DRAFT UNDERWATER DEVICE

Description

[0001] The present invention relates to an underwater device intended to be towed by a surface vessel, comprising a handling system suitable for installation on the surface vessel (a "surface ship") and enabling the storage and deployment of said underwater device. The invention is particularly useful in the field of active sonar-type underwater devices comprising a cable towing a towed body incorporating a transmission array. The towed body is sometimes called a "fish" because of its shape. A linear receiving antenna in the form of a flexible, elongated body is towed behind the fish. This is referred to as a tow-dependent system. The linear receiving antenna is sometimes also called a "flute" because of its shape.The towed body can be a volumetric body suspended from the tow cable or be elongated along a longitudinal axis and incorporating a linear transmitting antenna including transducers distributed along the longitudinal axis.

[0002] Handling such underwater devices is delicate. Specifically, when not in use, the underwater device is stored on a deck of the surface vessel, usually the aft deck. Deploying and retrieving the underwater device requires operators to be present on the aft deck of the surface vessel. These operators must handle heavy loads, which can be dangerous, especially in rough seas.

[0003] The tow cable of the towed body is called a "heavy cable" because its weight is used to pull the towline down. This tow cable typically consists of a core made of electrical and / or optical conductors that transmit power and information between sonar equipment on board the vessel and the antennas. The core cable is usually covered with a strand of metallic wires to provide mechanical strength. The towed body is generally massive. It may be equipped with fins to ensure its hydrodynamic stability. The linear receiving antenna can extend to a length of approximately one hundred meters to detect low-frequency sound waves propagating through the water. These may be echoes 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 applicant's name, a single winch is used to handle both the tow cable and the receiving antenna. These components are neutrally buoyant, and the cable is referred to as the "lightweight cable." The tow cable and the receiving antenna are permanently attached to each other. During launching, the towed body is hooked and connected at the junction between the tow cable and the receiving antenna to the antenna's lightweight cable, or even directly to the receiving antenna. The purpose of the lightweight cable is to isolate the antenna from the towing vessel's own noise. The elongated, flexible body then encloses the lightweight cable and the receiving antenna. Such an arrangement of the tow cable and the receiving antenna on the same winch presents certain challenges. In particular, the winch must be adapted to the maximum permissible bend radius of both the tow cable and the receiving antenna.This can lead to a significant oversizing of the winch reel. Furthermore, it can be useful to handle the haul cable and receiving antenna separately, which a single winch does not allow, unlike a set comprising two winches / reels – 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 applicant's name, two separate winches are used, one for the haul cable and the other for the receiving antenna. A rigid, movable arm is positioned between the towed body and the flexible elongated body. During the recovery of the towed body, the rigid arm is not always correctly positioned, and the connection between the rigid arm and the flexible elongated body must be free of any kinks to avoid damaging the receiving antenna. Such a kink can occur when the towed body does not fold up as expected during recovery at sea. Furthermore, the rigidity of the device, its off-center weight, combined with potential waves during deployment or recovery, could induce stresses leading to a risk 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 equipped to include a handling system for storing and deploying the underwater device. The handling system includes a tow cable and a towing cable. Said underwater device comprises: A flexible elongated body; a towed body, said towed body being suitable for placement between the haul cable and said flexible elongated body; an intermediate element suitable for placement between the hauled body and the flexible elongated body, said intermediate element being connected to the hauled body by a first connection, said intermediate element being connected to the flexible elongated body by a second connection, said first connection being a hinged mechanical connection. The intermediate element is a low-stiffness cable. The underwater device includes a retrieval rope connected to the flexible elongated body, said retrieval rope having, at an end opposite the flexible elongated body, a downstream carabiner, said downstream carabiner allowing the retrieval rope to be attached either to the haul cable via the hauled body or to the anchor cable 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 make the hooking. In the prior art, the intermediate element is a rigid articulated arm that imposes a specific distance between the two winches. Furthermore, the articulated arm prevents the towed body from being positioned at the stern edge if doors are located at the rear of the boat. The low-stiffness cable drastically reduces this distance, allowing the doors to remain closed and thus improving operator safety. In addition, using a low-stiffness cable eliminates the positioning constraint between the two winches and makes the connection operations easier and safer for the operator. Moreover, the use of a retrieval line facilitates subsequent retrieval of the connection between the flexible elongated body and the intermediate element.

[0009] The term "cable" refers to a protected metallic conductor wire. In this case, the cable is an opto-electro-traction cable.

[0010] By "low stiffness cable" we mean a cable having a stiffness k less than 10 N / m.

[0011] The term "rope" refers to a bundle of strands twisted together. These strands can be made of textile material, 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 includes an upstream carabiner adapted to be attached to the downstream carabiner of the retrieval rope.

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

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

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

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

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

[0019] In one particular embodiment, the handling system comprises two winches: a first winch capable of storing and deploying the haul rope, and a second winch capable of storing and deploying the anchor cable. In a first position, the intermediate element is aligned with the flexible elongated body to allow the first winch to haul the entire underwater device. In a second position, the intermediate element is misaligned with the flexible elongated body to allow the flexible elongated body to be aligned with the second winch.

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

[0021] Another object of the invention relates to a method for deploying a submersible device using a handling system belonging to a surface vessel. The handling system comprises a haul rope and a towing cable. The submersible device comprises: a flexible elongated body; a towed body, said towed body being suitable for being positioned between the haul cable and said flexible elongated body during use of the underwater device; an intermediate element suitable for being positioned between the hauled body and the flexible elongated body, said intermediate element being connected to the hauled 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 includes a recovery rope connected to the flexible elongated body, said recovery rope including, at an end opposite to the flexible elongated body, a downstream carabiner, said downstream carabiner allowing the recovery rope to be attached either to the haul cable via the hauled body or to the anchor cable. The handling system includes two winches. The first winch stores and deploys the haul rope. The second winch stores and deploys the anchor cable. In the first position, the intermediate element is aligned with the flexible extension body to allow the first winch to pull the entire underwater device. In the second position, the intermediate element is misaligned with the flexible extension body to allow the flexible extension body to be aligned with the second winch. The deployment procedure includes: 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 misaligned position; a step of putting the intermediate element in aligned position; a step of unwinding the second winch to slacken 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 unattaching said downstream carabiner from the attachment cable, so as to allow subsequent recovery of a junction between the flexible elongated body and the intermediate element; a step of unwinding the first winch.

[0022] The invention will be better understood and other advantages will become apparent upon reading the detailed description of an embodiment given by way of example, a description illustrated by the accompanying drawing in which: [ Fig. 1 ] there figure 1 schematically represents an underwater device in the first stage of a process for its deployment; Fig. 2 ] there figure 2 represents the underwater device of the figure 1 in a second stage of the process for its launch; [ Fig. 3 ] there figure 3 represents the underwater device of the figure 1 in a third stage of the process for its launch; [ Fig. 4 ] there figure 4 represents the underwater device of the figure 1 in a fourth stage of the process for its launch; [ Fig. 5 ] there figure 5 represents the underwater device of the figure 1 in a fifth step of the process for its launch; [ Fig.6 ] there figure 6 represents the underwater device of the figure 1 in a sixth step of the process for its launch; [ Fig.7 ] there figure 7 represents the underwater device of the figure 1 in a seventh step of the process for its launch; [ Fig.8 ] there figure 8 represents the underwater device of the figure 1 in an eighth step of the process for its launch; [ Fig. 9 ] there figure 9 is an enlarged view of the towed body of the underwater device of the figures 1 à 8 , in an initial connection setup; [ Fig. 10 ] there figure 10 is an enlarged view of the towed body of the underwater device of the figures 1 à 8 , in a second configuration of the connection of the figure 9 ; Fig. 11 ] there figure 11 schematically represents an intermediate element of the underwater system of figures 1 à 8 according to a first embodiment; [ Fig. 12 ] there figure 12 schematically represents an intermediate element of the underwater system of figures 1 à 8 according to a second embodiment; [ Fig. 13 ] there figure 13 schematically represents an intermediate element of the underwater system of figures 1 à 8 according to a third embodiment.

[0023] For the sake of clarity, the same elements will bear the same references in the different figures.

[0024] 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.

[0025] There figure 8 This represents 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. Hereafter, the towed body will be referred to as the fish 14 and the flexible elongated body as the flute 16. The sonar 12 also includes a cable 18 for towing the fish 14 and the flute 16. The cable 18 also carries signals and power between the vessel 10, the fish 14, and the flute 16.

[0026] The fish 14 and the flute 16 are mechanically attached and connected electrically and / or optically to the cable 18 in a suitable manner. Conventionally, the flute 16 consists of a linear, tubular antenna identical to those found in passive sonars, hence its name, while the transmitting antenna is integrated into a volumetric structure forming the towed body 14, which has a shape resembling that of a fish. The flute 16 is attached to the fish 14, which is itself attached to the end of the cable 18. During an active underwater acoustics mission, the antenna of the fish 14 emits sound waves into the water, and the receiving antenna of the flute 16 detects any echoes from targets reflecting the sound waves from the transmitting antenna.

[0027] A handling device 20 is located on a rear deck 22 of the vessel 10. The handling device 20 includes two winches 24 and 26. Winch 24 is used to store and deploy the haul rope 18 and the fish 14. Winch 26 is used to store and deploy the flute 16. In the deployed position of the active sonar 12, as shown in the figure 5 Only winch 24 is in operation. Winch 24 pulls the entire sonar assembly 12. More precisely, cable 18 pulls fish 14 and flute 16 is attached behind fish 14.

[0028] On the figure 8 Winch 24 is located on the port side of ship 10 and 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 winch 26. More generally, the two winches 24 and 26 are offset from each other.

[0029] The sonar 12 includes an intermediate element 30. This intermediate element 30 is positioned between the fish 14 and the flute 16. More specifically, the intermediate element 30 is connected to the fish 14 by a first connection 32. Furthermore, the intermediate element 30 is connected to the flute 16 by a second connection 34. The first connection 32 is a hinged mechanical connection. It can therefore be disassembled for replacement of the intermediate element during maintenance operations. This first connection 32 is shown here as fixed. Alternatively, this first connection 32 is disconnectable. The second connection 34 is, in this case, disconnectable. On the figure 8 In the deployed position of the active sonar 12, the intermediate element 30 is aligned with the flute 16. More precisely, the intermediate element 30 and the flute 16 both extend substantially along the same axis 36. When the vessel 10 is traveling in a straight line, the axis 36 is substantially parallel to the vessel's axis of travel. In practice, the drag forces experienced by the flute 16 naturally orient the intermediate element 30 and the flute 16 in the water along the axis 36, which can oscillate, particularly depending on weather conditions, especially swell conditions, which induce pitching and rolling of the towing vessel.

[0030] The fish 14 and the flute 16 are also connected to each other by a retrieval line 25a. More specifically, the retrieval line 25a includes a downstream carabiner 27a attached to an attachment point 28 belonging to the fish 14. The other end of the retrieval line 25a is connected to the flute 26 via the second connection 34.

[0031] There figure 2 represents the ship of the figure 8 whose sonar 12 is being deployed or retrieved. More precisely, the fish 14 is placed on the deck 22, possibly in a cradle designed to hold it. The winch 24 is stopped. The cable 18 is almost completely wound on the winch 24. The intermediate element 30 is misaligned with the flute 16, allowing the flute 16 to be aligned with the winch 26.

[0032] To ensure proper alignment of the intermediate element 30 and the flute 16 at the end 32, the joint between the fish 14 and the intermediate element 30 is advantageously of the ball-and-socket type, that is, having at least two degrees of freedom in rotation about axes perpendicular to the axis 36. Such a joint is notably disclosed to figures 8 And 9Similarly, at end 34, the joint between the intermediate element 30 and the flute 16 advantageously has at least one degree of rotational freedom about an axis allowing alignment of the flute 16 with the winch 26. The flute 16 advantageously retains one degree of rotational freedom about the axis 36. This degree of freedom can be provided either at end 32 by means of a ball joint or at end 34 by means of a ball joint with a finger. It is also possible to position this degree of freedom at both end 32 and end 34, which facilitates alignment of the flute 16 with the winch 26. Alternatively, it is possible to omit the ball joint at end 32. In this case, the intermediate element 30 extends directly from the fish. Similarly, it is possible not to provide a ball joint at the end 34.

[0033] The presence of the intermediate element 30 allows the operator responsible for connecting the flute 16 to the fish 14 to avoid moving behind the fish 14 to perform the connection, thus facilitating this operation. This connection can be made at the foot of the winch 26, that is, in a location far from the aft edge of the surface vessel 10. The operator can then face the sea to spot any approaching oversized waves and take shelter accordingly.

[0034] The intermediate element 30 is here a flexible cable.

[0035] In a first embodiment visible at the figure 11 The intermediate element 30 is a cable compatible with LTC (Light Tow-cable) technology. In the embodiment of the figure 8 This cable includes: an outer cable sheath 81; an outer sheath of electro-optical core 82; an inner sheath of electro-optical core 83; a fabric 84; an electric screen 85; an electro-optical core 86.

[0036] The outer cable sheath 81 is designed to protect lightweight cables, ensuring water resistance. It is made of PA12 type nylon material.

[0037] The outer sheath 82 and the inner sheath 83 provide intermediate rigidity in the element 30. These sheaths 82, 83 are made of a silicone and / or PE type rubber material.

[0038] The fabric 84 is positioned between the outer cable sheath 81 and the outer sheath of the electro-optical core 82. It provides stress absorption. This fabric 84 is made of a Kevlar-type material.

[0039] The electrical screen 85 is arranged between the outer sheath 82 and the inner sheath 83.

[0040] The electro-optical core 86 comprises electrical wires and fibers. It enables remote transmission of the receiving antenna, i.e., remote power supply to the antenna and transmission of the received signals.

[0041] In a second embodiment visible at the figure 12 The intermediate element 30 is a cable compatible with TANDEM technology.

[0042] This 30-meter cable includes the following: a first means of connection 91; a second means of connection 92; a transmission line 93; a first force recovery line 94; a second force recovery line 95; means of connection 96.

[0043] The first connection means 91 and the second connection means 92 allow the intermediate element 30 to be connected to, 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 load-bearing line 94 and the second load-bearing line 95 provide overall strength to the intermediate element 30, which allows both tensile strength and low stiffness for easier handling by the operator. The connecting means 96 allow the transmission line 93 to be linked to the load-bearing lines 94 and 95. In the embodiment of the figure 9 The transmission line 93 and the load transfer lines 94 and 95 are separate and parallel. However, the transmission line 93 is generally less taut than the load transfer lines 94 and 95.

[0044] On the figure 12 As an example, two load transfer lines 94, 95 are shown. Of course, the number of load transfer lines can be different from 2. This number is thus between 1 and N load transfer lines, with N an integer greater than or equal to 2.

[0045] In a third embodiment visible at the figure 13 The intermediate element 30 is a cable compatible with HTC JB LINK technology, in which the electro-optical core is armored and flexible. More specifically, at the figure 10 The cable includes: a sheath 101; a traction braid 102.

[0046] The sheath 101 is designed to surround and protect an information transmission line. It consists of a spiral spring made of stainless steel. This spring protects the electro-optical core inside. The tension braid 102 provides additional strength to the assembly. It is made of a self-tightening mesh of the "Chinese finger" type.

[0047] THE figures 1 à 8 describe the different stages of a process for deploying underwater device 12.

[0048] Thus, at the figure 1 The diagram shows a step in the deployment process for launching the flute 16. In this step, the flute 16 is attached to the second winch 26 by means of a retrieval rope 25a. The second winch 26 then rotates in a direction that allows the anchor cable 25 to be unwound, bringing the flute 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 flute 16.

[0049] In the stage of the figure 2 The intermediate element 30 is connected to the flute 16 via the second end 34. The intermediate element 30 is currently misaligned with the flute 16. This step can be carried out at the base of the winch 26, i.e., in a less exposed area where the operator can face the sea. This allows them to anticipate a potentially exceptional wave and take shelter.

[0050] In the stage of the figure 3 The recovery rope 25a is then unspooled, and the flute 16 continues its movement towards the water. This gradually puts tension on the intermediate element 30. The recovery rope 25a includes a downstream carabiner 27a, which is connected to a hauling cable 25b via an upstream carabiner 27b. The hauling cable 25b is unspooled from the second winch 26.

[0051] In the stage of the figure 4 The 25b suspension cable 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 the towing tension.

[0052] In the stage of the 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 cord 25a then relaxes.

[0053] In the stage of the figure 6 , the downstream carabiner 27a is attached to the fish 14 via the attachment means 28. The upstream carabiner 27b is then detached from the downstream carabiner 27a.

[0054] In the stage of the figure 7 The 25b lifting cable is wound onto the second winch 26 to free up the operator's working area. In a preferred embodiment, the upstream carabiner 27b is detached from the 25b lifting cable to allow the 25b lifting cable to be fully wound.

[0055] Finally, in the stage of the figure 8 The first winch 24 unwinds the traction cable 18, allowing the entire sonar 12 to be deployed. As already mentioned, during the operation of this sonar 12, the intermediate element 30 is aligned with the flute 16 along the axis 36. The retrieval rope 25a is attached to the fish 14 and the flute 16 and then extends generally parallel to the intermediate element 30.

[0056] The raising of the sonar 12 is done by reversing the order of the operations described above, that is to say: winding the traction cable 18 by means of winch 24 to bring the fish 14 back onto the deck 22, attaching the upstream carabiner 27a to the downstream carabiner 27a, detaching the downstream carabiner 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 flute 16 to its misaligned position, detaching the second connection 34 to release the flute 16.

[0057] 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 a less exposed area for 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 easier to change than the entire haul rope.

Claims

1. An underwater device intended to be towed by a surface ship (10), said surface ship (10) being capable of comprising a handling system (20) for stowing and deploying the underwater device (12), said handling system (20) comprising a tow cable (18) and an attachment cable (25b), said underwater device (12) comprising: - a flexible elongate body (16); - a towed body (14), said towed body (14) being capable of being arranged between the tow cable (18) and said flexible elongate body (16); - an intermediate element (30) capable of being arranged between the towed body (14) and the flexible elongate 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 elongate 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 cord (25a) connected to the flexible elongate body (16), said recovery cord (25a) comprising, at an end opposite the flexible elongate body (16), a downstream shackle (27a), said downstream shackle (27a) allowing the recovery cord (25a) to be fixed either to the tow cable (18) via the towed body (14) or to the attachment cable (25b).

2. The underwater device according to claim 1, wherein the attachment cable (25b) comprises an upstream shackle (27b) designed to be attached to the downstream shackle (27a) of the recovery cord (25a).

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

4. The 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 reacting strands (94, 95), said strands (93, 94, 95) being separate.

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

6. The underwater device according to claim 5, wherein the cable is reinforced by a tension braid (102).

7. The 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 capable of stowing and deploying the tow cable (18), a second winch (26) being capable of stowing and deploying the attachment 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 unaligned with respect to the flexible elongate body (16) to allow the flexible elongate body (16) to be aligned with the second winch (26).

8. The underwater device according to any one of the preceding claims, wherein said underwater device (12) comprises an electrical and / or optical link between the towed body (14) and the flexible elongate body (16), and in that said electrical and / or optical link can be disconnected.

9. A method for launching an underwater device (12) using a handling system (20) which is part of a surface ship (10), said handling system (20) comprising a tow cable (18) and an attachment cable (25b), said underwater device (12) comprising: - a flexible elongate body (16); - a towed body (14), said towed body (14) being capable of being arranged between the tow cable (18) and said flexible elongate body (16) during use of the underwater device (12); - an intermediate element (30) capable of being arranged between the towed body (14) and the flexible elongate 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 elongate 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) comprising a recovery cord (25a) connected to the flexible elongate body (16), said recovery cord (25a) comprising, at an end opposite the flexible elongate body (16), a downstream shackle (27a), said downstream shackle (27a) allowing the recovery cord (25a) to be fixed either to the tow 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 stowing and deploying the tow cable (18), a second winch (26) for stowing and deploying the attachment 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 unaligned with respect to the flexible elongate body (16) to allow said flexible elongate body (16) to be aligned with the second winch (26), said launching method comprising: - a step of paying out the second winch (26) to launch the flexible elongate body (16), the recovery cord (25a) being taut; - a step of connecting the flexible elongate body (16) to the second end (34) of the intermediate element (30) in the unaligned position; - a step of positioning the intermediate element (30) in alignment; - a step of paying out the second winch (26) to slacken the recovery cord (25a), the tension being reacted by the intermediate element (30); - a step of attaching the downstream shackle (27a) to the towed body (14) and a step of detaching said downstream shackle (27a) from the attachment cable (25b), so as to allow a subsequent recovery of a junction between the flexible elongate body and the intermediate element (30); - a step of paying out the first winch (24).