Towed submarine device

Abstract

The invention relates to a submarine device (12) that is intended to be towed by a surface vessel (10), the surface vessel (10) being able to comprise a handling system (20) for storing and deploying the submarine device (12). The handling system (20) comprising a tow cable (18) and an attachment cable (25b). The submarine device (12) comprises a flexible elongated body (16) and a towed body (14), the towed body (14) being capable of being arranged between the tow cable (18) and the flexible elongated body (16). The submarine device also comprises an intermediate element (30) that can be arranged between the towed body (14) and the flexible elongated body (16). The intermediate element (30) is connected to the towed body (14) by a first connection (32). The intermediate element (30) is connected to the flexible elongated body (16) by a second connection (34), the first connection (32) being an articulated mechanical connection. The intermediate element (30) is a low-rigidity cable. The submarine device (12) comprises a recovery line (25a).

Description

DESCRIPTION Towed underwater device

[0001] The present invention relates to an underwater device intended to be towed by a surface vessel comprising a handling system capable of being installed on the surface vessel and enabling said underwater device to be stored and deployed. The invention finds particular use in the field of underwater devices of the active sonar type comprising a cable towing a towed body incorporating a transmission antenna (transmission array). The towed body is sometimes called a "fish" due to its shape. A linear receiving antenna forming a flexible elongated body is towed behind the fish. This is then referred to as a dependent towing system. The linear receiving antenna is sometimes called a "streamer" also due to its shape.The towed body can be a volumetric body suspended from the towing cable (tow cable in English) or be elongated along a longitudinal axis and incorporating a linear transmission antenna comprising transducers distributed along the longitudinal axis.

[0002] Handling such underwater devices is delicate. More specifically, outside of periods of use, the underwater device is stored on a deck of the surface vessel, generally an aft deck. Launching and retrieving the underwater device requires the presence of operators on the aft deck of the surface vessel. Operators are required to handle heavy loads, which can be dangerous, especially in rough seas.

[0003] The towed body's hauling cable is called a "heavy cable" because it is heavy enough to make the hitch dive. This hauling cable generally includes a core formed of electrical and / or optical conductors to transmit energy and information between sonar equipment located on board the vessel and the antennas. The core cable is generally covered with a strand of metal wires ensuring the mechanical strength of the cable. The towed body is generally solid. It can be equipped with fins ensuring its hydrodynamic stability. The linear receiving antenna can extend over a length of around a hundred meters to allow the detection of sound waves propagating in the water at low frequencies. This may be an echo of sound waves emitted by the transmitting antenna when the sonar is operating in active mode.The sonar can also operate in passive mode without emitting sound waves.

[0004] In patent application WO 2018 / 065385A1 filed in the name of the applicant, a single winch is used to handle the towing cable and the receiving antenna. These are neutrally buoyant and this cable is called "light cable". The towing cable and the receiving antenna are integral with each other. When launching, the towed body is hooked and connected at the junction between the towing cable and the receiving antenna with the receiving antenna's light cable, or even directly to the receiving antenna. The purpose of the light cable is to distance the antenna from the towing vessel's own noise. The flexible elongated body then encompasses the light cable and the receiving antenna. Such an arrangement of the towing cable and the receiving antenna on the same winch poses certain problems. In particular, the winch must be adapted to the largest bending radius permissible by the towing cable and the receiving antenna. This can lead to significant oversizing of the winch drum.In addition, it may be useful to handle the towing cable and the receiving antenna separately, which is not possible with a single winch, unlike a set comprising two winches / drums, i.e. one winch for the heavy cable and one winch for the flexible elongated body.

[0005] In another patent application WO2021069640 filed in the name of the applicant, two separate winches are used, one for the towing cable and the other for the receiving antenna. A rigid and movable arm is positioned between the towed body and the flexible elongated body. When recovering the towed body, the rigid arm is not always positioned correctly and the connection between the rigid arm and the flexible elongated body must not have a baffle to avoid the risk of damaging the receiving antenna. Such a risk of baffle may arise when the towed body does not stow quite as expected, when it is recovered at sea. In addition, the rigidity of the device, its eccentric weight, increased by potential sea waves when launching or recovering could induce stresses leading to risks of breakage.

[0006] The invention aims to facilitate the launching and recovery maneuvers of the various elements of the towed underwater device while ensuring high safety for the operator during handling operations.

[0007] To this end, the invention proposes an underwater device intended to be towed by a surface vessel, said surface vessel being capable of comprising a handling system for storing and deploying the underwater device. The handling system comprises a towing cable and a hooking cable. Said underwater device comprises: - a flexible elongated body; - a towed body, said towed body being capable of being arranged between the towing cable and said flexible elongated body; - an intermediate element capable of being arranged between the towed body and the flexible elongated body, said intermediate element being connected to the towed body by a first connection, said intermediate element being connected to the flexible elongated body by a second connection, said first connection being an articulated mechanical connection. The element intermediate is a low stiffness cable. The underwater device comprises a recovery rope connected to the flexible elongated body, said recovery rope comprising, at an end opposite the flexible elongated body, a downstream carabiner, said downstream carabiner allowing the recovery rope to be attached either to the towing cable via the towed body or to the hooking cable coming from the winch of the flexible elongated body.

[0008] The low-stiffness cable allows the operator to avoid leaning too far behind the fish to hook it. In the prior art, the intermediate element is a rigid articulated arm that imposes a given distance between the two winches. In addition, the articulated arm prevents the towed body from being placed at the edge of the stern if doors are provided at the rear of the boat. The low-stiffness cable makes it possible to drastically reduce this distance and allows the doors to be kept closed and therefore improves safety for the operator. In addition, by using a low-stiffness cable, the positioning constraint between the two winches is eliminated and connection operations are made easier / safer for the operator. In addition, the use of a recovery rope makes it easier to subsequently recover the junction between the flexible elongated body and the intermediate element.

[0009] The term "cable" means a protected metallic conductive wire. The cable here is an opto-electro-tractor cable.

[0010] “Low stiffness cable” means a cable with a stiffness k of less than 10 N / m.

[0011] A rope is a collection of strands twisted together. These strands can be made of textile, KEVLAR, steel, or other materials.

[0012] By "carabiner" we mean a metal loop with a quick and secure closing system.

[0013] In a particular embodiment, the attachment cable comprises an upstream carabiner adapted to be attached to the downstream carabiner of the recovery rope.

[0014] In a particular embodiment, the intermediate element is a cable of lightweight cable technology.

[0015] In a particular embodiment, the intermediate element comprises an optoelectric strand and a plurality of force-recovery strands, said strands being separate.

[0016] In a particular embodiment, the intermediate element is a reinforced cable.

[0017] In a particular embodiment, the cable is reinforced by a traction braid.

[0018] It is thus possible to maintain traction while using a low stiffness cable.

[0019] In a particular embodiment, the handling system comprises two winches, a first winch being able to store and deploy the towing cable, a second winch being able to store and deploy the hooking cable. In a first position, the intermediate member is aligned with the flexible elongated body to enable the first winch to tow the entire underwater device. In a second position, the intermediate member is misaligned from the flexible elongated body to enable alignment of the flexible elongated body with the second winch.

[0020] In a particular embodiment, the underwater device comprises an electrical and / or optical connection between the towed body and the flexible elongated body. This electrical and / or optical connection is disconnectable.

[0021] Another subject of the invention relates to a method for launching an underwater device by a handling system belonging to a surface vessel. The handling system comprises a towing cable and a hooking cable. The underwater device comprises: - a flexible elongated body; - a towed body, said towed body being capable of being arranged between the towing cable and said flexible elongated body when using the underwater device; - an intermediate element capable of being arranged between the towed body and the flexible elongated body, said intermediate element being connected to the towed body by a first connection, said intermediate element being connected to the flexible elongated body by a second connection, said first connection being an articulated mechanical connection, said second connection being disconnectable, said intermediate element being a low stiffness cable and the underwater device comprises a recovery rope connected to the flexible elongated body, said recovery rope comprising, at an end opposite the flexible elongated body, a downstream carabiner, said downstream carabiner allowing the recovery rope to be attached either to the towing cable via the towed body or to the attachment cable. The handling system comprises two winches, a first winch for storing and deploying the towing cable. A second winch for storing and deploying the hooking cable. In a first position, the intermediate element is aligned with the flexible elongated body to allow the first winch to tow the entire subsea device. In a second position, the intermediate element is misaligned from the flexible elongated body to allow alignment of the flexible elongated body with the second winch. The launching method comprises: - a step of unwinding the second winch to put the flexible elongated body into the water, the recovery rope being taut; - a step of connecting the flexible elongated body to the second end of the intermediate element in the misaligned position; - a step of placing the intermediate element in an aligned position; - a step of unwinding the second winch to relax the recovery rope, the tension being taken up by the intermediate element; - a step of attaching the downstream carabiner to the towed body and a step of unhooking said downstream carabiner relative to the attachment cable, so as to allow subsequent recovery of a junction between the flexible elongated body and the intermediate element; - a stage of unwinding the first winch.

[0022] The invention will be better understood and other advantages will appear on reading the detailed description of an embodiment given by way of example, a description illustrated by the attached drawing in which:

[0023] [Fig. 1] Figure 1 schematically represents an underwater device in a first stage of a process for launching it into the water;

[0024] [Fig. 2] Figure 2 represents the underwater device of Figure 1 in a second stage of the process for its launching;

[0025] [Fig. 3] Figure 3 represents the underwater device of Figure 1 in a third stage of the process for its launching;

[0026] [Fig. 4] Figure 4 represents the underwater device of Figure 1 in a fourth step of the process for its launching;

[0027] [Fig. 5] Figure 5 represents the underwater device of Figure 1 in a fifth step of the process for its launching;

[0028] [Fig.6] Figure 6 represents the underwater device of Figure 1 in a sixth step of the process for its launching;

[0029] [Fig.7] Figure 7 represents the underwater device of Figure 1 in a seventh step of the process for its launching;

[0030] [Fig.8] Figure 8 represents the underwater device of Figure 1 in an eighth step of the process for its launching;

[0031] [Fig. 9] Figure 9 is an enlarged view of the towed body of the underwater device of Figures 1 to 8, in a first configuration of a connection;

[0032] [Fig. 10] Figure 10 is an enlarged view of the towed body of the underwater device of Figures 1 to 8, in a second configuration of the connection of Figure 9;

[0033] [Fig. 11] Figure 11 schematically represents an intermediate element of the underwater device of Figures 1 to 8 according to a first embodiment;

[0034] [Fig. 12] Figure 12 schematically represents an intermediate element of the underwater device of Figures 1 to 8 according to a second embodiment;

[0035] [Fig. 13] Figure 13 schematically represents an intermediate element of the underwater device of Figures 1 to 8 according to a third embodiment.

[0036] For the sake of clarity, the same elements will have the same references in the different figures.

[0037] The invention is described in relation to the towing of an active sonar by a surface vessel. It is understood that the invention can be implemented for any type of towed underwater device.

[0038] Figure 8 shows a vessel 10 towing an active sonar 12 comprising a towed body 14 incorporating an acoustic transmitting antenna and a flexible elongated body 16 forming an acoustic receiving antenna. Hereinafter, the towed body will be called fish 14 and the flexible elongated body will be called streamer 16. The sonar 12 also includes a cable 18 for towing the fish 14 and the streamer 16. The cable 18 also ensures the routing of signals and power supplies between the vessel 10, the fish 14 and the streamer 16.

[0039] The fish 14 and the streamer 16 are mechanically secured and electrically and / or optically connected to the cable 18 in a suitable manner. Conventionally, the streamer 16 is formed of a linear antenna of tubular shape identical to those found in passive sonars, hence its name streamer, while the transmitting antenna is integrated into a volumetric structure forming the towed body 14 having a shape similar to that of a fish. The streamer 16 is secured to the fish 14 which, itself, is secured to the end of the cable 18. During an underwater acoustic mission in active mode, the antenna of the fish 14 emits sound waves into the water and the receiving antenna of the streamer 16 picks up any echoes coming from targets on which the sound waves coming from the transmitting antenna are reflected.

[0040] A handling device 20 is arranged on a rear deck 22 of the vessel 10. The handling device 20 comprises two winches 24 and 26. The winch 24 allows the towing cable 18 and the fish 14 to be stored and deployed. The winch 26 allows the streamer 16 to be stored and deployed. In the deployed position of the active sonar 12, as shown in FIG. 5, only the winch 24 is in operation. The winch 24 tows the entire sonar 12. More precisely, the cable 18 tows the fish 14 and the streamer 16 is hooked behind the fish 14.

[0041] In Figure 8, the winch 24 is located on the port side of the ship 10 and the winch 26 on the starboard side. Other configurations are also possible, winch 24 on the starboard side and winch 26 on the port side, winch 24 above or below the winch 26. More generally, the two winches 24 and 26 are offset from each other.

[0042] The sonar 12 comprises an intermediate element 30. This intermediate element 30 is arranged between the fish 14 and the streamer 16. More particularly, the intermediate element 30 is connected to the fish 14 by a first connection 32. In addition, the intermediate element 30 is connected to the streamer 16 by a second connection 34. The first connection 32 is an articulated mechanical connection. It can thus be disassembled for replacement of the intermediate element for maintenance operations. This first connection 32 is shown here fixed. Alternatively, this first connection 32 is disconnectable. The second connection 34 is, here, disconnectable. In Figure 8, in the deployed position of the active sonar 12, the intermediate element 30 is aligned with the streamer 16. More precisely, the intermediate element 30 and the streamer 16 both extend substantially along the same axis 36. When the ship 10 is sailing in a straight line, the axis 36 is substantially parallel to the axis of movement of the ship. In practice, the drag forces experienced by the streamer 16 orient the intermediate element 30 and the streamer 16 naturally in the water along the axis 36 which can oscillate in particular depending on the weather conditions, more particularly depending on the swell conditions which induce pitching and rolling of the towing ship.

[0043] The fish 14 and the flute 16 are also connected to each other by a recovery rope 25a. More particularly, the recovery rope 25a comprises a downstream carabiner 27a attached to an attachment means 28 belonging to the fish 14. The other end of the recovery rope 25a is here connected to the flute 26 via the second connection 34.

[0044] Figure 2 shows the ship of Figure 8 whose sonar 12 is being launched or raised. More precisely, the fish 14 is placed on the deck 22, possibly in a cradle provided to accommodate it. The winch 24 is stationary. The cable 18 is almost entirely wound onto the winch 24. The intermediate element 30 is misaligned from the streamer 16, allowing the streamer 16 to be aligned with the winch 26.

[0045] To ensure good alignment of the intermediate element 30 and the flute 16, at the end 32, the articulation between the fish 14 and the intermediate element 30 is advantageously of the finger ball joint type, or ball joint, that is to say having at least two degrees of freedom in rotation around axes perpendicular to the axis 36. Such an articulation is disclosed in particular in Figures 8 and 9. Similarly, at the end 34, the articulation between the intermediate element 30 and the flute 16 advantageously has at least one degree of freedom in rotation around an axis allowing the alignment of the flute 16 with the winch 26. The flute 16 advantageously retains a degree of freedom in rotation around the axis 36. This degree of freedom can be ensured either at the end 32 by means of a ball joint connection or at the end 34, by means of a ball joint connection finger.It is also possible to position this degree of freedom at both end 32 and end 34, which makes it easier to align the flute 16 with the winch 26. Alternatively, it is possible not to provide a ball joint at end 32. In this case, the intermediate element 30 comes directly out of the fish. In the same way, it is possible not to provide a ball joint at end 34.

[0046] The presence of the intermediate element 30 allows the operator responsible for connecting the flute 16 to the fish 14 not to move behind the fish 14 to carry out the connection, which facilitates this connection operation. This connection can be made at the foot of the winch 26, that is to say in a place far from the rear edge of the surface vessel 10. The operator can then turn towards the sea to see a possible out-of-size wave coming and take shelter accordingly.

[0047] The intermediate element 30 is here a flexible cable.

[0048] In a first embodiment visible in Figure 11, the intermediate element 30 is a cable compatible with LTC technology (for “Light Tow-cable” in English). In the embodiment of Figure 8, this cable comprises: - an external cable sheath 81; - an external electro-optical core sheath 82; - an internal electro-optical core sheath 83; - a fabric 84; - an electric screen 85; - an electro-optical core 86.

[0049] The 81 cable outer sheath is designed to protect the lightweight cable. It thus ensures watertightness. It is made of PA12 type nylon material.

[0050] The outer sheath 82 and the inner sheath 83 provide intermediate rigidity in the element 30. These sheaths 82, 83 are made of a rubber material of the silicone and / or PE type.

[0051] The fabric 84 is arranged between the outer cable sheath 81 and the outer electro-optical core sheath 82. It allows for load absorption. This fabric 84 is made of a KEVLAR type material.

[0052] The electrical screen 85 is arranged between the outer sheath 82 and the inner sheath 83.

[0053] The electro-optical core 86 comprises electrical wires and fibers. It allows remote transmission of the receiving antenna, i.e. remote feeding of the antenna and transmission of the reception signals.

[0054] In a second embodiment visible in figure 12, the intermediate element 30 is a cable compatible with TANDEM technology.

[0055] This 30 cable includes here: - a first connection means 91; - a second connection means 92; - a transmission line 93; - a first line of effort recovery 94; - a second line of effort recovery 95; - means of connection 96.

[0056] The first connection means 91 and the second connection means 92 allow a connection of the intermediate element 30 with on the one hand the fish 14 and on the other hand the flute 16. The transmission line 93 allows the transmission of information between the first connection means 91 and the second connection means 92. This transmission line 93 constitutes an electro-optical core. The first force-recovery line 94 and the second force-recovery line 95 allow overall strength of the intermediate element 30, which allows both tensile strength and low stiffness for easy handling for the operator. The connecting means 96 allow the transmission line 93 to be connected to the force-recovery lines 94, 95. In the embodiment of FIG. 9, the transmission line 93 and the force-recovery lines 94, 95 are separate and parallel. However, the transmission line 93 is generally less taut than the force-recovery lines 94, 95.

[0057] In Figure 12, two load-recovery lines 94, 95 are shown, by way of example. Of course, the number of load-recovery lines may be other than 2. This number is thus between 1 and N load-recovery lines, with N an integer greater than or equal to 2.

[0058] In a third embodiment visible in Figure 13, the intermediate element 30 is a cable compatible with HTC JB LINK technology in which the electro-optical core is reinforced and flexible. More particularly in Figure 10, the cable comprises: - a sheath 101; - a 102 traction braid.

[0059] The sheath 101 is suitable for surrounding and protecting an information transmission line. It is a spiral spring made of stainless metal. This spring protects the electro-optical core inside. The traction braid 102 provides a certain solidity to the assembly. It consists of a self-tightening mesh of the "Chinese finger" type.

[0060] Figures 1 to 8 describe the different steps of a method for launching the underwater device 12.

[0061] Thus, in Figure 1, there is shown an unwinding step for putting the streamer 16 into the water. In this step, the streamer 16 is attached to the second winch 26 by means of a recovery rope 25a. The second winch 26 then rotates in a direction which allows unwinding of the attachment cable 25 to bring the streamer 16 closer to the water without going beyond the stern. The intermediate element 30 is connected to the fish 14. The intermediate element 30 is not yet connected to the streamer 16.

[0062] In the step of Figure 2, the intermediate element 30 is connected to the streamer 16 via the second end 34. The intermediate element 30 is here in a misaligned position relative to the streamer 16. This step can be done at the foot of the winch 26, that is to say in a less exposed area in which the operator can face the sea. It is thus possible to anticipate a possible exceptional wave in order to take shelter.

[0063] In the step of Figure 3, the recovery rope 25a is unwound and the streamer 16 continues its movement towards the water. This gradually tensiones the intermediate element 30. The recovery rope 25a comprises a downstream carabiner 27a which is here connected to a hooking cable 25b via an upstream carabiner 27b. The hooking cable 25b is unwound from the second winch 26.

[0064] In the step of Figure 4, the hooking cable 25b is sufficiently unwound so that the flute 16 and the intermediate element 30 are aligned. In this position, the intermediate element 30 reaches a certain tension, called towing tension.

[0065] In the step of Figure 5, the hanging cable 25b continues to unwind so that the tension generated by the mass of the flute 16 is entirely taken up by the intermediate element 30. The recovery rope 25a then relaxes.

[0066] In the step of figure 6, the downstream carabiner 27a is attached to the fish 14 via the attachment means 28. The upstream carabiner 27b is then unhooked from the downstream carabiner 27a.

[0067] In the step of Figure 7, the hooking cable 25b is wound onto the second winch 26 in order to free the operator's work area. In a preferred embodiment, the upstream carabiner 27b is detached from the hooking cable 25b to allow complete winding of the hooking cable 25b.

[0068] Finally, in the step of Figure 8, the first winch 24 unwinds the towing cable 18 allowing the entire sonar 12 to be launched into the water. As has already been specified, during operation of this sonar 12, the intermediate element 30 is aligned with the streamer 16 along the axis 36. The recovery rope 25a is fixed to the fish 14 and to the streamer 16 and it then extends generally parallel to the intermediate element 30.

[0069] The sonar 12 is raised by reversing the order of operations described above, that is to say: winding the towing cable 18 using the winch 24 to bring the fish 14 back onto the deck 22, attaching the upstream snap hook 27a to the downstream snap hook 27a, unhooking the downstream snap hook 27a from the fish 14, tensioning the recovery rope 25a via the second winch 26 to bring the intermediate element 30 from its position aligned with the streamer 16 to its misaligned position, unhooking the second connection 34 to release the streamer 16.

[0070] The invention thus allows: - to bring flexibility and greater safety in the handling of the underwater device 12; - to shift the connection position of the intermediate element to an area less exposed to the operator; - to be compatible with existing handling systems; - to facilitate maintenance operations, the intermediate element 30 being able to serve as a wear part that is easier to change than the entire towing cable.

Claims

CLAIMS 1. Underwater device intended to be towed by a surface vessel (10), said surface vessel (10) being capable of comprising a handling system (20) for storing and deploying the underwater device (12), said handling system (20) comprising a towing cable (18) and a hooking cable (25b), said underwater device (12) comprising: - a flexible elongated body (16); - a towed body (14), said towed body (14) being able to be arranged between the towing cable (18) and said flexible elongated body (16); - an intermediate element (30) capable of being arranged between the towed body (14) and the flexible elongated body (16), said intermediate element (30) being connected to the towed body (14) by a first connection, said intermediate element (30) being connected to the flexible elongated body (16) by a second connection, said first connection being an articulated mechanical connection, characterized in that said intermediate element (30) is a low stiffness cable and in that the underwater device (12) comprises a recovery rope (25a) connected to the flexible elongated body (16), said recovery rope (25a) comprising, at an end opposite the flexible elongated body (16), a downstream carabiner (27a), said downstream carabiner (27a) allowing the recovery rope (25a) to be attached either to the towing cable (18) via the towed body (14) or to the attachment cable (25b).

2. Underwater device according to claim 1, wherein the attachment cable (25b) comprises an upstream carabiner (27b) adapted to be attached to the downstream carabiner (27a) of the recovery rope (25a).

3. An underwater device according to any one of claims 1 or 2, wherein the intermediate element (30) is a lightweight cable.

4. Underwater device according to any one of claims 1 or 2, wherein the intermediate element (30) comprises an optoelectronic strand (93) and a plurality of force-recovery strands (94, 95), said strands (93, 94, 95) being separate.

5. Underwater device according to any one of claims 1 or 2, wherein the intermediate element (30) is a reinforced cable.

6. Underwater device according to claim 5, wherein the cable is reinforced by a traction braid (102).

7. Underwater device according to any one of claims 1 to 6, wherein the handling system (20) comprises two winches (24, 26), a first winch (24) being adapted to store and deploy the towing cable (18), a second winch (26) being adapted to store and deploy the hooking cable (25b) and in which, in a first position, the intermediate element (30) is aligned with the flexible elongate body (16) to allow the first winch (24) to tow the entire underwater device (12) and wherein, in a second position, the intermediate member (30) is misaligned from the flexible elongate body (16) to allow alignment of the flexible elongate body (16) with the second winch (26).

8. Underwater device according to any one of the preceding claims, wherein said underwater device (12) comprises an electrical and / or optical connection between the towed body (14) and the flexible elongate body (16) and in that said electrical and / or optical connection is disconnectable.

9. Method for launching an underwater device (12) by a handling system (20) belonging to a surface vessel (10), said handling system (20) comprising a towing cable (18) and a hooking cable (25b), said underwater device (12) comprising: - a flexible elongated body (16); - a towed body (14), said towed body (14) being able to be arranged between the towing cable (18) and said flexible elongated body (16) when using the underwater device (12); - an intermediate element (30) capable of being arranged between the towed body (14) and the flexible elongated body (16), said intermediate element (30) being connected to the towed body (14) by a first connection, said intermediate element (30) being connected to the flexible elongated body (16) by a second connection, said first connection being an articulated mechanical connection, said intermediate element (30) being a low stiffness cable and the underwater device (12) comprises a recovery rope (25a) connected to the flexible elongated body (16), said recovery rope (25a) comprising, at an end opposite the flexible elongated body (16), a downstream carabiner (27a), said downstream carabiner (27a) allowing the recovery rope (25a) to be attached either to the towing cable (18) via the towed body (14) or to the attachment cable (25b);said handling system (20) comprising two winches (24, 26), a first winch (24) for storing and deploying the towing cable (18), a second winch (26) for storing and deploying the hooking cable (25b), and wherein, in a first position, the intermediate element (30) is aligned with the flexible elongate body (16) to allow the first winch (24) to tow the entire underwater device (12), and wherein in a second position, the intermediate element (30) is misaligned from the flexible elongate body (16) to allow alignment of said flexible elongate body (16) with the second winch (26), said launching method comprising:; - a step of unwinding the second winch (26) to put the flexible elongated body (16) into the water, the recovery rope (25a) being taut; - a step of connecting the flexible elongated body (16) to the second end (34) of the intermediate element (30) in the misaligned position; - a step of placing the intermediate element (30) in an aligned position; - a step of unwinding the second winch (26) to relax the recovery rope (25a), the tension being taken up by the intermediate element (30); - a step of attaching the downstream carabiner (27a) to the towed body (14) and a step of unhooking said downstream carabiner (27a) relative to the attachment cable (25b), so as to allow subsequent recovery of a junction between the flexible elongated body and the intermediate element (30); - a step of unwinding the first winch (24).

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