NO20200043A1

NO20200043A1 - System and apparatus for recovering a vehicle

Info

Publication number: NO20200043A1
Application number: NO20200043A
Authority: NO
Inventors: Gunnar Brink; Alexei Keller; Eduard Maydanik
Original assignee: Fraunhofer Ges Forschung
Priority date: 2017-07-14
Filing date: 2020-01-14
Publication date: 2020-01-14
Also published as: DE102017212126A1; DE102017212126B4; WO2019011490A1

Description

System and Apparatus for Recovering a Vehicle

Description

Embodiments of the present invention relate to a system having at least two water vehicles allowing the recovery of a vehicle, such as an autonomous underwater vehicle. Further embodiments relate to a respective recovery method.

Autonomous underwater vehicles (AUV) can basically be recovered in two ways, namely either directly from the mother ship, i.e., either with a crane or with the help of a dinghy specifically configured for recovering the AUV. EP 2452868 B1 shows that the recovery represents one of the most critical operations of the entire mission of a submersible (AUV), since any damage has to be prevented. This patent document describes a crane that can be moved with a plurality of degrees of freedom such that alignment with the receiving underwater vehicle can be achieved in an optimum manner.

In order to prevent damages being caused by the recovery means, i.e., the hooks of the crane, it is a common recovery method to release a recovery buoy at the AUV (e.g., at the nose of the hull of the AUV) and then to recover the buoy first and haul in the AUV at a rope between buoy and AUV. In detail, the method is as follows. The recovery buoy releasably attached to the AUV is connected to the same via a rope after ejecting and can then be connected to a recovery system, for example via an operation platform (possibly by manual interventions of the crew). After attaching the recovery rope to the recovery system (crane) the rope is hauled in by the recovery system such that the underwater vehicle can successively be recovered.

EP 243911 B1 follows the approach of using existing cranes on the mother ship for launch and recovery. One advantage of this approach is the independence of the system with regard to the height differences between water surface and deck due to the varying freeboard heights of different ships. Such launch and recovery systems frequently include a cage that floats on the water surface by floating bodies and that is mounted to the mother ship by means of a rope. The operating personnel pull a rope from the submersible into the floating cage, for example, by using the teachings of EP 2452868 B1. For this, the cage can have, for example, a funnel-shape in which then the AUV (possibly with the help of further means, such as pins) is mechanically fixed. When the AUV is completely pulled into the funnel and then also into the cage, the cage can be pulled out of the water together with the AUV with the help of the crane in a last step.

In other concepts, the underwater vehicle to be recovered is not externally gripped or coupled but the vehicle maneuvers independently into some sort of cage also called garage. Here, reference is made, for example, to US 6,698,376 wherein the garage consists of two lifting arms between which the AUV can be controlled. When vertically folding these lifting arms, the AUV can be secured.

In practice, the above discussed recovery approaches of the prior art are frequently combined with catching concept (with the help of the rope or catching buoy) in order to allow reliable hauling. Unfortunately, no sufficiently automatable concepts are known how the buoy or catching rope (painter) of the autonomous vehicle can be reliably gripped.

Thus, it is the object of the present invention to provide a concept allowing reliable catching of a vehicle such as an autonomous underwater vehicle or a catching rope connected to the vehicle.

The object is solved by the independent claims.

Embodiments of the present invention provide a system having two water vehicles, wherein one of the two water vehicles is a surface vehicle and a different one of the two water vehicles is another vehicle, such as an autonomous underwater vehicle (AUV). The system includes a control which can be arranged, for example on one of the water vehicles. Both water vehicles have a catching rope, wherein the one of the surface vehicle can be lowered below the water line and the one of the underwater vehicle can be generally pulled out, i.e., by lowering or also by pulling out, e.g., rearwards or upwards. One of the catching ropes, namely the one of the first water vehicle, is provided with a catching apparatus (e.g., a hook or other catching means) such that the catching apparatus is connected to the first water vehicle via the catching rope. This catching apparatus is configured to establish a connection to the catching rope of the second one of the two water vehicles when engaging the same, e.g., by hooking in or gripping.

According to embodiments, for this purpose, the catching rope of the second water vehicle can comprise some sort of end stop or a weight which the catching apparatus engages in. For the two catching ropes and in particular the catching apparatus to come into contact with the other catching rope, the control controls the water vehicle with the catching apparatus in a curved path around the second water vehicle in which the catching rope, for example, hangs down or floats upwards vertically (essentially vertical, angle vertical with a maximum deviation of /-15° = 75° to 105° or ideally perpendicular). By the curved path, such as a circular path or a U-turn, the catching apparatus is pulled diagonally through the water, such that a contact between the two catching ropes or the catching apparatus and one catching rope results. Due to this contact, a mechanically fixed connection (engagement) of surface vehicle and autonomous underwater vehicle is implemented with the help of the catching apparatus.

Here, it should be noted that according to embodiments either the surface vehicle or the autonomous underwater vehicle can drive the curved path. Preferably, the speed of the vehicle not driving in the curved path is reduced or even stopped. Thus, according to embodiments, the control is configured to transmit control signals to the water vehicle driving the curves and/or to the other water vehicle.

According to embodiments, it is useful when the catching rope in the water vehicle not driving the curves projects in a straight manner, such as perpendicularly, upwards or downwards. This can, for example, be ensured in that a weight that can, for example, also be formed by some sort of end stop is provided at the catching rope. The reason for that is that the vehicle driving the curves can catch the vehicle not driving the curves in a more reliable manner.

Embodiments of the present invention are based on the knowledge that starting from a predetermined path of movement, such as a circular path, a catching rope with an anchor hauled along behind a water vehicle (e.g., the surface vehicle) is pulled diagonally through the water during movement due to the water resistance, such that the rope forms some sort of loop around a vertical (projecting upwards or downwards) catching rope of a second water vehicle (e.g., the underwater vehicle) and the second catching rope is contacted due to the diagonal movement of the first catching rope. The contact results in “entanglement” of the two catching ropes, wherein the entanglement is supported by a catching apparatus. Based on the entanglement, a fixed connection between the two ropes is established, such that the catching rope of the autonomous underwater vehicle can then be hauled in with the help of the catching rope of the surface vehicle in order to complete the recovery operation.

According to embodiments, a radius of the circular path driven by the first one of the two water vehicles depends on the length of the catching rope of the first water vehicle. The radius is, e.g., smaller than the length of the catching rope of the first water vehicle.

According to embodiments, recovery can take place in an automated or even fully automated manner, wherein then individual steps are controlled by the control. The control mainly controls the first one of the two water vehicles on its circular path. Further, the control can also be configured to reduce the speed of the second water vehicle or even to stop the same, such that the first one of the two underwater vehicles can reliably pull a loop around the catching rope of the second underwater vehicle with its catching rope. Further, the control can also control lowering of the catching rope of a surface vehicle and releasing the catching rope of the autonomous underwater vehicle. Here, for example, the release mechanism can be realized in that the catching rope comprises a weight or the catching hook of the catching apparatus comprises a weight and the catching rope is released such that the weight pulls the catching rope downwards. The weight then also allows vertical alignment of the catching rope in the water by stretching the catching rope downwards due to the weight force (perpendicularly). Releasing can be realized, for example, by a mechanical lock or also by a corrosive wire. In the corrosive wire, corrosion is induced by providing the same with an electric voltage.

A further embodiment provides a method for recovering a vehicle such as an autonomous underwater vehicle by means of a surface vehicle with the help of a system comprising two water vehicles, wherein one of them is a surface vehicle and another one the autonomous underwater vehicle. As explained above, the catching ropes can be lowered or pulled out, wherein the catching apparatus is arranged at the catching rope of the first water vehicle. The method includes the central step of controlling the first one of the two water vehicles such that the same is maneuvered in a curved path around the second one of the two water vehicles.

Additionally, according to further embodiments, the method can comprise the step of controlling the second water vehicle, e.g., such that the same stops or reduces its speed while the first water vehicle drives in a curved path. According to a preferred variation, the control is performed such that the radius of the curved path depends on the length of the catching rope of the respective water vehicle or is smaller than the same.

Further, according to a further embodiment, the method can comprise the step of pulling out or lowering the respective catching rope. Here, the pulling out process can again be supported by a weight.

Further developments are defined in the subclaims. Embodiments of the present invention will be discussed based on the accompanying drawings.

They show:

Fig. 1a-1f schematical illustrations of two water vehicles during catching for illustrating a system having two underwater vehicles according to embodiments, wherein Fig.1a to 1b show the constellations from the side while Fig.1c to 1f illustrate the constellation from above.

Before embodiments of the present invention will be discussed in detail below based on the accompanying drawings, it should be noted that equal elements and structures are provided with the same reference numbers such that the description of the same is interexchangeable.

Fig. 1a shows an autonomous underwater vehicle 10 as well as a surface vehicle 20. The autonomous underwater vehicle 10 comprises a catching rope 12, arranged here as catching rope that can be lowered, i.e., arranged at a bottom of the autonomous underwater vehicle. The catching rope 12 can be lowered, for example, with the help of an optional weight 14, for example by releasing the weight. The surface vehicle 20 also comprises a catching rope 22 which can be lowered below the water line 23 and comprises so-called catching means 24 at the end of the catching rope or generally at the catching rope. These catching means 24 can, for example, be formed by a hook. This hook has a weight, such that lowering can take place analogously by releasing the hook 24 and pulling down the catching rope 22 by means of a weight. This situation is illustrated in Fig.1b.

Fig. 1b shows the autonomous underwater vehicle 10 as well as the surface vehicle 20, wherein the catching ropes 12 and 22 are pulled out, i.e., here lowered. For example, the catching rope 12 of the autonomous underwater vehicle 2 can be lowered 2 m or generally in the range between 1 and 10 m, while the catching rope 22 of the surface vehicle is typically lowered further, e.g., for example 5 m or generally in the range between 2 and 30 m. As can be seen, lowering of the catching ropes 12 and 22 and also keeping them low takes place with the help of the weight force at the weight 14 or 24. In the autonomous underwater vehicle (the vehicle to be recovered) it is assumed that the same has significantly reduced its speed or has even stopped for the recovery process so that the same does not drive through water. This has the advantage that the catching rope 12 approximately projects perpendicularly downwards as illustrated herein. The recovery vehicle 20 now drives a maneuver, such that the catching ropes 12 and 22 get caught. Therefore, the recovery vehicle 20 drives through water, as a consequence the catching means 24 and the catching rope 22 are hauled behind. This results in a diagonal angle in the water.

Here, it should be noted that the submersion depth of the autonomous underwater vehicle is selected such that the hook 24 is at the same depth as the rope 12. If it is assumed that the rope 12 projects downwards and is approximately 2 m long while the rope 24 is approximately 5 m long, the AUV 10 is preferably close to the surface 23 since due to the diagonal course of the rope 22, the hook 24 (depending on the drive through water) will be hauled behind the surface vehicle 10 in a depth of 1 to 3 m below the water surface. If the rope 22 is longer or the rope 12 projects, for example, upwards, the height of the underwater vehicle 10 can obviously be adapted. In the case of a catching rope projecting (vertically) upwards, the underwater vehicle is e.g., 5 m below the water surface while the catching rope 12 is stretched upwards by means of a floating body (e.g., buoy, not illustrated) due to the buoyancy force. In this variation, the exact depth depends on the length of the rope and is selected such that the catching rope remains stretched when the buoyancy body is floating on the water surface. After it has been explained how the catching means 24 have been positioned at the same height as the rope 12, it will be explained below with reference to Fig. 1c to 1f how an engagement can be established by the lateral positioning of the catching means 24 with respect to the rope 12.

Fig.1c shows the autonomous underwater vehicle 10, wherein it is assumed that the same does not drive through water or only hardly drives through water as well as that the surface vehicle 20 is positioned relative to the autonomous underwater vehicle such that the surface vehicle 20 can pass the underwater vehicle. Here, the catching rope 10 of the second water vehicle (AUV) is essentially aligned vertically in the water. The drive through water of the surface vehicle 20 is illustrated by the arrow. As can be seen, the surface vehicle 20 passes the autonomous underwater vehicle laterally, approximately at a distance corresponding to the spacing of the anchor 24 hauled behind to the surface vehicle 20. In other words, this means that the maximum distance can be the length of the catching rope 22 hauled behind.

Shortly after passing, the surface vehicle 20 drives a curve around the autonomous underwater vehicle 10 or in particular around the catching rope 12 of the same. This curved path is illustrated in Fig.1d. This curved path or circular path is symbolized with the arrow. Normally, at this time, the anchor 24 has not yet passed the catching rope 12, i.e., is only hauled laterally by means of the catching rope 22. This situation is also indicated by an arrow.

In a situation illustrated in Fig.1e, the vehicle 20 has proceeded further on the curved path, such that the rope 22 pulls a loop around the autonomous underwater vehicle 10, in particular the rope 12. Due to this loop, the path of motion of the anchor 24 crosses the position of the catching rope 12 such that, for example, the ropes 12 and 22 touch.

This results in an engagement between the engagement means 24 and the rope 12 or the weight (end stop of the rope 12).

The final engagement is shown in Fig. 1f. As can be seen here, the weight 14 has been gripped by the anchor 24 such that the rope 12 is deflected diagonally out of the position projecting straight downwards and the autonomous underwater vehicle 10 can be hauled behind the surface vehicle 20. At this stage, the first phase of the recovery maneuver, namely catching the autonomous underwater vehicle is completed, such that then, for example, by hauling in the catching ropes 12 and 22, the autonomous underwater vehicle 10 can be pulled into a cage, e.g., a cage of the surface vehicle 20.

Even when it has been assumed in the above embodiments that the surface vehicle 20 drives the curved path, according to further embodiments, it can also be vice versa. Accordingly, the autonomous underwater vehicle circles around the surface vehicle that has reduced its speed or has stopped, and whose catching rope is lowered downwards. In this variation, preferably, the autonomous underwater vehicle comprises the catching means while the catching rope of the surface vehicle can be weighted down, for example by a weight or an end stop.

According to embodiments, the optional end stop 14 is configured to be brought in engagement with the engagement means 24 and to establish a mechanical connection.

Lowering the catching rope 12 or 22 can take place by different mechanisms. In one case, for example, the respective catching rope 12 or 22 can simply be lowered. In order to ensure that the catching rope 12 or 22 sinks downwards, according to embodiments, it is also useful to attach a respective weight 14 or 24. This weight also allows lowering of the catching ropes 12 and 22 by releasing the weight, for example, via a mechanical lock and sinks to the ground and accordingly pulls out the wound-up or folded catching rope 12 or 32 accordingly. The weight of, for example one kilo, stays connected to the water vehicle (surface vehicle or AUV) at the rope, e.g., at the end of the rope 12 and 22. According to embodiments, one operation can be as follows. After returning to the water surface, the submersible 10 AUV releases a weight 14 still connected to a rope 12 and the AUV 10. According to embodiments, this can take place via a metal wire or stainless steel wire to which the weight 14 is connected within the vehicle. If an electric voltage is applied to this wire/stainless steel wire in salt water for several minutes, the wire can corrode in several minutes and burns. As a consequence, the weight falls downwards. As already indicated, other methods are also suitable to release the weight, for example turning a lever by a heat engine releasing a lock by which the weight 14 is mounted in the AUV 10.

Even if it has been assumed above that the rope 12 and 22 is always lowered, it should also be noted herein that in particular the rope of the autonomous underwater vehicle not necessarily has to be lowered but can also be lifted upwards with the help of a floating body. In this embodiment, the surface vehicle also drives the same circular path around the rope 12.

According to embodiments, the above discussed system comprises a control coordinating, for example, releasing of the weights or generally the pulling out of the catching ropes 12 and 22. This control is configured to keep the water vehicle (in the other example in surface vehicle 20) driving the curves accordingly active, for example by the engines (outboard engine or inboard engine or water jet propulsion or propeller drive) in the case of a hull boat or generally to maneuver the respective water vehicle. Also, this control can control the maneuvering of the other water vehicle to be caught with the catching rope pulled diagonally through the water, e.g., such that the same is stopped or its speed is reduced for the recovery process. Here, according to embodiments, it can be advantageous that the water vehicles comprise navigation means, such as underwater navigation systems, such that in particular relative positioning of the two vehicles with respect to one another can be controlled and monitored optimally during the recovery maneuver.

Even when in the above embodiments a curved path, such as a circular path, has been assumed, it should be possible that also other paths, such as a sharp U-turn would also be possible. Generally, the driven curve should be at least 90° (towards the other water vehicle) or even at least 135° (or in the range of 90° to 180°), such that a significant change of direction results and the rope hauled behind forms a loop around the catching rope of the other water vehicle. In other words, this means that the surface vehicle is on one side of the rope between AUV and weight or floating body prior to the maneuver and approximately 180° on the other side of the rope after the U-turn maneuver. The exact path during the maneuver depends on the water resistance, the selected speed, the flexibility (material characteristic and thickness) of the rope and in particular the driven radius. By considering the marginal conditions, the path of motion is driven such that the anchor is pulled obliquely through the water and, when driving around the submersible, the same entangles with the rope of the vehicle to be recovered or the weight.

The anchor can have an optimized form such that the rope directly locks after catching. Examples for such anchors are a kedge anchor having three or four arms.

According to further embodiments, the surface vehicle, as already indicated, can also comprise a cage and secure the autonomous underwater vehicle in that way. According to embodiments, it would also be possible that the recovering ship can take over the data of the autonomous underwater vehicle and charge the accumulators of the autonomous underwater vehicle until the autonomous underwater vehicle is released again for the next mission.

Since the surface vehicle is normally provided with a drive, the surface vehicle can be moved to the mother ship together with the recovered autonomous underwater vehicle. In the simplest case, the surface vehicle is, for example, implemented as a life boat, but socalled rigid hull inflatable boats can also be used. Alternatively, surface vehicles having a catamaran shape, trimaran shape (or generally ships having several hulls) would be possible besides the monohull boat. After returning to the mother ship, the surface vehicle is recovered together with the autonomous underwater vehicle, e.g., with the help of a davit or crane. According to further embodiments, it would also be possible that a fixed permanent connection is always realized between the surface vehicle and the mother ship (e.g., by a rope). Here, it should also be noted that it is not mandatory that the surface vehicle returns to the mother ship, since the surface vehicle can also be used self-sufficiently at high sea (e.g., launched from the shore). In such concepts, it should be considered whether a so called semisubmersible or SWATH (small water plane area twin hull) is used, since the same float in a stable manner on the water surface. Here, it should further be noted that it is not mandatory that the surface vehicle floats completely on the water surface, since, according to further embodiments, it would also be possible that the same is used just below the water surface (typical for semisubmersibles).

Even when in the above embodiments an AUV or underwater vehicle has been assumed as the other vehicle, it should be noted that the other vehicle could also be a torpedo, another surface vehicle or an airplane landed on water (e.g., a rocket stage of space X).

Even when the above embodiments have mainly been discussed in the context of an apparatus, it should be noted that further embodiments also relate to a respective recovery method. The recovery method essentially includes the central step of controlling the curved path of one of the water vehicles, such that an engagement between the two ropes 12 and 22 and the engagement means at the ropes, respectively, results.

Although some aspects have been described in the context of an apparatus, it is obvious that these aspects also represent a description of the corresponding method, such that a block or device of an apparatus also corresponds to a respective method step or a feature of a method step. Analogously, aspects described in the context of a method step also represent a description of a corresponding block or detail or feature of a corresponding apparatus. Some or all of the method steps may be performed by a hardware apparatus (or using a hardware apparatus), such as a microprocessor, a programmable computer or an electronic circuit. In some embodiments, some or several of the most important method steps may be performed by such an apparatus.

Depending on certain implementation requirements, embodiments of the invention can be implemented in hardware or in software. The implementation can be performed using a digital storage medium, for example a floppy disk, a DVD, a Blu-Ray disc, a CD, an ROM, a PROM, an EPROM, an EEPROM or a FLASH memory, a hard drive or another magnetic or optical memory having electronically readable control signals stored thereon, which cooperate or are capable of cooperating with a programmable computer system such that the respective method is performed. Therefore, the digital storage medium may be computer readable.

Some embodiments according to the invention include a data carrier comprising electronically readable control signals, which are capable of cooperating with a programmable computer system, such that one of the methods described herein is performed.

Generally, embodiments of the present invention can be implemented as a computer program product with a program code, the program code being operative for performing one of the methods when the computer program product runs on a computer.

The program code may, for example, be stored on a machine readable carrier.

Other embodiments comprise the computer program for performing one of the methods described herein, wherein the computer program is stored on a machine readable carrier.

In other words, an embodiment of the inventive method is, therefore, a computer program comprising a program code for performing one of the methods described herein, when the computer program runs on a computer.

A further embodiment of the inventive method is, therefore, a data carrier (or a digital storage medium or a computer-readable medium) comprising, recorded thereon, the computer program for performing one of the methods described herein.

A further embodiment of the inventive method is, therefore, a data stream or a sequence of signals representing the computer program for performing one of the methods described herein. The data stream or the sequence of signals may, for example, be configured to be transferred via a data communication connection, for example via the Internet.

A further embodiment comprises a processing means, for example a computer, or a programmable logic device, configured to or adapted to perform one of the methods described herein.

A further embodiment comprises a computer having installed thereon the computer program for performing one of the methods described herein.

A further embodiment in accordance with the invention includes an apparatus or a system configured to transmit a computer program for performing at least one of the methods described herein to a receiver. The transmission may be electronic or optical, for example. The receiver may be a computer, a mobile device, a memory device or a similar device, for example. The apparatus or the system may include a file server for transmitting the computer program to the receiver, for example.

In some embodiments, a programmable logic device (for example a field programmable gate array, FPGA) may be used to perform some or all of the functionalities of the methods described herein. In some embodiments, a field programmable gate array may cooperate with a microprocessor in order to perform one of the methods described herein. Generally, the methods are preferably performed by any hardware apparatus. This can be a universally applicable hardware, such as a computer processor (CPU) or hardware specific for the method, such as ASIC.

The above described embodiments are merely illustrative for the principles of the present invention. It is understood that modifications and variations of the arrangements and the details described herein will be apparent to others skilled in the art. It is the intent, therefore, that the invention is limited only by the scope of the appended patent claims and not by the specific details presented by way of description and explanation of the embodiments herein.

Claims

1. System comprising two water vehicles and a control, wherein one of the two water vehicles is an autonomous surface vehicle (20) and a different one of the two water vehicles is an autonomous vehicle (10) below the water surface;

wherein the surface vehicle (20) comprises a catching rope (22) that can be lowered below the water line and the other vehicle (10) comprises a catching rope (12) that can be pulled out, wherein a first one of the two water vehicles comprises a catching apparatus (24) that is connected to the first water vehicle via the respective catching rope (12, 22) and is configured to establish a connection to the catching rope (12, 22) of the second one of the two water vehicles when engaging the catching rope (12, 22) of a second one of the two water vehicles;

wherein the control is configured to control the first one of the two water vehicles in a curved path in the shape of a U-turn around the second one of the two water vehicles, such that the catching rope (22) of the first water vehicle forms a kind of loop around the extensible catching rope (12) of the second water vehicle.

2. System according to claim 1, wherein the curved path results in a change of direction of the first one of the two water vehicles by at least 135° or 180°.

3. System according to claim 1 or 2, wherein a radius of the curved path depends on a length of the catching rope (12, 22) of the first one of the two water vehicles.

4. System according to claim 3, wherein the radius is smaller than the length of the catching rope (12, 22).

5. System according to one of the preceding claims, wherein the catching rope of the second water vehicle comprises means that align the catching rope of the second water vehicle vertically in the water.

6. System according to claim 5, wherein the means comprise a weight mounted to the catching rope of the second water vehicle configured to stretch the catching rope of the second water vehicle vertically downwards.

7. System according to claim 5, wherein the means comprise a floating body mounted to the catching rope of the second water vehicle configured to stretch the catching rope of the second water vehicle vertically upwards.

8. System according to one of the preceding claims, wherein the control is configured to reduce the speed of the second one of the two water vehicles before the first one of the two water vehicles is controlled in the curved path.

9. System according to one of the preceding claims, wherein the control is configured to lower the catching ropes (12, 22) of the two water vehicles before the first one of the two water vehicles is controlled in the curved path.

10. System according to one of the preceding claims, wherein the catching apparatus (24) comprises a catching hook.

11. System according to one of the preceding claims, wherein the catching rope (12, 22) of the first and/or second water vehicle is lowered or pulled out with the help of a weight (14) or stop element.

12. System according to claim 11, wherein the control is configured to drop the weight (14) or the stop element for lowering or pulling out.

13. System according to claim 12, wherein the weight (14) or the stop element is mounted by means of a mechanical lock and the mechanical lock is opened for dropping or pulling out.

14. System according to claim 12, wherein the weight (14) is connected to the second underwater vehicle via a metal wire or stainless steel wire and wherein the control is configured to provide the metal wire or stainless steel wire with a voltage such that the same corrodes when contacting salt water in order to drop or pull out the weight.

15. System according to one of the preceding claims, wherein the other vehicle is an autonomous underwater vehicle.

16. Method for recovering a different vehicle (10) by means of a surface vehicle (20) with the help of a system comprising two water vehicles, wherein one is the surface vehicle (20) and a different one is the vehicle below the water surface (10),

wherein the surface vehicle (20) comprises a catching rope (12, 22) that can be lowered below the water line and the other vehicle (10) comprises a catching rope (12) that can be pulled out, wherein a first one of the two water vehicles comprises a catching apparatus (24) that is connected to the first water vehicle via the catching rope (12, 22) and is configured to establish a connection to the catching rope (12, 22) of the second one of the two water vehicles when engaging the catching rope (12, 22) of a second one of the two water vehicles,

the method comprising:

controlling the first one of the two water vehicles such that the same is maneuvered in a curved path around the second one of the two water vehicles, such that the catching rope (22) of the first water vehicle forms a kind of loop around the extensible catching rope (12) of the second water vehicle.

17. Method according to claim 16, wherein the method comprises the step of controlling the second water vehicle such that the same stops or reduces its speed at a position around which the curved path of the first water vehicle runs.

18. Method according to claim 16 or 17, wherein the method includes the step of lowering or pulling out the catching ropes (12, 22).

19. Method according to one of claims 16 to 18, wherein the method comprises the step of dropping a weight (14) at the catching rope (12, 22) of the second one of the two underwater vehicles in order to lower or pull out the catching rope (12, 22) of the second one of the two underwater vehicles.

20. Method according to one of claims 16 to 19, wherein the first one of the two water vehicles is controlled such that the curved path comprises a radius that depends on the length of the catching rope (12, 22) of the first water vehicle or that is smaller than the length of the catching rope of the first water vehicle.

21. Computer program having a program code for performing a method according to one of claims 16 to 20 when the program runs on a computer.