Patent Publication Number: US-2022234692-A1

Title: Sonar device and sonar system

Description:
The invention relates to the field of the handling of sonar devices of the type comprising a so-called active part intended to be immersed and towed by a surface ship via a heavy tow cable. The active part comprises a linear acoustic wave emitting antenna which is elongate along a longitudinal axis of the antenna. This longitudinal axis is intended to extend substantially vertically in operation, when the antenna is fully immersed, so as to emit acoustic waves mainly in a horizontal plane. The sonar system may comprise a linear receiving antenna able to detect echoes of the acoustic waves emitted by the emitting antenna. The linear receiving antenna is intended to be towed by the tow cable via the linear emitting antenna. 
     Sonar devices in which the tow cable is fixed to a central part situated near the middle of the linear emitting antenna along the longitudinal axis thereof are known. In order to recover the, initially immersed, emitting antenna on board a surface ship, it is known practice to employ equipment of the arm type which allows the linear emitting antenna to be caught as soon as it exits the water, lifted and moved over the deck of the surface ship, through a pivoting and potentially translational movement of the arm. During this maneuver, the emitting antenna always remains vertical. It is intended that an operation of unhooking the emitting antenna from the tow cable be performed before the tow cable and the linear receiving antenna are wound onto the one same winch. The linear emitting antenna is stored on board the surface ship next to the winch. 
     Now, a linear emitting antenna generally has a length of several meters, which means that large openings have to be designed into the stern of the carrying ship in order to allow this antenna to be recovered. Furthermore, it is often the case that a “recess” has to be created in the main deck in order to store the emitting antenna which is too long to be housed between the main deck and the deck above. 
     Other types of sonar systems with large linear emitting antenna and in which the emitting antenna is connected to the cable in such a way that the antenna extends vertically when being towed by a cable are known. The emitting antenna is able to pivot with respect to the cable about a horizontal axis perpendicular to the axis of traction of the towed emitting antenna so as to extend longitudinally roughly parallel to the axis of the cable in a so-called capture orientation. These systems comprise recovery means that allow the emitting antenna to be brought back on board the carrying ship only by winding the cable, the cable pulling the emitting antenna toward the ship along the axis of the cable. The antenna adopts the capture orientation as it exits the water during the recovery step, either naturally or under the action of an actuator. As a result, when the antenna passes through the opening made in the ship, its limited bulk in a plane transverse to the axis of the ship means that the size of this opening may be limited. 
     However, recovering the antenna in this capture configuration is not favorable to storing it in a limited volume. Moreover, this solution is suitable only for sonar devices comprising a linear antenna to the rear of the emitting antenna. The absence of traction applied by a receiving antenna means that a bulky recovery mechanism, for example of the pivoting arm or crane type, has to be employed. 
     One example of a system of this type is disclosed in document U.S. Pat. No. 9,001,623. After recovery, the antenna is stored, onboard the surface ship, in an elongate position running lengthwise along the longitudinal axis of the surface ship, which entails a surface ship of long length capable of offering a place at the stern having a long length of volume available. Moreover, means are provided for disconnecting the cable from the emitting antenna so that the receiving antenna can be stored on the same winch as the tow cable. Document WO 2017/035660 A1 also discloses this type of sonar system. It proposes a solution that avoids disconnection and reduces the volume of the sonar device by storing the linear emitting antenna on the drum of the winch with its longitudinal axis substantially perpendicular to the axis of rotation of the winch. However, this orientation is not very stable and mechanical means, that have to be fitted by an operator, need to be provided in order to fix the antenna to the drum of the winch. 
     Furthermore, when recovering antennas in an elongate position, these have an orientation that is not very stable and is uncontrollable, therefore increasing the risk of collisions with the hull of the surface ship, particularly when the sea is rough. These solutions therefore require protection in order to protect the antenna from collisions. Document U.S. Pat. No. 9,001,623 provides a towed nest surrounding the antenna and into which the antenna is brought while elongate. This nest protects the antenna from potential collisions, but makes the solution very complex. 
     Another solution disclosed in patent application EP 2 232 294 A1 filed by the applicant company consists in providing a flexible emitting linear antenna configured and fixed to the towing cable and to the receiving antenna in such a way as to extend linearly substantially vertically during towing and so as to curve in order to be wound onto a drum of a winch like the towing cable and the receiving antenna. However, operational implementation of this solution involves adjustments and is confined to a lightweight antenna that is difficult to achieve with a high level of performance, the heavy electroacoustic transducers being able to emit with a good sound level. 
     Patent application WO2017/054795 A1 discloses a sonar device comprising a flexible emitting antenna and so-called tensioning means, such as a floating anchor for example, allowing the emitting antenna, when towed, to adopt a linear configuration in which it is vertical. This solution presents disadvantages similar to those of the solution disclosed in patent application EP 2 232 294 A. 
     It is an object of the invention to limit at least some of the aforementioned disadvantages. 
     To this end, one subject of the invention is a sonar device intended to be towed by a surface ship and comprising a tow cable and a set of at least one towed device, comprising a towed body, intended to be towed by the surface ship via the tow cable, the towed body being elongate along a longitudinal axis from a first longitudinal end of the towed body as far as a second longitudinal end of the towed body, the towed body incorporating a first linear acoustic antenna comprising a plurality of electroacoustic transducers substantially aligned along the longitudinal axis, the towed device, which could be the towed body, being balanced, or configured and connected to the tow cable in such a way that the towed body is able, when it is being towed and is fully submerged, to exhibit an orientation in which the longitudinal axis extends substantially along a vertical axis defined by the force of gravity, at least one towed body of the set of towed bodies being connected to the tow cable by a first hanger and a second hanger of substantially the same length, a first end of the first hanger and a first end of the second hanger being connected to the cable and a second end of the first hanger being attached to the towed body at a fixing point of the towed body, which point is situated near the first longitudinal end, and a second end of the second hanger being attached to the towed body at a second fixing point secured to the first fixing point and situated near the second longitudinal end. 
     In one particular embodiment, the towed device is the towed body. 
     Advantageously, the first hanger and the second hanger each have a fixed length. 
     Advantageously, the second end of the first hanger is attached to the first longitudinal end of the towed body and the second end of the second hanger is attached to the second longitudinal end of the towed body. 
     In one embodiment, the sonar device comprises a flexible elongate body of substantially neutral buoyancy intended to be towed by the tow cable and comprising a second acoustic antenna comprising a plurality of electroacoustic transducers distributed along the flexible elongate body, the flexible elongate body is connected to the tow cable via the set of at least one towed body, the towed body being connected to the flexible elongate body in such a way that the flexible elongate body applies traction to the towed body at a third fixing point situated near the first longitudinal end of the towed body and a fourth fixing point situated near the second longitudinal end of the towed body. 
     For example, at least one towed body of the set of at least one towed body is connected to the flexible elongate towed body by a third hanger and a fourth hanger, a first end of the third hanger being attached to the towed body at a third fixing point situated near the first longitudinal end of the towed body and a first end of the fourth hanger being attached to the towed body at a fourth fixing point situated near the second longitudinal end of the towed body. This towed body is the same towed body as or a different towed body than the one that is connected to the first and to the second hanger. 
     The set of at least one towed body comprises a single towed body or a plurality of towed bodies. 
     In one particular embodiment, the set of at least one towed body comprises a plurality of towed bodies, the sonar device comprising at least one line joining together two bodies of the towed set and comprising at least one electroacoustic transducer. 
     The invention also relates to a sonar system comprising the sonar device and a handling device intended for launching and recovering the sonar device from the surface ship, the handling device comprising a winch comprising a first drum able to rotate about a first axis of rotation to wind the tow cable onto the first drum. 
     Advantageously, the handling device comprises a set of at least one convex deflector having the overall shape of a portion of a cylinder extending longitudinally along an axis of the deflector, the deflector being arranged in such a way as to extend substantially horizontally, in a calm sea state, and substantially perpendicular to a vertical plane substantially parallel to an axis of the traction applied to the tow cable by the handling device during a first step of winding during which the first drum is rotationally driven about the first axis so that the tow cable is wound onto the first drum and so that the first hanger and the second hanger come to bear against the deflector so as to be deflected by the deflector so that the longitudinal axis of the towed body is oriented substantially parallel to the axis of the deflector when the towed body is fully emerged and suspended from the first hanger and from the second hanger. 
     Advantageously, the axis of at least one deflector of the set is substantially parallel to the first axis of rotation. 
     Advantageously, at least one deflector of the set of at least one deflector is arranged in such a way that, during the first winding step, the first hanger and the second hanger are able to come to bear against the deflector, when the towed body is fully immersed. 
     Advantageously, the set comprises at least one deflector arranged upstream of the first drum, viewed from the first hanger and from the second hanger initially immersed, during the first winding step. 
     The invention also relates to a sonar system wherein the winch comprises a set of at least a second drum surrounding the first drum and able to rotate with respect to a frame of the winch about a second axis of rotation substantially parallel to the first axis of rotation, the winch being able to be in an uncoupled state in which the first drum and the second drum are uncoupled in terms of rotation about the first axis of rotation and about the second axis of rotation, so as to allow the tow cable to be wound onto the first drum during the first winding step during which the first drum is rotationally driven about the first axis, the second drum being able to be in an open state in which the second drum exhibits a receiving opening through which the towed body is able to pass in order to enter a volume surrounding the first drum and which is surrounded by the second drum, the winch being able to be in a coupled state in which the first drum and the second drum are coupled in terms of rotation about the second axis of rotation so as to allow the flexible elongate body to be wound about the second axis of rotation during a second winding step during which the second drum is rotationally driven about the second axis. The towed body may be capable of passing through the receiving opening during the first winding step or outside of this step. 
     Advantageously, the second drum is able to be in a receiving angular position, about the second axis with respect to the frame, in which position the tow cable and the towed body pass through the receiving opening during the first winding step. 
     Advantageously, the handling device is configured to implement the following step during a method of recovering the initially immersed sonar device and connected to the drum via the tow cable  2 : the first winding step during which the first drum is rotationally driven about the first axis so that the tow cable is wound onto the first drum and so that the first hanger and the second hanger come to bear against the deflector to be deflected by the deflector so that the longitudinal axis of the towed body is oriented substantially parallel to the axis of the deflector, when the towed body is fully emerged and suspended from the first hanger and from the second hanger. 
     The invention also relates to the recovery method which comprises this step. 
     Advantageously, the handling device is configured to implement the first winding step until the towed body enters the volume delimited by the second drum through the receiving opening, and then a second winding step during which the second drum of the handling device, which is in the second state, is rotationally driven about the second axis of rotation so as to wind the flexible linear body onto the second drum. 
    
    
     
       Further features and advantages of the invention will become apparent from reading the detailed description which follows, which is given by way of nonlimiting example and with reference to the attached drawings in which: 
         FIG. 1  schematically depicts an underwater system according to the invention comprising a handling device according to a first embodiment and an underwater device according to a first embodiment in a state of being towed, 
         FIG. 2  schematically depicts the underwater system of  FIG. 1  when the towed body comes out of the water, 
         FIG. 3  schematically depicts the underwater system of  FIG. 1  when the towed body approaches the surface ship and is suspended from the first hanger and from the second hanger, 
         FIG. 4  schematically depicts the underwater system of  FIG. 1  when the towed body is recovered onboard the surface ship, 
         FIG. 5  schematically depicts a sonar system comprising a handling device, according to a second embodiment, during a phase of towing an underwater device, according to a second embodiment, 
         FIG. 6  schematically depicts the sonar system of  FIG. 5  during a phase of recovering the towed body, 
         FIG. 7  schematically depicts the sonar system of  FIG. 5  during a phase of storage of the towed body, 
         FIG. 8  schematically depicts a sonar system comprising a handling device, according to a third embodiment, during a phase of recovering the sonar device of  FIG. 5 , 
         FIG. 9  schematically depicts various phases of a method for recovering the sonar device of  FIG. 5  using the handling device of  FIG. 8 , 
         FIG. 10  schematically depicts an example of towed body of a different shape than that of  FIGS. 1 to 7 , 
         FIG. 11  schematically depicts an underwater device comprising a plurality of towed bodies, 
         FIG. 12  schematically depicts an underwater device comprising a plurality of towed bodies connected to one another in a different way than that of  FIG. 12 . 
     
    
    
     From one figure to another, the same elements are identified by the same references. 
     The invention relates to a sonar device  301  of which a first embodiment is depicted in  FIG. 1 . The sonar device  301  according to the invention is intended to be towed by a surface ship B. The invention also relates to a sonar system comprising the sonar device  301  according to the invention and a handling device  310  for launching and recovering the sonar device  301  according to the invention from the surface ship B. The invention additionally relates to a surface ship B comprising the sonar system according to the invention in which the sonar device  301  is connected to the handling device  310  installed onboard the surface ship. 
     The sonar device  301  according to the invention comprises an active part intended to operate in a fully immersed state when the sonar device is being towed. 
     The active part comprises a linear acoustic wave emitting antenna  40 , or more generally, a linear emitting acoustic antenna which is elongate along the longitudinal axis I comprising a plurality of electroacoustic transducers  41  substantially aligned along the longitudinal axis I. 
     The longitudinal axis I of the linear emitting antenna  40  is intended to extend substantially along a vertical axis z during operation when the sonar device  301  is immersed and being towed by the carrier ship, with the linear acoustic antenna  40  fully immersed. In that way, the linear emitting antenna  40  emits acoustic waves mainly in a horizontal plane. The vertical axis z is defined by the force of gravity. This is an axis substantially perpendicular to the surface of the sea in a calm sea state which then defines a horizontal plane. 
     The linear emitting antenna  40  is integrated into a towed body  4  along the longitudinal axis I. The towed body  4  extends, along the longitudinal axis, from a first longitudinal end  42  of the towed body  4  as far as a second longitudinal end  43  of the towed body  4 . 
     The first longitudinal end  42  is advantageously securely attached to the second longitudinal end  43 . 
     Thus, the linear emitting antenna  40  integrated into the body  4  deforms neither during towing by the surface ship when fully immersed, nor while the antenna is being recovered onboard the surface ship, nor while it is being stored onboard the surface ship. This configuration means that the characteristics of the emission pattern of the antenna are precisely known. This configuration improves the technical ease of production of the sonar device by guaranteeing that the electroacoustic transducers are aligned. Tricky steps of adjusting the sonar device to ensure this geometry during towing are not required. 
     A towed device, which in the nonlimiting example of the figures is the towed body  4 , is configured and connected to the tow cable  2  and to the body  3  in such a way that the towed body  4  is able to adopt a substantially vertical orientation (I substantially parallel to z) when it (the towed body) is being towed, fully immersed, via the cable  2 . 
     To make it easier to obtain a vertical orientation of the linear emitting antenna  40  during operation, the towed device, for example the towed body  4  in the example of the figures, is balanced in such a way as to exhibit, in hydrostatic equilibrium, namely when subjected only to the force of gravity and to Archimedean upthrust, a hydrostatic-equilibrium orientation in which the longitudinal axis I is substantially vertical (parallel to the axis z) and in which the first longitudinal end  42  of the towed body  4  is at a greater depth than its second longitudinal end  43 . In other words, in this hydrostatic-equilibrium orientation, the first longitudinal end  42  is further from the mean sea surface level than the second longitudinal end  43 . 
     To this end, the towed body  4  comprises, for example, a ballast weight of density greater than the density of the water near the first longitudinal end  42  and a float exhibiting positive buoyancy near the second longitudinal end  43 . 
     As a variant, the towed body comprises a ballast weight of density greater than the density of the water near the first longitudinal end  42  or a float exhibiting positive buoyancy near the second longitudinal end  43 . 
     The towed body  4  may exhibit substantially neutral buoyancy, but this is not indispensable. As a variant, the body exhibits negative buoyancy, thereby allowing it to reach greater depths. 
     In the embodiment of the figures, the towed device is the towed body. 
     In a variant, the towed device comprises the towed body and a set of at least one ballast weight and/or a set of at least one float. The towed body being configured and the set of at least one ballast weight and/or the set of at least one float being configured and connected to the towed body in such a way that the towed body exhibits the required orientation (I substantially vertical) in hydrostatic equilibrium. 
     The sonar device  301  comprises a tow cable  2  intended to be connected to the surface ship B and, more particularly, to the handling device  310 . The tow cable  2  is connected to the towed body  4  which is intended to be towed by the surface ship B via the tow cable  2 . The tow cable may be a bare cable, a jacketed cable, or a faired cable. 
     The tow cable  2  advantageously exhibits negative buoyancy. It is then said to be a heavy cable. The weight of the cable therefore allows the towed body to be positioned at depth. 
     The underwater device  301  further comprises an attachment device comprising, as visible in  FIG. 5 , a first hanger  6  and a second hanger  7  of substantially the same length, each connecting the tow cable  2  to the towed body  4 . In other words, the length of the two hangers differs from the length of one of the hangers by 5% at most. 
     If the lengths between the hangers differ slightly, while remaining within the 5% tolerance, the first hanger  6  has a length less than or equal to the length of the second hanger  7  in order to achieve proper control over the orientation of the towed body, but the hangers preferably have the same length in order to permit better control over the orientation of the towed body. 
     The hangers are flexible elongate bodies. These are, for example, cables or ropes, belts or chains. Each hanger may be a portion of a flexible element longer than the hanger, extending beyond the first end and/or beyond the second end of the hanger, or else may be a flexible element of the same length as the hanger. 
     The hangers  6  and  7  each have a fixed or invariable length. In other words, the hangers do not lengthen during the operations of launching, recovering, storing and towing the sonar device  301 . This embodiment offers the advantage of being simple, economical and robust. It requires no mechanism for varying the lengths of the hangers. 
     As a variant, at least one of the two hangers  6  and  7  has a length that is variable. For example, the hangers  6  and  7  have a variable length. The length of one or of a plurality of hangers can thus be varied during the recovery or the launch of the towed body. 
     In a variant, the towed device comprises the hangers  6  and  7  and one of the hangers comprises a ballast weight and the other hanger comprises a float so that the towed body exhibits a vertical orientation when the towed body  4  is being towed by the tow cable  2 . 
     The tow cable  2  comprises a first end, which is intended to be connected to the surface ship B and more particularly to the handling device  310 , and a second end  2   b  connected to a first end  6   a  of the first hanger  6 . A second end  6   b  of the first hanger  6  is attached to the towed body at a first fixing point  44  of the towed body  4  situated near the first longitudinal end  42 . The second hanger  7  comprises a first end  7   a  connected to the second end  2   b  of the tow cable  2  and a second end  7   b  attached to the towed body  4  at a second fixing point  45  of the towed body  4  situated near the second longitudinal end  43 . The two fixing points  44  and  45  are distant from one another along the longitudinal axis I. The second fixing point  45  is securely attached to the first fixing point  44 . 
     What is meant by a fixing point is the point at which the hanger applies a force of traction to the towed body  4 . The traction force applied by the tow cable  2  to the hanger is transferred to the fixing point by the hanger. 
     In the figures, the ends  6   a  and  7   a  are fixed with respect to the end  2   b  of the tow cable  2 . 
     The two hangers may be attached to the tow cable. 
     Advantageously, each of the two hangers has a stiffness lower than that of the tow cable  2 . 
     As a variant, one of the two hangers is a portion of the tow cable. In other words, the diameter of the continuous cable is substantially the same along the entire length of the continuous cable. 
     Advantageously, the stiffness of the continuous cable is substantially fixed along the continuous cable. In other words, the stiffness has substantially the same value along the entire length of the continuous cable. 
     The hangers  6  and  7  are arranged in such a way as to form a V shape when taut. The V comprises a pointed end to which the second end  2   b  of the cable is fixed. 
     The hangers  6 ,  7  may be fixed permanently or removably to the towed body  4 . 
     The towed body  4  may be connected to the tow cable by just two hangers, these being the first hanger  6  and the second hanger  7 . In a variant, the sonar device has a set of at least one intermediate hanger connecting the tow cable to the towed body by being fixed to the towed body at a fixing point positioned between the first fixing point  44  and the second fixing point  45 . 
     The sonar device according to the invention offers, on account of its special attachment device, the advantage of allowing simple and relatively safe recovery and launch of the towed body  4  from a surface ship B while keeping the geometry of the linear emitting antenna  40  fixed, ensuring easy adjustment of the device. The use of a pivoting arm or of a crane is not indispensable. 
     The sonar device  301 , initially immersed such that the towed body  4  is fully immersed, can be recovered and launched simply from the surface ship B, using a lightweight and simple handling device  310  comprising: 
     a winch  311  comprising a first drum  13  intended to rotate about a first axis of rotation x 1  with respect to a frame  12  of the winch which is fixed to a structure S of the surface ship B, so as to wind the tow cable  2  onto the first drum  13 , 
     a deflector  60 , being a convex friction surface exhibiting roughly the shape of a portion of a cylinder (not necessarily one with a circular cross section) extending longitudinally along an axis x of the deflector, the deflector  60  being positioned in such a way as to extend substantially horizontally, in a calm sea state, and substantially perpendicular to a vertical plane substantially parallel to an axis of traction applied to the tow cable  2  by the handling device  310  during a first winding step during which the first drum  13  is rotationally driven about the first axis x 1  with respect to the frame  12 , so that the tow cable  2  is wound onto the first drum  13 . 
     The deflector  60  is also positioned in such a way that the first hanger  6  and the second hanger  7  come to bear against the deflector  60  to be deflected by the deflector  60  during the first winding step so that the longitudinal axis I extends substantially parallel to the axis x of the deflector  60 , when the towed body  4  is fully emerged and suspended from the hangers  6  and  7  as visible in  FIGS. 2 and 3  and explained in greater detail hereinafter. The hangers  6  and  7  are therefore taut and linear between the deflector and the elongate body. In other words, when the towed body  4  is suspended from the hangers  6  and  7  deflected by the deflector  60 , the longitudinal axis I is substantially parallel to the axis of the deflector x. 
     Specifically, as depicted in  FIG. 1 , when the sonar device is being towed by the surface ship B, with the towed body  4  fully immersed and towed by the tow cable  2 , the two hangers  6  and  7  are substantially taut and the towed body  4  is substantially vertical (namely with its longitudinal axis substantially vertical) because of the hydrostatic forces and the forces of drag acting on the towed body when the shape of the elongate body is suitable, for example when the shape of the towed body  4  is substantially symmetrical with respect to a plane perpendicular to the longitudinal axis I and with respect to a plane containing the longitudinal axis I and intended to contain the tow cable during towing. 
     The tow cable  2  is able to bear against the deflector  60  in order to be deflected by the deflector  60  into the vertical plane containing the tow cable  2  during the towing of the sonar device with the elongate body fully immersed. This is true when the towing speed of the ship is below or equal to a certain threshold for a given installation of the handling device onboard the surface ship B. 
     As long as the towed body  4  is fully immersed (even stationary), the towed body  4  remains substantially vertical (longitudinal axis I substantially vertical) because of the hydrostatic forces when it is configured to be substantially vertical when subjected only to Archimedean upthrust and to the gravity, for example when it comprises a float near the second end  43  and a ballast weight near the first end  42 . 
     During a first winding step, during which the first drum  13  is rotationally driven about the first axis x 1 , the tow cable  2  is wound onto the first drum  13 . 
     The towed body  4  progressively rises up toward the surface. Because of the balance of the towed body  4 , the second end  43  reaches the water surface before the first end  42 . When the second end  43  is above the water surface, the Archimedean upthrust is no longer enough to keep the towed body  4  vertical, and so the second longitudinal end  43  of the towed body  4  has a tendency to topple, under the effect of its weight, which is to say move away from the vertical orientation and attempt to adopt a substantially horizontal orientation (the longitudinal axis I is substantially horizontal) as depicted in  FIG. 2 . 
     In the nonlimiting example of  FIG. 2 , the two hangers  6 ,  7  are long enough to bear against and be deflected by the deflector  60  as depicted in  FIG. 2 , while the towed body  4  is still immersed, while the towed device is being towed by the surface ship. 
     Advantageously, the two hangers  6 ,  7  are long enough to bear against and be deflected by the deflector  60  as depicted in  FIG. 2  when the towed body  4  is still immersed, when the towed device is being towed by the surface ship when the speed is below or equal to a maximum towing speed during recovery of the sonar device, in a calm sea state. The maximum towing speed during recovery of the body is below 10 knots and preferably equal to 6 knots or more. 
     In that case, when the towed body  4  reaches the water surface, with the first hanger  6  bearing against the deflector  60  and deflected by the deflector  60 , the towed body  4  topples under the effect of its weight, the second end  43  of the towed body  4  taking with it the second end  7   b  of the second hanger  7  which tends to remain taut. The towed body  4  thus progressively topples over during the first winding step, namely as the rotation of the first drum  13  about the axis x 1  continues in the same sense of rotation so that the cable  2  applies to the hangers  6 ,  7  traction toward the first drum in a plane substantially perpendicular to the axis x, until such point as the second hanger  7  comes to bear against the deflector  60  to be deflected by the deflector  60  as depicted in  FIG. 2 . 
     When the two hangers  6  and  7  are bearing against and being deflected by the deflector  60 , they are taut between the deflector  60  and the towed object  4 . Because the two hangers  6  and  7  have the same length and the deflector  60  has a cross section that is substantially fixed along the axis x, those portions of the hangers  6  and  7  that are situated between the regions via which they respectively bear against the deflector  60  and the towed body  4  have the same length, and the towed body  4 , in a calm sea state, adopts what is referred to as a handling orientation in which the longitudinal axis I is substantially parallel to the axis x of the deflector  60 . 
     By continuing the rotation of the first drum  13  in the first sense of rotation, the fully emerged towed body  4  suspended from the hangers  6  and  7  exhibits, in a calm sea state, the handling attitude in which its longitudinal axis I is substantially parallel to the axis of the deflector as depicted in  FIG. 3 . When the sea state is rough, the orientation of the towed body  4  may vary, but the closer the towed body  4  comes to the deflector  60 , namely the more the length of those portions of the hangers  6  and  7  that are situated between the regions via which they bear on the deflector  60  and the towed body  4  decreases, the more firmly it is held in the handling orientation. The freedom of movement of the towed body  4  is reduced, as visible in  FIGS. 3 and 4 , until it comes to bear against the deflector  60  and is recovered onboard the surface ship B as visible in  FIG. 4 . 
     Conversely, during a method of launching the sonar device, the towed body is kept substantially in the handling orientation by the two hangers bearing against the deflector until immersion is achieved. 
     The attachment device, using hangers  6 ,  7  for attachment of the sonar device  301  according to the invention, makes the launching and recovery of a towed body  4  from a surface ship B safer, thereby limiting the risk of collision between the towed body  4  and the stern of the surface ship B. 
     Owing to the simplicity and relative safety of the recovery and launch of the towed body  4  from a surface ship, this sonar device  301  is well suited to use onboard a USV. 
     Moreover, recovery of the towed body  4  in the handling orientation means that it is possible to provide an opening of reduced height in the stern of the surface ship, thereby avoiding the creation of recesses in the deck of the surface ship and limiting the size of the storage zone for storing this towed body along the longitudinal axis of the surface ship, namely along the axis perpendicular to the axis x. The handling orientation also encourages its stable and fairly compact storage on the drum of a winch of axis substantially parallel to the axis x. 
     The axis x is advantageously substantially perpendicular to the longitudinal axis of the surface ship. This allows the towed body to be stored secured against rolling and pitching. 
     The deflector  60  substantially exhibits a shape of an angular portion, created about the axis x, of a cylinder of axis x. In the nonlimiting embodiment of  FIGS. 1  to  4 , the deflector  60  is formed by a roller mounted with the ability to turn with respect to the carrier ship, about its axis of rotation x. This makes it possible to limit friction between the deflector  60  and the sonar device during launch and recovery operations. As a variant, the roller R is fixed relative to the surface ship B. 
     In the embodiment of  FIGS. 1 to 4 , the handling device comprises a set of adjacent cylindrical rollers R with longitudinal axes substantially parallel to one another and aligned along an axis which, in a calm sea state, is substantially horizontal and perpendicular to the axis x. 
     Advantageously, as visible in  FIG. 4 , the rollers R are configured and positioned in such a way that the towed body  4 , oriented in such a way that the axis I is substantially parallel to the axis x, is able to rest on two rollers R which prevent the towed body  4  from moving along the axis along which the rollers R are aligned. Thus, the two adjacent rollers form a nest on which the towed body  4  can be stored. 
     Advantageously, the axis along which the rollers R are aligned may be inclined with respect to the horizontal in a calm sea state, as visible in  FIG. 4 , or may be horizontal in a calm sea state, as depicted in  FIGS. 5 to 7 . Inclination encourages the towed body to be secured stably against pitching under the effect of the force of gravity and the traction of the hangers. Furthermore, inclination allows for easier relaunch. 
     Advantageously, the rollers R are dimensioned so that the towed body  4  resting on two adjacent rollers is in direct physical contact only with the two adjacent rollers R. That makes it possible to limit the risk of damage to the towed body  4 . 
     In  FIGS. 1 to 4 , the axis x of the deflector  60  is substantially parallel to the first axis of rotation x 1  of the first drum  13 . As a variant, these axes could be non-parallel, for example in the event that a pulley were to deflect, in a horizontal plane, the axis of the tow cable  2  between the deflector  60  and the first drum. 
     In  FIGS. 1 to 4 , the hangers  6  and  7  are fixed to the longitudinal ends of the elongate body. In other words, the fixing points  44  and  45  are situated at, which means to say a zero distance from, the respective longitudinal ends  42  and  43  along the longitudinal axis I. This embodiment limits the risks of the ends of the elongate body becoming jammed during recovery of the body. 
     In a less advantageous variant, at least one of the two fixing points  44 ,  45  is situated at a distance, along the longitudinal axis I, from the longitudinal end near which it is situated. 
     Advantageously, the distance separating the first fixing point  44  from the first longitudinal end  42  along the axis I is substantially the same as the distance separating the second fixing point  45  from the second longitudinal end  43  along the axis I. That makes it possible to encourage a vertical orientation of the longitudinal emitting antenna during towing. As a variant, these two distances are different, but this is less advantageous for the stability of the towed body during towing. 
     In  FIGS. 1 to 4 , the length of the hangers  6  and  7  and the position of the deflector  60  are defined in such a way that the hangers  6  and  7  come to bear against the deflector, during the first winding step, when the towed body  4  is fully immersed or at least partially immersed, in a calm sea state, when the towing speed is below or equal to the maximum towing speed for recovery. This characteristic allows the towed body to be stabilized, namely makes it possible to begin to limit its freedom of movement, before it exits the water. This makes it possible to limit the movements of the elongate object as it exits the water, notably when the sea state is rough, compared with a situation in which the towed body  4  emerged and suspended from the tow cable  2  while the tow cable  2  is still bearing on the deflector and deflected thereby. In the latter situation, an uncontrolled rotational movement of the longitudinal axis of the elongate body about the tow cable is brought about by a rough sea. 
     This is obtained through a suitable choice of the position of the deflector and of the length of the hangers according to the maximum towing speed. 
     As a variant, the length of the hangers  6  and  7  and the position of the deflector  60  are defined in such a way that the tow cable  2  bears against the deflector  60  and is deflected by the deflector  60  during the first winding step, when the towed body  4  is emerged and suspended from a portion of the tow cable  2  extending between the hangers and a region of the tow cable that is bearing against the deflector  60 . 
     In the first embodiment of  FIGS. 1 to 4 , the towed body  4  is situated at the end of the sonar device  301 . The sonar device  301  does not have a flexible towed body of the type incorporating a receiving antenna and intended to be towed by the tow cable  2  via the towed body  4 . 
     In the embodiment of  FIGS. 5 to 7 , the sonar system differs from that of  FIGS. 1 to 4  in that it comprises a sonar device  1  according to a second embodiment which differs from that of  FIGS. 1 to 4  in that it comprises a flexible elongate body  3  incorporating a receiving antenna  50  and intended to be towed by the tow cable  2  via the towed body  4 . The receiving antenna  50  comprises a plurality of electroacoustic transducers  41  distributed along the flexible elongate body  3 . 
     The flexible elongate body  3  potentially comprises, as visible in  FIGS. 6 to 7 , an intermediate cable  31  of neutral buoyancy connecting the receiving antenna  50  of neutral buoyancy to the towed body  4  and/or a tail rope  32  of neutral buoyancy connected to the towed body  4  by the receiving antenna  50 . 
     As visible in  FIGS. 6 and 7 , the flexible elongate body  3  advantageously has substantially neutral buoyancy so that it extends horizontally when immersed and towed by the surface ship B. 
     Advantageously, the flexible elongate body  3  is connected to the tow cable  2  via the towed body  4  which is itself connected to the flexible elongate body  3  in such a way that the flexible elongate body  3  applies traction to the towed body  4  at a third fixing point  46  situated near the first longitudinal end  42  of the towed body  4  and at a fourth fixing point  47  situated near the second longitudinal end  43  of the towed body  4 . That allows better control over the orientation of the towed body when it is being recovered onboard the surface ship B. 
     The sonar device  1  comprises, for example, a third hanger  8  comprising a first end  8   a  attached to the towed body  4  at a third fixing point  46  (which is situated at the first longitudinal end  42 , along the axis I, in the nonlimiting embodiment of  FIG. 5 ) of the towed body  4  and a second end  8   b  connected to a first end  3   a  of the flexible elongate body  3  and a fourth hanger  9  comprising a first end  9   a  attached to the towed body  4  at a fourth fixing point  47  (which is situated at the second longitudinal end  43 , along the axis I, in the nonlimiting embodiment of  FIG. 5 ) of the towed body  4  and a second end  9   b  connected to the first end  3   a  of the flexible elongate body  3 . The third fixing point and the fourth fixing point are securely attached to one another. 
     The variants concerning the positionings of the first fixing point and of the second fixing point and which were described with reference to  FIGS. 1 to 4  also apply to the new fixing points of  FIGS. 5 to 7 . Likewise, the properties and arrangement of the first hanger and of the second hanger which were set out hereinabove, and the variants pertaining thereto, also apply to the third and fourth hanger. 
     In the figures, the ends  8   b  and  9   b  are fixed with respect to the end  3   a  of the flexible elongate element  3 . 
     Advantageously, the third fixing point  46  for the first end  8   a  of the third hanger  8  is situated the same distance from the first longitudinal end  42  of the towed body  4  as the first fixing point  44  for the second end  6   b  of the first hanger  6 , and the fourth fixing point  47  for the first end  9   a  of the fourth hanger  9  is situated the same distance from the second longitudinal end  43  of the towed body  4  as the second fixing point  45  for the second end  7   b  of the second hanger  7 . 
     As a variant, these distances are not all equal. 
     The hangers  8  and  9  may have substantially the same length as the hangers  6  and  7  or a different length. 
     The hangers  8  and  9  are arranged in such a way as to form a V shape when taut. The V has a pointed bottom secured to the first end  3   a  of the flexible elongate body  3 . 
     The way in which the towed body  4  behaves differs from that of  FIGS. 1 to 4  in that during a first winding step, during which the first drum  13  is rotationally driven about the first axis x 1  to wind the tow cable  2  onto the first drum  13 , the traction applied by the flexible elongate element  3  to the towed body  4  via the third hanger  8  and the fourth hanger  9  limits the inclination of the towed body  4  with respect to the vertical plane containing the towing cable  2 . 
     Even if the two hangers  6  and  7  are too short, as in  FIG. 6 , for the first hanger  6  to be bearing on the deflector  60  and deflected by the deflector while the towed body  4  is still immersed, then the toppling of the towed body  4  is limited by the traction applied by the flexible elongate body  3  to the towed body  4  as it exits the water. Thus, the orientation of the towed body is better controlled than in the embodiment of  FIGS. 1 to 4 . Furthermore, the traction applied by the elongate flexible element  3  to the towed body holds it away from the stern of the surface ship. The presence of the flexible elongate body  3  makes it possible to limit the risk of collisions with the surface ship. 
     In a variant, if the two hangers  6  and  7  are long enough, as in  FIGS. 1 to 4 , for the first hanger  6  to be bearing against the deflector  60  and deflected by the deflector while the towed body  4  is still immersed, then the traction applied by the flexible elongate body  3  to the towed body holds the towed body back and slows its toppling as it exits the water until such point as the two hangers come to bear against the deflector  60  and are deflected by the deflector  60 . Thus, the orientation of the towed body is even between controlled. 
     In  FIGS. 1 to 7 , the towed body  4  is rigid so as not to be deformed during use, namely during the towing of the immersed sonar device, during recovery of the sonar device, and during the launching thereof. 
     The towed body  4  may be cylindrical or the body may be hydrodynamically profiled. It may have roughly the shape of a teardrop in a plane substantially perpendicular to the axis I, like the towed body  400  depicted in  FIG. 10 . 
     The towed body  4  may be equipped with a hydrodynamic covering exhibiting, nonlimitingly in  FIG. 5 , the form of a sail  5 . This covering has not been depicted in  FIGS. 6 to 7 . The sail  5  is, for example, installed between the hangers  8  and  9  connecting the towed body  4  to the flexible elongate body  3 . This sail limits the vibrations induced by vortex effect. Other types of hydrodynamic covering such as, for example, hairy jackets or inflatable sails may be provided. 
     In  FIGS. 1 to 4 , the winch  311  comprises only the first drum  13  able to store the sonar device  301  in  FIGS. 1 to 4  by continuing the rotation of the first drum in the same sense of rotation until the towed body  4  comes to bear against the first drum  13 . However, this winch  311  is not optimal for storing a sonar device  1  like that of  FIGS. 5 to 7  of the type comprising a flexible elongate body  3  at the tail. Specifically, it is not optimal to wind up the flexible elongate body  3 . It is an object of the invention to propose a sonar system for which the handling device allows this type of sonar device to be stored and which is compact and not excessively heavy. As a preference, although not necessarily, the handling device is configured to allow this device to be stored without the need to disconnect between the towed body and the flexible elongate body  3  and/or automatically. 
     One example of an underwater system comprising a handling device  10  according to another embodiment of the invention is depicted schematically in perspective in  FIG. 8  and in side view in  FIG. 9  in successive phases  1  to  4  during the implementation of a method for storing (or recovering) the underwater device  1  by means of the handling device  10  in order to store the underwater device onboard the surface ship. It should be noted that  FIG. 9  depicts a phase positioned between the phases  2  and  3  visible in  FIG. 3 . 
     The handling device  10  comprises a winch  11  comprising a frame  12  visible only in  FIG. 8  for the sake of greater clarity. The frame  12  is intended to be fixed to a structure S of the surface ship B. 
     The winch  11  comprises a first drum  13  able to rotate with respect to the frame  12  about a first axis of rotation x 1 . This winch differs from that of  FIGS. 1 to 4  in that it comprises a second drum  14  surrounding the first drum  13  and able to rotate with respect to the frame  12  about a second axis of rotation x 2 . The drums  13  and  14  are concentric in the nonlimiting embodiment of  FIGS. 8 and 9  which means that the axis x 2  is the axis x 1 . 
     The second drum  14 , surrounding the first drum  13 , has a greater diameter than the first drum  13 . 
     The winch  11  is able to be in an uncoupled state in which the first drum  13  is able to be rotationally driven about the axis of rotation x 1  with respect to the frame  12  and is uncoupled from the second drum  14  in terms of rotation about the first axis of rotation x 1  and about the second axis of rotation x 2 . 
     This allows the tow cable  2  to be wound onto the first drum  13  during a first winding step during which the first drum  13  is rotationally driven about the first axis x 1 . 
     The second drum  14  is able, at least when the winch is in the uncoupled state, to be in an open state, as depicted in  FIGS. 8 and 9  (phases  1  and  2 ) in which state the second drum  14  exhibits a receiving opening  15 . The receiving opening  15  can have the towed body  4  passed through it to enter the volume  140  delimited by the drums  13  and  14 . This volume surrounds the first drum  13  and is surrounded by the second drum  14 . 
     The second drum  14  delimits a substantially cylindrical internal volume of which the diameter corresponds to the diameter of the second drum. 
     The winch  11  is able to be in a coupled state in which the first drum  13  and the second drum  14  are coupled in terms of rotation about the second axis of rotation x 2 . 
     As a preference, the drums  13  and  14  are secured to one another in terms of rotation about the second axis when the winch  11  is in the coupled state. 
     Thus, by driving the second drum  14  in rotation with respect to the frame  12 , about the axis x 2 , when the winch  11  is in the coupled state, once the towed body  4  is stored in the volume  140 , the flexible elongate body  3  winds onto the second drum  14 . 
     Thus, the handling device  10  according to the invention allows the storage, in a limited volume and on a single winch  11 , of a tow cable  2  and a linear emitting antenna active sonar  3 ,  6 . The handling device according to the invention allows the tow cable  2  to be stored on the first drum  13 , with the emitting linear antenna inside the volume delimited by the second drum and with the receiving linear antenna wound onto the second drum. 
     This handling device is less expensive, more compact, and less heavy than a device using separate winches, one to recover the tow cable and another to recover the flexible elongate body. 
     In general, this configuration is particularly advantageous for storing underwater devices according to the invention comprising an elongate towed body  4  intended to be stored without being deformed, such as the sonar device according to the invention. 
     Specifically, the form of a drum  14  allows the creation of a receiving opening  15  in the shape of a slot extending longitudinally along the axis x 1  as depicted in  FIGS. 8 and 9 , and through which an elongate towed body  4  can pass with its longitudinal axis substantially parallel to the axis x 1  during the first winding step without suffering deformation. The device thus allows the creation of towed bodies with linear emitting antenna that are relatively heavy and long and nondeformable. 
     Advantageously (although not necessarily), as visible in  FIGS. 8 and 9 , the receiving opening  15  extends substantially along the entire length of the second drum  14  along the first axis of rotation x 1 . As a variant, the receiving opening  15  extends over part of the length of the second drum  14  along the first axis of rotation x 1 . 
     Advantageously, the second drum  14  is able to be positioned, and preferably immobilized, in a receiving angular position, about the second axis x 2 , in which the receiving opening  15  is able to have the tow cable  2  and/or the towed body  4  passed through it preferably, although not necessarily, during the first winding step, as visible in  FIGS. 8 and 9 . 
     When the tow cable and the towed body  4  pass through the opening under the effect of the rotation of the first drum  13 , the cable  2  and the towed body entering the volume  140  through the one same receiving opening  15 , the storage of the underwater device requires no manual or automatic operation for disconnecting the towed body and the tow cable. 
     The receiving opening therefore has to be dimensioned so that the towed body can pass through it during the first winding step according to the orientation it adopts with respect to the opening. It notably needs to have a length that is greater, along the axis x 1 , than the length of the towed body  4  along the longitudinal axis I. 
     Advantageously, if the first winding step continues, the towed body  4  comes to bear against the first drum  13  under the effect of the rotational driving of the first drum about the axis x 1 . 
     The method for handling an underwater device can thus be easily automated, making it possible to avoid the intervention of a human operator and the associated risks, and allowing an underwater device to be stored onboard a USV. 
     As a variant, the step of inserting the towed body  4  into the volume  140  by passing through the receiving opening  15  may be performed subsequently to the first winding step, for example by a human operator or tooling. 
     Advantageously, the one same plane perpendicular to the axis x 1  is situated equal distances from the two longitudinal ends of the first drum  13  and equal distances from the two longitudinal ends of the second drum  14 . 
     Advantageously, the first drum  13  and the second drum  14  have the same length along the axis x 1 . The second drum  14  surrounds the first drum over the entire length of the first drum  13  along the axis x 1 . As a variant, the drums  13  and  14  are offset from one another along the axis x 1 . 
     As a variant, the second drum  14  is longer than the first drum  13  along the axis x 1 , which means that a greater length of flexible elongate body  3  can be wound on or, conversely, the second drum  14  is not as long as the first drum  13  along the axis x 1 , which means that a greater length of tow cable  2  can be wound on. 
     Advantageously, the towed body  4  is able to enter the volume  140  through the receiving opening  15  to be stored in the volume  140  without extending radially (with respect to the axis x 2 ) beyond the volume  140 . In other words, the towed body  4  is inside the cylinder, the diameter of which is the diameter of the second drum, formed about x 2  over the entire length of this second drum along the axis x 1 . The winding of the flexible elongate body  3  onto the second drum  14  after the towed body  4  has been stored in the volume  140  is therefore not impeded by the towed body  4 . 
     Advantageously, the towed body  4  is able to enter the volume  140  through the receiving opening  15  to be stored in the volume  140  without extending radially (with respect to the axis x 2 ) beyond the volume  140  once the tow cable has been wound onto the first drum  13 . 
     In  FIGS. 7 and 9 , the towed body  4  is able to be stored entirely inside the volume  140 . As a variant, the towed body  4  could protrude beyond the volume  140  along the axis x 2 , for example when the first drum  13  is longer than the second drum  14 . 
     The invention also relates to a method for recovering and launching the underwater device, which recovery and launch are able to be implemented by the handling device according to the invention. The handling device may be configured to implement these methods when a recovery or launch condition is met, for example, when a control device controlling the handling device receives a command to store or, respectively, to deploy. 
     The recovery method of the handling device  10 , initially deployed and connected to the drum  13  via the tow cable  2 , comprises: 
     a first winding step during which the winch  11  is in the uncoupled state, the first drum  13  being rotationally driven about the axis of rotation x 1 , with respect to the frame  12  so as to wind the tow cable  2  onto the first drum  13  (phases  1  and  2  of  FIG. 9 ), the tow cable  2  passing through the receiving opening  15  or, in a less advantageous variant, through another opening formed in the second drum  14 , 
     a step of inserting the towed body  4  into the volume  140  (phase  3  of  FIG. 9 ), through the receiving opening  15 , 
     a second winding step (phase  4  of  FIG. 9 ) during which the winch  11  is in the coupled state, the second drum  14  being rotationally driven about the second axis of rotation x 2  so that the flexible linear element  3  is wound onto the second drum  14 . 
     In a first scenario, when the winch  11  is in the uncoupled state, the first drum  13  being rotationally driven about the axis of rotation x 1 , the tow cable  2  is wound onto the first drum  13  (phases  1  and  2  of  FIG. 9 ) by passing through the receiving opening  15  and then the towed body  4  passes through the receiving opening  15 , under the effect of the driving of the first drum  13  in rotation about the axis of rotation x 1  (phase  3  of  FIG. 9 ) to enter the volume  140  delimited by the second drum  14 . 
     To this end, the second drum  14  is able to be positioned, and preferably immobilized, in what is referred to as a receiving angular position, about the axis x 2 , in which position the receiving opening  15  can have the tow cable  2  and the towed body  4  passed through it, during the first winding step. The receiving opening  15  therefore needs to be dimensioned such that the towed body can pass through it during the first winding step according to the orientation in which it arrives with respect to the opening. 
     Advantageously, if the first winding step continues, the towed body  4  comes to bear against the first drum  13 , under the effect of the driving of the first drum  13  in rotation about the axis x 1 . 
     During the second winding step, the second drum  14  is rotationally driven about the axis x 2  in the same sense of rotation as the sense of rotation of the first drum  13  during the first winding step. 
     The method for recovering the initially deployed underwater device is thus easy to automate, making it possible to avoid the intervention of a human operator and the associated risks, and allowing the underwater device to be stored onboard a USV. 
     In a second scenario, the towed body  4  does not enter the volume  140  through the receiving opening  15  under the effect of the rotation of the first drum  13  about the axis x 1 . The step of inserting the towed body  4  into the volume  140  by passing through the receiving opening  15  may be performed subsequently to the first winding step, for example by a human operator or tooling. 
     The method advantageously comprises the following steps: 
     uncoupling the first drum  13  from the second drum  14  in terms of rotation about the axes x 1  and x 2  with respect to the frame  12  to place the winch  11  in the uncoupled state, this step being implemented by means for coupling/uncoupling the winch  11 , 
     immobilizing the second drum  14  in the open state, in terms of rotation with respect to the frame  12  about its axis of rotation x 2 , in the receiving angular position, this step being implemented by immobilizing means, such as, for example, a brake, an aligning pin or meshing gears. 
     The method also comprises, once the body has been inserted into the volume  140 , a step of coupling the first drum  13  and the second drum  14  in terms of rotation about the second axis of rotation x 2  with respect to the frame  12  so as to bring the winch  11  into the coupled state. This step is implemented by the coupling/uncoupling means. 
     In the embodiment of  FIGS. 8 and 9 , the drums  13  and  14  are concentric. This embodiment makes it possible to offer a handling device that is simple and lightweight. The two drums may, for example, be rotationally driven with respect to the frame, when the winch is in the uncoupled state and in the coupled state, by the one same shaft which is itself rotationally driven by the one same motor. The coupling/uncoupling means may be produced in a very simple way by mounting the first drum solid with the shaft, mounting the second drum in a pivoting connection on the first shaft and providing a coupler that allows the second drum to be rendered alternatively solid with the shaft and free to rotate with respect to the shaft about the axis of rotation x 1 . 
     The coupling/uncoupling means, just like the first coupling/uncoupling means that will be described later on, are, for example, means conventional to a person skilled in the art and produced, for example, in the form of a clutch or else based on a brake coupled to a jaw solid with one of the parts or else based on a motor coupled to a ring gear or else a connecting peg. 
     The handling device with concentric drums is particularly well suited to the storage of an underwater device  1  exhibiting a towed body  4 , for example an emitting linear antenna, produced in the form of a cylindrical object of circular or noncircular cross section, for example of substantially teardrop-shaped cross section. The cylindrical towed body  4  may come to bear on a wound length of the tow cable  2 , already wound onto the first drum  13 , on each turn of a layer of this winding, thus encouraging the stability of the towed body  4  on the first drum  13 . 
     When, during the first winding step, the cylindrical towed body comes to bear against the first drum  13  under the effect of the traction applied to the cylindrical towed body by the cable  2  or by an attachment system connecting the towed body to the cable, the traction applied by the cable or the attachment system keeps the body bearing against the first drum  13  without the need to provide fixing means for fixing the towed body  4  to the first drum  13 . This traction is maintained during the second winding step. That avoids human intervention for performing this fixing or costly means for protecting the body against potential collisions that could be caused by destabilization of the body. Furthermore, this type of towed body can be stored in a compact volume formed around the drum  13 . 
     In the embodiment depicted in  FIGS. 5 to 7 , the axis x 1  is distant from the axis x 2 . This embodiment makes it possible to store, inside the volume delimited by the second drum  214 , an object that has significant dimensions in the plane perpendicular to the axis x 1  without the need to increase the diameter of the second drum  214  significantly and/or allows a body of complex shape to be stored. 
     The axes are, for example, separated along an axis which, in a calm sea state, is horizontal and perpendicular to the axis x 1 . 
     The first drum  13  is, for example, mounted with the ability to rotate about a shaft of axis x 1  fixed to the second drum  214 , for example to a shell  212  of the second drum  214 . The shell  212  will be described later on. 
     The coupling/uncoupling means may comprise first coupling/uncoupling means allowing the first drum  13  to be permanently secured to and disconnected from the shaft on which it is mounted and means for immobilizing the second drum, about the axis x 2  with respect to the frame  12 , allowing the second drum to be alternately secured to and disconnected from the frame in terms of rotation about the axis x 2 . The uncoupled state is obtained by uncoupling the first drum  13  from the shaft about the axis x 1  and by immobilizing the second drum  214  about the axis x 2  with respect to the frame  12 . The coupled state is obtained by coupling the first drum  13  to the shaft. A first motor is provided to allow the first drum  13  to be rotationally driven about the axis x 1  with respect to the frame. A second motor is provided to allow the second drum  214  to be rotationally driven about the axis x 2  with respect to the frame. 
     In the embodiment of  FIGS. 8 and 9 , the second drum  14 , as visible in  FIG. 9 , has a shell  114  taking the form of a roughly cylindrical shell in which the receiving opening  15  is made. 
     The drum  14  of  FIGS. 8 and 9  is able only to be in an open state. The second drum  14  is configured so that an elongate flexible element  3  can be wound onto the second drum  14  when the second drum  14  is in the open state. 
     Advantageously, the receiving opening  115  extends over an angle less than or equal to 20° and preferably less than or equal to 15° so as to allow the flexible elongate body  3  to be wound correctly onto the second drum  14 . 
     As a variant, the winch  11  of  FIGS. 8 and 9  could be capable of being alternately in the open state and in a closed state in which the receiving opening is at least partly closed as depicted in  FIGS. 5 to 7 . The flexible elongate element can then be wound on only in the closed state or in the closed state and in the open state. 
     In the embodiment of  FIGS. 5 to 7 , the handling device  210  differs from the handling device of  FIGS. 8 and 9  notably in terms of the winch  211  which comprises a second drum  214  which differs from the second drum  14  of  FIGS. 8 and 9  in that it is able to be alternately in an open state, as depicted in  FIGS. 5 and 6 , in which it exhibits a receiving opening  215  through which the towed body  4  can pass to enter the inside of the volume  240  delimited by the second drum  214  and the first drum  13  and surrounding the first drum  13 , and in a closed state, as depicted in  FIG. 7 , in which the receiving opening  215  is at least partially closed. The same could also be true for coaxial drums, just like the more specific device and method features described hereinafter, considered alone or in combination. This type of configuration makes it possible to create a large receiving opening in the drum and thus receive, inside the volume delimited by the second drum  214 , towed bodies of large size, for example in a plane perpendicular to the axis x 2 . Furthermore, a large opening leaves more space for potential manipulation of the towed body by a machine or by an operator. 
     The second drum  214  comprises a mobile cowl  213  able to move with respect to a first part  212  of the second drum  214  and able to adopt a first position ( FIGS. 5 and 6 ) in which the cowl  213  opens the second drum  214  so that it comprises the receiving opening  215  and a second position ( FIG. 7 ) in which the cowl  213  substantially closes the receiving opening  15  so that the second drum  214  exhibits a substantially cylindrical form. A residual slot advantageously allows a region of connection between the towed body and the flexible elongate body  3 , or the flexible elongate body  3  itself, to pass. 
     In the nonlimiting example of  FIGS. 5 to 7 , the second drum  214  comprises a shell  212  having substantially the shape of an angular portion of a cylinder formed about the axis x 2 . The shell  212  extends angularly about the axis x 2 , from a first axial edge  216  substantially parallel to the axis x 2  as far as a second axial edge  217  substantially parallel to the axis x 2 . The cowl  213  has a shape that substantially complements the shell  212  and is mounted with the ability to pivot with respect to the shell  212  about an axis of rotation of the cowl x 3  parallel to the axis x 2  near the edge  216  so that the cowl  213  is able to pass from the first position depicted in  FIG. 5  to the second position depicted in  FIG. 7  by a rotation with respect to the first part about the axis x 3 . 
     The storage (or recovery) method comprises a step of opening, which is implemented by opening means or by an operator, to cause the second drum to move from the closed state into the open state. This step of opening may be performed before the first winding step or else during or after the first winding step but before the insertion of the towed body. The method comprises, after the step of inserting the towed body and before the second winding step, a step of closing the second drum  214  to allow the elongate element  3  to be wound onto the second drum. 
     In the embodiment of  FIGS. 5 to 7 , the step of inserting the towed body  4  into the volume  140  through the receiving opening  15  is performed subsequently to the first winding step, for example, by a human operator or by tooling. As a variant, the step is performed, as in  FIGS. 8 and 9 , during the first winding step under the effect of the rotation of the first drum about the axis x 1 . 
     The handling device advantageously comprises fixing means SF, SP as depicted in  FIG. 7 , for fixing the towed body  4  to the second drum  214  and, more particularly, to the shell  212 , and configured to secure the towed body to the second drum  14  in terms of rotation about the axis x 2 . These fixing means comprise, for example, a support SP intended to support the towed body  4  and fixed with respect to the shell  212  or with respect to the cowl, and fixing means SF for fixing the towed body  4  to the support SP. This type of means may also be provided when the drums are coaxial. 
     The second drum  214  able to be in the open state and closed state is configured, for example, as in  FIGS. 5 and 6 , so that the winding of a flexible elongate body, for example the body  3 , onto the second drum  214  is impossible in the open state and is possible in the closed state. 
     As a variant, the second drum is configured so that the winding of a cable onto the second drum is possible in the open state and in the closed state. The cowl is, for example, of the rotary flap type having, for example, the shape of a portion of a cylinder of a diameter very slightly smaller than the diameter of the second drum and able to pivot about the axis x 2  in order to close or to open the second drum. 
     As depicted in  FIG. 8 , the winch may comprise two endplates F 1 , F 2  delimiting the drums along the axis x 1 . Advantageously, at least one endplate has an opening  0  allowing an operator to access the volume  140  so as to allow maintenance on the towed body  4  stored in the volume  140 . This type of means may also be provided when the drums are coaxial. 
     In  FIGS. 1 to 7 , the handling device comprises a deflector  60  positioned upstream of the first drum  13  viewed from the towed body  4  with the first hanger  6  and the second hanger  7  initially immersed, during the first winding step. In other words, the hangers are able to come to bear on the deflector  60  before they start to be wound onto the first drum  13  during the first winding step. 
     More particularly, the deflector  60  is positioned near the stern PO of the surface ship B so that the towed body  4  adopts the handling orientation (x substantially parallel to I) before it arrives onboard the surface ship B. The deflector  60  is, for example, the first element of the handling device and/or of the surface ship that the hangers encounter during a method of recovering/storing the sonar device initially deployed and towed by the surface ship. This makes it possible to limit the risk of collisions between the towed body  4  and the stern of the ship. It also makes it possible to avoid designing large-sized openings into the stern of the carrier ship in order to allow the recovery of an emitting linear antenna and to avoid the creation of a recess in the main deck of the surface ship in order to be able to store an emitting linear antenna that is too tall to be housed between the main deck and the deck above. 
     The deflector  160  of the handling device of  FIGS. 8 and 9  differs from that of  FIGS. 1 to 7  in that it is closer to the first drum  13  and, more particularly, to the opening  15  so that the towed body passes through the opening  15  substantially in the handling orientation (I substantially parallel to the axis of the deflector  160  along which the deflector  160  extends longitudinally). That makes it possible to limit the risk of collisions between the towed body  4  and the second drum  14  as it passes through the receiving opening  15  and thus limits the risks of it becoming jammed as it arrives on the drum. It also, when the axis of the deflector is substantially parallel to the axis x 1 , allows the towed body  4  to be brought naturally, and without the intervention of tooling or of an operator, into an orientation favorable for passing through the receiving opening  15  and being stored easily and in a stable manner on the first drum  13  (axis I substantially parallel to the axis x 1 ), it being possible for the towed body  4  to be kept bearing against the first drum  13  over its entire length. In the nonlimiting example of  FIGS. 8 and 9 , the deflector  160  is positioned upstream of the drum  13  and mounted on the second drum  14  so as to delimit the receiving opening  15 . 
     More generally, a deflector  160  may be positioned in such a way that the towed body  4  passes through the opening  15  substantially in the handling orientation and/or comes into a position of bearing on the drum  13  substantially in the handling orientation. 
     This type of deflector  160  is positioned between the stern of the surface ship and the first drum  13 , for example, between a deflector  60  and the first drum  13 . This deflector  160  forms, for example, part of the winch being, for example, positioned upstream of the first drum  13 , for example upstream of the receiving opening  15  (during the first winding step), or at the receiving opening  15 . 
     Different deflectors occupying different positions described hereinabove may, as a variant, be provided in the one same handling device. 
     It should be noted that the first drum  13  also constitutes a deflector allowing the towed body  4  to be brought substantially into the handling orientation on the first drum  13 . In a variant which has not been depicted, the handling device comprises a single deflector formed by the first drum  13 . 
     The invention relates to a method for recovering the sonar device from a surface ship comprising a first winding step during which the first drum  13  is rotationally driven about the first axis x 1  so that the tow cable  2  is wound onto the first drum  13 , and so that the first hanger  6  and the second hanger  7  come to bear on the deflector  60  to be deflected by the deflector so that the longitudinal axis of the towed body  4  is oriented substantially parallel to the axis of the deflector x, when the towed body  4  is fully emerged and suspended from the first hanger  6  and from the second hanger  7 . The invention relates to a sonar system configured for implementing this step during a recovery method which is, for example, implemented when a recovery condition is met. The sonar system then comprises control means for controlling the handling device to implement the method. 
     The invention relates to a method for launching the sonar device from a surface ship comprising a first pay-out step during which the first drum  13  is rotationally driven about the first axis x 1  so that the tow cable  2  is unwound off the first drum  13  and so that the first hanger  6  and the second hanger  7  come to bear on the deflector  60  to be deflected by the deflector so that the longitudinal axis of the towed body  4  is oriented substantially parallel to the axis of the deflector x, when the towed body  4  is fully emerged and suspended from the first hanger  6  and from the second hanger  7 . The invention relates to a sonar system configured for implementing this step during a launch method which is implemented for example when a recovery condition is met. The sonar system then comprises a control device for controlling the handling device to implement the method. 
     In the examples depicted in the figure, the winch comprises a single second drum  14 . In a more complex variant, the winch comprises a set of a plurality of second drums as defined hereinabove. These second drums have different diameters so as to surround one another. Each second drum  14  has an opening providing access to the volume situated between this second drum and the directly next drum of smaller diameter. That, for example, allows different towed bodies to be recovered into the volume delimited by each second drum and the drum of directly next smaller diameter, or allows portions of flexible elongate elements of different flexibilities to be wound onto drums of different diameters. 
     All the drums may be rotationally coupled and each drum may be rotationally uncoupled from the other drums. 
     In the examples depicted in  FIGS. 1 to 9 , the underwater device comprises a single towed body. 
     As a variant, the underwater device comprises a set of several towed bodies. The handling device may then comprise one or a plurality of second drums. 
     Each towed body is advantageously elongate along a longitudinal axis and have the same length, although this is not compulsory. 
     The underwater device, for example, comprises a set of a plurality of towed bodies  4 . The towed bodies  4  are connected to one another, to the tow cable  2  and to the flexible elongate element  3  so as to be distributed along a curved towing line defined by the tow cable and the flexible elongate element when the underwater device is being towed by the surface ship, with all the towed bodies being distributed along the towing line. 
     An example of this type of device is depicted in  FIG. 11 . The underwater device  1000  comprises a plurality of towed bodies  4  distributed along the towing line defined by the cable  2  and the flexible elongate body  3  and drawn in dotted line between the two. The towed bodies  4  are connected to one another by intermediate lines  1001   a,    1001   b,    
     The system is, for example, configured to store or to allow a plurality of towed bodies to bear on the first drum  13  or, more generally, between the first drum  13  and the second drum  14  or so as to store or allow the storage of different towed bodies in the successive volumes defined between the successive adjacent drums or bearing against successive drums. 
     In the example of  FIG. 11 , the towed bodies  4  are connected pairwise by intermediate lines  1001   a,    1001   b  via hangers. Each intermediate body is fixed to a first and a second hanger  6 ,  7  connecting it to the tow cable and to a third and a fourth hanger  8 ,  9  connecting it to the flexible elongate body. 
     As a variant, in the underwater device  1002  of  FIG. 12 , the towed bodies  4  are connected pairwise by assemblies of intermediate lines  1003 ,  1004  and  1005 ,  1006 . One of the towed bodies is fixed to a first and a second hanger  6 ,  7  connecting it to the cable. This towed body is connected to the adjacent towed body by several intermediate lines  1003 , 1004  which are substantially parallel during towing. This towed body is itself connected to the adjacent last towed body by intermediate lines  1005 , 1006 . The last towed body is fixed to a third and a fourth hanger  8 ,  9  connecting it to the flexible elongate body. 
     Each intermediate line is a flexible elongate element that may be produced in the form of a cable, for example an electric-mechanical cable. Each intermediate line may comprise at least one electroacoustic transducer. It may incorporate an acoustic antenna, for example an acoustic receiving antenna. 
     The control device for controlling the handling device (coupling/uncoupling means, first coupling/uncoupling means, drive means, immobilizing means, opening means) may comprise one or more dedicated electronic circuits or a general purpose circuit. Each electronic circuit may comprise a reprogrammable computing engine (a processor or a microprocessor for example) and/or a computer executing a program comprising a sequence of instructions and/or a dedicated computing engine (for example a set of logic gates such as an FPGA, a DSP or an ASIC, or any other hardware module).