Patent Publication Number: US-6698376-B2

Title: Device for launching and recovering an underwater vehicle and implementation method

Description:
FIELD OF THE INVENTION 
     The present invention relates to a device for launching and recovering an underwater vehicle. 
     BACKGROUND OF THE INVENTION 
     The operation of submerging an underwater vehicle several meters under the surface of the sea, from a platform of a boat is made tricky by the vertical movements of the boat which are caused on the surface of the water by the swell, and are conventionally known as “heave”. The vertical movements due to the swell at a depth of a few meters are attenuated but since the launch and recovery device is generally fixed to the boat by means of a cable, it is driven vertically by the boat. The relative movements of the underwater vehicle and of the launch and recovery device may cause damage to the said underwater vehicle. 
     Document U.S. Pat. No. 3,807,335 discloses a submerged platform intended for submerging an underwater vehicle fixed vertically under the platform which is secured to a boat by cables connected to the platform via dampers, so as to attenuate the vertical movements of the platform which are due to the vertical movements of the boat. 
     Nonetheless, this device for launching and recovering an underwater vehicle does not make it possible to completely get around the problem of the vertical movements, which can merely be attenuated. 
     SUMMARY OF THE INVENTION 
     The invention proposes a device for launching and recovering an underwater vehicle which makes it possible to get around the disadvantages associated with the heave. 
     The invention also proposes a device for launching and recovering an underwater vehicle which is suited to the storage of the underwater vehicle on a boat. 
     The invention finally proposes a device which allows an underwater vehicle to be launched and recovered near to its working depth. 
     A device for launching and recovering an underwater vehicle according to the invention comprises a submersible assembly comprising a lower chassis and an upper chassis, the lower and upper chassis being connected by a flexible connection, so that the distance between the said upper and lower chassis is adjustable to make it easier for the underwater vehicle to move in a zone lying between the lower and upper chassis. 
     The flexible connection and the lower and upper chassis form a receiving cage provided with an opening  28 , the vertical dimension of which can be adjusted. Moving the lower and upper chassis apart makes it possible to enlarge the vertical dimension of the said opening so that the underwater vehicle can enter or leave the cage without the movements of the cage due to the heave impeding the entry or departure of the underwater vehicle. Moving the lower and upper chassis closer together in the vertical direction makes it possible, in spite of the vertical movements of the cage as a whole as a result of the heave, to support the underwater vehicle on the lower chassis and hold it in place using the upper chassis. By moving the lower and upper chassis closer together quickly enough, successive impacts between the underwater vehicle and the lower chassis are avoided. 
     In one embodiment, the lower and upper chassis are connected by a cable bundle, the cables of which can easily be wound onto pulleys so as to reduce the distance between the lower and upper chassis, or unwound so as to increase the distance between the lower and upper chassis. 
     In one embodiment, the launch and recovery device comprises means of winding up and unwinding the cables, which allows the length of the cables and therefore the separation between the lower chassis and the upper chassis to be adjusted. 
     In one embodiment, the device comprises at least one motor used to rotate a number of pulleys onto which the flexible connection is wound. 
     As a preference, the device is secured to a boat situated at the surface by at least one cable of adjustable length. Thus, the submersible assembly can be submerged to the desired depth, for example a depth close to the working depth of the underwater vehicle. 
     Advantageously, positioning means are arranged between the upper chassis and the lower chassis. The positioning means, in the form of stops for example, vertically limit the closeness of the lower and upper chassis so as not to damage the underwater vehicle when the said vehicle is being recovered. The positioning means guide the positioning of the lower chassis with respect to the upper chassis in a horizontal plane so as to make sure that the underwater vehicle is held correctly in the launch and recovery device. 
     In one embodiment, the lower chassis comprises a lower cradle for receiving the underwater vehicle. The receiving cradle makes recovering the underwater vehicle onto the lower chassis easier. 
     As a preference, the cradle comprises at least one receiving concave wall, the profile of which guides the underwater vehicle as contact is made between the lower chassis and the underwater vehicle while the said underwater vehicle is being recovered. 
     Advantageously, the cradle can be detached from the lower chassis. Thus, when the device is returned, with the underwater vehicle, to the device situated at the surface, it is possible easily to access the underwater vehicle, for example for maintenance operations, by moving away the cage formed by the launch and recovery device so as to gain access to the underwater vehicle. 
     In one embodiment, the upper chassis comprises an upper holding cradle, which allows the underwater vehicle to be held in place in the launch and recovery device. 
     The invention also relates to a method for launching and recovering an underwater vehicle, in which method a launch and recovery device comprising an upper chassis and a lower chassis is submerged, the upper and lower chassis being connected by a flexible connection, so that the distance between the said upper and lower chassis is adjustable, and in which device an underwater vehicle is placed. The distance between the upper and lower chassis is increased to release the underwater vehicle, and the distance between the upper and lower chassis is reduced for recovering the underwater vehicle once the underwater vehicle has moved into a zone lying between the lower and upper chassis. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention and its advantages will be better understood from studying the detailed description of one embodiment which is taken by way of non-limiting example and illustrated by the appended drawings, in which: 
     FIG. 1 is a schematic perspective view of an underwater vehicle situated on the cradle of a device according to one aspect of the invention; 
     FIG. 2 is a schematic perspective view of a device according to one aspect of the invention in which an underwater vehicle is held; and 
     FIG. 3 is a schematic perspective view of a device according to one aspect of the invention situated at a depth under the surface of the sea, in which the lower and upper chassis are distant from one another. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In FIG. 1, a cradle  1 , provided with a front part  1   a  and with a rear part  1   b , has a tubular framework  2  comprising two longitudinal tubes  3 ,  4  arranged parallel to each other in a horizontal plane and connected by a number of transverse tubes  5  running at right angles to the longitudinal tubes  3 ,  4 . 
     A seating surface  6  comprises a support tube  7  situated longitudinally above the transverse tubes  5 , more or less mid-way between the longitudinal tubes  3 ,  4 , and vertically some distance from the transverse tubes  5 . 
     On the portion of the support tube  7  that is situated on the front part  1   a  of the cradle  1 , the seating surface  6  comprises a wall  8  which is concave upwards and convex downwards, in the form of a metal sheet bent into a V with the opening uppermost and facing away from the framework  2 , and running from the support tube  7  on each side of a vertical plane of symmetry passing through the support tube  7 . The concave wall  8  runs longitudinally from a first end of the support tube  7 , over a limited length of the support tube  7 . The seating surface  6  comprises a tubular reinforcing structure  9  arranged under the concave wall  8  on each side of the plane of symmetry so as to reinforce the concave wall  8 . On the portion of the support tube that is situated on the rear part  1   b  of the cradle  1 , the seating surface  6  comprises a front bearing plate  10  running longitudinally along the support tube  7  from the zone on the concave wall  8  that is in contact with the support tube  7 . 
     The seating surface  6  rests on the framework  2  via two similar support tubes  11 ,  12  arranged symmetrically with respect to the concave wall  8 , both in the same transverse plane, the support tube  12  not being visible in FIG.  1 . An absorption stop  13 , for example made of an elastomeric material, is arranged between the upper end of the support tube  11  and an upper end of the reinforcing structure  9 , to absorb impacts that may arise when recovering an underwater vehicle. The support tube  11  is arranged roughly vertically between the longitudinal tube  3  on the one hand, and the reinforcing structure  9  on the other. The support tube  11  is situated in the same transverse plane as a transverse tube  5 . A reinforcement  14  in the form of a triangular plate connecting the adjacent ends of the support tube  11  and of the said transverse tube  5  stiffens the connection between the support tube  11  and the framework  2  so as to take up loads applied by the bearing plate  6  to the holding tube  11 . 
     On the rear part  1   b  of the cradle  1 , the seating surface  6  rests on the framework  2  via blocks  15  and absorption stops  16  which are similar to the absorption stop  13 , and arranged on a transverse tube  5 . 
     The concave wall  8  comprises two rectangular openings  17 ,  18  which run transversely more or less from the support tube  7  as far as the free ends of the concave wall  8  so as to allow a fixing strap  19  to be passed through. 
     An underwater vehicle referenced  20  in its entirety, running longitudinally, rests on the seating surface  6 . The front  20   a  of the vehicle  20  rests on the concave wall  8 , the rear  20   b  of the underwater vehicle  20  rests on the bearing plate  10 . The underwater vehicle comprises a number of thrusters  21  situated at the rear of the underwater vehicle  20  to move it vertically or horizontally or cause it to turn. The fixing strap  19  holds the front  20   a  of the underwater vehicle  20  against the concave wall  8  of the seating surface  6 . A strap  22  arranged transversely holds the rear  20   b  of the underwater surface  20  against the bearing plate  10 , being arranged longitudinally at the thrusters  21 . 
     In FIG. 2, a parallellepipedal cage  23  is formed by a lower chassis  24 , an upper chassis  25 , a cable bundle  26  and a protective screen  27 . The cage  23  comprises an opening  28  allowing the underwater vehicle to enter and exit. 
     The lower chassis  24 , in the form of a tubular frame of rectangular shape, comprises two longitudinal tubes  29 ,  30  connected by two transverse tubes  31 ,  32  running at right angles between the ends of the longitudinal tubes  29 ,  30 . The chassis  24  fixed to the tubular framework  2  of the cradle  1 , for example by screw-nut systems, can be detached from the tubular framework  2  of the cradle  1 . The frame of the lower chassis  24  forms an opening  33  allowing the underwater vehicle  20  to pass through vertically and having at least one dimension that is shorter than a corresponding dimension of the framework  2  of the cradle  1 . 
     Securing yokes  34 , formed on the longitudinal tubes  29 ,  30  towards the inside of the tubular frame formed by the lower chassis  24 , can be used to secure cables  24  that form a cable bundle connecting the lower chassis  24  to the upper chassis  25  at right angles to the plane of the framework  2  of the cradle  1 . 
     The upper chassis  25 , in the form of a tubular framework similar to the tubular framework  2  of the cradle  1  and comprising two longitudinal tubes  35 ,  36  and a number of transverse tubes  37 , is connected to a boat situated at the surface, and not depicted in the figures, via a flexible connection in the form of a cable  38  fixed to a roughly central part  39  of the upper chassis  25 . 
     Pulleys  40 , arranged vertically facing the yokes  34  and rotating as one with longitudinal spindles  41 ,  42  fixed so that they can rotate to, the corresponding longitudinal tubes  35 ,  36  by a device which has not been depicted in order to make the drawing clearer, allow the cables  26  to be wound up or unwound. A motor  43  arranged longitudinally on the central part  39  of the upper chassis  25  drives the rotation, via a mechanical angle gearbox  44 , of a shaft  45  arranged transversely, provided at its ends with mechanical angle gearboxes  46 ,  47  for driving the rotation of the spindles  41 ,  42  respectively. Rotating the motor  43  in a first direction causes the cables  26  to be wound onto the pulleys  40  and causes the lower  24  and upper  25  chassis to be brought closer together. Rotating the motor  43  in the opposite direction to the first direction of rotation causes the cables  25  to be unwound and the lower  24  and upper  25  chassis to be parted. 
     Longitudinal tubular rails  48 ,  49 , the ends of which are outwardly curved, fixed to the upper chassis  25  via connecting tubes  50  arranged vertically, form an upper cradle which comes into contact with the upper surface of the underwater vehicle  20  to hold the latter in place. As can be seen in FIG. 3, the rail portions  48 ,  49  in contact with the surface of the underwater vehicle  20  may be covered with a flexible coating  51 , for example of a material of the elastomeric type, so as to avoid impacts with the surface of the underwater vehicle  20  while the underwater vehicle  20  is being recovered. 
     Positioning means in the form of tubular supports  52  fixed to the upper chassis  25  drop down vertically towards the transverse tubes  5  situated longitudinally at the ends of the lower chassis  24 . The supports  52  are provided at their lower end adjacent to the lower chassis  24  with receiving stops  53  of frustoconical shape which widen towards the bottom. The receiving stops  53  collaborate with studs  54  arranged on the lower chassis  24  and visible in FIG. 3, which project vertically from the said transverse tubes  5 . The supports  52  define the minimum vertical distance between the lower and upper chassis so that the underwater vehicle  20  is held by the seating surface  6  and the rails  48 ,  49  without causing damage to the underwater vehicle  20  as the lower  24  and upper  25  chassis are moved closer together. 
     The protective screen  27  comprising a number of bars  55  held by two lines  57 ,  58  deploys in the manner of a blind stacked up between the facing longitudinal ends of the upper  25  and lower  24  chassis so that the bars  55  are contiguous when the lower chassis  24  is in contact with the stops  53 . 
     As illustrated in FIG. 3, unwinding the cables  26  makes it possible to enlarge the said cage  23  in the vertical direction, so as to enlarge the said opening  28  to make the passage of the underwater vehicle  20  easier. 
     Before launching the underwater vehicle  20 , the latter is fixed to the cradle  1  using the straps  19  and  22 . The cage  23  is lifted up by a crane present on the boat and not depicted in the figures. As the lower chassis  24  allows the underwater vehicle  20  to pass vertically through the opening  33 , the cage  23  is set down on the cradle  1 . As the lower chassis  24  has at least one dimension smaller than a corresponding dimension of the framework  2  of the cradle  1 , the chassis  24  rests on the framework  2  of the cradle  1 . The lower chassis  24  is then fixed manually to the cradle  1  using screw-nut systems. 
     When the underwater vehicle  20  is launched, the launch and recovery device, as in FIG. 2, is lowered into the water to the desired depth by unwinding the cable  38  using a winch, not depicted in the figures, which controls the rate of descent, and the tension in the cable  38 . The rate at which the cable  38  is unwound is monotonous and may be roughly constant. The unwind rate may be several meters per second, for example 3 meters per second, which allows the underwater vehicle to be lowered quickly to the desired depth. 
     Once the cage  23  has reached the desired depth, the unwinding of the cable  38  is halted, and the unwinding of the cables  26  is commenced so as to increase the distance between the lower and upper chassis so as to release the underwater vehicle  20 . The cables  26  are unwound quickly to prevent the underwater vehicle from becoming unbalanced or damaged by the movement of the cage  23  which is due to the heave at the surface. The unwinding of the cables  26  may be accompanied by a winding up of the cable  38  at a rate slower than the rate at which the cables  26  are unwound, simultaneously parting the lower  24  and upper  25  chassis from the underwater vehicle  20 . At the same time as the cage  23  is opened up, the underwater vehicle reverses so as to leave the said cage  23  via the opening  28 . As a preference, the vertical dimension of the opening  28  of the cage  23  exceeds the amplitude of the vertical movement due to the heave, so that this movement cannot give rise to any impact between the cage  23  and the underwater vehicle  20 . 
     While the underwater vehicle  20  is carrying out its mission, the cage  23  can be raised back on board the boat, or can remain in the water at the depth at which the underwater vehicle  20  is released. 
     When recovering the underwater vehicle and the cage which has remained or has been lowered back into the water, the cables  26  are unwound so as to obtain an opening  28 , the vertical dimension of which is appreciably larger than the amplitude of the vertical movements due to the heave, namely a dimension of the order of 5 m, and which may be as much as 7 m. The underwater vehicle  20 , which may comprise guide means, for example acoustic beacons and sonars, which collaborate with guide means belonging to the cage  23 , for example sonar reflectors arranged on the elements of the cage  23 , is guided or remote-guided from the boat, by transmission means to enter the cage  23  via the opening  28 , preferably at the mean depth of the launch and recovery device, given the vertical movements of the said device. As the vertical dimension of the opening  28  is significantly greater than the amplitude of the vertical movements of the cage  23  which are brought about by the heave at the surface, the underwater vehicle  20  does not risk being damaged or unbalanced by knocking into the lower chassis  24  or the upper chassis  25 . 
     Once the underwater vehicle  20  is in position inside the cage  23 , in a space situated between the lower chassis  24  and the upper chassis  25 , the cables  26  are wound up so as to close the cage again to hold the underwater vehicle between the seating surface  6  of the cradle  1  and the rails  48 ,  49  of the upper chassis  25 . As a preference, the rate at which the cables  26  are wound up is high, to avoid successive impacts due to the relative movements between the underwater vehicle  20  and the seating surface  6  of the cradle  1  as the cradle  1  and the underwater vehicle  20  come into contact, as this could damage the underwater vehicle or unbalance it. For this purpose, use may be made of a rate of winding for the cables  26  which exceeds the maximum rate of vertical travel of the cage  23  due to the heave at the surface. Thus, the cradle  1  always moves vertically upwards relative to the underwater vehicle  20  which is subjected to little or no vertical movement due to the heave at the surface. 
     The concave wall  8  of the seating surface  6  allows the underwater vehicle  20  to be received on the cradle  1 , guiding it to position it in the horizontal plane. The shape of the concave wall  8  which has a vertical plane of symmetry, allows the underwater vehicle to be both centered on the cradle  1  and aligned longitudinally. The absorption stops  13 ,  16  make it possible to absorb the impacts as the underwater vehicle  20  and the seating surface  6  come into contact so as not to damage the underwater vehicle. 
     The cables  26  are wound up until the lower chassis  23  comes into contact with the stops  53  whose shape, frustoconical and open at the bottom, guides the studs  54  of the lower chassis  24  so as to position the lower chassis  24  accurately in the horizontal plane with respect to the upper chassis  25 . At the same time, the upper part of the underwater vehicle  20  comes into contact with the rails  48 ,  49  of the upper chassis  25 . Thus, when the cage  23  is closed again, the underwater vehicle is held between the cradle  1  and the rails  48 ,  49  which prevent any movement of the underwater vehicle  20  inside the cage  23 . The launch and recovery device can be raised back up to the surface by winding up the cable  38 . 
     The use of a single motor  38  driving a number of pulleys  40  on which the cables  26  are wound using mechanical angle gearboxes  44 ,  46 ,  47  and spindles  41 ,  42 ,  45  allows the winding-up of all the cables  26  to be synchronized so as not to unbalance the lower chassis  24  and so as to keep the lower chassis  24  roughly in a horizontal plane. The winding-up of the cables  26  can be synchronized in a different way, for example by using sensors and a number of slaved motors. 
     Furthermore, any connection between the lower chassis and the upper chassis that allows the vertical dimension to be varied will suit. A flexible connection, such as cables, chains or straps is particularly suitable because it can easily be wound up, for example onto pulleys. The use of rams may be envisaged. 
     When launching and recovering the underwater vehicle, the device according to the invention makes it possible to avoid the use of weighting ballast. What happens is that to accelerate the descent of the underwater vehicle  20  to its working depth and avoid the use of vertical propulsion means, the said underwater vehicle is generally provided with additional weighting ballast known as descent ballast which is jettisoned when the underwater vehicle reaches its working depth. To accelerate the raising of the underwater vehicle, weighting ballast known as raising ballast is jettisoned at the time of raising. 
     Now, the launch and recovery device allows the underwater vehicle to be launched and recovered directly at the working depth. Thus, during preparation, the underwater vehicle is directly weighted with a view to submerging it to the working depth. The mass of the vehicle at the times of its submersion is thus reduced because it does not contain any descent or raising weighting ballast, which may represent up to 10% of the total weight of the underwater vehicle. The time spent preparing the weighting ballast of the underwater vehicle is reduced. The jettisoning of this weighting ballast is also avoided, which represents a saving and at the same time avoids polluting the sea bed. 
     In addition, as the underwater vehicle does not use its own vertical propulsion means during the descent, it is possible to make a saving on the energy used by these propulsion means. As the amount of energy on board limits the operating autonomy of the underwater vehicle, an energy saving during the descent or the raising may increase the autonomy of the underwater vehicle or reduce the amount of energy held on board. 
     When the launch and recovery device is returned to the boat, the said device constitutes a support on which the underwater vehicle can be stored. In addition, as the lower chassis can be detached from the cradle, and as the lower chassis, resting on the framework  2  of the cradle  1  allows the underwater vehicle to pass through it vertically, the cage  23  can be lifted up, without lifting the cradle, as illustrated in FIG.  1 . Thus, access can be had to the underwater vehicle  20  to facilitate maintenance or preparation operations. The straps  19  and  22  allow the underwater vehicle  20  to be held more firmly on the cradle  1  in the absence of the upper cradle consisting of the rails  48 ,  49  of the upper chassis. 
     On one and the same boat, the device for launching and recovering an underwater vehicle allows the use of a number of underwater vehicles each stored on a cradle, using just the one cage for successively submerging the various underwater vehicles. 
     The device for launching and recovering an underwater vehicle from a boat in the form of a recovery cage with an opening the vertical dimension of which can be adjusted makes it possible to get around the drawbacks due to the vertical movements of the recovery cage which have as their origin the heave, that is to say the vertical movements of the boat to which the cage is connected and which are due to the swell at the surface of the water. 
     The device for launching and recovering an underwater vehicle therefore allows an underwater vehicle to be launched and recovered quickly at a depth close to the working depth of the said underwater vehicle, so that more of the on-board energy can be saved for the mission that the underwater vehicle is to carry out, and the use of descent ballast and raising ballast can be avoided. A saving is made in the time preparing the ballast on the underwater vehicle, and a saving in weighting ballast used and jettisoned onto the sea bed is also made. 
     The device for launching and recovering an underwater vehicle also allows the underwater vehicle to be stored on the boat, while at the same time affording the possibility of easy access to the underwater vehicle with a view to carrying out maintenance and preparation operations for a specific mission.