns apparatus , systems , and methods for launching and recovering an underwater vehicle , and particularly an unmanned underwater vehicle , such as an autonomous underwater vehicle (AUV) . The present disclosure is especially relevant to powered apparatus and systems , as well as associated methods for deploying and retrieving subsea devices from marine bodies such as ships , submarines , docks and of fshore structures .Background of Invention

[0002] Autonomous underwater vehicles , AUVs , include submarine drones which operate without continuous input from a crew or operator, as well as underwater vehicles which receive continuous inputs from acoustic sensors (pingers ) which provide updates on the positioning of the AUV from a surface vessel . These vehicles are typically used for underwater search and exploration, providing oceanography data, and for underwater extraction . Advantageously, AUVs can be s i zed to house the equipment needed to carry out the speci fic task they are intended to perform, without having to provide for other support functions such as housing crew . Further, they can be specialised to operate in challenging underwater environments automatically for extended periods , thereby minimising safety risks and costs , whilst maximising data capture in the underwater environment . However, because of the si ze and speciali zation, AUVs are not usually equipped to travel to and from an onshore location . Instead, they are typically deployed from of fshore structures , or manned ships or boats , often referred to as mother vessels . Thisallows a support team located on the ship or offshore structure to collate data, reassign tasks to the AUV, as well as recharge and perform maintenance on the AUV. In some scenarios, data can also be uploaded and instructions updated by a remote team using a data link.

[0003] AUVs come in a large range of sizes, and currently different launch and recovery systems are needed depending on the type and size of the AUV being used.

[0004] For smaller AUVs, an over-the-side method of launch and recovery can typically be utilized. In this method, the AUV is manually dropped over the side of a ship or structure in an offshore location to launch, and is then autonomously piloted back to the side of the ship or structure to be manually lifted back up from the water to recover it. This method, however, is limited in that it requires an operator to lean over from the offshore location to drop the AUV. This limits the weight of the AUV that can be used, the maritime conditions within which it can be deployed, and the types of ships or structures they can be deployed from. For instance, a particular challenge is deployment during high sea states where waves and the resulting movements of the ship can make it dangerous or impossible to launch or recover the AUV manually.

[0005] For larger AUVs, a winch or crane is typically used for launch and recovery. In these methods, whilst launch is relatively simple, the recovery can include manual attachment of a tether to the AUV to connect it to the winch or crane. Systems using a cradle have been developed to overcome this, however there are drawbacks to these systems as well. For instance, these systems provide further complexity in operation and are again limited to useduring calm maritime conditions . For instance , deployment during high sea states is often prevented because larger AUVs may damage the li fting equipment or impact the ship as it moves in the waves . Waves can also make connecting to or detaching from the AUV challenging . Accordingly, usage is limited to low sea states , which in turn limits the weather window for operations , increasing logistics costs and risk of prolonged / delayed data campaigns .

[0006] The present invention therefore seeks to addres s the above issues .Summary of Invention

[0007] According to a first aspect of the invention, there is provided a cradle for underwater launching and recovery of an underwater vehicle from a marine body, the cradle comprising : a receptacle for receiving the underwater vehicle ; a tether attachment for connecting the cradle to the marine body via a tether ; and a propulsion means for manoeuvring the receptacle in water relative to the marine body .

[0008] In this way, a cradle for launching and recovery of an underwater vehicle , such as an AUV, can be controlled whilst underwater to co-ordinate its relative position with the underwater vehicle during launch and recovery . For example , the cradle and underwater vehicle can both be controlled to co-ordinate their respective propulsion systems to align and provide for controlled engagement and disengagement during deployment and recovery operations . At the same time , the cradle can be maintained in a stable position in the water, with the propulsion system operating to mitigate any forces applied by the tether or the water itsel f acting thereon which would otherwise make alignmentof the cradle and underwater vehicle more challenging . For instance , where the marine body is a surface vessel , and the motion of the vessel could otherwise impart forces on the tether, which would create instability in the cradle relative to the underwater vehicle as they separate during deployment or engage together during recovery . The propulsion means or unit allows slack to be created in the tether by moving the underwater vehicle upwards , which thereby allows the cradle to be stabilised, either in a static position or relative to the heading of the vessel or underwater vehicle . In other scenarios , the propulsion system may drive the cradle against a taut tether to stabilise the cradle . Further, recovery to an unmanned marine vessel is also possible because the cradle and the underwater vehicle are operable to automatically align themselves using their respective propulsion systems and engage , with the tether then being retractable to draw the cradle back to the unmanned marine vessel . Equally, in embodiments , a communication system may be used to communicate with the unmanned marine vessel (unmanned surface vessel ) to enable an operator in a Remote Operation Centre to control the propulsion unit on the cradle to assist the launch or recovery process or to monitor the process via the sensors on the cradle ( e . g . cameras ) .

[0009] In embodiments the propulsion means is controllable to manoeuvre the receptacle through the water to positionally stabilise the cradle against underwater forces applied thereto . In this way, the position of the cradle in the water may be maintained such that an underwater vehicle can be safely and easily launched or recovered into the receptacle . For example , some autonomously guided underwater vehicles are configured to maintain theirabsolute position by resisting the forces of underwater currents . Accordingly, by providing a sel f-propelled cradle , it can move in a corresponding manner to avoid the need for the underwater vehicle to constantly adj ust its position to dock and safely release from the cradle .

[0010] In embodiments the cradle further comprises a locking mechanism configured to releasably retain the underwater vehicle in the receptacle . In this way, the underwater vehicle may be securely stowed as it is lowered or li fted during deployment and retrieval operations . The underwater vehicle may also be securely stowed during transit operations where the underwater vehicle is secured in the cradle and, for instance , suspended under a surface vessel or housed on the deck of the vessel . The underwater vehicle can also be secured while the surface vessel is anchored . In this way, the underwater vehicle can be securely retained in the receptacle when it is stored, lowered, or raised in the cradle .

[0011] In embodiments , the cradle further comprises a power and / or data interface for establ ishing a power and / or data connection between the underwater vehicle to the cradle . In embodiments , the power and / or data interface may be integrated into the locking system, but in other arrangements is provided separately . The power connection may be used for recharging the underwater vehicle , for example using power transmitted from the marine body / surface vessel . The power for recharge could be delivered, for instance , using an inductive or conductive interface . For data trans fer, in embodiments a wireless transceiver is provided ( e . g . WiFi , Bluetooth, acoustic etc ) .

[0012] In embodiments the propulsion means comprises one or more thrusters operable to manoeuvre the receptacle through six degrees of freedom . In this way, the cradle can be operated to counter forces in three planes and in three degrees of rotation, allowing for improved stability of the cradle in the water .

[0013] In some embodiments the tether attachment comprises an interface for connection to an interface line in the tether for establishing a power and / or data connection between the marine body and the cradle . The tether may therefore be provided as a line comprised of several layers or cores . For instance , in one arrangement an outer polymer layer is provided, with a metal cable layer or core for providing tensional strength and one or more layers or strands for power and data connections . A " slip ring" connection may be provided on the winch for handling the power and data connection when the reeling device / winch is turned . With the above arrangements , power and control data may be transmitted to the cradle , and in turn the underwater vehicle when docked . Similarly, control and sensor data may be transmitted back from the cradle , or the underwater vehicle when docked . As such, the cradle can be powered and / or controlled remotely from the marine body . Further, data can be trans ferred to the marine body . For example , feedback sensor data, such as position or video data, water velocity data, underwater vehicle location data, may be transmitted for processing on the marine body, with this then being used to control the position of the underwater vehicle . In embodiments , data can be transmitted directly from the cradle to the marine body ( surface vessel ) using acoustic transmitters and receivers . This may allow the marine body to continuously confirm the relativeposition of the cradle. In embodiments where the cradle has its own onboard power, the tether may also only perform a load bearing function (i.e. no data / power link) .

[0014] In embodiments, the cradle further comprises a wireless transceiver for transmitting and receiving data between at least one of the marine body and the underwater vehicle .

[0015] In some embodiments the cradle comprises a battery for powering the propulsion means. In this way, the cradle can be remotely deployed and can be deployed from marine bodies which do not have a power supply.

[0016] In embodiments, the cradle comprises one or more sensors for deriving positional information relating to at least one of the underwater vehicle, the cradle, and the marine body. In this way, the position of the underwater vehicle and / or the cradle may be determined using sensors such as accelerometers, inertia sensors, IMU's, gyroscopes, fibre optic gyroscopes, Doppler Velocity Log (DVL) sensors, GPS sensors (transmitted via a surface vessel) , laser scanning and LiDAR sensors, proximity sensors, cameras, depth sensors, pressure sensor, magnetic field sensors, a sonar sensor, acoustic position sensors, visual position sensors, and water current meters.

[0017] In embodiments, the cradle comprises a controller for controlling the propulsion means to positionally stabilise the cradle by maintaining a vertical, horizontal and rotational position within the water. In this way, the cradle may operate autonomously to resist movement in the water, including movement in all six degrees of freedom also understood as surge, sway, heave, roll pitch and yawmotions . This may facilitate eas ier launch and recovery of the underwater vehicle .

[0018] According to a second aspect , there is provided an underwater vehicle launch and recovery system, the system comprising : a cradle according to any of the above ; and a tether for connecting the tether attachment to a marine body; a reeling device for mounting on the marine body; and a tether for connecting the tether attachment on the cradle to the reeling device mounted on the marine body, wherein the reeling device is operable to reel out or in the tether for lowering and raising the cradle , respectively .

[0019] In embodiments , the underwater vehicle launch and recovery system further comprises a tether management system . The tether management system may resist the tether from entangling and allow it to operate reliably and autonomously . The tether management system may include a controller for controlling the reeling device to prevent the tether becoming loose on the winch, as the propulsion on the cradle is activated . As such, the system may maintain tension on the winch drum, allowing to the tether section between drum and cradle to be tensionless . For this , the tether management system may include a locking mechanism which holds or clamps the tether and / or the tether on the drum, with this working in combination with the controller controlling the drum to maintain tension in the tether cable . The drum is thereby prevented from becoming loose and unwinding, which could otherwise lead to entanglement . The system may also include a safety mechanism for preventing the tether locking mechanism from causing over tension or excess compression of the tether . This may comprise an automatic release mechanism calibrated torelease the locking of the tether before the forces would cause damage to the tether and / or the overall system .

[0020] In embodiments , the reeling device is a winch .

[0021] According to a third aspect , there is provided a marine body comprising the underwater vehicle launch and recovery system according to the above .

[0022] According to a fourth aspect of the invention, there is provided a method of launching an underwater vehicle from a marine body, the method comprising : lowering, from the marine body, a cradle according to any of the above in water using a tether attached to the tether attachment , wherein the underwater vehicle is received in the receptacle of the cradle ; operating the propulsion means to li ft the cradle for introducing slack into the tether ; and, releasing the underwater vehicle from the receptacle of the cradle .

[0023] According to a fi fth aspect , there is provided a method of recovering an underwater vehicle to a marine body, the method comprising : lowering from the marine body a cradle according to any of the above in water using a tether attached to the tether attachment ; operating the propulsion means to li ft the cradle for introducing slack into the tether ; receiving the underwater vehicle in the receptacle of the cradle ; and, raising the cradle to the marine body via a tether attached to the tether attachment . In this way, easy recovery of the underwater vessel may be achieved because the position of the cradle may be stabilised by removing the influence of the tether and, in embodiments , by further controlling its position relative to the AUV .

[0024] In some embodiments , the step of operating the propulsion means comprises controlling the propulsion means to positionally stabilise the cradle by maintaining a vertical , hori zontal and rotational position within the water .

[0025] According to a further embodiment , the method further comprises controlling the propulsion unit to position the cradle into the direction of the current . According to a further embodiment , the method further comprises controlling the propulsion unit to position the cradle to automatically follow the marine body . The cradle may be controlled to maintain a stable directional position or a fixed position in all other motional directions to enable AUV recovery when the surface vessel is moving

[0026] According to a further aspect , there is provided a method of preventing entanglement of the tether in the underwater vehicle launch and recovery system of the above , wherein the method comprises : operating the propulsion means to li ft the cradle for introducing slack into the tether ; controlling the reeling device to prevent the tether becoming loose on a winch drum by engaging a locking mechanism for clamping the tether and tensioning the winch drum to maintain tension in the tether cable between the locking mechanism and the reeling device . The method may further comprise automatically releasing the locking of the tether i f the forces applied thereto exceed a threshold . In embodiments , a tether management system is provided for implementing this method .Brief Description of Drawings

[0027] I llustrative embodiments of the present invention will now be described with reference to the accompanying drawings in which :Figure 1 shows an AUV cradle according to an illustrative embodiment of the present invention;Figure 2 ( a ) shows an AUV for use with the AUV cradle of Figure 1 , and (b ) shows the AUV cradle i f Figure 1 with the AUV received therein;Figure 3 shows an underwater launch and recovery system incorporated the AUV cradle of Figure 1 ;Figure 4 shows a ship compri sing the underwater launch and recovery system of Figure 3 ;Figure 5 ( a ) and (b ) shows a schematic illustration of the thrust directions appliable by the AUV cradle shown in Figure 1 ;Figure 6 shows a schematic of a method of launching an AUV using the underwater launch and recovery system of Figure 3 ; andFigure 7 shows a schematic of a method of recovering an AUV using the underwater launch and recovery system of Figure 3 .Detailed Description

[0028] Figure 1 shows an AUV cradle 100 for use in an AUV launch and recovery system according to an embodiment of the invention . As described below, the AUV launch and recovery system may be incorporated into a marine body, for instance a marine vessel such as a ship or submarine , or a marine structure such as a dock or of fshore structure . This may thereby allow the AUV to be deployed into an underwater environment from the marine body .

[0029] The launch and recovery cradle 100 has a receptacle 102 for receiving an AUV during a launch or recovery operation. In this embodiment, the receptacle 102 is provided as a rigid mesh container into which the AUV can be securely seated. In other embodiments, the body of the receptacle may be formed of a flexible mesh material. In such arrangements, the opening of the receptacle 102 may be rigid or semi-rigid to allow the AUV to enter into the interior of the mesh body. A mesh material is preferable because it allows sea water to drain from the interior when the receptacle 102 is retracted and avoids air pockets when the receptacle 102 is submerged. The receptacle 102 is designed to be hydrodynamic, lightweight and strong, and designed to be able to support the weight of the AUV when lifted in air and underwater. It will be understood that shape and size of the receptacle 102, as well as the other systems of the cradle 100, can be dimensioned according to the AUV. Equally, the receptacle 102 may be configured to receive multiple different types of AUV. The cradle 100 may also comprise buoyancy elements for balancing the cradle.

[0030] The cradle 100 further comprises a propulsion unit 104, attached to the receptacle 102 via a mounting 116. The mounting 116 may allow different receptacles 102 to be attached to the propulsion unit 104 for use with different underwater vehicles. As such, different receptacles 102 can be customized for different shapes and sizes of underwater vehicles and attached as needed depending on the underwater vehicle being used. This may thereby allow the same overall system to be used for a variety of types of underwater vehicle .

[0031] The propulsion unit 104 forms a propulsion system for maneuvering the AUV cradle 100 underwater. Thepropulsion unit 104 comprises a plurality of thrusters 108 , 110 arranged on the body of the unit for creating thrust to allow the cradle 100 to hover under its own propulsion in the water column and to move the receptacle 102 in the water to direct its opening for receiving the AUV .

[0032] When the cradle 100 is lowered into the water from a marine body, a tether 106 , such as a wire , umbilical , cable , line or chain, is provided attached to a tether attachment 107 provided on the propulsion unit 104 for constraining the movement of the cradle 100 from the attachment location on the marine body . The tether attachment comprises a bend restrictor for preventing overbending of the tether . This may be especially important for power and data cables embedded in the tether umbilical . In use , the tether 106 can be reeled out to lower the cradle 100 into the water from the attachment location, reeled in to retract the cradle 100 . The tether 106 can also be locked to prevent the cradle 100 from dri fting more than a predetermined distance from the attachment location . The tether can also be locked for preventing the tether on the drum becoming overly slack such that it is at risk of entangling as the cradle propulsion is engaged .

[0033] During use when an AUV is being engaged into , or withdrawn from, the receptacle 102 , the propulsion unit 104 can be used to move the cradle 100 to hover in the water column with the tether 106 slack . As such, no forces from the attachment location on the marine body are trans ferred via the tether 106 , thereby allowing the cradle 100 to remain stationary in the water, or stationary relative to other obj ects in the water, such as the AUV . This thereby allows movement of the cradle in the water to be mitigated, thereby providing relative stability during underwaterengagement and disengagement between the AUV and the cradle 100 .

[0034] In this respect , once the tether 106 is no longer fully extended, the propulsion unit 104 can then be used to stabilise the cradle 100 with respect to underwater forces applied to the cradle 100 by movement of the water . The propulsion unit 104 can move the cradle through six degrees of freedom, as shown with reference to Figure 5 . To achieve this , in this embodiment , the propulsion unit 104 has vectored thrusters 108 and 110 . . These thrusters comprise four thrusters placed at 45-degree angles at the corners of the ROV for allowing precise control over both f orward / backward and side-to-side movements for mitigating the ef fect of Surge and Sway . Two or more vertically oriented thrusters are provided for countering heave , and Roll , Pitch, and Yaw is controlled using di f ferential thrust between pairs of thrusters .

[0035] It will be understood that alternative thruster configurations are also possible . For example , in a lateral thrusters configuration, surge could be countered by having two thrusters aligned along the AUV' s longitudinal axis , Sway could be countered by two lateral thrusters placed on the sides of the AUV, Heave could be countered by having two or more vertically oriented thrusters , and Roll , Pitch, and Yaw could be countered through varying the thrust levels between the thrusters , with some configurations using additional dedicated thrusters for yaw control . In an X-conf iguration, Surge , Sway, and Yaw could be countered using four thrusters arranged in an X-pattern on the hori zontal plane , Heave could be controlled using two or more vertically oriented thrusters , Roll and Pitch could be controlled through di f ferential thrust between the X-pattern thrusters. In a T-Conf iguration, Surge could be countered using one or two thrusters aligned along the AUV' s longitudinal axis, Sway could be countered using one or two lateral thrusters, Heave could be countered using two vertically oriented thrusters, and Roll, Pitch, and Yaw could be countered using differential thrust. Although, additional thrusters could be used for improved roll and pitch control. In a H configuration, Surge could be countered using Two or more thrusters aligned horizontally at the front and back of the AUV, Sway could be countered by providing one or more thrusters on each side of the AUV, Heave could be countered by providing two or more vertically oriented thrusters, and Roll, Pitch, and Yaw may be controlled through differential thrust and positioning of the horizontal and vertical thrusters. In a Combination Thruster Configuration, Surge may be controlled through multiple thrusters placed to provide forward and backward motion. Sway can be controlled using Thrusters placed laterally on either side of the AUV. Heave can be controlled using Vertically oriented thrusters, and Roll, Pitch, and Yaw can be countered using a mix of vectored and dedicated thrusters for precise control.

[0036] In other embodiments, the thrusters may comprise one or more directable thrusters, each of which can be rotated to provide the required direction of thrust. Further, an arrangement of thrusters can be used to provide the required direction of thrust using thrust vectoring. In embodiments, each thruster comprises a propeller for generating thrust. Other thrusters types may be used including: electric thrusters, hydraulic thrusters, magnetically coupled thrusters, jet propulsion thrusters, variable-pitch propellers, ducted fans (e.g. shroudedpropellers ) , turbine propulsion systems, hybrid propulsion systems . It will be understood in the art that di f ferent thruster types provide di f ferent advantages and disadvantages , and hence the selection may be based on balancing the ef ficiency, power, flexibility and reliability of the di f ferent thruster types depending on the application . The thrusters may also be distributed around the periphery of the cradle , rather than contained within one body as shown in Figure 1 . As such, di f ferent propulsion system arrangements are envisaged .

[0037] As the cradle 100 incorporates a propulsion system to manoeuvre the cradle underwater, the release and capture of the AUV from / to the cradle 100 may be made less challenging . In particular, aligning the AUV with the cradle 100 during release and capture may be simpli fied . To further assist with alignment , the cradle 100 may have an enlarged opening 115 to guide the AUV into the cradle 100 .

[0038] The propulsion unit 104 includes a controller 114 for controlling the thrusters . In other embodiments the propulsion unit 104 may receive control information remotely, for instance from a controller provided on the marine body . The controller controls the maneuvering of the cradle 100 . In one scenario , the propulsion unit 104 may be controlled in an automatic hovering mode , where the cradle 100 remains stationary in the water column . For this , sensor data may be used by the controller to provide feedback on location and acceleration forces being applied by water flow, with the controller controlling the thrusters to counteract these forces . The propulsion unit controller 114 may also have an automatic positioning mode for maintaining the relative position of the cradle 100 relative to the marine body where it is deployed from . Thecontroller 114 communicates with the marine body to maintain a safe distance between them to ensure that the connecting tether 106 remains slack during release and capture operations , and to ensure that the tether 106 does not entangle with the AUV . The controller 114 may also have a current heading hold mode , in which the thrusters are controlled to position the cradle in the direction of the current . This gives a high precision of control for the AUV . The controller 114 may also have an automatic positioning in relation to AUV mode , where the controller 114 communicates with the AUV to monitor their relative positions and controls its thrusters to position the cradle in 6 degrees of freedom to align with the AUV for docking .

[0039] The cradle 100 further comprises a locking mechanism 117 to releasably retain the AUV in the receptacle 102 of the cradle 100 . The locking mechanism 117 may be include an electromechanical actuator, and may be provided anywhere in the receptacle 102 . For instance , the locking mechanism may be actuatable to clamp the AUV, or close the opening for restraining the AUV . In some embodiments , the locking mechanism may engage with the AUV body to form a docking interface with the AUV for establishing a data and / or power connection between the cradle 100 and the AUV for trans ferring collected data or charging the AUV . The cradle 100 may in turn connect this data and / or power connection to the marine body . The locking mechanism 117 may be controlled by the controller 114 or remotely from a controller on the marine body . In some embodiments the locking mechanism 117 may automatically lock once the AUV is received within the receptacle 102 . Figure 2 (b ) shows an AUV 200 retained in the receptacle 102 of the cradle 100 by the locking mechanism 117 .

[0040] Referring to Figure 1 , the tether 106 may contain an interface cable for carrying power or data signals between the marine body and the cradle 100 . Accordingly, the cradle 100 may form a docking station for connecting the AUV to this interface cable , thereby allowing power, sensor data and control signals to be transmitted therebetween .

[0041] The cradle 100 therefore can be directly powered via the tether from the marine body supporting it . Control , data and sensor information can also be provided to and / or from the marine body . In embodiments , the tether can contain an Ethernet or Fiber Optic cable for carrying data, or data and control signals may be sent using an ethernet over mains , or power over ethernet , system, to minimise cables in the tether .

[0042] The cradle 100 further comprises a sensor module 112 . The sensor module may comprise a camera or an acoustic sensor for communicating with the AUV and confirming its position during the docking procedure . The sensor module 112 may also contain a motion sensor to provide data indicative of the relative position of the cradle , preferably, in all six degrees of freedom . The motion sensor may contain sensors including one or more of an inertial measurement unit ( IMU) , an accelerometer, and a fiber optic gyroscope . The sensor module 112 may also contain other position sensors for determining the relative position between the cradle , the marine body, and / or the AUV . For example , the sensor module 112 may include one or more of a depth sensor, pressure sensor, a proximity sensor, a sonar sensor, acoustic position sensors , an IMU, a visual position sensors , a water temperature sensor, an altimeter, and a water current meter, such as a sound velocity profile meter, for determining the speed anddirection of the current . In embodiments , a camera may be used to determine the relative position of the marine body and / or the AUV based on lights or characteristic features provided on these bodies . Power sent via the tether 106 may also be used to charge the AUV, for instance , via the locking mechanism or an inductive charging system between the cradle 100 and the AUV .

[0043] The cradle 100 may contain a wireless receiver (not shown) for receiving instructions and for sending and receiving data from, for instance , the marine body, the AUV, or other source . In such arrangements , the cradle 100 may still be powered via the tether 106 , and / or the cradle 100 may contain a battery for powering the propulsion unit 104 and controller 114 . When the cradle 100 is recovered back to the marine body, the battery may be charged from this location . The AUV battery may also be charged through the cradle 100 . In embodiments where the cradle 100 is sel f-powered, and the tether 106 omits a power cable , the overall system costs may be reduced, and the raising and lowering mechanism, such as that described below with respect to Figure 3 can be smaller and simpler .

[0044] Figure 3 shows an AUV launch and recovery system 300 comprising the cradle 100 described above . The system further comprises a lowering and raising mechanism 302 which can be mounted on or within the marine body . The lowering and raising mechanism 302 in this embodiment comprises a winch which is operable to lower or raise the cradle 100 by reeling out and reeling in the tether 106 .The winch 302 rotates to wind the tether onto and of f a drum to reel out or draw in the cradle 100 . However, other lowering and raising means may be suitable depending on the launch and recovery depth, such as an A-Frame typemechanism, or a friction-based mechanism for pulling or releasing the tether . To monitor the depth of the cradle 100 , the winch 302 may comprise a line counter for tracking the length of tether 106 deployed . The winch 302 further comprises a clamping device 303 which forms a locking mechanism part of a tether management system . The clamping device 303 is operable under control of a controller to maintain tension on the tether 106 on the winch drum when cradle propulsion is engaged and tether in water column is slack . The controller may also control a spooling device that automatically lays the tether onto the drum of the winch to avoid entanglement .

[0045] Figure 4 shows a marine body 400 , in this case a ship, with the underwater launch and recovery system as described with reference to Figure 3 incorporated therein . The marine body 400 is a surface vessel floating in the sea 404 , and functions as a mother vessel for deploying the AUV 200 . The mother vessel 400 comprises a moonpool 402 into which the propulsion unit 104 and the mounting 116 can be received when the tether 106 is fully retracted . This forms a wet porch which allows the propulsion unit 104 to enter or leave the water when the tether 106 is lowered or raised from the mother vessel 104 . In other embodiments , a larger moonpool 402 may be provided which may allow the entire cradle 100 , and the AUV when received therein, to be retracted into .

[0046] In this embodiment , the marine body 400 comprises a winch 302 as described in Figure 3 , as well as a data controller 408 and a power source 406 which connect to a docking interface 409 . When the propulsion unit 104 is received within the moonpool 402 , it connects to the docking interface 409 for connecting its controller 114 .The power source 406 may comprise a power management module and the data controller 408 may comprise a control and / or communication module for providing communication to the cradle 100 and to the AUV. In other embodiments, power and / or communication may be provided via the tether 106 or a wireless network. The marine body 400 may also comprise a docking station for the cradle 100. In some embodiments, this can be provided on the deck of the marine body 400, with the entire cradle 100 and AUV 200 being lifted free of the water column and onto the deck for docking. In other embodiments, the dock could be provided in the moonpool 402, where the cradle 100 and AUV is retracted into the cavity formed by the moonpool 402 inside the vessel. In embodiments, the cradle 100 can either remain in the water column in contact with the mother vessel, or be partially lifted from the water, or fully lifted from the water column inside the moonpool.

[0047] In use, the cradle 100 may be lowered into the water column from the mother vessel 400 to a safe depth beneath the mother vessel 400, typically 20-80 meters below the surface, and the propulsion means 104 is then activated to control the cradle 100 to hover in the water column in such a way that the tether 106 to the mother vessel 400 becomes slack. As such, no forces from the mother vessel 400 are transferred to the cradle 100.

[0048] Figure 5 shows how the cradle 100 can move in the water in six degrees of freedom. In figure 5(a) , diagram 500 demonstrates the available thrust directions of the cradle 100 in this embodiment. The cradle 100 can therefore move vertically in a Y axis 502, horizontally longitudinally in an X axis 506 and horizontally laterally in a Z axis 510. Further, the cradle 100 can rotate aroundthe Y axis as shown by arrow 504, around the X axis as shown by arrow 508 and around the Z axis as shown by arrow 512. As such, the cradle 100 has complete freedom of movement in the water. Thus, when stabilising the cradle in the water with respect to underwater forces applied to the cradle by waves and other water flows, the cradle 100 can apply thrust via its propulsion unit 104 to help to maintain its vertical, horizontal and rotational position within the water. This position can also be adjusted as described with reference to the propulsion modes described above, to follow the heading of a vessel or to align with the current of the water.

[0049] Figure 6 shows a method of launching an AUV using a cradle as described above. At step 6.1, the cradle 100 containing an AUV 200 held in the receptacle 102 is lowered from the marine body 400 in the water via the tether 106. At step 6.2, the propulsion unit 104 is controlled by controller 114 to stabilise the position of the cradle 100 against the underwater forces applied to the cradle 100. At step 6.3 the AUV is released from the receptacle 102 of the cradle 100 by unlocking locking mechanism 117. To exit the receptacle 102, the AUV' s propulsion system may move to reverse the AUV out of the receptacle to exit the receptacle of the cradle 100.

[0050] Figure 7 shows a method of recovering an AUV 200 using a cradle 100 as described above. At step 7.1. the cradle 100 is lowered from the mother vessel 400 in the water 404 via the tether 106. At step 7.2, the propulsion unit 104 is controlled to stabilise the position of the cradle 100 against the underwater forces applied to the cradle 100.

[0051] At step 7.3, the AUV is received in the receptacle of the cradle. The AUV may therefore propel itself forward to enter the receptacle 102. The AUV 200 may, for instance, locate the position of the AUV cradle 100 using underwater positioning, e.g. acoustic positioning. The cradle 100 may be in communication with the AUV 200 and provide information about its position and orientation. As such, position and orientation information may be continuously shared between the cradle 100 and the AUV 200 to determine steering inputs for the AUV, and / or provide position adjustment control inputs for AUV Cradle 100. This may thereby allow for reliable recovery of the AUV. The positional unit 104 is thereby used to position the AUV Cradle 100, while also maintaining slack on tether 106 to mother vessel 400.

[0052] At step 7.4, the cradle 100 is raised back up to the marine vessel 400 by operating the winch 302 to reel in the tether 106.

[0053] In this way, embodiments of the invention provide for a launch and / or recovery system for an underwater vessel which enables a larger operation envelope for different types and sizes of AUV. Furthermore, the underwater deployment enables launch and recovery in high sea states, thereby allowing for a greater number of operational days. As such, weather limitations and risk related to weather are mitigated which would otherwise drives up costs of the overall operation, and risks associated with prolonging offshore operations. This addresses the main challenge with the current solutions in the market. In high sea states, embodiments of the invention allow the cradle to be lowered to a depth deep enough under the surface vessel where there is little to noinfluence from the waves on the surface (typically below 30-50 meters in storm conditions) . As such, deployment and recovery can be achieved even under relatively extreme sea conditions .

[0054] The system is also adaptable in that embodiments allow the propulsion unit and receptacle to be provided as separate connectable parts. As such, different receptacles can be attached (e.g. as a bolted connection and power and data cable sub-surface connectors) to a standardized propulsion unit. The propulsion unit can thereby contain the more expensive sensors, electronics, and thruster elements. At the same time, the receptacle can thereby be provided as a relatively low-cost part, customized for a particular AUV, allowing for seamless docking, charging and data offload etc. AUV manufacturers could, for instance, design their own receptacle for their AUV to interface with the propulsion unit. This flexibility also allows operators to use multiple AUV' s of different designs with the same propulsion unit, where each AUV type has its own cradle to connect to the same thruster section.

[0055] The above-described embodiments may also enable AUVs to be safely launched and recovered from other marine bodies, such as Uncrewed Surface Vessels (USVs) , such as autonomous vessels and remote-controlled vessels. As such, USVs can be used as launch and recovery platforms for AUVs, thereby allowing for reduced operational costs. For example, in addition to avoiding crew costs, by launching the AUV from a USV, the AUV can remain out at site for much longer periods of time than a conventional AUV launched from a manned vessel. The USV is also able to weather storms and launch the AUV in high seas states. These factors mean that the USV and AUV combination is able to achieve fasterresponse times and more operational days than conventional systems , whilst also achieving a lower operational cost . Previously, the recovery of AUVs has been a particular challenge due to the vessel motion from the sea state , making it di f ficult and dangerous to safely control the AUV back into or onto marine bodies such as USVs or manned vessels .

[0056] Embodiments of the invention thereby provide a reliable launch and recovery system for AUVs , and in particular for launches from USVs , thereby opening up the possibility of AUVs to be designed in a more cost optimal way, in which the USV functions as a docking station for recharging of the AUV . As such, the AUV can be designed with smaller batteries , with batteries typically contributing a signi ficant proportion of the cost of AUVs , as well as making up a large part of their si ze and weight . Reducing the si ze of AUVs may therefore make the overall system cheaper . Moreover, the AUV also does not need to be optimi zed for longer single-mission endurance , which would otherwise be needed to fit into the workflow of a manned mother vessel . Accordingly, the time and personnel cost associated with manned mother vessels can be avoided .

[0057] Embodiments of the invention al so provide for the launch and recovery of small AUVs , which could enable these to be more widely used commercially in the of fshore industry . Generally, such smaller AUVs are not suitable for this because manual launch and recovery processes , which would otherwise be used, increase safety risks and therefore are generally not permitted in commercial of fshore operations . Enabling smaller AUVs to be used may therefore allow for a reduction of of fshore survey costs due to the much lower cost of small AUVs .

[0058] It will be understood that the embodiments illustrated above show applications only for the purposes of illustration. In practice, embodiments may be applied to many different configurations, the detailed embodiments of which those skilled in the art will be able to implement.

[0059] It will be appreciated that steps of the foregoing may be carried out in different orders depending on the requirements of each specific application. That is some method steps may be taken out of order and carried out when otherwise appropriate for a specific application.

[0060] Furthermore, although the above embodiments are described in the context of an autonomous underwater vessel (AUV) , it will be understood that embodiments may be applied to other types of underwater vessel, including unmanned underwater vessels.

Claims

CLAIMS1 . A cradle for underwater launching and recovery of an underwater vehicle from a marine body, the cradle comprising : a receptacle for receiving the underwater vehicle ; a tether attachment for connecting the cradle to the marine body via a tether ; and a propulsion means for manoeuvring the receptacle in water relative to the marine body .2 . The cradle according to claim 1 , wherein the propulsion means is controllable to manoeuvre the receptacle through the water to positionally stabilise the cradle against underwater forces applied thereto .3 . The cradle according to claim 1 or 2 , further comprising a locking mechanism configured to releasably retain the underwater vehicle in the receptacle .4 . The cradle according to any of claims 1 to 3 , wherein the propulsion means comprises one or more thrusters operable to manoeuvre the receptacle through six degrees of freedom .5 . The cradle according to any preceding claim, wherein the tether attachment comprises an interface for connection to an interface line in the tether for establishing a power and / or control connection between the marine body and the cradle .6 . The cradle according to any preceding claim, further comprising a wireless transceiver for transmitting and receiving data between at least one of the marine body and the underwater vehicle .7 . The cradle according to any preceding claim, further comprising a battery for powering the propulsion means .8 . The cradle according to any preceding claim, further comprising one or more sensors for deriving positional information relating to at least one of the AUV, the cradle , and the marine body .9 . The cradle according to any preceding claim, further comprising a controller for controlling the propulsion means to positionally stabilise the cradle by maintaining a vertical , hori zontal and rotational position within the water .10 . An underwater vehicle launch and recovery system, the system comprising : a cradle according to any of claims 1 to 9 ; and a tether for connecting the tether attachment to a marine body; a reeling device for mounting on the marine body; and a tether for connecting the tether attachment on the cradle to the reeling device mounted on the marine body, wherein the reeling device is operable to reel out or in the tether for lowering and raising the cradle , respectively .11 . The system according to claim 10 , wherein the reeling device is a winch .12 . A marine body comprising the underwater vehicle launch and recovery system according to claim 10 or 11 .13 . A method of launching an underwater vehicle from a marine body, the method comprising : lowering, from the marine body, a cradle according to any of claims 1 to 9 in water using a tether attached to the tether attachment , wherein the underwater vehicle is received in the receptacle of the cradle ; operating the propulsion means to li ft the cradle for introducing slack into the tether ; and, releasing the underwater vehicle from the receptacle of the cradle .14 . A method of recovering an underwater vehicle to a marine body, the method comprising : lowering from the marine body a cradle according to any of claims 1 to 9 in water using a tether attached to the tether attachment ; operating the propulsion means to li ft the cradle for introducing slack into the tether ; receiving the underwater vehicle in the receptacle of the cradle ; and, raising the cradle to the marine body via a tether attached to the tether attachment .15 . The method of claims 13 or 14 wherein the step of operating the propulsion means comprises controlling the propulsion means to positionally stabilise the cradle by maintaining a vertical , hori zontal and rotational position within the water .

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