WO2019011490A1

WO2019011490A1 - System and device for recovering a vehicle

Info

Publication number: WO2019011490A1
Application number: PCT/EP2018/060359
Authority: WO
Inventors: Gunnar Brink; Alexei Keller; Eduard Maydanik
Original assignee: Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.
Priority date: 2017-07-14
Filing date: 2018-04-23
Publication date: 2019-01-17
Also published as: DE102017212126B4; NO20200043A1; DE102017212126A1

Abstract

A system comprises two watercraft (10, 20) and a steering means. In each case one of the two watercraft is a surface vehicle (10). The surface vehicle (20) and the other vehicle (20) each comprise a painter (12, 22), wherein a catching device is arranged on one painter. The catching device makes it possible, on engaging with the other painter, to form a connection therewith. The steering means is configured to steer a first of the two watercraft in a curved path about the second of the two watercraft.

Description

System and device for recovering a vehicle

description

Embodiments of the present invention relate to a system having at least two vessels which enables the recovery of a vehicle such as an autonomous underwater vehicle. Further exemplary embodiments relate to a corresponding recovery method.

Autonomous underwater vehicles (AUV) (autonomous underwater vehicle) can be retrieved in basically two different ways, namely once directly from the mothership, z. B. with a crane or by means of a dinghy, which is specially designed to recover the AUVs. EP2452868 B1 shows that recovery is one of the most critical operations of the entire mission of a submersible (AUV), as any damage must be avoided. This patent describes a crane which can be moved with a plurality of degrees of freedom, so that alignment with the underwater vehicle to be picked up can take place in the best possible way.

To further prevent damage caused by the recovery facility, z. For example, if the hook of the crane is caused, it is a common method of recovery to release a salvage buoy on AUV (eg on the nose of the AUV's hull) and then first recover the buoy and the AUV on a leash between the buoy and the buoy AUV to catch up. In detail, the method is as follows. The salvage buoy attached to the AUV is connected to the same after ejection via a line and can then z. B. via an operation platform (possibly by manual intervention of the crew) to be connected to a recovery system. After attaching the recovery line to the recovery system (crane) then the leash is obtained by the recovery system, so that a successive salvage of the underwater vehicle can take place.

EP24391 1 B1 follows the approach of using existing cranes on the mothership for deployment and recovery. An advantage of this approach is the independence of the system in terms of height differences between water surface and deck due to the different freeboard heights of different ships. Such launch and recovery systems often include a cage, which can be replaced by floats on the Floats and is attached to the mothership with a leash. For example, operating personnel draw a line from the submersible into the floating cage using the teaching of EP2452868 B1. For this purpose, the cage can, for example, have a funnel shape in which the AUV is then mechanically fixed (possibly with the aid of other means, such as pins). When the AUV is fully drawn into the hopper and then into the cage, the cage can be pulled out of the water together with the AUV with the help of the crane. In other concepts, the underwater vehicle to be sheltered is not gripped or coupled externally, but the vehicle autonomously maneuvers into a kind of cage, also called a garage. Here, for example, reference is made to US 6,698,376, in which the garage consists of two lifting arms between which the AUV can be controlled. With vertical folding of these lifting arms, the AUV can thus be secured.

In practice, the above-described prior art Berge approaches are often combined with a fishing concept (with the aid of the leash or buoy buoy) to allow a reliable catching here. Unfortunately, there are currently no known concepts that can be used to reliably grasp the buoy or the line of the autonomous underwater vehicle.

Therefore, it is an object of the present invention to provide a concept that enables a reliable catching of a vehicle, such as an autonomous underwater vehicle o- and a vehicle connected to the line.

The object is solved by the independent claims.

Embodiments of the present invention provide a two-vehicle system wherein one of the two vessels is a surface vehicle and another of the two vessels is another vehicle such as an autonomous underwater vehicle (AUV). The system includes a controller that may be located on one of the craft, for example. Both vessels have a safety line, whereby the surface vehicle can be lowered below the waterline and the underwater vehicle can generally be pulled out, e.g. B. by lowering or by pulling, z. B. backwards or upwards. One of the suspension lines, namely, that of the first watercraft is equipped with a safety gear (eg a hook or other safety gear), so that the safety gear is connected to the first watercraft via the safety line. This safety gear is designed to establish a connection to the same upon engagement with the suspension line of the second of the two vessels, for. B. by hooking or gripping.

According to embodiments, for this purpose, the suspension line of the second vessel may have a kind of end stop or a weight in which the safety device engages. In order for the two suspension lines, and in particular the safety gear, to come into contact with the other catch line, the controller controls the watercraft with the safety gear in a curved path around the second watercraft, where the suspension line is vertical (substantially vertical, angle normal to maximum) deviation of +/- 15 ⁰ = 75 ° to 105 ° or, ideally, perpendicular) hangs down or pushing up. Through the curved path, such. B. a circular path or a U-turn, the safety gear is pulled obliquely through the water, so that there is a contact between the two suspension lines and the safety gear and a suspension line. As a result of this contact, a mechanically strong connection (engagement) is then formed by the surface vehicle to the autonomous underwater vehicle with the aid of the safety gear.

It should be noted at this point that, according to embodiments, either the surface vehicle or the autonomous underwater vehicle can travel the curved path. Preferably, the vehicle that is not traveling in the curved path is reduced in speed or even stopped. Therefore, according to embodiments, the controller is configured to send control signals to the curving vessel and / or to the other vessel.

According to embodiments, it makes sense that in the non-curving watercraft, the suspension line straight, such. B. protrudes vertically upwards or downwards. This can be ensured, for example, by providing a weight, which may be formed, for example, by a type of end stop, on the suspension line. The background is that the curving vehicle can capture the non-curving vehicle more reliably. Embodiments of the present invention is based on the finding that starting from a predetermined trajectory, such. B. a circular path, a behind a watercraft (eg the surface vehicle) tow line towed with an anchor due to the water resistance is pulled obliquely through the water during the movement so that this line forms a loop around a vertical (downwardly or upwardly projecting) line of a second vessel (eg Underwater vehicle) forms and the second suspension line is touched due to the oblique movement of the first suspension line. As a result of the contact there is a "catching" of the two suspension lines, the capture being assisted by a safety gear, starting from the catch a firm connection is made between the two lines so that the suspension line of the autonomous underwater vehicle can be leashed using the Surface vehicle can be obtained to complete the recovery process.

According to embodiments, a radius of the circular path that travels the first of the two vessels depends on the length of the line of the first vessel. The radius is e.g. smaller than the length of the leash of the first vessel.

According to embodiments, the recovery can be automated or even fully automated, in which case individual steps are controlled by the controller. The controller primarily controls the first of the two vessels to its orbit. Further, the controller may also be configured to reduce or even halt the speed of the second vessel so that the first of the two submersibles can reliably pull a sling with its sling around the sling of the second underwater vehicle. Furthermore, the controller can also control the lowering of the line of a surface vehicle and the leash of the autonomous underwater vehicle. In this case, for example, the trigger mechanism can be realized in that the suspension line has a weight or the catch hook of the safety gear has a weight, and the safety line is triggered, so that the weight pulls the suspension line down. The weight then also allows the vertical alignment of the suspension line in the water by tensioning the suspension line downwards as a result of the weight force. The triggering can be realized for example by a mechanical locking mechanism or by a corroding wire. In the corroding wire, this corrosion is excited by applying an electrical 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 assistance of a surface vehicle. a two-vessel system, one being the surface vehicle and another being the autonomous submersible. The suspension lines are lowered or extended as explained above, wherein the safety gear is arranged on the suspension line of the first vessel. The method includes the central step of controlling the first of the two watercraft to maneuver it in a curved path around the second of the two watercraft.

In addition, according to other embodiments, the method may include the step of controlling the second watercraft, e.g. B. such that this stops or reduces its speed, while the first watercraft drives in a curved path, have. According to a preferred variant, the control is performed so that the radius of the curved path depends on the length of the line of the respective vessel or is smaller than this. Furthermore, according to a further embodiment, the method may comprise the step of extending or lowering the respective suspension line. In this case, the extraction process can in turn be supported by means of a weight.

Further developments are defined in the subclaims. Embodiments of the present invention will be explained with reference to the attached drawings.

Show it:

Fig. 1 a-1 f schematic representations of two vessels when capturing to illustrate a system with two underwater vehicles according to

Embodiments, wherein Fig. 1 a to 1 b represent the constellation from the side, while Figs. 1 c to 1 f illustrate the constellation from above.

Before the embodiments of the present invention are explained in detail below with reference to the accompanying drawings, it should be noted that like-acting elements and structures are provided with the same reference numerals, so that the description of which is interchangeable.

1 a shows an autonomous underwater vehicle 10 and a surface vehicle 20. The autonomous underwater vehicle 10 has a safety line 12, which here is arranged as a lowerable safety line, ie at an underside of the autonomous underwater vehicle. is net. The suspension line 12 can be lowered, for example, with the aid of an optional weight 14, for example, by the weight is released. The surface vehicle 20 likewise has a catching line 22, which can be lowered below the waterline 23 and has catching means 24 at the end of the catching line or generally on the catching line. These catching means 24 may be formed for example by a hook. This hook has a weight, so that the lowering here can be done analogously by the hook 24 is disengaged and by means of a weight pulls the suspension line 22 down. This situation is shown in Fig. 1 b.

Fig. 1 b shows the autonomous underwater vehicle 10 and the surface vehicle 20, in which the suspension lines 12 and 22 extended, d. H. lowered here. For example, the tether 12 of the autonomous submersible may be lowered 2 m, or generally in the range between 1 and 10 m, while the leash 22 of the surface vehicle is typically further lowered, i. H. for example 5 m or generally in the range between 2 and 30 m. As can be seen, the lowering and now holding down the suspension lines 12 and 22 takes place with the aid of weight on the weight 14 and 24. In the autonomous underwater vehicle (the vehicle to be sheltered) it is assumed that this for the recovery process his Speed has significantly reduced or even stopped, so this makes no drive through the water. This has the advantage that the fishing line 12 approximately perpendicularly projects downwards, as shown here. The recovery vehicle 20 now maneuvers, so that the suspension lines 12 and 22 get tangled. Therefore, the recovery vehicle makes 20 drive through the water, as a result, the catch 24 and the leash 22 are dragged behind. This results in an oblique angle through the water.

It should be noted that the depth of the autonomous underwater vehicle is chosen so that the hook 24 is at the same depth as the line 12. Assuming that the line 12 protrudes downwards and is about 2 meters long, while the line 24 is about 5 meters long, the AUV 10 is preferably near the surface 23 because of the oblique course the leash 22 of the hooks 24 (depending on the drive through the water) will be towed behind the surface vehicle 10 at a depth of 1 to 3 m below the water surface. Should the line 22 be longer or the line 12 z. B. protrude upward, of course, then the height of the underwater vehicle 10 can be adjusted. In the case of a (vertically) upstanding line, for example, the underwater vehicle is 5m below the water surface. che, while the suspension line 12 by means of a float (eg buoy, not shown) is stretched upward due to the buoyancy force. The exact depth in this variant depends on the length of the rope and is chosen so that the suspension line remains taut when swimming the buoyant body on the water surface. Having now explained how the catching means 24 has been positioned at the same height as the line 12, reference will now be made to FIG. 1c to 1f as to how an engagement can be made by the lateral positioning of the catching means 24 with respect to the line 12. FIG. 1 c shows the autonomous underwater vehicle 10 assuming that it makes little or no water passage and positions the surface vehicle 20 relative to the autonomous underwater vehicle 10 so that the surface vehicle 20 can pass the underwater vehicle. Here, the tether 10 of the second vessel (AUV) is oriented substantially vertically in the water. In the surface vehicle 20, the drive through the water is shown by means of the arrow. As can be seen, the surface vehicle 20 laterally passes the autonomous submersible approximately at a distance corresponding to the spacing of the trailed anchor 24 from the surface vehicle 20. In other words, this means that the distance can be at most as large as the length of the subsequently towed line 22.

Shortly after passing, the upper 20 makes a turn around the autonomous underwater vehicle 10 or, in particular, around the suspension line 12 thereof. This cornering is illustrated in Fig. 1d. This curved path or circular path is symbolized by the arrow. As a rule, at this time the armature 24 has not yet passed the suspension line 12, so it is now towed laterally by means of the suspension line 22. The situation is also marked with an arrow.

In the situation shown in Fig. 1e then the curved path of the vehicle 20 is further advanced, so that the line 22 a loop around the autonomous underwater vehicle 10, in particular the line 12 pulled. As a result of this loop, the trajectory of the armature 24 crosses the position of the tether 12, so that, for example, the lines 12 and 22 touch. This results in engagement between the engagement means 24 and the line 12 and the weight (end stop at the line 12). The final intervention is shown in Fig. 1f. As can be seen here, the weight 14 has been gripped by the anchor 24 so that the line 12 is obliquely deflected from the straight-down position and the autonomous underwater vehicle 10 can be towed behind the surface vehicle 20. At this stage, then the first phase of the mountain maneuver, namely the trapping of the autonomous underwater vehicle is completed, so then, for example, by retrieving the suspension lines 12 and 22, the autonomous underwater vehicle 10 in a cage, z. B. can be pulled into a cage of the surface vehicle 20.

Although it has been assumed in the above exemplary embodiments that the surface vehicle 20 drives the curved path, it can also be exactly the other way round according to further exemplary embodiments. Accordingly, the autonomous underwater vehicle revolves around the slowed down or stopped surface vehicle, for example, in which the suspension line is lowered downwards. In this variant, the autonomous underwater vehicle preferably has the catching means, while the catching line of the surface vehicle may be weighted, for example, with a weight or an end stop. According to embodiments, the optional end stop 14 is adapted to be engaged with the engagement means 24 and here form a mechanical connection.

The lowering of the suspension line 12 or 22 can take place by means of different mechanisms. In one case, for example, the respective suspension line 12 or 22 can simply be lowered. To ensure that the suspension line 12 or 22 drops down, it is also appropriate according to embodiments, to attach a corresponding weight 14 and 24 respectively. This weight also makes it possible to lower the suspension lines 12 and 22 by unlatching the weight, for example, by means of a mechanical lock, thus sinking to the ground and pulling out the wound-up or collapsed suspension line 12 and 32, respectively. The weight, which weighs, for example, one kilogram, then remains on the leash, z. B. at the end of the line 12 and 22 connected to the vessel (surface vehicle or AUV). A procedure may be as follows, according to embodiments. The submersible 10 AUV, upon return to the water surface, triggers a weight 14 still attached to a line 12 and to the AUV 10. This can be done in accordance with embodiments via a metal made wire or stainless steel wire to which the weight 14 is connected within the vehicle. If one sets this wire / stainless steel wire for a few minutes in salt water of an electrical voltage, the wire can corrode in a few minutes and burns through. As a result, the weight falls down. As already indicated, other methods are also suitable for triggering the weight, such as by a heat engine rotating a lever that releases a latch that secures the weight 14 to the AUV 10.

Even if it was assumed above that the leash 12 and 22 is always lowered, it should also be noted at this point that in particular the leash of the autonomous underwater vehicle does not necessarily have to be lowered, but can also be lifted upwards with the aid of a floating body. Also in this embodiment then moves the surface vehicle the same circular path around the line 12th

According to exemplary embodiments, the system explained above has a control which, for example, coordinates the triggering of the weights or in general the extension of the suspension lines 12 and 22. This control is designed to make the curving vessel (in the above example the surface vehicle 20) active, e.g. B. by the engines (outboard or inboard engine or jet propulsion or propeller drive) coordinate in the case of a hull boat or generally to maneuver the corresponding vessel. Also, this control can be used to control the maneuvering of the other vessel to be caught with the tether pulled obliquely through the water, e.g. For example, it may be stopped for the recovery or reduced in speed. It may be advantageous according to embodiments that the watercraft navigation means, such. B. has underwater navigation systems, so that in particular a relative positioning of the two vehicles to each other during the mountain maneuver can be controlled and monitored as best as possible.

Although in the above embodiments of a curved path, such. B. a circular path was assumed, it should be noted at this point that other tracks, such. B. a sharp U-turn would be possible. In general, the driven curve should be at least 90 ° (towards the other vessel) or even at least 135 ° (or in the range of 90-180 °) so that there is a significant change of direction and the trailing rope is looped around the suspension line of the other watercraft. In other words, before the maneuver, the surface vehicle will be on one side of the rope between the AUV and the weight or float and, after the U-turn maneuver, about 180 ° on the other side of the rope. The precise path of the maneuver depends on the water resistance, the selected speed, the flexibility (material properties and thickness) of the cable and in particular the radius traveled. Taking into account the boundary conditions, the trajectory is then traversed so that the anchor is pulled obliquely through the water and caught when driving around the submersible with the leash of the vehicle to be sheltered or the weight.

The anchor may have an optimized shape so that the line locks directly after catching. Examples of such anchors is a throw anchor with three or four arms.

According to further embodiments, the surface vehicle, as already indicated, also have a cage and thus secure the autonomous underwater vehicle. According to exemplary embodiments, it would also be conceivable that the rescending ship can take over the data of the autonomous underwater vehicle and recharge the batteries of the autonomous underwater vehicle until the autonomous underwater vehicle is released again for the next mission.

Since the surface vehicle is usually equipped with a drive, the surface vehicle can be moved together with the salvaged autonomous underwater vehicle to the mothership. The surface vehicle is implemented, for example, in the simplest form of a lifeboat, but so-called rig hull inflatable boats can also be used. Alternatively, surface vehicles in catamaran form, trimaran form (or generally ship with several hulls) next to the monohull would be conceivable. After returning to the mothership then the surface vehicle is recovered together with the autonomous underwater vehicle, for example with the aid of a davit or crane. According to further exemplary embodiments, it would also be conceivable that a fixed permanent connection between the surface vehicle and the mothership is always realized (eg by a leash). It should also be noted at this point that it is not mandatory for the surface vehicle to return to the mothership, since the surface vehicle can also be deployed autonomously on the high seas (eg started from land). In such concepts, it should be considered whether a so-called semi-submersible or SWATH (small waterplane area twin-hull - comparable to a catamaran) is used, since it is stable on the waterway. Surface float. It should be further noted that it is not mandatory that the surface vehicle also floats completely on the water surface, since it would also be conceivable according to further embodiments, that this just below the water surface (typical of semi-divers) is used.

Although in the above embodiments an AUV or underwater vehicle was assumed to be the other vehicle, it should be noted here that the other vehicle may also be a torpedo, another surface vehicle or a watered-down aircraft (e.g., a Space X rocket stage).

Even if the above exemplary embodiments were explained in particular in connection with a device, it should be pointed out that further exemplary embodiments relate to a corresponding recovery method. The recovery method essentially comprises the central step of controlling the curved path of one of the watercraft, so that there is an engagement between the two lines 12 and 22 or the engagement means on the lines.

Although some aspects have been described in the context of a device, it will be understood that these aspects also constitute a description of the corresponding method, so that a block or a component of a device is also to be understood as a corresponding method step or as a feature of a method step , Similarly, aspects described in connection with or as a method step also represent a description of a corresponding block or detail or indicia of a corresponding device. Some or all of the method steps may be performed by a hardware device (or using a hardware device). Apparatus), such as a microprocessor, a programmable computer or an electronic circuit. In some embodiments, some or more of the most important method steps may be performed by such an apparatus.

Depending on particular implementation requirements, embodiments of the invention may be implemented in hardware or in software. The implementation may be performed using a digital storage medium, such as a floppy disk, a DVD, a Blu-ray Disc, a CD, a ROM, a PROM, an EPROM, an EEPROM or FLASH memory, a hard disk, or other magnetic disk or optical memory on which are stored electronically readable control signals compatible with a programmable computer system. can cooperate or cooperate, that the respective procedure is carried out. Therefore, the digital storage medium can be computer readable.

Thus, some embodiments according to the invention include a data carrier having electronically readable control signals capable of interacting with a programmable computer system such that one of the methods described herein is performed.

In general, embodiments of the present invention may be implemented as a computer program product having a program code, wherein the program code is operable to perform one of the methods when the computer program product runs on a computer.

The program code can also be stored, for example, on a machine-readable carrier.

Other embodiments include the computer program for performing any of the methods described herein, wherein the computer program is stored on a machine-readable medium.

In other words, an embodiment of the method according to the invention is thus a computer program which has a program code for carrying out one of the methods described herein when the computer program runs on a computer.

A further embodiment of the method according to the invention is thus a data carrier (or a digital storage medium or a computer-readable medium) on which the computer program for performing one of the methods described herein is recorded.

A further embodiment of the method according to the invention is thus a data stream or a sequence of signals, which represent the computer program for performing one of the methods described herein. The data stream or the sequence of signals may be configured, for example, to be transferred via a data communication connection, for example via the Internet. Another embodiment includes a processing device, such as a computer or a programmable logic device, that is configured or adapted to perform one of the methods described herein. Another embodiment includes a computer on which the computer program is installed to perform one of the methods described herein.

Another embodiment according to the invention comprises a device or system adapted to transmit a computer program for performing at least one of the methods described herein to a receiver. The transmission can be done for example electronically or optically. The receiver may be, for example, a computer, a mobile device, a storage device or a similar device. For example, the device or system may include a file server for transmitting the computer program to the recipient.

In some embodiments, a programmable logic device (eg, a field programmable gate array, an FPGA) may be used to perform some or all of the functionality of the methods described herein. In some embodiments, a field programmable gate array may cooperate with a microprocessor to perform one of the methods described herein. Generally, in some embodiments, the methods are performed by any hardware device. This may be a universal hardware such as a computer processor (CPU) or hardware specific to the process, such as an ASIC.

The embodiments described above are merely illustrative of the principles of the present invention. It will be understood that modifications and variations of the arrangements and details described herein will be apparent to others of ordinary skill in the art. Therefore, it is intended that the invention be limited only by the scope of the appended claims and not by the specific details presented in the description and explanation of the embodiments herein.

Claims

claims

A two-vessel system and a controller, wherein one of the two vessels is a surface vehicle (20) and another of the two vessels is another vehicle (10); wherein the surface vehicle (20) comprises a suspension line (22) which can be lowered below the waterline and the other vehicle (10) comprises an extendable suspension line (12), wherein a first of the two vessels has a safety device (24) which is accessible via the respective suspension line (12 , 22) is connected to the first vessel and is adapted, upon engagement with the tether (12, 22) of a second of the two vessels, to connect to the tether (12, 22) of the second of the two vessels; wherein the controller is configured to control the first of the two watercraft in a curved path about the second of the two watercraft.

The system of claim 1, wherein the curved path results in a change of direction of the first of the two vessels by at least 90 °.

A system according to claim 1 or 2, wherein a radius of the curved path depends on the length of the tether (12, 22) of the first of the two vessels.

The system of claim 3, wherein the radius is less than the length of the tether (12, 22).

A system according to any one of the preceding claims, wherein the tether of the second vessel has means which vertically align the tether of the second vessel in the water.

A system according to claim 5, wherein said means comprises a weight attached to the tether of the second vessel and configured to vertically tension the tether of the second vessel. The system of claim 5, wherein said means comprises a float attached to the tether of the second vessel and configured to vertically bias the tether of the second vessel.

A system according to any of the preceding claims, wherein the controller is configured to reduce the speed of the second of the two watercraft before the first of the two watercraft in the curved path is controlled.

A system according to any one of the preceding claims, wherein the controller is arranged to lower the catches (12, 22) of the two vessels before the first of the two vessels is controlled in the camming path.

System according to one of the preceding claims, wherein the safety gear (24) has a catch hook.

System according to one of the preceding claims, wherein the safety line (12, 22) of the first and / or second watercraft is lowered or extended with the aid of a weight (14) or stop piece.

The system of claim 1 1, wherein the controller is configured to drop the weight (14) or the stop piece for lowering or extending.

The system according to claim 12, wherein the weight (14) or the stopper is fixed by means of a mechanical shutter and the mechanical shutter is opened for ejection or extension.

The system of claim 12, wherein the weight

(14) is connected to the second underwater vehicle via a metal wire or stainless steel wire, and wherein the controller is configured to apply a voltage to the metal wire or stainless steel wire so that it corrodes upon contact with salt water to drop or strip the weight.

A system according to any one of the preceding claims, wherein the other vehicle is an autonomous underwater vehicle. A method of recovering another vehicle (10) by means of a surface vehicle (20) using a two-vessel system, one being the surface vehicle (20) and another being the other vehicle (10), the surface vehicle (20) being one of Waterline lowerable leash (12, 22) and the other vehicle (10) comprises an extendable safety line (12), wherein a first of the two vessels has a safety device (24), which via the tether (12, 22) connected to the first vessel and is adapted, when engaged with the tether (12, 22) of a second of the two vessels, to connect to the tether (12, 22) of the second of the two vessels, the method comprising the steps of:

Controlling the first of the two watercraft to maneuver in a curved path around the second of the two watercraft.

17. The method according to claim 16, wherein the method comprises the step of controlling the second vessel to stop or reduce its speed at a position about which the curved path of the first vessel passes.

18. A method according to claim 16 or 17, wherein the method comprises the step of lowering or extending the suspension lines (12, 22).

A method according to any of claims 16 to 18, wherein the method comprises the step of dropping a weight (14) on the tether (12, 22) of the second of the two submersibles to the tether (12, 22) of the second of the two Lower or remove underwater vehicles.

20. The method of claim 16, wherein the first of the two watercraft is controlled so that the curved path has a radius that is dependent on the length of the line (12, 22) of the first vessel or less than the line of the first vessel is long. A computer program comprising program code for performing a method according to any of claims 16 to 20 when the program is run on a computer.