Patent Publication Number: US-11046403-B2

Title: Underwater body having a variable volume and method for operating such an underwater body

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. National Stage Entry of International Patent Application Serial Number PCT/EP2018/068489, filed Jul. 9, 2018, which claims priority to German Patent Application No. DE 10 2017 115 601.1, filed Jul. 12, 2017, the entire contents of both of which are incorporated herein by reference. 
     FIELD 
     The present disclosure generally relates to an underwater body having a movable component which can be moved into an extended position. 
     BACKGROUND 
     An underwater body, for example an autonomous unmanned underwater vehicle (AUV) or an underwater mobile body or underwater glider, often has to be transported in an aircraft or watercraft to a site of use if a coast has poor land-side or sea-side accessibility, an entry device is not installed on land or a floating transport platform cannot be used, for example on account of a high swell or rocks. Transporting an underwater body in an aircraft, for example in a helicopter, requires the underwater body to be very compact in shape. Such a compact design of the underwater body, however, creates the disadvantages in the water of insufficient buoyancy and/or unfavorable thickness of the underwater body and, where applicable, unfavorable running characteristics. 
     Then again, on account of the tight space available in an aircraft, small dimensioning of the underwater body and, in many cases on account of dropping the underwater body from the aircraft, a high thickness of the underwater body is desired for quick immersion into the water. 
     DE 836603 C shows a small submarine boat, the boat body of which consists of two parts a and b which are inserted into one another. More precisely: The longitudinal wall of part a has two individual walls, between which part b is inserted. Part b can be displaced linearly relative to part a. By part b being moved away from part a, the volume of the small submarine is increased. Two oppositely situated gear racks e each engage in a transmission. The rear ends of the gear racks e are fixedly connected to part b and the two transmissions are fixedly connected to part a. The two drives of the gear racks e are coupled together. 
     FR 2830837 A1 shows an underwater vehicle (PAP  104 —«Poisson Auto Propulse», P), which is guided by a cable (filoguidé) and, for example, is able to destroy mines on the seabed. After use, said underwater vehicle PAP  104  is to come back up to the surface. Consequently, two balloons are received in the folded state (deux ballons replies  1   c ) in a hollow space which is closed by a two-part closure (deux demi carénage  1   c ), cf.  FIG. 1 . A lock (verrou  1   h ) connects the two closure parts  1   c  together (deux demi carenage  1   c , fixes entre eux, pour la navigation, par les verrous  1   h ). Each balloon  1   a  is mounted by means of a holding element (contre-forme  1   e ) onto the inner wall of a closure part  1   c . Each closure part  1   c  is mounted in such a manner on a receiving unit (adapteur  4 ) that the closure part  1   c  is pivotable about an axis  1   g.    
     Each balloon is able to receive, for example, seven liters in the inflated state  1   b , cf.  FIG. 1 . From a compressed air source (l&#39;actionneur d&#39;air  6 ), compressed air can be conducted via a pneumatic connection (distribution de l&#39;air  5 ) into a balloon  1   a ,  1   b  in order to inflate it. Said source  6  includes, for example, a compressed air bottle  6   a  (bouteille de gaz comprime  6   a ) with a connection body (corps  6   b ) and a displaceable piston (piston coulissant  6   c ) which selectively enables or prevents the outlet of compressed air, cf.  FIG. 3 . 
     FR 2943615 A1 shows an underwater body (flotteur) having a hull (fuselage  101 ) on which two movable cylindrical components (deux appendices mobiles  121 ,  122  cylindriques) are mounted. Each component  121 ,  122  can be displaced along an axis  12  which is perpendicular to the longitudinal axis  11  of the hull  101 .  FIG. 1 a    shows the two components  121 ,  122  in a retracted position (position rentre),  FIG. 1 b    in an extended position (position sorti). If the components  121 ,  122  are retracted, the underwater body has its minimum volume and when they are extended, it has its maximum volume. 
     In one design, a double-acting piston-cylinder unit (verin à double effet) can displace a component  121  relative to the hull  101 , cf.  FIG. 2 a   . The cylinder  151  is mounted on the hull  101  and the piston rod  152  is mounted on the component  121 . A ball bearing  161 ,  162 ,  163  prevents the ingress of water. In another design, a flexible membrane (membrane souple  181 , membrane  182 ) is mounted between the component  121  and the hull  101 , cf.  FIG. 2 b    and  FIG. 2   c.    
     U.S. Pat. No, 6,923,105 B1 describes an underwater mobile body (counter-measure device  10 ) having a cylindrical shell  12 , said mobile body being able to destroy an attacking torpedo. A drive (thrusters  22 ), a weapon (gun  14 ) and multiple inflatable chambers (inflatable chambers  24 ) are mounted on the shell  12 . Thanks to said inflatable chambers  24 , the center of gravity (center of mass) of the body  10  is close to the center of buoyancy. 
     Thus a need exists for an underwater body which cause, in a simple manner, the movable component to be moved into the extended position and to remain there. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a schematic sectional view of an underwater body with a folding shell. 
         FIG. 2  is a schematic sectional view of an underwater body with a displaceable shell segment in the front region of the underwater body. 
         FIG. 3  is a schematic sectional view of an underwater body with a slide-out shell segment and a propeller drive arranged thereon. 
     
    
    
     DETAILED DESCRIPTION 
     Although certain example methods and apparatus have been described herein, the scope of coverage of this patent is not limited thereto. On the contrary, this patent covers all methods, apparatus, and articles of manufacture fairly falling within the scope of the appended claims either literally or under the doctrine of equivalents. Moreover, those having ordinary skill in the art will understand that reciting “a” element or “an” element in the appended claims does not restrict those claims to articles, apparatuses, systems, methods, or the like having only one of that element, even where other elements in the same claim or different claims are preceded by “at least one” or similar language. Similarly, it should be understood that the steps of any method claims need not necessarily be performed in the order in which they are recited, unless so required by the context of the claims. In addition, all references to one skilled in the art shall be understood to refer to one having ordinary skill in the art. 
     The invention relates to an underwater body having a movable component which can be moved into an extended position and, as a result, increases the volume of the underwater body. In addition, the invention relates to a method for operating such an underwater body. 
     The underwater body according to the solution includes
         a shell,   a movable component,   an expansion means and   a hollow space.       

     The movable component can be moved relative to the shell from a retracted position into an extended position. When the movable component is moved from the retracted into the extended position, the volume of the underwater body is increased. 
     The expansion means is able to conduct a fluid into the hollow space. The hollow space is operatively connected to the movable component. The operation of conducting fluid into the hollow space causes the movable component to be moved into the extended position. 
     The fluid in the hollow space hardens. The hardened fluid holds the movable component in the extended position. 
     The underwater body according to the invention is able to change its volume automatically. If the movable component is in its retracted position, the underwater body thus has a smaller volume. If the movable component is in the extended position, the underwater body thus has a larger volume. As a result, the underwater body meets the two contradictory requirements, namely that the underwater body, on the one hand, is to have as small as possible a volume during transport and, on the other hand, is to have a sufficiently large volume when used in water. It is generally well-known that the buoyancy that a body experiences in the water is equal to the weight of the water displaced by the body. Attempts are made in many applications for the buoyancy of an underwater body to be approximately equal to the weight so that it is not necessary or is only necessary to a certain extent to hold the underwater body at a desired depth of water with the help of an elevator. An elevator only changes the diving depth when the underwater body is moved, whilst a change in volume is also effective on an underwater body which is not currently being moved through the water. 
     A further advantage of the invention is achieved, in particular, when the underwater body is to be thrown out of an aircraft or a surface craft. The underwater body is to reach a desired water depth once it has contacted the water. As long as the underwater body is in the water and above said water depth, the buoyancy is to be less than the weight so that the underwater body sinks. The invention makes it possible to move the movable component such that it assumes the extended position once it has reached the desired water depth. 
     It is also possible for the underwater body with the movable component to carry out a predetermined task in the retracted position and then to move the movable component into the extended position. The underwater body can comprise a desired hydrodynamic form when the movable component is in the retracted position. By the movable component being moved into the extended position, the volume of the underwater body is increased in such a manner that the buoyancy is greater than the weight and the underwater body floats to the surface where it can be collected again. 
     The movable component in the retracted position additionally reduces the risk in many cases of the underwater body being damaged during transport and also when being thrown into the water. 
     According to the solution, the expansion means conducts a fluid into the hollow space. The hollow space is connected to the movable component. The movable component is moved into the extended position by the fluid being introduced into the hollow space. Said feature avoids the necessity for an actuating drive, for example an electric linear motor or a hydraulic piston-cylinder unit, to move the movable component. Such an actuating drive has to be supplied with power and has to be coupled mechanically with the movable component. The expansion means just needs to be fluidically connected to the hollow space. Such a fluidic connection can be produced in an easier manner in many applications than a mechanical connection between an actuating drive and the movable component. However, it is possible to combine the expansion means according to the solution with an actuating drive for the movable component. 
     According to the solution, the fluid in the hollow space hardens. The hardened fluid holds the movable component in the extended position. The hardened fluid prevents the pressure of the surrounding water moving the movable component away from the extended position again. The volume of the underwater body and consequently substantially also of the buoyancy remain constant. 
     Said features result in a particularly simple design in order to hold the movable component in the extended position. The fluid hardens by itself in the hollow space without it being necessary to measure a characteristic of the fluid or to act upon the fluid in the hollow space. It is possible, but thanks to the invention not necessary, for a locking unit to be activated and to hold the movable component in the retracted position. The mechanism to increase the volume of the underwater body consequently requires only a few components which are moved actively and in a controlled manner, in particular a component which triggers the introduction of the fluid into the hollow space. The movable component itself can be designed as a purely passive component. 
     In one embodiment, the movable component surrounds the hollow space fully or at least in part. The expansion means conducts the liquid fluid therefore into a hollow space in the interior of the movable component. The introduction of fluid results in the movable component being moved into the extended position relative to the shell. The fluid hardens in the interior of the movable component and, as a result, holds the movable component in the extended position. Said design makes a particularly compact construction possible. 
     In a further embodiment of the invention, the hollow space is connected to the movable component via a piston-cylinder unit. The hollow space is formed in a chamber of the piston-cylinder unit. The expansion means therefore conducts the fluid into said chamber, the fluid in the chamber displaces the piston, the displacement of the piston displaces the movable component into the extended position and the fluid hardens in said chamber. Said design makes it possible to arrange the further component remotely in space from the hollow space for the fluid. The further component does not necessarily need to have a hollow space. Said design makes it easier to design the movable component and to adapt it to the predetermined requirements, for example to a desired hydrodynamic form of the underwater body. 
     In one design, a flat element is mounted on the outside of the shell of the underwater body. The flat element is associated with the movable component and can be pivoted relative to the shell. By the flat element being pivoted away from the shell, the flat element is moved into an extended position and the volume of the underwater body is increased. The hollow space is formed between the flat element and the outside of the shell. Said design makes it easier to produce the shell of the underwater body from one single piece and/or to design it such that the shell can withstand a predefined water pressure. The space in the interior of the shell is available entirely for further components of the underwater body. 
     In one embodiment, the flat element surrounds the hollow space fully. In another design, the flat element only surrounds the hollow space in part in the extended position. The hardened fluid in the hollow space comes into contact with the surrounding area, for example with the surrounding water. 
     In one design, the shell of the underwater body extends along a longitudinal axis. The movable component can be displaced relative to the shell along the longitudinal axis, that is to say in a direction of movement parallel to the longitudinal axis. The movable component can form a segment of the shell. It is possible for the movable component to overlap in a telescopic manner with the shell or the rest of the shell in the retracted position. A flexible seal can be arranged between the movable component and the shell or the rest of the shell. 
     By the movable component being displaced into the extended position along the longitudinal axis, the length and the volume of the underwater body are increased. Said design makes it possible for the diameter or more generally the dimension of the underwater body in a plane perpendicular to the longitudinal axis to remain constant, irrespective of the position of the movable component. The hydrodynamic characteristics of the underwater body are not modified essentially when the movable component is moved into the extended position. 
     The movable component can be arranged, in particular, at the stern or at the bow of the shell of the underwater body. It is also possible for the movable component to be moved into the extended position in a direction perpendicular to the or at an angle to the longitudinal axis. 
     The expansion means is arranged in a preferred manner in the interior of the shell and in one design outside the movable component. The shell protects the expansion means from environmental influences. When the expansion means is arranged outside the movable component, it is not entrained when the movable component is moved relative to the shell. As a result, only a small mass needs to be moved. 
     The fluid is in a liquid or gaseous state when it flows into the hollow space and hardens in the hollow space. In one design the fluid is completely present on board the underwater body. In another design, a substance is conducted into the hollow space on board the underwater body. The operation where the fluid in the hollow space hardens is brought about at least in part as a result of surrounding water being conducted into the hollow space. The water in the hollow space causes the substance in the hollow space to harden. The fluid in the hollow space hardens for example by a chemical process or by being heated. 
     In one design, the fluid is an assembly foam and/or includes polyurethane. It is possible to use an assembly foam which is also usable for sealing buildings. Said design saves it being necessary to produce a special fluid. Rather, commercially available assembly foam can be used. The expansion means includes at least one container, for example a cartridge, with the assembly foam. By an opening being opened in said or any cartridge, the assembly foam leaves the cartridge and is conducted into the hollow space. The expansion means preferably includes multiple cartridges so that even if one cartridge fails there is still sufficient fluid available. The fluid is preferably held in a liquid state at an overpressure in the or each cartridge. In a preferred manner, the or each cartridge is a single-use container for the fluid. 
     In one design, at least one container is produced beforehand with the fluid and is moved into the underwater body. In another design, the fluid or at least one component of the fluid is generated in the underwater body itself, for example by means of a chemical process. 
     After hardening, the fluid in the hollow space is mechanically stable. At least prior to hardening, the fluid includes, for example, isocyanate and polyalcohol in an aerosol mixture. As soon as the fluid has left the container and has been admitted into the hollow space, the fluid foams and reacts with the moisture in the air or with the moisture on the inside walls of the hollow space. It is also possible for the liquid fluid in the container to include two different components which react with one another in the hollow space, the one component functioning as a cross-linking agent and or as a hardener. Said two components can be mounted in two different containers and only react together in the hollow space. 
     Fluid is preferably admitted into the hollow space at the same time via multiple inlets. Said design leads to a uniform distribution of the fluid in the hollow space compared to a design where the fluid only flows into the hollow space through one single inlet. 
     According to the solution, the movable component is moved as a result into the extended position where the expansion means conducts the fluid into the hollow space. In one design, an actuating drive additionally moves the movable component into the extended position relative to the shell. The combination of said two mechanisms in order to move the movable component saves time and causes redundancy. If the one mechanism fails, in a preferred manner the other mechanism thus brings about the desired volume increase on its own. 
     In one design, a locking unit can be moved from a locking state into a release state. The locking unit includes, for example, a flap element and/or a wedge element. In the locking state, the locking units locks the movable component. In the release state, the locking unit makes it possible for the movable component to be moved relative to the shell. The locking unit in the locking state prevents an unwanted movement of the movable component relative to the shell. It is possible for the actuating drive to function additionally as the locking unit or for a locking unit to be used in addition to the actuating drive. 
     In a continuation of said design, the locking unit holds the movable component in the retracted position. As a result, the locking unit prevents, in particular, the movable component being moved out of the retracted position unintentionally during transport of the underwater body. This ensures that the underwater body retains its smallest possible volume during transport. It is also possible for the locking unit to hold the movable component in an extended position. 
     In one design, an actuating member transfers the locking unit from the locking state into the release state. In another design, the introduction of fluid into the hollow space causes the locking unit to be transferred into the release state, for example by the pressure of the fluid in the hollow space forcing the locking unit into the release state or also by the locking unit breaking so that it no longer exerts a locking function. 
     In one design, a fluid sensor on board the underwater body measures how much fluid is conducted into the hollow space. Said fluid sensor measures a measurement for the amount of fluid, for example a time interval or a pressure which the fluid exerts on the outer shell or, in the event of a movable component with a flexible outer shell, a measurement for the pressure which the fluid exerts on the outer shell. The expansion means conducts fluid into the hollow space until a predetermined amount of fluid is in the hollow space. The expansion means works independently of signals from the fluid sensor. As soon as the predetermined amount of fluid is in the hollow body, the expansion means terminates the operation conducting fluid into the hollow space. Said design is a possibility to move the movable component into a certain extended position and consequently to obtain a certain volume of the underwater body. 
     According to the solution, the movable component can be moved from the retracted into the extended position. In this connection, the movable component executes a movement relative to the shell. In one design, a stop element delimits the possible movement of the movable component away from the shell. Said stop element consequently defines the extended position of the movable component and accordingly the maximum achievable volume of the underwater body. Said design makes it superfluous to monitor the fluid flowing into the hollow space and to control or regulate the enclosed amount of fluid in order to obtain a desired extended position of the movable component and consequently a desired volume of the underwater body. It is sufficient to introduce at least one predetermined amount of fluid into the hollow space and to allow it to harden there. The stop element delimits the movement of the movable component, even if the entire amount of fluid is conducted into the hollow space. Said design further reduces the number of actively moved components necessary and/or of underwater body sensors. 
     In a continuation of said design, the stop element can be fixed in a position relative to the shell, said position being selected from multiple possible positions. The operation to fix the stop element in a selected position can be carried out prior to the use of the underwater body. By a certain position being selected and the stop element being fixed in said selected position, a volume of multiple volumes of the underwater body can be obtained with the movable component in an extended position. Said design leads to a particularly simple mechanism for obtaining a desired volume and saves on an actuatable actuating drive which holds the movable component in a desired position, as well as a fluid sensor. The designs with the stop element and with an actuating drive or the fluid sensor can also be combined together. 
     In one design, the movable component is moved into the extended position once the underwater body has been thrown out of, for example, an aircraft or a surface craft and then a predetermined interval has passed. In one design, the underwater body activates the expansion means automatically and as a result automatically triggers the step of conducting fluid into the hollow space as a reaction to the detection of an event. A sensor which automatically detects said event is present on board the underwater body. The event can be, for example, that the underwater body is situated in the water or that the underwater body is situated at a water depth that is greater than or equal to a predetermined water depth. The sensor measures, for example, the pressure of the surrounding water. It is possible for the expansion means to be activated after the sensor has detected the event and a predetermined interval has passed. It is also possible for a time switch to be activated and to detect the event where a predetermined interval has passed since activation of the time switch. The detection of said event triggers the step of activating the expansion means. 
     The design with the sensor makes it easier to carry out the increase in volume such that the underwater body with the increased volume is held at a certain water depth. If the underwater body itself can measure the current water depth, it is not necessary to predetermine an interval and the correct point in time for increasing the volume depends to a lesser extent on the environmental conditions such as water currents and water temperature and saline content. 
     In one design, the movable component is a rigid component or has at least a rigid outside shell. As a result, the movable component is only deformed insignificantly when the underwater body is exposed to the water pressure underwater. The underwater body retains its hydrodynamic form substantially also at different diving depths. 
     In another design, the movable component has a flexible outer shell, for example in the manner of a balloon or a windsock. Said design makes it possible to mount the flexible component with little space, for example in the interior of the shell, for as long as the flexible component is to remain in the retracted state. In order to move the movable component into the extended position, the fluid is conducted into the movable component. The introduced fluid expands the flexible outer shell, as a result increases the volume of the movable component and then hardens in the enlarged movable component. For example, the fluid inflates the flexible outer shell and then hardens in the inflated outer shell. 
     The underwater body is designed for the purpose of being used underwater and can comprise its own drive or can be towed through the water by another vehicle. The underwater body can be designed for civil and/or for military purposes and can include sensors and/or actuators. 
     In one design, the underwater body can operate autonomously, i.e. without instructions from the outside. For example, the underwater body is an unmanned autonomous underwater vehicle (AUV) or also a manned submarine. The underwater body automatically triggers the step of the expansion means conducting the fluid into the hollow space. 
     In another design, the underwater body is designed for the purpose of receiving control commands from a spatially remote platform, for example from a surface ship or an aircraft. The underwater body is, for example, a remotely controlled unmanned underwater vehicle (ROV, remotely operated vehicle), an underwater robot, an underwater glider or an underwater mobile body, for example a torpedo, which is controlled via fiber optic cable. Such a control command causes, for example, the expansion means to conduct the fluid into the hollow space. The control commands are directed to the underwater body wirelessly, in particular via underwater communication or via a cable from the spatially remote platform. 
     In a possible application, the underwater body is thrown out of an aircraft, for example a helicopter or an airplane, and falls into the water. The aircraft transports the underwater body to a desired site of use. In another possible application, the underwater body is thrown into the water from a platform in the water, for example from a surface ship or a stationary platform in the water. The movable component is in the retracted position, whilst the underwater body is transported by the aircraft or marine craft so that the underwater body has the smallest possible volume during transport. The ejected underwater body sinks in the water. Once the underwater body is fully in the water and, for example, a predetermined water depth has been reached, the movable component is moved into the extended position and the volume of the underwater body in the water is increased so that the buoyancy which acts on the underwater body is also increased. 
     In one design, the underwater body now has such a volume where the weight of the displaced water is approximately equal to the weight of the underwater body and the underwater body roughly floats in the water. In another design, the weight of the displaced water is greater than the weight of the underwater body so that the underwater body rises to the surface of the water again and can be collected. 
     The three figures show an underwater body  101 ,  201 ,  301  which travels from left to right in a direction of travel. 
       FIG. 1  shows a first exemplary embodiment of the invention. An underwater body  101  comprises a shell  103 . A folding shell  107  is arranged on the outside of the shell  103 . The folding shell  107  is segmented and in a preferred manner is arranged extending all around a longitudinal axis of the underwater body  101  and is fastened by means of pivot joints  109  to the shell  103  of the underwater body  101 . The pivot joints  109  are connected to an actuating motor  111 . A first assembly foam cartridge  113 , a second assembly foam cartridge  115 , a third assembly foam cartridge  117  and a fourth assembly foam cartridge  119  are situated in the interior of the underwater body  101  in each case on an underside and upper side, therefore there is a total of eight cartridges. A respective outlet of the respective assembly foam cartridges  113 ,  115 ,  117  and  119  is guided to the outside through the shell  103  of the underwater body  101  and they are situated between the folding shell  107  and the outside of the shell  103 . The cartridges  113  to  119  are associated with the expansion means of the first exemplary embodiment. 
     In addition, the expansion means includes a component which holds the assembly foam  121  in the cartridges  113  to  119  in the liquid or foam state and as a result prevents the assembly foam  121  from hardening already in a cartridge  113  to  119 , which is unwanted. The underwater body  101  comprises a propeller drive  105  at the stern. 
     Whilst the underwater body  101  is transported, for example, in an aircraft, the folding shell  107  is in a transport position in which the flap  107  abuts directly against the shell  103  of the underwater body. The folding shell  107  is locked in said stowed position by means of a predetermined breaking point. The underwater body  101  is thrown out of the aircraft, not shown, above the planned site of use into the sea or another body of water and is immersed into the water. 
     The underwater body  101  is automatically transferred from the transport position into a driving position when a predetermined event has occurred.  FIG. 1  shows the folding shell  107  in said driving position. Said predetermined event occurs, for example, when a predetermined interval since the ejection from the aircraft has passed. Or a sensor (not shown) of the underwater body  101  detects the event where the underwater body  101  has reached the water and the predetermined event then occurs when a predetermined interval has passed after said detection. Or a depth sensor on-board the underwater body  101  measures the current diving depth of the underwater body  101  sinking in the water and situated in the transport position. As soon as the measured current diving depth matches a predetermined diving depth, the step of transferring the underwater body from the transport position into the driving position is automatically triggered. 
     The following steps are carried out during the transfer from the transport position into the driving position: The actuating motor  111  releases the pivot joints  109 . The four assembly cartridges  113 ,  115 ,  117  and  119  are activated. For example, one opening in each cartridge  113  to  119  is opened. As a result, assembly foam  121  is released from the assembly foam cartridges  113 ,  115 ,  117  and  119 , for example because the liquid assembly foam  121  in the cartridges  113  to  119  was under overpressure. The releasing of the assembly foam  121  causes the predetermined breaking point to break and the lock is freed as a result. The released assembly foam  121  presses against the flap  107 . In addition, the actuating motor  111  pivots the folded shell  107  away from the shell  103  of the underwater body  101 . As a result of said two effects combined together the flap  107  is moved away from the shell  103  and folded out to its maximum position. A hollow space is formed between the folded-out folding shell  107  and the shell  103 . Said hollow space is filled with assembly foam  121 . The assembly foam  121  hardens and as a result locks the folding shell  107  permanently. The folding shell  107  now has the form of a truncated cone which surrounds the shell  103 . The diameter of the folding shell  107  increases in a direction toward the stern of the underwater body  101  so that a favorable hydrodynamic form continues to be obtained. 
     Because the folding shell  107  is held permanently in the maximum position, the volume of the underwater body  101  is permanently increased. It is also possible for the folding shell  107  only to be pivoted out to an intermediate position and for the assembly foam  121  to hold the folding shell  107  in said intermediate position. In one design, the position into which the folding shell  107  is to be folded out and locked there is set in advance in a control program. Said position can depend on a desired water depth and/or on a water temperature. In another design, a stop element (not shown) delimits the possible movement of the folding shell  107  away from the shell  103 . In a preferred embodiment, said stop element can be fixed in one of multiple possible positions so that a volume selected from multiple possible volumes of the underwater body  101  is obtained. 
     In a modification, each folding shell  107  is connected respectively to a spring element. Said spring element attempts to hold the folding shell  107  in the transport position, that is to say in the position at which the folding shell  107  abuts against the shell  103  of the underwater body  101 . The released assembly foam  121  pivots the folding shell  107  against the spring force of said spring element away from the shell  103 . The position which the pivoted-out folding shell  107  reaches depends, on the one hand, on the spring force and, on the other hand, on the amount of assembly foam  121  released. At least one of said two parameters can be set in dependence on the desired water depth and/or the water temperature. 
       FIG. 2  shows a second exemplary embodiment of the invention. The underwater body  201  comprises a shell  203  and a propeller drive  205 . The shell  203  of the underwater body  201  includes a sequence with four shell segments, namely when seen in the direction of travel from left to right, a first shell segment  223 , a second shell segment  225 , a third shell segment  227  and a fourth shell segment  229 . A first assembly foam cartridge  213  and a second assembly foam cartridge  215  are fastened to the shell  203  for example to the first shell segment  223 . In each case an outlet of the cartridge  213  and  215  leads into the interior of the second shell segment  225 . The second shell segment  225  can be displaced relative to the third shell segment  227  along the longitudinal axis of the underwater body  201 . An optional linear motor  231  can move the second shell segment  225  relative to the shell  203 . A guide device (not shown) preferably guides the second shell segment  225  in a movement relative to the third shell segment  227 . 
     In the transport position, the second displaceable shell segment  225  is pushed above the third shell segment  227 , for example telescopically, such that the second shell segment  225  overlaps in part with the third shell segment  227 . The second shell segment  225  abuts in part against the first shell segment  223 . Consequently, the underwater body  201  comprises a compact form with the shortest possible length and the smallest possible volume. A flexible seal is preferably arranged between the second shell segment  225  and the third shell segment  227 . A flexible seal is also arranged in a preferred manner between the second shell segment  225  and the first shell segment  223 . Said flexible seals retain their sealing effect even when the second shell segment  225  is moved. 
     As soon as the above-described event has occurred, the underwater body  201  is automatically transferred into a driving position.  FIG. 2  shows the underwater body  201  in said driving position. The following steps are carried out during the transfer: Assembly foam  221  exits from the first assembly foam cartridge  213  and the second assembly foam cartridge  215 . The emerging assembly foam  221  causes the second shell segment  225  to be displaced away from the third shell segment  227 . As a result, the length and the volume of the underwater body  201  are increased. In addition, as an option, the linear motor  231  moves the second shell segment  225 . It is additionally possible for a gas, for example compressed air, to be admitted into the second shell segment  225  and additionally to contribute to the displacement of the second shell segment  225 . By the second shell segment  225  being displaced, a hollow space is formed in the interior of the second shell segment  225 . The assembly foam  221  flows into the second shell segment  225  and hardens there. The hardened assembly foam  221  prevents ingress of water into the hollow interior of the shell segment  225 . 
     In one design, the first segment  223  is fixedly connected to the shell segment  225  and is also displaced away from the third shell segment  227 . In another design, the diameter of the second shell segment  225  is greater than the diameter of the first shell segment  223 . As a result, the volume of the underwater body  201  is also increased when the first shell segment  223  is fixedly connected to the third shell segment  227 . 
     In both designs, the emerging assembly foam  221  hardens in the hollow space generated and, as a result, fixes the displaceable second shell segment  225  relative to the third shell segment  227 . The amount by which the volume is increased depends on the amount of assembly foam  221  released, which can be adjusted. In one design, the linear motor  231  and/or a stop element (not shown) delimit the possible movement of the second shell segment  225  away from the third shell segment  227  and, as a result, establish the amount of the volume increase. 
       FIG. 3  shows a third exemplary embodiment of the invention. The underwater body  301  has a shell  303  which is subdivided into a sequence of five shell segments, namely into a first shell segment  323 , a second shell segment  325 , a third shell segment  327 , a fourth shell segment  329  and a fifth shell segment  333 . The fifth shell segment  333  is arranged at the stern of the underwater body  301  and carries the propeller  305 . At the bow-side, the fifth shell segment  333  is connected to a first assembly foam cartridge  313  and a second assembly foam cartridge  315 . The cartridges  313  and  315  are mounted on the rear wall of the fourth segment  329  and their outlets lead into the fifth shell segment  333 . The first four shell segments  323  to  329  are fixedly connected together. The fifth shell segment  333  surrounds a hollow interior and can be displaced rearward relative to the fourth shell segment  329  along the longitudinal axis of the underwater body  301 . A guide device preferably guides the fifth shell segment  333  in a movement relative to the fourth shell segment  329 . 
     When the underwater body  301  is in the transport position, the fifth shell segment  333  is inserted into the fourth shell segment  329 . A locking wedge, not shown, locks the fifth shell segment  333  in said position. The propeller drive  305  abuts directly against the stern-side end of the fourth shell  329 . 
       FIG. 3  shows the underwater body  301  in the driving position. In order to transfer the underwater body  301  into the driving position, the following steps are carried out: The lock of the fifth shell segment  333  is released. The assembly foam  321  is released from the first assembly foam cartridge  313  and the second assembly foam cartridge  315 . The released assembly foam  321  penetrates into the hollow space in the interior of the fifth shell segment  333 . The released assembly foam  321 , as a result, exerts a pressure on the fifth shell segment  333 . As a result of said pressure, the fifth shell  333  including the propeller drive  305  is pushed out of the fourth shell segment  329 , away from the fourth shell segment  329 . The released assembly foam  321  fills the hollow space in the fifth shell segment  333  entirely or at least in part and hardens. As a result, the fifth shell segment  333  is permanently fixed in the extended position. 
     In one design, the optional linear motor  331  pushes the fifth shell segment  333  away from the fourth shell segment  329 . It is possible additionally for a gas, for example compressed air, to be conducted into the fifth shell segment  333 . In one design, the linear motor  331  and/or a drive element (not shown) delimits the linear movement of the fifth shell segment  333  away from the fourth shell segment  329 . Once again, the amount of the volume increase can be adjusted by the amount of the released assembly foam  321  and/or the distance over which the linear motor  331  displaces the fifth shell segment  333  being correspondingly adjusted or by the stop element being correspondingly fixed. 
     LIST OF REFERENCES 
     
         
           101  Underwater body of the first exemplary embodiment 
           103  Shell of the underwater body  101   
           105  Propeller drive of the underwater body  101   
           107  Folding shell with which the pivoting joint  109  is pivotably mounted on the shell  103   
           109  Pivot joint in which the flap  107  is pivotably mounted on the shell  103   
           111  Actuating motor, can pivot the folding shell  107   
           113  First assembly foam cartridge, mounted in the interior of the shell  103   
           115  Second assembly foam cartridge, mounted in the interior of the shell  103   
           117  Third assembly foam cartridge, mounted in the interior of the shell  103   
           119  Fourth assembly foam cartridge, mounted in the interior of the shell  103   
           121  Assembly foam from the four cartridges  113  to  119   
           201  Underwater body of the second exemplary embodiment 
           203  Shell of the underwater body  201   
           205  Propeller drive of the underwater body  201   
           213  First assembly foam cartridge, mounted in the first shell  223   
           215  Second assembly foam cartridge, mounted in the first shell  223   
           221  Assembly foam from the two cartridges  213  and  215   
           223  First shell segment of the shell  203   
           225  Second, displaceable shell segment of the shell  203   
           227  Third shell segment of the shell  203   
           229  Fourth shell segment of the shell  203   
           231  Linear motor for displacing the second shell segment  225   
           301  Underwater body of the third exemplary embodiment 
           303  Shell of the underwater body  301   
           305  Propeller drive of the underwater body  301 , mounted on the fifth shell segment  333   
           313  First assembly foam cartridge, mounted in the fourth shell segment  329   
           315  Second assembly foam cartridge, mounted in the fourth shell segment  329   
           321  Assembly foam from the two cartridges  313  and  315   
           323  First shell segment of the shell  303   
           325  Second shell segment of the shell  303   
           327  Third shell segment of the shell  303   
           329  Fourth shell segment 
           331  Linear motor for displacing the fifth shell segment  333   
           333  Fifth, slide-out shell segment, carries the propeller drive  305