Connecting an Underwater Vehicle to a Tether

Abstract

The connection of an underwater vehicle by a tether and apparatus for such connection is disclosed. The apparatus comprises a drum which has a helical surface and which stores the tether so that the tether is unwound from the drum to allow the underwater vehicle to move away from the apparatus. The apparatus also includes a pulley system which engages with the tether and which also unwinds the tether from the drum. The apparatus further includes a pulley-drive and a drum-drive. The pulley-drive is operable in a forward mode to drive the pulley system for the unwinding of the tether and operable in a braking mode to resist the re-winding of the tether and the drum-drive is operable in a forward mode to drive the drum for the re-winding of the tether and operable in a braking mode to resist the unwinding of the tether.

What we claim is: 
     
         1 . Apparatus for connection to an underwater vehicle by a tether, comprising:
 a drum having a helical surface and which is configured to store said tether such that said tether is unwound from said drum to allow said vehicle to move away from the apparatus;   a pulley system configured to engage with said tether and unwind the tether from said drum;   a pulley-drive operable in a forward mode to drive said pulley system for the unwinding of the tether and operable in a braking mode to resist the re-winding of said tether; and   a drum-drive operable in a forward mode to drive said drum for the re-winding of said tether and operable in a braking mode to resist the unwinding of the tether.   
     
     
         2 . The apparatus of  claim 1 , wherein said tether conveys power, control signals and communication signals. 
     
     
         3 . The apparatus of  claim 2 , connectable to a surface device by an umbilical cable. 
     
     
         4 . The apparatus of  claim 3 , wherein said power and said control signal are received from said umbilical cable. 
     
     
         5 . The apparatus of  claim 1 , connectable to a surface device by an umbilical cable. 
     
     
         6 . The apparatus of  claim 4 , wherein said underwater vehicle is a remotely controlled vehicle configured to receive control signal from said surface device. 
     
     
         7 . The apparatus of  claim 1 , wherein said tether is buoyant in water. 
     
     
         8 . The apparatus of  claim 1 , wherein said helical surface is provided by a helical sleeve applied over a substantially smooth drum. 
     
     
         9 . The apparatus of  claim 1 , wherein said pulley-drive includes a first hydraulic motor and said drum drive includes a second hydraulic motor. 
     
     
         10 . The apparatus of  claim 9 , wherein:
 said pulley-drive receives a drive pressure and said drum-drive receives a lower braking pressure when unwinding the tether; and   said drum-drive receives a drive pressure and said pulley-drive receives a lower braking pressure when rewinding said tether.   
     
     
         11 . A method of unwinding a tether connected to an underwater vehicle, from an underwater drum to allow movement of said vehicle, said drum having a continuous groove defining a substantially helical surface, said method comprising the steps of:
 driving a pulley system configured to engage with said tether so as to unwind said tether from said drum; and   activating said drum so as to maintain transported tether between the drum and said pulley system in tension.   
     
     
         12 . The method of  claim 11 , wherein said pulley system includes:
 a primary pulley defining a radius of curvature for the tether and configured to engage on an internal surface of the tether; and   a plurality of support pulleys configured to engage with an external surface of the tether in opposition to said primary pulley.   
     
     
         13 . The method of  claim 11 , wherein said primary pulley defines a groove and said groove is configured to maintain contact with the tether during tether shrinkage at depth. 
     
     
         14 . The method of  claim 11 , including an exit port for allowing the unwinding of the tether from the apparatus in a substantially vertical direction. 
     
     
         15 . The method of  claim 14 , including a flexible support conduit for supporting the tether between the pulley system and said exit port. 
     
     
         16 . A method of rewinding a tether connected to an underwater vehicle, onto an underwater drum, said drum having a continuous groove defining a substantially helical surface, said method comprising the steps of:
 driving said drum so as to rewind said tether onto the drum; and   activating a pulley system configured to engage with the tether so as to maintain transported tether between the pulley system and the drum in tension.   
     
     
         17 . The method of  claim 16 , wherein a first layer of rewound tether is forced into said groove due to the activation of said pulley system maintaining the tether in tension. 
     
     
         18 . The method of  claim 17 , wherein said first layer of rewound cable defines a secondary helical groove and a second layer of rewound tether is forced into said secondary groove. 
     
     
         19 . The method of  claim 16 , wherein said underwater vehicle is restrained by a spring-loaded device when the tether has been fully re-wound. 
     
     
         20 . The method of  claim 18 , wherein said underwater vehicle is restrained by a spring-loaded device when the tether has been fully re-wound.