Underwater exploration method and mooring device for an underwater exploration drone

Abstract

The present invention relates to an underwater exploration method, in which at least one anchors (4) a vessel (3) upstream of an exploration site and moors (5) with a mooring cord (50) with a stop (51) placed along it; one puts into the water a wire-guided underwater drone-type ROV (1) by means of a cable (100); one controls its descent while submerged; characterized in that one submerges a sliding pigtail (6) along said cord (50) with said cable (100) connected to said pigtail (6); during the descent, the sliding of said pig (6) is jointly controlled to said stop (51). The invention also relates to a device (7) for mooring an underwater exploration drone (1), comprising a mooring cord (50) and a pig (6), mounted to slide along said mooring cord (50); said pig (6) comprising means (70) for attaching a cable (101) of said drone (1). Figure for the abstract: Fig. 1

Description

Title of the invention: Method of underwater exploration and device for mooring an underwater exploration drone

[0001] The subject of the invention is an underwater exploration method, as well as a device for mooring an underwater exploration drone. Technical field of the invention

[0002] The present invention falls within the field of underwater and seabed exploration.

[0003] The invention will find preferential, but in no way limiting, applications in the recovery of submerged objects, in particular scientific equipment such as a hydrophone, but also in the inspection of structures, such as submerged parts of infrastructures, in particular a quay or a dike, an offshore wind turbine or an oil platform, but also in investigations and refloating operations on the site of a shipwreck.

[0004] Usually, underwater exploration of a site at sea requires the deployment of divers from a ship. Proportionally to the depth to be reached and the exploration tasks to be carried out, as well as the equipment to be submerged, the divers must have extremely specialized training and skills, without however ensuring their total safety. In particular, the marine conditions of the site make a human dive all the more complex and dangerous, due to the swell, the amplitude of the tides, the strength of the currents and the constant fluctuation of these environmental conditions. For this reason, underwater and seabed exploration involves submarines, or specific pressurized submerged structures, capable of carrying humans. These solutions require a dedicated floating structure on the surface, which is substantial and expensive to deploy, limiting their use both technically and financially, particularly for less important tasks, such as structural inspection or the recovery of scientific equipment.

[0005] In this context, since the 1960s and 1970s, underwater exploration has used remote-controlled or preferably wire-guided underwater robots, commonly called "ROVs" (for "Remotely Operated Underwater Vehicles"), essentially classified into two categories. The first category includes work ROVs ("Workclass ROVs"), heavy machines equipped with arms and tools for carrying out work, particularly at great depths (up to -6,000 meters). Once again, these heavy ROVs require the deployment of a substantial floating structure. dedicated with a crew trained with very specific skills, well beyond a conventional teleoperator. A second category includes OBServation ROVs ("OBSROVs"), light wire-guided vehicles, with a mass of at least 50 kg (kilograms), generally at least 100 kg. These light ROVs are simpler to deploy from a conventional vessel, but which must once again be equipped with dedicated on-board equipment, such as a crane and a surface power supply. In addition, these light ROVs can only perform inspection or measurement tasks, without being able to physically intervene, as they do not have the on-board tools necessary for an intervention.

[0006] Recently, the observation ROV category has seen the emergence of ultralight devices, commonly referred to as "underwater drones". This class includes wire-guided drones with a mass of less than 100 kg, generally less than 50 kg. Less expensive and easy to deploy, these drones are limited to exploration, and cannot carry tools due to their low carrying capacity. In addition, drones must operate in "calm" marine conditions, particularly with few marine currents. Indeed, the low weight of these ultralight drones makes them extremely sensitive to currents, making their deployment complex or even impossible if marine conditions are not optimal.

[0007] In particular, during the dive of an ultra-light underwater drone, wire-guided and therefore connected to the surface by an umbilical cable, the currents act as much on the walls of said drone as on the umbilical. The force exerted on the umbilical, depending on the depth to be reached, generates sufficient traction forces to destabilize it and which it is not possible to counteract with the weak motorization on board this ultra-light type of drone. For example, for an umbilical with a diameter of 8 mm (millimeters), a 50 m cable represents a projected surface area of ​​0.4 m2 (square meter). This surface area is therefore similar to a sail, taking the current as well as the wind, in proportion to its surface area. Additionally, for a lightweight ROV, in addition to the umbilical dedicated to control and power supply, there is usually a safety tether, similar to a lifeline, connecting the ROV to a fixed attachment point on the surface and located on the boat or floating structure. Such a tether also takes the force of the current, increasing the pull and further reducing its ability to operate in the current. State of the art

[0008] An existing solution consists of deploying a wire-guided ROV, regardless of its category, by submerging a cage carrying it until it is positioned on the seabed. The cage then serves as an anchor point and relay, allowing the drone to operate around it, unwinding its cabling as it progresses. This solution limits the impact of the current only to the length of unwound cabling, generally in a hemispherical area around the cage, rather than to a length equivalent to the immersion depth.

[0009] However, resorting to immersing a cage requires the use of suitable lifting means on board, such as a marine crane, for lowering and raising the cage and the ROV. Furthermore, placing the cage on the seabed limits the drone's range of action around it to the length of the unwound cable and from the point of said placement. In particular, if the drone has to operate at an intermediate depth, a few dozen meters above the seabed, constraints induced by currents are reproduced, further complicating the control of the drone's movements.

[0010] To solve this problem of diving to an intermediate depth, it is possible to lower the cage with an underlying anchor, i.e. deployed lower down to the seabed. However, the cage is subject to the force of the currents, destabilizing it and impairing the control of the ROV connected to it. It would then be necessary to connect the cage to several anchors on the seabed, complicating the operations relating to its immersion. Presentation of the invention

[0011] The invention aims to overcome the drawbacks of the state of the art by proposing an underwater exploration method adapted to the immersion of light or ultra-light ROVs, in particular of the drone type, wire-guided, ensuring the absorption of the forces exerted by the current on its wiring, as well as possibly on a grappling link provided for the recovery of a submerged object. To do this, the invention provides a specific and dedicated mooring, allowing the immersion depth to be adjusted and a pig provided to slide along said mooring up to said stop.

[0012] To do this, the underwater exploration method comprises, in a non-limiting manner, the following steps: - a ship is anchored upstream of an underwater exploration site; - anchoring is carried out directly above said exploration site, with a mooring cord of a length adapted to the depth of the seabed, with a stop placed at a position along said cord; - a wire-guided underwater drone ROV is launched into the water using a cable; - the descent of the drone into immersion is controlled; characterized in that it comprises at least the following steps: - a sliding pig is immersed along said mooring cord, said cabling of the drone being connected to said pig; - during the submersion of said drone, the sliding of said pig is jointly controlled along said mooring cord to said stop.

[0013] According to additional, non-limiting characteristics, said mooring is carried out downstream of said anchoring.

[0014] According to one embodiment, prior to wetting, the position of said stop is adjusted along said wetting cord, said position corresponding to an immersion depth of said pig.

[0015] According to one embodiment, said exploration method consists of, beforehand: - equipping said drone with a hook connected by a cable to said ship, said hook being removably mounted on said drone; - connect said rope to said pig through a releasable mooring point; then successively - once the drone is immersed at said stop, the movements of said drone are controlled until it grapples by means of said hook with a submerged object present on said exploration site; - a release of said cable is ordered by separation with said mooring point with said pig; - said submerged object is raised by pulling said rope from said vessel.

[0016] According to one embodiment, the ascent of said drone is controlled in a synchronized manner with the ascent of the mooring.

[0017] The invention also relates to a device for mooring an underwater exploration drone, comprising - a mooring cord, with a fixed surface end and an opposite end provided with an anchor; characterized in that it comprises - a pig, mounted to slide along said mooring cord; - said pig-tail comprising means for attaching at least one cable of said wire-guided drone.

[0018] According to additional, non-limiting characteristics, such a wetting device comprises - an adjustable stop at a position along said mooring cord; - said pig having a sliding stroke along said mooring cord, said stroke extending between said fixed surface end and said stop.

[0019] According to one embodiment, said pig iron comprises an internal profile with an internal diameter varying along the length of said pig iron, said internal diameter being at least one and a half times greater than the diameter of the mooring cord.

[0020] According to one embodiment, said stop comprises at least one disc.

[0021] According to one embodiment, said stop is light in color, preferably white.

[0022] According to one embodiment, said attachment means comprise - a means for mooring a cable connected to said drone in a removable manner, said mooring means being designed to be releasable.

[0023] (resumption of the characteristics of the dependent claims M+).

[0024] According to one embodiment, said mooring device may be provided for implementing said underwater exploration method according to the invention. Presentation of the drawings

[0025] Other characteristics and advantages of the invention will emerge from the detailed description which follows of the non-limiting embodiments of the invention, with reference to the appended figures, in which:

[0026] [Fig. 1] schematically represents a perspective view of an embodiment of a wetting device;

[0027] [Fig.2] schematically represents a simplified side view of a first step of implementation of the exploration method, showing in particular a ship with a first anchorage upstream relative to the current, as well as the descent of the mooring device along a second mooring directly above an object submerged on the seabed, the descent being carried out in a coordinated manner with the dive of a wire-guided drone;

[0028] [Fig.3] represents a view similar to [Fig.2] of a second step of said exploration method, showing in particular the movement of the underwater drone, once the mooring device has reached the required depth;

[0029] [Fig.4] represents a view similar to [Fig.2] of a third step of said exploration method, showing in particular the securing of the submerged object by hooking, followed by the start of the ascent of the drone and the mooring device;

[0030] [Fig.5] represents a view similar to [Fig.2] of a fourth step of said exploration method, showing in particular the ascent of the object once secured; and

[0031] [Fig.6] schematically represents a top view, showing four successive stages of a mode of implementation of the exploration method, from the first anchoring of the vessel, until the launching of the underwater drone. Detailed description

[0032] The present invention relates to underwater and seabed exploration, using an underwater drone 1.

[0033] For the purposes of the present invention, the term “drone” includes any type of light or ultra-light ROV, namely with a mass less than 100 kg, preferably with a mass less than 50 kg. Such an underwater drone 1 is an autonomous submersible. In order to control its movements in the water, said drone 1 is remotely or wire-guided, preferably wire-guided.

[0034] Further, the invention will find preferential, but in no way limiting, applications in the recovery of submerged objects 2, in particular scientific equipment such as a hydrophone, but also in the inspection of engineering structures, but also in investigations and refloating operations on the site of a shipwreck. For the purposes of the invention, the operations to be carried out are located at a so-called “exploration” site. Such an exploration site can be located in a river or lake environment, but preferably in a maritime, port or sea environment. The location of such an exploration site is determined in advance, in particular by geolocation, for example with two-dimensional coordinates (latitude, longitude) or two- or three-dimensional coordinates of the GPS type (for "Global Positioning System"), or even by location within an identified zone, in particular with mapped seabeds. [Fig.6] shows an exploration site represented by a cross and by an area delimited by a circle, inside which is located the said submerged object 2 to be inspected or recovered.

[0035] That being said, the invention firstly concerns an underwater exploration method. Such exploration is carried out by means of a drone 1, from the surface, from a floating structure. It should be noted that the floating structure can be of any type, capable of receiving on board the marine personnel required for exploration, as well as the necessary equipment, in particular said drone 1. By way of non-limiting example, such a floating structure may be a platform, a barge, or any type of river or maritime vessel, such as a ship 3, hereinafter referred to as “ship”.

[0036] Advantageously, the exploration method according to the invention comprises a first step, in which an anchoring 4 of a ship 3 is carried out. This anchorage 4 is carried out upstream of an underwater exploration site. In particular, upstream is understood in relation to the direction of marine forces, such as the direction of currents and / or tides. [Fig.6] shows an example of the anchorage 4 of a vessel 3 upstream relative to the direction of the currents, modelled by a wavy arrow. Furthermore, anchor 4 may be located within the delimited area of ​​the exploration site, or outside this delimited area. Furthermore, anchor 4 is carried out, so that the submerged object 2 is located vertically close to, but preferably within the avoidance circle of said vessel 3.

[0037] Then, once the ship 3 is positioned, a mooring 5 is carried out directly above said exploration site, in particular directly above or close to the submerged object 2. Furthermore, the positioning of vessel 3 in a plumb position can be achieved by letting it drift along its turning circle. It will be noted that, as visible in the example of [Fig.6], the plumb line can be located close to the submerged object 2 to be inspected or explored, in particular inside a circle centered on said mooring 5 and representing the travel path of the drone 2.

[0038] According to one embodiment, said mooring 5 is carried out downstream of said anchor 4, as visible in [Fig.6] with the anchor 4 located at the bow of the ship 3 while the mooring 5 is located at the stern. This configuration of the mooring 5 relative to the anchor 4 forms an embossment (“or head and stern mooring”), with the anchor 4 as the main anchor and the mooring 5 as the strait anchor. According to another embodiment, the configuration of the mooring 5 relative to the anchoring 4 forms a cross-section, the anchoring 4 and the mooring 5 extending in a V, in particular at an angle between 60° and 120°. It should be noted that it is possible to envisage other additional anchorages or moorings, upstream and downstream, at the bow and / or stern of vessel 3, as well as along its edges, namely to port and / or starboard. In particular, anchorage 4 can be confused with mooring 5. It will be noted that the anchor 4 may comprise a conventional system, namely a ballast, such as an anchor, connected to the vessel 3 by a suitable link, in particular a chain and / or a rope. Furthermore, the length of the link of the anchor 4 is adapted in relation to the operations of positioning the vessel 3 in relation to the exploration site.

[0039] Further, the mooring 5 is carried out by means of a mooring cord 50. Such a mooring cord 50 may be of any type. Preferably, said mooring cord 50 is a rope or a winding of ropes, made of natural, plastic or composite material, in particular from an ultra-resistant polyethylene fiber.

[0040] Usually, the mooring cord 50 comprises a fixed surface end, connected to the ship 3, and an opposite end provided with an anchor, intended to be submerged. The mooring cord 50 comprises a length adapted to the depth of the seabed, in particular a greater length, necessary for attaching its anchor to the seabed. As such, a portion of the cord 50 may comprise a chain, connected to the anchor, and intended to rest on the seabed.

[0041] Advantageously, a stop 51 is placed at a position along said cord 50. Said stop 51 is therefore placed between the fixed end and the opposite end provided with the anchor. According to one embodiment, the stop 51 is placed at a position along the cord 50, so that said stop 51 is located above the seabed, in particular at least one meter above the seabed. Preferably, prior to the anchoring 5, the position of said stop 51 is adjusted along said anchor cord 50. Said stop 51 is therefore provided to be adjustable to a position along said anchor cord 50. Once the position of the stop 51 is adjusted, kept fixed on said cord 50, after immersion of the anchor 5, said stop 51 is then located at a determined depth, between the seabed and the ship 3.

[0042] Then, according to the exploration method, an ROV of the underwater drone type 1 is launched into the water. As mentioned previously, the drone 1 is wire-guided, namely that it is connected by wire to the ship 3 and to a control terminal, allowing an operator to control the movements of said drone 1. This wire-guided character is achieved by means of a cabling 100, commonly called an “umbilical” or “umbilical link”. It will be noted that the wiring 100 may also include a safety link, like a lifeline, permanently connecting the drone 1 to the ship 3. This link may be independent or wrapped around said umbilical.

[0043] After launching the drone 1, its descent into immersion is controlled. This descent is carried out by an operator located on board the ship 3, from the control terminal. The immersion is carried out at least in part by actuating the motorization specific to said drone 1.

[0044] Advantageously, according to the invention, the exploration method consists of immersing a sliding pig 6 along said mooring cord 50. The pig 6 is therefore mounted to move in translation relative to said cord 50. Such a pig 6 serves as ballast, capable of moving along the cord 50, in particular under the simple effect of gravity, due to its own weight. It should be noted that the positioning of the pig 6 on the cord 50 can take place before the anchoring 5, on board the ship 3.

[0045] In addition, the wiring 100 of the drone 1 is connected to said pig 6. Such a connection is provided fixed or removable, preferably fixed, through attachment means of any type. In short, in the case of a fixed connection, it is not possible to unhook the wiring 100 of said drone 1 from the pig 6, whereas it is possible to disconnect them for a removable connection. Once the pig 6 is submerged, during the lowering of said drone 1 into immersion, the sliding of said pig 6 along said mooring cord 50 is jointly controlled. In short, it is decided to lower the pig 6 and the drone 1 together, in particular in a synchronized manner (i.e. approximately at the same speed). or not (i.e. by lowering one or the other more or less quickly).

[0046] Furthermore, said sliding of the pig 6 along the cord 50 takes place up to said stop 6.

[0047] Therefore, when adjusting the position of said stop 6 along said mooring cord 50, said position corresponds to the immersion depth of said pig 6. Thus, the cabling passing through the pig 6, held fixed thereon, once the pig is at its immersion depth, blocked by the stop 6, the length of cabling between the pig 6 and the surface, namely the ship 3, can float with the currents, without disturbing the drone 1. Indeed, said drone 1 is connected by the remaining submerged portion of its cabling 100 to the pig 6, which then serves as a fixed relay point.

[0048] Furthermore, during its descent into immersion, the drone 1 can be pulled towards the bottom by the sliding descent of the pig 6, without using its motors or by accompanying it by controlling the actuation of its motorization. In particular, according to one embodiment, as seen in [Fig.2], the drone 1 is kept at a distance, by actuating its motorization, to tighten the portion of its wiring 100 extending to the pigtail 6, during the descent. This action makes it possible to separate the drone 1 and its portion of wiring 100 from the cord 50, preventing one or the other from becoming entangled around said cord 50 or the wiring 100. Furthermore, the sliding control of said pig 6 can be carried out by simple release, its descent being carried out in a completely gravitational manner, without controlling its speed, or by means of a link whose unwinding speed is controlled, by an operator on the deck of the ship 3 or by a suitable device, such as a winch, making it possible to control the speed of descent of said pig 6.

[0049] Thus, depending on the position of fixing of the stop 6 along the cord 50, an immersion depth of said pig 6 is determined. Once the depth has been reached by the pig 6, the drone 1 which is connected to it can move around this fixed point. In this respect, the length of the portion of cabling 100 between the drone 1 and the pig 6 is determined beforehand, depending on the distance to be covered by said drone 1. This length is sufficient to enable the movement of the drone 1 to be controlled to inspect all or part of the exploration site, in particular until it can reach the submerged object 2 to be inspected or recovered. This length of the portion of the cabling 100 may be several meters, preferably less than twenty meters. This length may be reduced, in particular due to the strength of the currents, to limit the traction on the drone 1 by the sea currents, while maintaining a sufficient length to allow the movement of said drone 1 up to the submerged object 2 to be inspected.

[0050] According to one embodiment, in the context of a recovery of the submerged object 2, the exploration method provides for equipping said drone 1 with a hook 101. This hook 101 is then connected by a cable 102 to said ship 3. Furthermore, this cable 102 is independent of the cabling 100. Said cable 102 can be made of any type of material, preferably synthetic fiber, in particular ultra-resistant polyethylene. In addition, said hook 101 is removably mounted on said drone 100. In short, it is possible to release the hook 101, in a controlled manner from the surface. Such attachment can be carried out by any type of means, in particular by an articulated and motorized clamp, carried by said drone 1, the opening / closing of said clamp being controlled from the control terminal by the operator. It should be noted that the removable attachment of the hook 101 is carried out prior to launching the drone 1 into the water.

[0051] Furthermore, the exploration method provides for connecting said rope 102 to said pig 6, through a releasable mooring point. Said releasable mooring point can be provided with any type of means, preferably attachment means equipping the pig 6 and provided with a releasable mooring means for said cable 102 connected to said drone 1 in a removable manner. It will be noted that the removable attachment of the rope 102 to the pig 6 at the level of the releasable mooring point is carried out prior to the immersion of said pig 6, namely before carrying out the anchoring 5.

[0052] With this specific configuration, once the drone is immersed at the required depth, the movements of said drone 1 are controlled until grappling by means of said hook 101 of the submerged object 2 present on said exploration site. Then, the release of said rope 102 is ordered, by separation from said mooring point at the level of said pig 6. Finally, all that remains is to raise said object 2 by pulling said rope 102 from said ship 3. Thus, it is possible, on the one hand, to descend with the drone 100 carrying the hook 101, down to the object 2, to grapple it, then, on the other hand, to release the hook 101 from the drone 1 and unhook its rope 102 from the pig 6, to pull on said rope 102 and raise said object 2 towards the surface. The rope 102 remaining attached to the pig 6, during the descent and the time that the drone 1 moves until catching the object 2 by securing it with the hook 101, only the portion of said rope 102 between the hook 101 (i.e. the drone 1) and the pig 6 is subjected to the forces of the sea currents, facilitating the maneuvers of said drone 1.

[0053] According to one embodiment, the exploration method provides for controlling the ascent of said drone 1 in a synchronized manner with the ascent of the mooring 5. Furthermore, as previously mentioned at the time of descent, to avoid entanglement, it is possible to control the movements of said drone 1 to move it away from the pig 6, by tensioning its wiring 100. It is possible to do the same during its ascent. Furthermore, in the case where the pig 6 is connected to the surface by its link, controlling its descent, it is then possible to raise the pig 6 alone along the cord 50 of the mooring 5 (the latter being raised after). The raising of the pig 6 therefore takes place jointly with the raising of the drone 1, preferably by controlling its movements from the terminal. In addition, the simultaneous ascent of the drone 1 and the mooring 5 (or of the pig 6 alone) can take place before, at the same time or after the ascent of the object 2, preferably before to limit the risks of entanglement.

[0054] With reference to [Fig.6], showing certain steps of an embodiment of the exploration method: - top left, ship 3 has been positioned in an area around the exploration site and anchor 4 is carried out at the bow of ship 3, upstream in relation to the direction of the currents; - at the top right, we leave the boat drifting to position itself correctly, with the stern aligned or substantially aligned with the submerged object 2 to be inspected or recovered; - at the bottom left, the anchoring 5 is carried out, at a distance allowing the drone 1 to access said object 2 (depending on the portion of the depth of the stop 50 and the length of the portion of its wiring 100 between the pigtail 6 and said drone 1); - at the bottom right, said drone 1 is launched and the descent of the pig 6 is ordered along the mooring 5 to the stop 51, together with the descent of said drone 1.

[0055] The invention also relates to a device 7 for mooring an underwater exploration drone 1. Such a mooring device 7 can be used specifically for implementing the exploration method according to the invention, as previously described. Subsequently, indiscriminately for ease of understanding, the same elements as mentioned above will bear the same references. In addition, the means and materials mentioned above may be identical for the same elements.

[0056] According to the invention, such a mooring device 7 comprises a mooring cord 50, with a fixed surface end and an opposite end provided with an anchor. Said fixed surface end is intended to be mounted in a fixed position on the ship 3, or on a buoy (like a mooring line), while the opposite end provided with an anchor is intended to be submerged to the seabed.

[0057] Advantageously, said wetting device 7 comprises a pig 6, mounted to slide along said wetting cord 50. In addition, said pig 6 comprises means 70 for attaching at least said wiring 100 of said wire-guided drone 1. Said attachment means 70 may be of any type. According to one embodiment, said attachment means 7a are mounted on the periphery of a ring 72 free to rotate relative to said pig iron 6. This freedom of rotational movement allows in particular the wiring 100 of the drone 1 not to become tangled around the pig iron 6, if it were to turn on itself during its descent, in particular due to the helical braiding of the strands of said cord 50.

[0058] According to a preferred embodiment, the wetting device 7 comprises a stop 51 adjustable to a position along said wetting cord 50. Therefore, said pig 6 has a sliding stroke along said mooring cord 50, said stroke extending between said fixed surface end and said stop 51.

[0059] Concerning the stop 51, it can be of any shape and made of any type of material. According to a preferred embodiment, said stop 6 comprises at least one disc 510. This disc shape provides an offset extending transversely relative to the axis of the cord 50, limiting the risks of the wiring 100 of the drone 1 becoming entangled with the portion of the cord 50 located under said stop 51. Such an offset is notably visible in [Fig.l]. Preferably, the stop 51 comprises two separate discs 510 held in position with each other. In addition, the positioning of said two discs 510 relative to each other can ensure the fixing at the position when adjusting the location of said stop 51 along the cord 50. Furthermore, the fixing of said two discs 510 together can be carried out in such a way as to confer a shearing effect on the cord 50, blocking the movement of said discs 510 along said cord 50. Said at least one disc 510 can be attached to the cord 50 at any location, preferably by a through orifice, in particular located in its center. In this case, the attachment of two discs to each other with a shear locking effect can be carried out by offsetting the orifice of one of the discs relative to the other. Each of said discs 510 may be made of any type of material, preferably plastic or composite.

[0060] According to one embodiment, the stop 51 is light in color, preferably white. In the case of at least one disc 510, one and / or the other of its faces, and / or its peripheral edge may be light in color, preferably white. The term "clear" is understood here as distinguishing itself from the surrounding, conversely dark, colors present in the seabed. The said light color can also be made reflective, returning part of the light radiation emitted by lighting means equipping said drone 1 (said radiation being in a visible or invisible spectrum, in particular infrared). Thus, the light color of the stop 6 serves as a visual reference, allowing the operator to find his way when controlling the movements of said drone 1, in particular by means of video capture means equipping said drone 1, such as cameras. In addition, once the drone 1 is at the required depth, lowered away from the mooring 5 to avoid any risk of entanglement, the operator can

[0061] According to one embodiment, in the case of the recovery of a submerged object2, said means for attaching the pig 6 comprise a means 71 for mooring a rope 102 connected to said drone 1 in a removable manner. In particular, it is a hook 101 which is fixed to the end of said rope 102, the hook 101 being on board so as to be able to be released by the drone 1, in particular by means of an articulated and motorized clamp equipping said drone 1 and controlled by the operator from the terminal on the surface. It will be noted that the distal end of the cable 102 connected to the hook 101 can be sheathed over a certain length, stiffening this portion and avoiding the risk of tangling with the motorization in the form of propellers of said drone 1. In addition, said mooring means 71 is designed to be releasable, namely that the rope 102 can be unhooked from the pig 6 in a controlled manner.

[0062] Said releasable mooring means 71 may be of any type. According to one embodiment, it comprises a clamp, in particular a fuse-type clamp. This clamp provides sufficient clamping force to ensure locking of the rope during the descent of the pig 6, while resisting currents. In addition, the clamp can be opened to release the rope 102. Furthermore, the opening of said clamp can be controlled by traction along said rope 102, by means of the extraction of a pin for holding said clamp closed, or with a traction force greater than that experienced during the descent of the pig 6. In particular, the traction force exerted is greater, due to the tension exerted on said rope 102, once the hook 101 is gripped by the object 2, adding its weight, including the weight of the pig 6; this greater force then ensures the opening of said clamp.

[0063] Concerning the pig 6, it can have any shape and be made of any type of material. Preferably, the pig 6 is made of metallic material, with sufficient mass to give it its ballast capacity for its gravity descent. According to the embodiment, as visible in [Fig.l], the pig iron 6 is in the form of a sheath, namely generally a tube, crossed by said cord 50. This elongated shape makes it possible to maintain the parallel or substantially parallel alignment of the longitudinal axis of the pig iron 6 relative to the cord 50.

[0064] According to one embodiment, said pig 6 comprises an interior profile with a internal diameter varying along the length of said pig iron 6. In short, the internal profile of the pig iron 6 has at least one convergent (or divergent) portion. Preferably, the lower end of the pig iron 6 has an internal profile converging from said lower end towards the opposite upper end. In short, the interior of the pig iron 6 widens upwards, forming a funnel, limiting the risks of the lower edge catching against the strands of the cord 50 during its descent. According to one embodiment, the inner profile of the upper end may also be convergent from the outside to the inside of the pig. Such a converging internal profile can be obtained by boring the corresponding end.

[0065] Furthermore, in order to ensure the proper sliding of the pig iron by sliding along the mooring 5, said internal diameter of the pig iron 6 is at least one and a half times greater than the diameter of the mooring cord 50. Preferably, the internal diameter (the smallest due to the converging portions) is at least twice greater than the external diameter of said cord 50.

Claims

Claims

1. Method of underwater exploration, in which at least: - an anchoring (4) of a ship (3) is carried out upstream of an underwater exploration site; - a mooring (5) is carried out directly above said exploration site, with a mooring cord (50) of a length adapted to the depth of the seabed, with a stop (51) placed at a position along said cord (50); - a wire-guided underwater drone type ROV (1) is launched into the water by means of a cable (100); - the descent into immersion of said drone (1) is controlled; characterized in that it comprises at least the following steps: - a sliding pigtail (6) is immersed along said mooring cord (50), said cable (100) of the drone (1) being connected to said pigtail (6); - during the submersion of said drone (1), the sliding of said pig (6) along said mooring cord (50) is jointly controlled to said stop (51).

2. Exploration method according to the preceding claim, characterized in that - said mooring (5) is carried out downstream of said anchoring (4).

3. Exploration method according to any one of the preceding claims, characterized in that - prior to the mooring (5), the position of said stop (6) is adjusted along said mooring cord (50), said position corresponding to an immersion depth of said pig (6).

4. Exploration method according to any one of the preceding claims, characterized in that it consists of, beforehand: - equipping said drone (1) with a hook (101) connected by a cable (102) to said ship (3), said hook (101) being removably mounted on said drone (1); - connecting said cable (101) to said pig (6) through a releasable mooring point; then successively - once the drone (1) is submerged at said stop (6), the movements of said drone (1) are controlled until grappling by means of said hook (101) of an immersed object (2) present on said exploration site; - a release of said cable (101) is ordered by separation with said mooring point with said pig (6); - said submerged object (2) is raised by pulling said cable (101) from said ship (3).

5. Exploration method according to any one of the preceding claims, characterized in that it consists of: - controlling the ascent of said drone (1) in a synchronized manner with the ascent of the mooring (5).

6. Device (7) for mooring an underwater exploration drone (1), comprising - a mooring cord (50), with a fixed surface end and an opposite end provided with an anchor; characterized in that it comprises - a pigtail (6), slidably mounted along said mooring cord (50); - said pigtail (6) comprising means (70) for attaching at least one cable (100) of said wire-guided drone (1).

7. Mooring device (7) according to the preceding claim, characterized in that it comprises - a stop (51) adjustable to a position along said mooring cord (50); - said pig (6) having a sliding stroke along said mooring cord (50), said stroke extending between said fixed surface end and said stop (50).

8. Mooring device (7) according to the preceding claim, characterized in that - said pig iron (6) comprises an internal profile with an internal diameter varying along the length of said pig iron (6), said internal diameter being at least one and a half times greater than the diameter of the mooring cord (50).

9. Moistening device (7) according to one of claims 7 or 8, characterized in that - said stop (50) comprises at least one disc (510).

10. Moistening device (7) according to the preceding claim, characterized in that - said stop (50) is light in color, preferably white.

11. Mooring device (7) according to claims 6 to 10, characterized in that said attachment means (70) comprise - a means (71) for mooring a cable (100) connected to said drone (1) in a removable manner, said mooring means (71) being designed to be releasable.

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