Patent Publication Number: US-8967067-B2

Title: System for launching and recovering underwater vehicles, notably towed underwater vehicles

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. patent application Ser. No. 13/311,885, which claims priority to foreign French patent application No. FR 10 04764, filed on Dec. 7, 2010. This application claims priority to foreign French patent application No. FR 12 01573, filed on Jun. 1, 2012. The disclosures of each of the above-noted applications are incorporated by reference in their entireties. 
    
    
     FIELD OF THE INVENTION 
     The invention falls within the naval field and relates more specifically to the handling and lifting systems mounted on ships for launching and recovering marine or underwater vehicles from these ships, the vehicles in question being either towed vehicles or self-propelled vehicles, the latter then being fitted with a temporary tether while they are being launched and recovered. 
     The operations of launching and recovering a marine or underwater vehicle from a ship which also has the task of transporting this vehicle generally include a phase that is critical, especially in rough seas, which is the transition from the fully emerged state in which the vehicle is secured to the handling means used, to the fully immersed state in which the vehicle has no further contact with these means, and vice versa. This is because it is during these critical phases that the movements of the swell are most dangerous to the integrity of the vehicle, this vehicle being tossed about by the swell while it is in a region on the surface where it is likely violently to strike either the structure of the ship or that of the lifting and handling means. 
     This is particularly true of a self-propelled vehicle in the launch or recovery phase when, with the vehicle already in the water or still in the water, the lifting and handling means do not yet (or any longer) have full control over its movements. This is also true of a towed vehicle in the phases in which the towing cable is holding it near the hull of the ship while the lifting and handling means have not yet (or any longer) got full control over its movements. 
     BACKGROUND 
     To limit these risks of collision there are known solutions, which generally employ means that involve the intervention of human operators. 
     Thus, as far as the self-propelled vehicles are concerned, these not being towed by the ship, one known solution is to provide mooring means on the hull of the vehicle, for example securing rings, these securing means being arranged in such a way that the vehicle can be lifted while maintaining a horizontal position. Launch and recovery can then, for example, be performed using a winch mounted on a mobile gantry positioned at the rear of the ship, or even a crane, the gantry or the crane allowing the lifting winch to be positioned over the recovery zone. As a result, launch and lift are performed vertically, thus limiting the possibilities of collision with the ship during lowering or raising. As an alternative, the vehicle can be lifted by placing it in a gondola-like device which itself comprises suitable fixing points. 
     This type of solution can be applied, notably autonomously, to vehicles towed from the middle but is not, however, readily applicable to the case of vehicles that are towed from the front because, for obvious reasons of efficiency, it is desirable for it to be possible for the vehicle to be towed and handled using the one same cable. Handling using means such as those described hereinabove using a single cable would prove tricky because it entails the vehicle passing from the vertical position to the horizontal position during launch and vice versa during recovery. This handling further requires additional operations the purpose of which, once the vehicle has been lifted and positioned over the deck of the ship, is to lay the vehicle down flat on the deck of the ship or, more generally, on a storage area. These operations themselves generally require the intervention of human operators, which intervention is made trickier and more hazardous when the sea is rough. 
     As a result, as far as vehicles towed from the front are concerned, the solution generally preferred is to use a handling cable secured temporarily above the centre of gravity of the vehicle. 
     Another solution that is also used is handling based on the installation of means comprising an inclined ramp along which the vehicle slides in order to reach the surface of the water or leave the water and return to the ship. The ramp is generally configured so that it guides the vehicle in a straight path, thus avoiding the vehicle having to follow a lateral course. However, such a ramp is generally ill suited to use in heavy seas, because lateral movements of the vehicle could then damage that vehicle. 
     The use of such means advantageously allows the vehicle to be launched and deployed at the rear of the ship in a simple way by letting the towing cable out and, conversely, allows the vehicle to be returned on board the ship simply by winding the cable in, onto the drum of a winch for example. The launch and recovery of the vehicle can therefore moreover be performed while the ship is under way, which means that the vehicle, towed by the ship, naturally positions itself along the line of forward travel of the ship. 
     Nonetheless, the use of such means involves a critical phase which occurs between the moment the vehicle comes into contact with the ramp and the time it is fully in position thereon. Specifically, the transition of the vehicle from the surface of the water to the ramp involves the nose of the vehicle coming into contact with the ramp, and this contact, notably when the sea is rough, can be fairly violent and cause damage to the vehicle but also prevent the vehicle from being brought up. 
     In order to alleviate these difficulties of initial contact, various solutions have been developed, which solutions are generally best suited to one given type of vehicle. These known solutions generally involve reinforcing the structure of the vehicle, mainly the nose, so that it is able to withstand the knocks resulting from its coming into contact with the end of the ramp. It also involves the use of means for minimizing these impacts, particularly by configuring the ramp in such a way that its end lies beneath the surface of the water so that the vehicle floating on the surface comes into contact with the inclined surface of the ramp rather than with the end thereof. Such solutions nonetheless prove to be insufficient in rough seas, the slamming effect of the waves then being heightened by the movement of the ship. 
     SUMMARY OF THE INVENTION 
     It is one object of the invention to propose means for launching and recovering a marine or underwater vehicle in the safest possible way, it being possible for these means to be deployed entirely automatically, with no human intervention or monitoring. A more particular object of the invention is to provide means suited to the handling of underwater vehicles that are towed from the front or of underwater vehicles that do not have any means of vertical lifting but which are temporarily connected to hauling means, a cable driven by a winch for example, during the launch and recovery phases. 
     To this end, the subject of the invention is a system for automatically, even in rough seas, launching and recovering a marine or underwater vehicle from an under way carrier ship, of the type comprising an inclinable articulated ramp comprising a bottom and edges, first drive means for lowering and raising the ramp and hauling means for controlling the sliding of the vehicle along the ramp during the launch and for hoisting the vehicle up along the ramp during recovery, the ramp having an emerged end and an end intended to be immersed, the ramp being able to move in terms of rotation with respect to the carrier ship about a rotation axis, known as the rotation axis of the ramp, under the action of the first drive means. The rotation axis of the ramp is located at a distance from the emerged end and from the end intended to be immersed. The ramp also comprises buoyancy means configured and arranged on the ramp in such a way that the free end of the ramp floats at the surface or near the surface of the water when the ramp is lowered. The bottom of the articulated ramp has an external face that forms streamlining so as to minimize the lift and drag forces imparted to the ramp by the movement of the ship and the vertical dynamic movements brought about by the waves when its free end is in contact with the water. 
     Advantageously, the rotation axis of the ramp is located between the emerged end and the end intended to be immersed. 
     Advantageously, the edges of the ramp are configured so that they, jointly with the streamlining of the lower part of the ramp, provide the free end of the ramp with buoyancy. 
     Advantageously, the edges of the ramp are configured to hold the vehicle on the ramp and limit the rolling movements imparted to the vehicle. 
     Advantageously, the system further comprises holding and guiding means comprising a holding device configured to hold the end of the vehicle and remain in contact with the vehicle during the launch and recovery operations, the holding device being driven with the vehicle by the hauling means. 
     Advantageously, the hauling means comprise a towing cable driven by hauling means. 
     Advantageously, the system includes means for changing the direction of the cable. 
     Advantageously, the bottom has a slot, through which the cable is able to pass. 
     Advantageously, the means for changing the direction of the cable include a pulley that has a pulley axis coincident with the rotation axis of the ramp. 
     Advantageously, the means for changing the direction of the cable include a cylinder portion that has an axis coincident with the rotation axis of the ramp. 
     Advantageously, the holding device comprises vertical protection elements on which the wings of the vehicle rest when its end is engaged in the holding device, the frontal support thus afforded contributing to keeping the vehicle along the axis of the ramp. 
     Advantageously, the holding and guiding means further comprise drive means configured to keep the holding device in contact with the end of the vehicle as long as the vehicle is progressing along the ramp. 
     Advantageously, the bottom has a V-shaped or W-shaped cross-sectional profile. 
     Advantageously, the rotation axis of the ramp is able to undergo translational movement with respect to the ship, between a first position and a second position located in front of the first position with respect to the ship. 
     Advantageously, the system includes damping means on which the part of the ramp that is located between the end that can be immersed and the rotation axis can rest when the ramp is in the second position. 
     The device according to the invention thus consists of a recovery system that advantageously limits the vertical relative movements between this system and the underwater or marine vehicle when this vehicle is floating at the surface, particularly at the critical moment of contact between these two entities during recovery. It allows the vehicle to be launched automatically from its storage position and then allows this vehicle to be recovered following use and returned to its storage position. 
     The vertical relative movements are successfully limited by means of an inclinable ramp that is articulated in its upstream part and that in its rear part comprises buoyancy means that allow its free end to float at the surface. Moreover, the streamlined underside of the ramp advantageously limits the impact of the speed of forward travel of the ship and the slamming effects due to the waves on the relative positioning of the rear end of the ramp with respect to the surface of the water, and does so for different sea conditions and different speeds of travel in relation to the water. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The features and advantages of the invention will be better assessed through the description which follows, which description introduces one particular embodiment which embodiment does not limit the scope of the invention. This description relies on the attached figures which depict: 
         FIG. 1 , and  FIG. 1   a  a schematic overview of one particular embodiment of the system according to the invention, showing the ramp in the lowered position; 
         FIGS. 2   a ,  2   b ,  2   c  partial schematic views, in different planes, relating to the hydrodynamic features of the ramp that forms the device according to the invention; 
         FIG. 3 , a schematic overview of one particular embodiment of the system according to the invention, showing the ramp in the raised position, 
         FIG. 4  schematically shows a side view of another example of the system according to the invention, in which the ramp is in a lowered position, 
         FIG. 5  schematically shows a side view of another example of the system according to the invention, in which the ramp is in a lowered position, 
         FIG. 6  schematically shows a top view of the system from  FIG. 4 , 
         FIGS. 7   a  to  7   d  schematically show another example of the system according to the invention, in a side view in which the ramp is lowered ( 7   a ), in a top view in which the ramp is lowered ( 7   b ) and in which the ramp is raised and in a storage position ( 7   c  in a side view and  7   d  in a top view). 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the rest of the text, the terms front, rear, in front of and behind are defined with respect to the ship, and more precisely with respect to the longitudinal axis of the ship, extending from the rear to the front of the ship. 
     As stated earlier, the description which follows introduces a number of embodiments of the device according to the invention, which embodiments do not limit the scope of the invention. These embodiments introduce both the essential features of the invention and additional features connected with the embodiments in question. 
       FIG. 1  shows an overview of an example of the system according to the invention. However, the arrangement of the emerged end  111  with respect to the position of the rotation axis x of the ramp, which axis x is shown in  FIG. 1  and also in  FIG. 3 , which will be described below, is not part of the ramp that is the subject of the present invention. In this view, the device is shown on a ship  10  of the catamaran type, between the two hulls thereof. As this figure illustrates, the device according to the invention chiefly comprises the following elements:
         a streamlined articulated ramp  11  preferably situated at the rear of the ship and having a first end or emerged end  111  and a second end or free end  112 . The emerged end  111  of the ramp is connected to the carrier leaving at least one degree of freedom to rotate about a horizontal axis perpendicular to the main axis of the ramp so that the free end  112 , which is also known as the end intended to be immersed  112 , can be raised or lowered in the manner of a drawbridge.       

     In other words, the ramp  11  is articulated to the ship  10  about a rotation axis x of the ramp, which axis x is perpendicular to the main axis of the ramp. In  FIG. 1 , the rotation axis x is located at the emerged end  111 . 
     The rotation axis x of the ramp is horizontal. 
     The horizontal plane is defined by the plane of the deck of the ship. The expression “horizontal axis” is understood to mean an axis parallel to the deck of the ship. 
     According to the invention, the ramp  11  is in the overall shape of a chute or channel section with a bottom  113  and edges  114  and  115  the height of which is notably determined according to the size and geometry of the vehicle  15  being handled.
         means  12  mounted on the ramp and intended to encourage the vehicle to progress along the ramp under the action of the hauling performed by the cable (in the case of recovery) or under the effect of gravity (in the case of launch). These means are, for example, rollers or rolling runners positioned laterally on the bottom  113  of the ramp and over which the vehicle  15  rolls.   holding and guiding means the function of which is to ensure that the vehicle is aligned with the axis of the ramp so as to allow the vehicle to roll or slide correctly throughout its travel along the ramp (up or down). These means include, for example, as illustrated in  FIG. 1 , a device  13  acting as a fairlead, through which the towing cable  14  used to haul the vehicle passes. This element is configured so that it moves along the ramp  11 , for example on rails positioned along the longitudinal axis thereof (not depicted in  FIGS. 1 and 3  but depicted in  FIGS. 4 ,  7   b  and  7   d ).   buoyancy means, the main purpose of which is to ensure that the free end  112  of the ramp can naturally remain at the surface of the water when there are no waves or when the waves have a wavelength that is long in comparison with the dimensions of the recovery system. In the embodiment of  FIG. 1 , these means consist of lateral floats forming the edges  114  and  115  of the ramp, and of the bottom of the ramp that forms the streamlined part. However, in an alternative embodiment, these means may simply consist of floats  30  attached to the ramp  11 , to the part of the ramp that is able to be immersed, as depicted in  FIGS. 4 ,  5 ,  7   a  and  7   c , or to the free end  112 , or of any other combination of suitable means. The vertical protection elements  131  can also be part of the buoyancy means. During a phase of launching the vehicle or bringing it back on board the ship, the end  151  of the vehicle, attached to the towing cable  14 , is inserted into the element  13  and remains in close contact therewith, and this has the advantageous effect of keeping the axis of the vehicle along the axis of the ramp  11  as the vehicle travels along this ramp.       

     This enduring contact is obtained naturally inasmuch as the holding element  13  is a solid element that has a tendency, under the effect of its weight, to drop down along the ramp, thus checking the progress of the fish as it is being raised back up and assisting with its lowering. 
     However, in one particular embodiment, the holding and guiding means may also comprise drive means (not present in the example of  FIG. 1 ) configured so that the holding element  13  is kept in contact with the end of the vehicle  15  as long as the latter is progressing along the ramp  11 . These means work for example by applying a certain resistance to the travel of the fairlead towards the fixed end of the ramp. 
     According to the embodiment considered, these drive means may for example consist of an auxiliary winch which pulls the holding device  13  (the fairlead) towards the free end  112  of the ramp  11  (downward) by means of a cable returned by a pulley situated at the free end of the ramp. Adjusting the tension of the auxiliary winch in relation to the tension generated by the towing winch  16  then allows contact between the vehicle  15  and the fairlead  13  to be actively maintained as the vehicle  15  is being raised back up along the ramp  11 , without, however, impeding this raising. 
     Alternatively, according to another embodiment, the vehicle can be secured to the holding element when its end is inserted therein. In this case, the action of drive means becomes less necessary. 
     Illustrations  2 - a ,  2 - b  and  2 - c  of  FIG. 2  illustrate an essential feature of the invention. Illustration  2 - a  is a schematic side view of the ramp  11 , in a lowered configuration for which the free end  112  is immersed in the water. This configuration corresponds to the use of the ramp for operations of launching and recovering the vehicle  15 . Illustration  2 - b  shows, for the same configuration (ramp lowered), a view of the ramp with a horizontal plane of section passing through the axis Δ 2  shown in the side view  2 - a . Illustration  2 - c  on the other hand shows a view of the ramp on a vertical plane of section passing through the axis Δ 1  shown on the side view  2 - a  and perpendicular to the axis of the ramp  11 . 
     According to this feature, the bottom  113  of the articulated ramp  11  includes an external face  21  intended to come into contact with the surface of the water, which forms streamlining the cross-sectional profile of which is defined, as illustrated by views  2 - b  and  2 - c , in such a way as to minimize the lift and drag forces caused, when the free end of the ramp is in contact with the water (ramp lowered) according to the schematic view  2 - a , by the speed of forward travel of the ship on the one hand and so as to minimize the effect of slamming caused by the waves on the other. In other words, the profile of the external face  21  of the bottom  113  of the ramp  11  is defined so that it acts like a breakwater to break the wave front likely to collide with the ramp  11  as a result notably of the movement of the ship  10 , before these waves reach the free end  112  of the ramp and, at the pace of the waves passing under the ramp  11 , cause sharp variations in the vertical position of the free end  112  of the ramp  11  in relation to the surrounding water surface. These sharp variations, if not compensated for, notably result in an uncontrolled variation in the vertical position of the end  112  of the ramp  11  relative to that of the end  151  of the vehicle  15 , which can cause damage to the latter if it occurs just at the moment that the vehicle enters the ramp. 
     In one particular embodiment, illustrated by  FIG. 2 , the external face  21  of the bottom  113  of the ramp  11  forms streamlining with a V-shaped cross-sectional profile. In an alternative embodiment, this face  21  forms streamlining with a W-shaped cross-sectional profile. 
     Advantageously, the use of a ramp  11  fitted with buoyancy means that act chiefly on the free end  112  of the ramp so as to keep the latter at a given position with respect to the water surface, either at the surface or slightly immersed for example, and the underside  21  of which has the cross-sectional profile defined hereinabove, allows two significant effects to be minimized:
         the dynamic rise of the free end  112  of the ramp  11  above the surface (surfing effect) connected with the resistance of the ramp to the forward travel of the ship and to the lift of the ramp: this phenomenon, which is a result of the speed of the ship, is likely to make it difficult for the end of the vehicle  15  to come into contact with the fairlead  13  without colliding with it, particularly during operations of recovering the vehicle  15 ;   the sharp vertical dynamic movements performed by the free end  112  of the ramp  11  as a result notably of the slamming effect caused by the waves particularly when the waves are short (the combined effect of a deflection of the water and significant hydrostatic return), which movement is also likely to make it difficult for the end of the vehicle  15  to come into contact with the fairlead  13  without colliding with it, particularly during operations of recovering the vehicle  15  and which may have the additional effect of causing the vehicle to jump when installed on the ramp and of causing it to collide with the bottom of the ramp with the risk of damaging it.       

     The minimizing of these two effects, which has been obtained by implementing the invention, thus represents an essential factor in limiting the instances of heavy knocks between the vehicle  15  and the ramp  11 , notably during the phase in which the vehicle is approaching the ramp and in which its end, hauled by the cable, is ready to enter the fairlead  13  and take up position on the ramp  11  and during the phases in which the vehicle is sliding along the ramp. This factor is particularly essential inasmuch as launch and recovery of the vehicle are performed when, in order to ensure good overall stability, the ship is still under way. 
     These two complementary means, the buoyancy means and the streamlining of the external face of the ramp, thus advantageously ensure a stable vertical position with respect to the surface for the rear end  112  of the ramp  11  and therefore for the holding device  13 , particularly during that critical phase when the vehicle is approaching the ship  10  in order to take up position on the ramp. 
     Thus, by virtue of the essential features described in the foregoing text, the device according to the invention allows an underwater or marine vehicle to be recovered safely even when the ship tasked with recovering it is under way at a non-zero speed in a sea that is not calm. 
     The fact that the device is designed to be used from a ship under way, advantageously allows this ship to have greater manoeuvrability and limits the amplitude of its movements under the action of the movements of the sea. As a result, adopting a suitable heading facing into or out of the swell means that rolling movements can be greatly limited. The speed of forward travel of the carrier ship  10  also, as has already been stated, makes it easier to stabilize the position of the vehicle  15  along the axis of the ramp  11 . 
     The device according to the invention also has the advantage that it can be installed on a wide variety of ships of varying shapes and tonnages. It may also, depending on the target application, in addition to comprising the essential characteristic elements described above, comprise additional elements which, for example, make it easier to operate in the target operational context. 
     In the embodiment of  FIG. 1 , the device according to the invention is, for example, positioned between the two hulls of a ship of the catamaran type, preferably towards the rear of the ship. The vehicle  15  considered here is a towed underwater vehicle with wings  151  that perform a depressing function. The size and construction of these winglets also make them relatively fragile. The vehicle  15  here is towed by means of a towing cable  14 , an electric towing cable, for example, which may be wound or unwound by means of hauling means  16 ,  161 , including a towing winch  16  shown in  FIGS. 4 to 7 . The system includes means  20  for changing the direction of the cable. 
     The system also includes means  20  for changing the direction of the cable from the hauling means  16 ,  161  by limiting its travel. The hauling means  16 ,  161  apply, to the cable, a hauling force in a predetermined hauling direction. 
     Furthermore, the device  13  (fairlead) locally and simultaneously ensures the functions of the means  161  and  20 . According to the above explanations, the device comprises the essential constituent elements described hereinabove and, in particular, a narrow ramp  11  the width of which substantially corresponds to the cross section of the body of the vehicle, combined with buoyancy means the action of which is essentially applied to the free end of the ramp and with holding and guiding means consisting of the device  13 . Likewise, the external face  21  of the bottom  113  forms streamlining. Advantageously, the ramp has a streamlined shape, which is V-shaped or W-shaped. This streamlined shape is advantageously narrow. 
     The streamlined shape of the external face  21  is inherently an aerodynamic shape. 
     In  FIG. 1 , the ramp  11  is mounted on the ship via fixing means  17  which allow it to pivot, with respect to the ship, about a horizontal rotation axis x perpendicular to the main axis of the ramp and also perpendicular to the longitudinal axis of the ship. The fixing means  17  are mounted on the end  111  of the ramp that faces towards the front of the ship  10 , and this allows the end  112  of the ramp directed towards the rear to be free of the pitching movements of the carrier ship. 
     Moreover, as far as the holding and guiding means are concerned, the device (the fairlead)  13  in this example comprises vertical protection elements  131  against which the wings  151  of the vehicle rest when the end of the vehicle is engaged in the guide element  13 , the support thus provided contributing towards keeping the vehicle  15  along the axis of the ramp  11 . 
     In the embodiment illustrated in  FIG. 1 , the device according to the invention also comprises lifting means allowing the free end  112  of the ramp  11  to be raised when the device is not in use, notably outside of periods of launching and recovering the vehicle and allowing the ramp  11  and, where appropriate, the vehicle  15  to be brought into a horizontal storage position illustrated in  FIG. 3  above the surface of the water. 
     These additional lifting means may, as illustrated in  FIG. 1 , consist of a winch  18  which winds and unwinds two cables  181  and  182  in synchronism. The cables  181  and  182  are returned by pulleys placed on a gantry  19  and are attached on each side of the ramp  11 , preferably near the free end  112 . The raised position of the ramp is, for example, determined by a system of end stops positioned on the gantry. The lowered position is not itself identified by an end stop because the ramp is supposed to float. 
     Moreover, in this exemplary embodiment, the edges  114  and  115  of the ramp  11 , in addition to being configured to make the free end  112  of the ramp  11  buoyant, are also configured to form semirigid longitudinal support elements. The thickness of the edges is therefore suited to the dimensions of the vehicle  15  concerned so that when this vehicle is installed on the ramp  11 , its body rests on the means  12  while its wings  151  rest on the edges  114  and  115  along which they slide. 
     It should be noted that although the stability of the vertical position of the rear end  112  of the ramp with respect to the water surface is normally assured, by optimizing the hydrostatic properties (mass, volume) and the hydrodynamic properties of the ramp, through the presence of the buoyancy means and via the cross-sectional profile of the streamlined hull formed by the bottom  113  of the ramp  11 , it is nonetheless possible, for certain specific applications, to supplement the action of these means by controlling the position of the free end  112  of the ramp in the vertical plane using additional means, for example rams, or even by using lifting means capable of effecting this control, it being possible for these means to be those used to raise the ramp and keep it in the raised position. 
     From an operational standpoint, the device according to the invention advantageously allows the operations of launching and recovering marine or underwater vehicles, particularly towed vehicles, to be carried out without any need for any human intervention for mooring or handling. 
     Thus, in order to recover a vehicle after use, all that is required is for the free end of the ramp  11 , initially in a horizontal position, to be lowered by operating the motor  18  of the lifting means. 
     The ramp  11  thus lowered advantageously, thanks to the means that provide its free end  112  with buoyancy and thanks to its streamlining, keeps the holding and guiding means in position, and in particular keeps the entry to the device  13  (the fairlead) level with the surface of the sea irrespective of the height of the waves. The fairlead  13  thus follows the surface of the water just like the towed vehicle  15  floating at the surface thereof. 
     As a result, the vehicle  15  can be towed into a position in which it comes into contact with the fairlead  13  while these two elements are positioned substantially at one and the same height. In that way, the end of the vehicle  15  can insert itself into the fairlead  13  with a minimal risk of violent frontal and vertical collision. 
     Once the end of the vehicle  15  has thus been inserted into the device  13 , the forward travel of the ship  10  has the effect of causing the vehicle to position itself, through inertia, along the longitudinal axis of the ramp  11 . Moreover if, as in the example of  FIG. 1 , the device  13  is equipped with vertical protection elements  131 , the fact of the wings  151  of the vehicle  15  coming into contact with these vertical elements  151  encourages the vehicle  15  to realign itself along the axis of the ramp  11  at the moment of contact with the device  13 . The presence of these vertical elements further limits yawing, surging and swaying of the vehicle  15  when full contact with the device  13  is made. 
     Correct positioning of the vehicle with respect to the ramp now having been assured, the actual raising of the vehicle  15  up along the ramp  11  can be performed by continuing to actuate the towing winch  16 , the movement of the vehicle  15  causing that of the fairlead  13  through which the towing cable  14  passes and in which its end  151  is inserted, while the wings  151  of the vehicle  15  are supported across a broad front. 
     The assembly thus rises up along the ramp, sliding or rolling thereon, towards the fixed end  111 , the holding element  131  being kept in contact with the end of the vehicle by the drive means described earlier. 
     Thereafter, as the vehicle gradually ascends and emerges from the water, contact between the vehicle  15  and the ramp  11  becomes increasingly close. The ramp  11  becomes heavier which means that it swings down into the water and becomes more inclined. Collisions between the vehicle and the ramp are therefore attenuated, notably as a result of the increased angle of inclination of the ramp as a result of the weight of the vehicle. Moreover, the fact that the wings  151  are resting against the edges  114  and  115  of the ramp limits any potential rolling of the vehicle during this raising operation. Any pitching of the vehicle is itself gradually attenuated until it becomes zero when upthrust becomes insufficient to lift the vehicle in relation to the ramp  11 . The vehicle  15  is then fully resting on the ramp  11  and all six of its degrees of freedom are under control. 
     It should be noted that in one particular embodiment suited to operation in heavy seas leading to relative vertical accelerations of more than 1 g, the device according to the invention may comprise an additional means, a rigid arm for example, that immobilizes the vehicle with respect to the holding device  13  and therefore with respect to the ramp. 
     According to the invention, once the vehicle  15  is completely resting on the ramp  11 , it is possible to return the ramp  11  to a horizontal position using the lifting means. 
     Thereafter, with the vehicle  15  placed in a stable manner on the ramp  11 , it is possible, by adopting a configuration known as the “transit” configuration illustrated in  FIG. 3 , to transport it, keeping it stored on the ramp  11 . In this configuration, additional fasteners  1011  that hold the vehicle  15  firmly on the ramp  11  are used. Thus, the device according to the invention and the vehicle can, without damage, be subjected to vertical accelerations of several g. 
     Alternatively, if suitable handling means are available on board the ship, the vehicle can, from this stable position, be detached from the towing cable  14  and placed in a dedicated storage area. In such a case, the action of the lifting means during the transit phases is confined to keeping the ramp in the raised position. 
     From an operational standpoint, the manoeuvre of launching the vehicle is a manoeuvre that is the opposite of that of recovering it. 
     Thus, during that manoeuvre, with the vehicle  15  positioned on the ramp  11 , the latter is lowered, the lifting means ensuring a controlled lowering of the free end  112  of the ramp  11  towards the surface of the water. Once the free end  112  has been fully lowered, the free part of the ramp  11 , still fitted with the towed vehicle  15 , floats, sinking slightly below the surface of the water at its rear end  112 . Next, the towing winch  16  is actuated to release the vehicle  15  which slides along the ramp  11  under its self weight or, in the alternative form of embodiment described earlier, under the action of drive means which act on the holding device  13 , until it completely leaves the ramp  11 , the end of the vehicle  15  then being separated from the fairlead  13 . 
     During the phase of releasing the vehicle, the lifting means are preferably kept under tension to prevent the lifting cables  181  and  182  which are unloaded from containing any “slack” which would be detrimental to the correct execution of the operation. 
       FIGS. 4 to 7  show further embodiments of the system according to the invention. In these examples, the ramp is installed on a ship  10  which is, in this case, single hulled. The elements and means described hereinabove can be integrated into the examples in  FIGS. 4 to 7  except for the arrangement of the end  111  with respect to the ship and more particularly with respect to the rotation axis x of the ramp. However, some elements, such as the means  12 ,  1011 , have not been shown in  FIGS. 4 to 7  for reasons of greater clarity. 
     In  FIG. 4 , the rotation axis x of the ramp with respect to the ship  10  is located at a distance from the emerged end  111 . In the embodiment in  FIG. 4 , the axis x is more particularly located between the end  112  intended to be immersed and the emerged end  111  of the ramp  11 . In other words, the rotation axis x is located between the two ends  111 ,  112  at a distance from these two ends  111 ,  112 . This feature is also reproduced in  FIGS. 5 ,  6  and  7   a  to  7   d . It makes it possible to move the centre of gravity of the ramp closer to its rotation axis x, thereby making it possible to carry out lifting and lowering operations of the ramp. 
     In this example, the ramp  11  is provided with floats  30  that are fixed to the edges  114  and  115 . 
     In the example in  FIG. 4 , as in the preceding example, the system includes means for changing the direction of the cable. These means are arranged so as to send the towing cable  14 , and more particularly the part of the cable  14  that is located between the means for changing the direction of changing the direction of the cable and the vehicle  15 , in a different direction from the one located between the hauling means  16 ,  161  and these means for changing the direction of the cable. The means for changing the direction of the cable also play the role of cable deflector. 
     In this example, the means for changing the direction of the cable include a pulley  200  for changing the direction of the towing cable  14  when the latter comes into contact with the pulley. The circular shape of the pulley ensures circular inflection of the cable. The radius of the pulley is chosen so as to ensure circular inflection of the cable with a radius sufficient not to damage the cable and notably its internal conducting wires. The pulley is arranged such that its axis, known as the pulley axis, is coincident with the rotation axis x of the ramp. 
     In the example shown in  FIG. 1 , the means for changing the direction of the cable include a cylinder portion  20 , on which the cable  14  is able to slide. The cylinder portion  20  is advantageously a cylinder portion having an opening angle less then 360°. 
     The cylinder portion  20  is arranged such that its axis is coincident with the rotation axis x of the ramp. The cylinder portion is fixed, either with respect to the ship, or with respect to the ramp. In the example shown in  FIG. 1 , the cylinder  20  is secured to the ramp and able to move in rotation with respect to the ship about the rotation axis x. 
     It is also possible to install this type of cylinder portion  20  in the embodiment of  FIG. 4  or in one of the following embodiments, in place of the pulley  200 . 
     The fact that the axis of the pulley  200  or of the cylinder portion  20  is coincident with the rotation axis x of the ramp makes it possible to make the movements of the ramp insensitive to the tension in the towing cable  14 . This is explained by the fact that the force {right arrow over (F)} exerted by the towing cable  14  on the bearing means  20  or  200  and resulting from the tension in the cable passes through the axis of the pulley or of the cylinder portion. Thus, this force passes, in these two examples, through the rotation axis x of the ramp, irrespective of the inclination of the ramp. 
       FIG. 5  schematically shows a side view of an example of a system in which the ramp  11  is, just like in  FIG. 4 , connected to the ship such that the rotation axis x is fixed with respect to the ship by means of fixing means  171 . In this example, the means for changing the direction of the cable include a pulley  200 . The pulley  200  is positioned on the ramp  11  such that the pulley axis p is located at a distance from the rotation axis x of the ramp. More precisely, in this example, the pulley  200  is mounted at the emerged end  111  of the ramp. 
     In  FIGS. 4 and 5 , for reasons of greater clarity, the lifting means for raising and lowering the end  112  of the ramp are not shown. These drive means are conventional means to a person skilled in the art. They may be lifting means such as described hereinabove. Use can also be made of lifting means that include, as can be seen in  FIGS. 7   a  and  7   b , a lifting winch  18  able to wind and unwind two cables  181  and  182  in synchronism. The lifting cables  181 ,  182  are fixed at the emerged end  111  of the ramp. In the example in  FIGS. 7   a  and  7   b , the lifting cables  181 ,  182  are fixed to the edges  114 ,  115  on each side of the indentation  116 . This arrangement is best suited to single-hulled ships  10 . In this embodiment, the winch  18  is installed in front of the ramp  11 . 
       FIG. 6  shows a top view of the ramp  11  from  FIG. 4 . In this figure, it can be seen that the ramp  11  is in the overall shape of a chute or channel section with a bottom  113  and edges  114  and  115  the height of which is notably determined according to the size and geometry of the vehicle  15  being handled. The bottom  113  has a slot  116  in which the pulley  200  is inserted. The pulley  200  is articulated to the ramp  11  about the rotation axis x. 
     The slot  116  is arranged such that the part of the cable  14  located between the hauling means  16 ,  161  and the pulley  200  can pass through the slot. The slot  116  thus allows the towing cable  14  to reach the pulley  200  without diversion between the hauling means  16 ,  161  of the wire and the pulley  200 , no matter whether the ramp is inclined with respect to the horizontal (lowered position) or is in a raised position (that is to say it extends parallel to the horizontal plane). This slot  116  is advantageously present in the embodiment of  FIGS. 7   a  to  7   d.    
     By contrast, the bottom  113  has, as shown in  FIGS. 2   a  to  2   c , a streamlined continuous external face  21 , as described hereinabove, on the part of the ramp  11  that can be immersed. In this case, it is the part that is located behind the pulley  200 . 
       FIGS. 7   a  to  7   d  schematically show another embodiment of the system according to the invention. It differs from the one in  FIG. 4  in that the rotation axis x of the ramp  11  with respect to the ship  10  is able to undergo translational movement with respect to the ship in a horizontal direction d. In this way, the rotation axis x is able to undergo translational movement with respect to the ship between a first position shown in  FIGS. 7   a  and  7   b  and a second position located in front of the first position on the deck of the ship. 
     In this example, the system according to the invention includes displacement means  201  for displacing the ramp with respect to the ship in a horizontal translational direction d between its first and second positions. This direction d is advantageously located in a plane parallel to the main axis of the ramp. 
     Advantageously, the displacement means  201  are arranged such that when the rotation axis of the ramp is in its second position, the end  112  does not protrude from the rear of the ship. This makes it possible to protect the ramp while it is being transported by means of the ship  10 . In this case, the displacement means  201  include a carriage  202  and rails  203 . 
     In the example of  FIGS. 7   a  to  7   d , the ramp is articulated to a carriage about the rotation axis of the ramp. The carriage  202  is able to undergo translational movement with respect to the ship in the translational direction d between a first position and a second position located in front of the first position on the deck of the ship. More particularly, the carriage is able to move along guide rails  203  that extend in the translational direction d. 
     In  FIGS. 7   a  and  7   b , the ramp  11  is in the lowered position and the end  112  is immersed. The vehicle  15  is in the water, is hauled by the towing cable  14  and is in contact with the holding element  13  which is disposed at the end  112  of the ramp. The carriage  202  occupies its first position, in which the rotation axis x of the ramp occupies its first position at the rear of the deck of the ship. 
     In  FIGS. 7   c  and  7   d , the ramp is in the raised position, and the vehicle  15  has been hoisted onto the ramp. Moreover, the carriage  202  occupies its second position, in which the rotation axis x of the ramp occupies its second position in front of its first position on the deck of the ship  10 . The ramp occupies what is known as its storage position. 
     Advantageously, the device according to the invention includes damping means  204  that are arranged such that the part of the ramp located between its rotation axis and the end  112  rests on these damping means when the carriage occupies its second position. This makes it possible to avoid deterioration of the ramp and to ensure greater stability of the ramp when it is in the raised position.