EP2621796B1 - System comprising an underwater vehicle and a base situated at the surface - Google Patents

Description

FIELD OF THE INVENTION

The present disclosure relates to a system comprising an underwater vehicle and a surface-based base.

Such a system can be used to perform any type of underwater work and, more particularly, for underwater exploration. The underwater vehicle is generally provided with various on-board equipment (sensors, cameras, articulated arms, sampling means, etc.).

STATE OF THE PRIOR ART

Systems already exist with an underwater vehicle and a base, located on the surface, in which the underwater vehicle is remotely controlled from the base.

In most cases, the underwater vehicle is a remotely operated submarine vehicle or ROV (for "Remotely Operated Vehicle"). This unmanned vehicle is usually remotely controlled from a larger vehicle such as a boat, which is the base, on which the ROV pilot is located.

An example of a known system using an ROV is described in published French patent application no. FR 2668446 .

In this example, a negative buoyancy profiled body is interposed between the ROV and a boat on the surface. The shaped body is maintained substantially at the same depth of immersion as the ROV. The profiled body is wired to the ROV via a first cable. In addition, the profiled body is bonded to the boat by means of a second cable, a diameter greater than that of the first cable. Both the first and second cables allow the transmission of electrical power and control signals from the boat to the ROV. The propulsion means of the ROV are supplied with electrical energy via these cables, the ROV having no onboard energy reserve. It should be noted that, in this system, the length of the first cable is dependent, on the one hand, on the need for the vehicle to travel around the position of the profiled body and, on the other hand, on the need to hold the fixed point of the vehicle. vehicle when the profiled body moves in the case where holding the boat at the fixed point is not sufficient.

It is provided in published application no. FR 2668446 to use a first cable of the type described in published French patent application no. FR 2668643 . However, as the drag of this cable increases with its length, beyond a limit value of cable length, this drag becomes so high that the traction forces exerted by the cable on the ROV and / or on the boat prevent maneuvering. these correctly.

In particular, it is impossible to use this type of cable with a small ship, having no dynamic positioning means, because the length of cable necessary to work on the seabed generally exceeds the aforementioned limit value and the forces The pulling forces exerted by the cable on the ship are too great to allow proper maneuvering of the ship.

Another example of a known system is described in published PCT patent application no. WO 2008/130682 .

To allow work at great depths and, typically, between 7000 and 11000 m depth, this other system uses a Hybrid Remotely Operated Vehicle (HROV). This vehicle is said to be hybrid because it is equipped with on-board propulsion means powered by an onboard battery.

In this other system, a depressor ballast and a float pack are interposed, in that order, between the boat and the HROV. The depressant ballast is tied to the boat directly or via a cable, and is tied to the HROV by an optical fiber that passes through the float pack. The HROV is therefore tied to the diver and the float only by the optical fiber. This optical fiber being of diameter (250 microns) and of very low linear density, its length can be very important (between 20 and 60 km) without generating a drag or a too important weight and, thus, without that hindering the maneuverability HROV or boat.

This other system, however, has some drawbacks detailed below.

Once the operation of the HROV is complete, the optical fiber is cut with a shear present on the float pack. Moreover, a gripping member can be provided on the step-down to recover the cut optical fiber. However, it seems difficult to recover the entirety of the optical fiber with such an organ. There is therefore a risk of pollution of the seabed by unrecovered fiber debris. In all cases, the pieces of optical fiber recovered are damaged and are not reusable. These pieces must be discarded, which also pollutes.

Moreover, this other system proves poorly suited to work on two relatively distant areas of each other. Indeed, in this case, a first mode of operation consists, if the autonomy of the HROV allows, to remotely control the HROV from the first to the second zone but, then, the autonomy of the HROV may be insufficient to work on the second zone. A second mode of operation consists of working on the first zone, cutting the optical fiber, raising the HROV to the surface, recovering the HROV on the boat, moving the boat from the first to the second working area, using a new fiber optic, down the HROV to the seabed of the second zone. This second mode of operation is therefore laborious and takes a lot of time.

PRESENTATION OF THE INVENTION

This presentation concerns a system comprising an underwater vehicle and a surface-based base capable of working at all depths, to the most important depths (eg 11000m), this system being devoid, at least in part, of aforementioned drawbacks.

• un élément de flottabilité positive, dit flotteur, lié filairement à l'engin sous-marin, uniquement par l'intermédiaire de la (des) première(s) fibre(s) optique(s), et
• un élément de flottabilité négative, dit plongeur, lié à la base.

According to one embodiment, it is a system comprising an underwater vehicle and a surface-based base, in which the underwater vehicle comprises an onboard energy reserve and is remotely controlled from the base by the intermediate of at least one first optical fiber, this system comprising:

• a positive buoyancy element, referred to as a float, connected by wire to the underwater vehicle, solely via the first optical fiber (s), and
• a negative buoyancy element, called diver, linked to the base.

• un premier dispositif d'enroulement et de déroulement de la première fibre optique, prévu sur le flotteur et/ou l'engin sous-marin, et
• un deuxième dispositif d'enroulement et de déroulement du premier lien souple, prévu sur le flotteur et/ou le plongeur.

In this system, the float and the plunger are wired together via a first flexible link, and the system further comprises:

• a first device for winding and unwinding the first optical fiber, provided on the float and / or the underwater vehicle, and
• a second device for winding and unwinding the first flexible link, provided on the float and / or the plunger.

Thus, the system can, on the one hand, be deployed by unfolding the first optical fiber and the first flexible link and, on the other hand, be retracted by winding the first optical fiber and the first flexible link.

In this presentation, the term "surface-based base" means any type of installation or device, whether terrestrial or marine, situated at or above the surface of the surface of water, from which it It is possible to remotely control the underwater vehicle. Typically, the base is a boat. It could however be a platform, an off-shore platform, etc. In particular, the proposed system offers the possibility of working with, as a basis, a small ship with no means of dynamic positioning.

Moreover, said underwater vehicle is, more particularly, a submarine engine without crew and self-propelled like, for example, a HROV. It could however be a drone, a torpedo, etc. The energy reserve of this machine is usually a reserve of electrical energy such as a battery.

When the system is in deployed configuration, the diver hangs in the water under the base, the float is remote from the diver and the underwater vehicle is distant from the float.

Such an extended configuration avoids that the efforts exerted by the boat on the diver, especially in case of poor conditions of navigation, have repercussions on the underwater vehicle. The plunger and the float allow a decoupling that limits the forces exerted on the underwater vehicle to those exerted by the first optical fiber. This first optical fiber being of limited linear density and diameter (compared to known cables, metal or Kevlar), the forces exerted by the fiber on the underwater vehicle are also limited, even for long fiber lengths. This ensures good maneuverability of the underwater vehicle. It will be noted that the first optical fiber may be reinforced, in particular by an outer envelope, so as to have sufficient mechanical strength to withstand the traction forces between the float and the machine, in particular during the winding phase of the fiber .

In addition, the geometry of the system in deployed configuration can be adapted by increasing / decreasing the lengths of the first flexible link and the first optical fiber, which is possible due to the presence of the first and second winding devices and unwinding .

Moreover, such a system makes it possible to recover the first optical fiber at the end of the operation by rewinding it by means of the first winding / unwinding device. This first optical fiber can then be reused for a next operation. Thus, the production of waste is limited.

The proposed system is, moreover, well adapted to work on two relatively distant areas of each other. Indeed, in this case, after having worked on the first zone, the first optical fiber and the first flexible link are wound, respectively, by means of the first and second winding / unwinding devices, so that the sub-machine marine, float and diver are united in a unit. This unitary assembly can then be easily pulled by the boat that is moved from the first to the second zone. The first optical fiber and the first flexible link are then unwound to find the deployed configuration and to work on the second site. Thus, unlike the system described in published application no. WO 2008/130682 , the energy used for the movement of the underwater vehicle between the two work areas is not taken from the energy reserve of the machine and the autonomy of the machine is therefore preserved. In addition, it is not necessary to raise the underwater vehicle surface and install a new optical fiber, which simplifies operations and saves time.

In some embodiments, the underwater vehicle comprises an onboard remote-controlled, propulsion system via the first optical fiber (ie the control signals pass through the first optical fiber), the on-board energy reserve being adapted to power this propulsion system. The propulsion system is powered solely by said onboard energy reserve and therefore receives no energy from a source external to the underwater vehicle. In particular, it should be noted that the connection between the float and the underwater vehicle is not used to supply energy to the propulsion system. For example, the underwater vehicle is a HROV.

As indicated above, the first winding and unwinding device of the first optical fiber is provided on the float and / or on the underwater vehicle.

In some embodiments, the first winding / unwinding device is provided on the underwater vehicle, the onboard energy reserve being adapted to feed this first winding device / unwinding. Advantageously, the onboard energy reserve of the underwater vehicle is used.

In other embodiments, the first winding / unwinding device is provided on the float. In this case, an on-board energy reserve is provided on the float, or energy is transferred from the base to the float, via the plunger and the first flexible link.

In some embodiments, the first winding and unwinding device is a constant voltage winch for maintaining the first optical fiber under a certain tension when unwound. This makes it possible to keep this optical fiber relatively stretched between the float and the underwater vehicle and, thus, to prevent it from dragging on the ocean floor where it could be damaged, or that too much length of fiber is generating loops in open water, likely to hang on.

As indicated above, the second winding and unwinding device of the first flexible link is provided on the float and / or the plunger.

In some embodiments, the second winding device is provided on the plunger.

In some embodiments, the system includes a first attachment device adapted to detachably attach the float and the underwater vehicle together. This makes it possible to create a unitary subassembly uniting the float and the underwater vehicle. This subassembly can be easily moved in the water and, in particular, can be moved closer and / or away from the diver. In this case, generally, the subset moves using the propulsion system of the underwater vehicle and is remotely controlled from the base.

In some embodiments, the system includes a second fastener adapted to releasably secure the plunger to the underwater vehicle and / or the float. Thus, it is possible to create a unitary assembly bringing together the diver, the float and the underwater vehicle. This assembly can be moved easily in the water and, in particular, can be pulled by the boat from a first work area to a second work area. In addition, such a unitary assembly can be more easily launched and out of the water.

In some embodiments, the plunger includes a cage defining a housing within which at least a portion of the underwater craft can penetrate. This makes it possible to create a compact assembly uniting the plunger, the float and the underwater vehicle. In addition, when the machine is housed at least partly in the cage, it is protected by it against external shocks. In particular, it is necessary to protect the fragile parts of the machine (e.g. possible fins, possible articulated arms, etc.). Advantageously, to protect the underwater vehicle as much as possible, it is housed entirely in the cage.

In some embodiments, the float includes a locating system for determining, at a given moment, the position of the float underwater, and a remotely controlled propulsion system from the base. Thus, it is possible to monitor and change the position of the float so that it remains at a sufficient distance from the plunger. This limits the risk of damage to the float and entanglement of the first flexible link. The position of the plunger may, when it is, be estimated from the position of the base, or be determined by means of another locating system attached to the plunger.

The first optical fiber must be strong enough to withstand the tensile forces between the plunger and the machine, especially during the winding of the fiber. However, the breaking strength of the fiber is related to the diameter of the fiber and a high tensile strength is accompanied by a large diameter. However, as explained above, the diameter of the fiber must remain small in order to limit the drawbacks associated with the weight, drag and bulk of the fiber when it is wound up. A breaking strength is therefore a disadvantage. For these reasons, in some embodiments, the first optical fiber has a breaking strength of between 500 and 1500 N, which constitutes a good compromise between the mechanical strength and the weight / volume of the optical fiber.

In the same way, in some embodiments, the first flexible link has a breaking strength of between 3,000 and 10,000 N. This is, again, a good compromise between the mechanical strength and the weight / volume. flexible link.

In some embodiments, at least one second optical fiber is connected to the first and is associated with the first soft link. The second optical fiber can be integrated inside the first flexible link so as to be protected.

In some embodiments, at least one first electrical cable is associated with the first flexible link, this first electrical cable being adapted to supply power to the potential equipment of the float, such as, for example, the propulsion means thereof. The first electrical cable can be integrated inside the first flexible link so as to be protected.

In some embodiments, the plunger is wire bonded to the base by a second flexible link. This second flexible link is a solution to keep the diver away from the base while controlling the diver's altitude relative to the ocean floor. In this case, a device for winding and unwinding the second flexible link is provided on the base.

This second flexible link must be strong enough to withstand the pulling forces between the plunger and the base. The breaking strength of the second flexible link therefore depends in particular on the weight / volume of the plunger.

In some embodiments, at least one third optical fiber is associated with the second flexible link, this third optical fiber being connected to the second optical fiber. The third optical fiber can be integrated inside the second flexible link so as to be protected. The first, second and third optical fibers provide an optical connection between the base and the underwater vehicle, this optical connection allowing the transfer of the control signals from the base to the machine and being able to allow, in the other direction, the transfer of data from the machine to the base.

In some embodiments, at least a second electrical cable is associated with the second flexible link, the second electrical cable being adapted to supply power to the potential equipment of the plunger and / or the float. The second electric cable can be integrated inside the second flexible link so as to be protected.

In this presentation, reference is often made, for the sake of clarity, to the first, second and third optical fibers. However, it should be remembered that the proposed system comprises at least a first, at least a second and at least a third optical fiber and that, therefore, several first, several second and several third optical fibers can be provided. This also applies to the first and second electric cables.

Several modes or examples of embodiments are described in this presentation. However, unless otherwise specified, the features described in connection with any one embodiment or embodiment may be applied to another embodiment or embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are diagrammatic and are not to scale, they are primarily intended to illustrate the principles of the invention.

• La FIG 1 représente, un exemple de système selon le présent exposé, comprenant un engin sous-marin, une base située en surface, un plongeur et un flotteur.
• La FIG 2 est une vue de détail de la FIG 1 représentant le flotteur, la première fibre optique et le dispositif d'enroulement/déroulement de cette première fibre optique.
• La FIG 3 est une vue de détail d'un autre exemple de flotteur.
• Les FIG 4 à 7 illustrent les étapes successives du déploiement du système de la FIG 1 dans l'eau.

In these drawings, from one figure (FIG) to the other, identical elements (or element parts) are identified by the same reference signs.

• The FIG 1 represents an example of a system according to the present disclosure, comprising an underwater vehicle, a surface-based base, a plunger and a float.
• The FIG 2 is a detail view of the FIG 1 representing the float, the first optical fiber and the winding / unwinding device of this first optical fiber.
• The FIG 3 is a detail view of another float example.
• The FIG 4 to 7 illustrate the successive stages of the deployment of the FIG 1 in water.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Exemplary embodiments are described in detail below, with reference to the accompanying drawings. These examples illustrate the features and advantages of the invention. However, it is recalled that the invention is not limited to these examples.

The FIG 1 represents a system comprising an underwater vehicle 10 and a base 40 located on the surface. The underwater vehicle 10 is remotely controlled from the base 40 via one or more (in the example only one) first optical fiber 15.

• un élément de flottabilité positive, dit flotteur 20, lié filairement (i.e. par un lien filaire) à l'engin sous-marin 10;
• un élément de flottabilité négative, dit plongeur 30, lié filairement à la base 40 et au flotteur;
• une (ou plusieurs) première(s) fibre(s) optique(s) 15 constituant la seule liaison filaire entre l'engin sous-marin 10 et le flotteur 20;
• un (ou plusieurs) premier(s) lien(s) souple(s) 25 formant une liaison filaire entre le plongeur 30 et le flotteur 20; et
• un (ou plusieurs) deuxième(s) lien(s) souple(s) 35 formant une liaison filaire entre le plongeur 30 et la base 40.

This system includes:

• a positive buoyancy element, said float 20, connected by wire (ie by a wire bond) to the underwater vehicle 10;
• a negative buoyancy element, said plunger 30, bonded to the base 40 and the float;
• one (or more) first optical fiber (s) 15 constituting the only wired connection between the underwater vehicle 10 and the float 20;
• one (or more) first flexible link (s) 25 forming a wire connection between the plunger 30 and the float 20; and
• one (or more) second (s) flexible link (s) 35 forming a wire connection between the plunger 30 and the base 40.

• un premier dispositif 12 d'enroulement/déroulement de la première fibre optique 15, prévu sur l'engin sous-marin 10 (voir FIG 2),
• un deuxième dispositif 32 d'enroulement/déroulement du premier lien souple 25, prévu sur le plongeur 30, et
• un troisième dispositif 45 d'enroulement/déroulement du deuxième lien souple 35, prévu sur la base 40.

This system also includes:

• a first device 12 for winding / unfolding the first optical fiber 15, provided on the underwater vehicle 10 (see FIG 2 )
• a second device 32 for winding / unfolding the first flexible link 25, provided on the plunger 30, and
• a third device 45 for winding / unfolding the second flexible link 35, provided on the base 40.

In this example, the base 40 is a boat.

The underwater vehicle 10 is unmanned and includes an electric battery 14 on board constituting a reserve of energy within the meaning of this presentation. The underwater vehicle 10 is self-propelled, its embedded propulsion system 16 being powered by the battery 14 on board. This propulsion system 16 is remotely controlled from the base 40, via the first optical fiber 15, the link 25 and the link 35. In example, the underwater vehicle 10 is a HROV. The battery 14 also supplies the first winding / unwinding device 12 with electrical energy.

The first winding / unwinding device 12 is a winch with constant tension and it makes it possible to keep the first optical fiber 15 under a certain tension when it is unwound. For example, the main technical characteristics of such a winch may be the following: winding of 200 to 500 m of optical fiber; holding force from 10 to 50 N.

In this example, the plunger 30 comprises a cage 33 (eg a metal cage) defining a housing 31 open laterally via an opening 31a. The shape and dimensions of the housing 31 are such that the underwater vehicle 10 and the plunger 20 can enter (see FIG 4 ). The second device 32 for winding / unfolding the first flexible link 25 is, in the example, a winch. This winch is mounted on the cage 33. For example, the main technical characteristics of such a winch can be, the following: winding 50 to 100 m of link; winding force of the order of 5000 N. In the example, the winch is disposed above the housing and pulleys 34 fixed on the cage 33 can deflect the path of the first flexible link 25. One of the pulleys 34 is located on the opposite side to the lateral opening 31a, so that link 25 passes through the housing 31.

The system comprises a first attachment device adapted to detachably attach together the float 20 and the underwater vehicle 10. In the example, this first fixing device comprises a hook (not shown) integral with the underwater vehicle 10, which can be switched on and off automatically or piloted. This hook blocks the float as soon as the float is in contact with the bottom of its housing in the underwater vehicle. The system also comprises a second fixing device adapted to detachably attach the plunger 30 to the underwater vehicle 10 and / or to the float 20. In the example, this second fixing device comprises a hook integral with the structure of the plunger 30, which can be switched on or off automatically or controlled. This hook blocks the float 20 and the underwater vehicle as soon as they come into contact with the bottom of the housing 31 of the cage 33. A particular example of a float 120 is shown in FIG. FIG 3 . As for the float 20, the first and second optical fibers 15, 25 are connected to the body of the float 120. In addition, this float 120 comprises a propulsion system 127 and a positioning system 126 allowing, at a precise moment, to determine the position of the float 120 under water. The propulsion system 127 can be remotely controlled from the base 40 via the second and third optical fibers 25, 35. Thus, it is possible to monitor and modify the position of the float 120 so that it remains at a sufficient distance from the plunger 30. The position of the plunger 30 is known by means of another locating system 36 fixed on the cage 33 (see FIG 1 ). This limits the risk of shocks between the float 120 and the plunger 30, and the risks of entanglement of the first flexible link 25 with the cage 33 or the second flexible link 35. Finally, the float 20 comprises a fastening element 128 for its fixing on the plunger 30 and a fixing element 129 for its attachment to the machine 10. These two fastening elements 128, 129 have at their free end a flange configured to cooperate, respectively, with the hooks of the plunger 30 and of the cage 33.

In the example, the first optical fiber 15 has a tensile strength of between 500 and 1500 N, a diameter typically between 5 and 8 mm and a linear density typically between 0.4 and 0.8 N / m in the water. This optical fiber 15 is, for example, reinforced by an aramid fiber envelope. This optical fiber 15 is sufficiently strong to withstand the tensile forces between the float 20 and the machine 10, particularly during the winding phase of the fiber 15, while generating a limited weight, drag and space. Note that the size of the housing provided in the machine 10 for housing the fiber 15, when it is wound around the winch 12, depends on the length and the diameter of the fiber 15.

In the example, the first flexible link 25 has a breaking strength of between 3000 and 10000 N, a diameter typically between 10 and 20 mm and a linear density in the low water making it practically neutral in water. This first flexible link 25 is, for example, a cable having a multilayer coaxial structure with an outer Kevlar protection layer.

This first flexible link 25 integrates one (or more) second (s) optical fiber (s), this second optical fiber being close to the core of the link and thus protected by the outer protective layer.

The first flexible link 25 may also include one (or more) first (s) electric cable (s). This cable makes it possible to supply energy to the equipment of the float, that is to say the propulsion system 127 and the locating system 126 in the example of the float 120.

In the same way, the second flexible link 35 integrates one (or more) third (s) optical fiber (s) and one (or more) second (s) electric cable (s).

The third optical fiber is connected to the second optical fiber which, itself, is connected to the first optical fiber 15. Thus, the first, second and third optical fibers provide an optical connection between the base 40 and the underwater vehicle. 10, this optical connection allows the transfer of the control signals from the base 40 to the machine 10.

The second electric cable makes it possible to supply power to the equipment of the plunger, that is to say, in the example, the winch 32 and the locating system 36.

With reference to FIGS 1 , 4-7 , the system of FIG 1 can be deployed in the following manner.

First, the base 40 is moved substantially over the work area. At this point, the machine 10, the float 20 and the plunger 30 are aboard the base 40 and are united in a unitary assembly. Specifically, the float is fixed and locked on the machine 10, and the machine 10 is locked in the waiting position inside the cage 33. The driver of the machine 10 is aboard the base 40.

The cage 33 is then launched and lowered to the bottom by unwinding the second flexible link 35. The cage 33 is stabilized, for example, about 50 meters from the bottom. The FIG 4 represents the cage in this last position. The altitude of the cage 33 is controlled using the location system 36.

As shown on the FIG 5 , the machine 10 is then unlocked vis-à-vis the cage on command of the pilot. The pilot remotely controls the craft 10 (and the float 20 still fixed and locked on the craft 10) out of the cage 33, the craft 10 moving by means of its propulsion system 16. During this step, the winch 32 of the cage 33 is actuated, on command of the pilot, to unwind the first flexible link 25. The first flexible link 25 is unwound, for example, over 50 meters. At this stage, the movements of the base 40 are retransmitted to the cage 33 but almost not to the machine 10, due to the decoupling allowed by the first flexible link 25.

As shown on FIGS 6 and 7 , the float 20 is then unlocked vis-à-vis the machine 10, on command of the pilot. The course (ie unwinding) of the first optical fiber 15 is then done automatically through the winch 12, depending on the movements of the machine 10 (the machine 10 applying a slight traction on the fiber 15 in s' away from the float 20). The machine 10 is remotely controlled by the pilot to reach the work area. At this stage, the machine 10 is completely decoupled from the movements of the base 40 and the cage 33. When the float is of the type of that of the FIG 3 , the position of the float can be checked and modified by the pilot to control the configuration adopted by the first flexible link 25 and the fiber 15.

Once the work is done, the system can be retracted as follows.

First, the machine 10 is reassembled at the pilot's command at the same altitude as the cage 33, so as to clear the bottom. The machine is then moved towards the cage 33, preferably in reverse, so as to facilitate the automatic winding (ie rewinding) of the fiber 15 around the winch 12. At the end of the winding, the float 20 is automatically locked on the machine 10. The machine 10 and the float then form a unit subset. The pilot then controls the winding of the winch 32 of the cage 33, which has the effect of bringing the machine 10 (and the float 20) to the cage. Preferably, the pilot remotely navigates the machine 10 to the approach of the cage 33 to ensure proper alignment of the machine with the opening 31a of the housing 31 of the cage 33 and thus limit the risk of shocks. The machine 10 is then pulled inside the housing 31 by the winch 32, via the first flexible link 25. Once the machine retracted inside the cage 33, it is locked in this position on command of the pilot to prevent it from coming out of the cage 33. The plunger 30, the float 20 and the craft 10 then form a unitary unit. This assembly can either remain in the water and be pulled by the base 40 to another work area, or be raised to the surface by winding the second flexible link 35 and be recovered on board the base 40.

Claims (10)

1. A system comprising an underwater device (10) and a base (40) situated on the surface, wherein the underwater device (10) is remotely controlled from the base via at least one first optical fiber (15) and includes an onboard supply of energy, the system comprising:

   a positive buoyancy element, referred to as a "float" (20) that is connected by wire to the underwater device (10) solely via the first optical fiber (15); and

   a negative buoyancy element referred to as a "plunger" (30) connected to the base (40);

   wherein the float (20) and the plunger (30) are connected together by wire via a first flexible link (25) ;

   the system being characterized in that it further comprises:

   a first winder and unwinder device (12) for winding the first optical fiber (15) in and out, which device is provided on the float (20) and/or on the underwater device (10); and

   a second winder and unwinder device (32) for winding the first flexible link (25) in and out, which device is provided on the float (20) and/or on the plunger (30).
2. A system according to claim 1, wherein the underwater device (10) includes a propulsion system (16) remotely controlled from the base (40), via the first optical fiber (15), the onboard energy supply being adapted to power the propulsion system (16).
3. A system according to claim 1 or claim 2, wherein the first winder and unwinder device (12) is provided on the underwater device (10), the onboard supply of energy being adapted to power this first device (12).
4. A system according to claim 3, wherein the first winder and unwinder device (12) is a constant-tension winch enabling the first optical fiber (15) to be maintained at a certain tension while it is being unwound.
5. A system according to any one of claims 1 to 4, including a first fastener device adapted to fasten the float (20) and the underwater device (10) together in detachable manner.
6. A system according to any one of claims 1 to 5, including a second fastener device adapted to fasten the plunger (30) to the underwater device (10) and/or to the float (20) in detachable manner.
7. A system according to any one of claims 1 to 4, wherein the plunger (30) includes a cage (33) defining a housing (31) into which at least a portion of the underwater device (10) can penetrate.
8. A system according to any one of claims 1 to 5, wherein the float (120) includes a locating system (126) making it possible, at a given moment, to determine the position of the float under water, and a propulsion system (127) remotely controlled from the base (40).
9. A system according to claim 1, wherein the first optical fiber (15) presents breaking strength lying in the range 500 newtons (N) to 1500 N.
10. A system according to claim 1, wherein the first flexible link (25) presents breaking strength lying in the range 3000 N to 10,000 N.

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