Abstract:
A system for retrieving a device from the bottom of a body of water includes a clamp configured to be slidably affixed to the device above the water bottom. The clamp has a selectively engageable lock to fix a position of the clamp on the device. A line ratchet is coupled to the clamp. A line is disposed through the line ratchet. A first flotation device is coupled to one end of the line. A second flotation device is coupled to the other end of the line. The system includes means for applying tension to the line disposed proximate the second flotation device. The line ratchet is arranged to enable movement of the line therethrough toward the means for applying tension, and is also arranged to substantially prevent motion therethrough in the opposite direction.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    Not applicable. 
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not applicable. 
       BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    The invention relates generally to the field of equipment such as cables and conduits deployed on the bottom of a body of water. More specifically, the invention relates to devices for recovering such cables or conduits after they have been deployed on the water bottom for a selected length of time. 
         [0005]    2. Background Art 
         [0006]    The invention is related to a device that is intended to be attached to equipment or material, e.g., a seismic sensor cable or a conduit, disposed on the bottom of a body of water such as a lake or the ocean. When so disposed, recovery can be difficult due to the device being covered with ocean bottom material. As a result, recovery of the equipment can be a slow difficult process. Recovery of the equipment requires that the equipment is pulled laterally and axially out of the entrapping bottom sediments. The equipment will eventually come out of the bottom sediments if pulled on with sufficient stresses and for a long enough period of time. A difficulty with the foregoing recovery method is that the equipment is often damaged from the stresses applied and personnel and recovery equipment spend a substantial amount of time pulling on the equipment to dislodge it from the water bottom sediment rather than attending to the other duties. 
         [0007]    Accordingly, there exists a need for better methods and devices for recovering equipment deployed on the bottom of a body of water. 
       SUMMARY OF THE INVENTION 
       [0008]    A system according to one aspect of the invention for retrieving a device from the bottom of a body of water includes a clamp configured to be slidably affixed to the device above the water bottom. The clamp has a selectively engageable lock to fix a position of the clamp on the device. A line ratchet is coupled to the clamp. A line is disposed through the line ratchet. A first flotation device is coupled to one end of the line. A second flotation device is coupled to the other end of the line. The system includes means for applying tension to the line disposed proximate the second flotation device. The line ratchet is arranged to enable movement of the line therethrough toward the means for applying tension, and is also arranged to substantially prevent motion therethrough in the opposite direction. 
         [0009]    A method for retrieving a device disposed on the bottom of a body of water according to another aspect of the invention includes slidably affixing a cable clamp to a part of the device disposed above the water bottom. The cable clamp is moved proximate the water bottom. The clamp is locked in place on the device. Lifting force is applied to one end of a line. The line is functionally coupled to the clamp through an element enabling movement of the line in only one direction. Lifting force is applied to the other end of the line. The line is retracted from one of the ends thereof. The retracting includes moving the line through the element. 
         [0010]    Other aspects and advantages of the invention will be apparent from the following description and the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  shows an example water bottom device retrieval system according to the invention. 
           [0012]      FIG. 2  shows internal components of an example cable or conduit clamp according to the invention. 
           [0013]      FIG. 3  shows an example opening in a housing of the cable or conduit clamp. 
           [0014]      FIG. 4  shows a side view of the cable/conduit clamp of  FIG. 3  including an actuator. 
           [0015]      FIG. 5  shows a top view of the cable/conduit clamp of  FIG. 3 . 
           [0016]      FIG. 6  shows an example line of cable ratchet. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    An example system for retrieving devices deployed on the bottom of a body of water is shown schematically in  FIG. 1 . A device, such as a cable or conduit  26  may be deployed on the bottom of a body of water  10  such as a lake or the ocean. The cable or conduit  26  (referred to for convenience hereinafter as the “cable”) may be, for example, a seismic sensor cable. After the cable  26  has been deployed for a selected length of time, parts of the cable  26  may become partially or totally buried by water bottom sediment  28 . The weight of such sediment may make retrieval of the cable  26  by pulling upwardly on its axial end difficult and may risk breakage of or damage to the cable  26  by reason of excessive axial tension required to lift the cable  26  from the sediment  28 . 
         [0018]    The present system may include a first floatation device such as a buoy  12  coupled to a storage element  14 . The storage element  14  may be a bag or a reel (a bag is shown in  FIG. 1 ) and is configured to store portions of the cable  26  that are lifted from the sediment  28  and water bottom using the system. The lifted portions of the cable  26  may be manually inserted into the storage element, or the storage element  14  may include automatic devices (not shown) for storing the lifted cable  26 . 
         [0019]    A second floatation device such as a buoy  18  may be coupled proximate one end of a lifting line, rope or cable  20  (hereinafter for convenience referred to as the “line”). The line  20  may be used to apply lifting force to the cable  26  by pulling on or near the end of the line  20  proximate the second floatation device  18 . Pulling may be performed by a winch (not shown) or similar device. The winch (not shown) may be associated with the second buoy  18 , or may be on a vessel (not shown). In the latter example, after the vessel mounted winch (not shown) is used to apply tension to the line  20 , the vessel (not shown) may be disconnected from the line  20  and allowed to attend to other functions. The second buoy  18  provides a location of the upper end of the line  20  for later retrieval as needed. 
         [0020]    The line  20  may be functionally coupled to a cable clamp  24  (explained below in more detail with reference to  FIGS. 2 through 5 ). When axial tension is applied to the line  20 , the axial tension is transferred to the cable  26  through the cable clamp  24 . Such axial tension tends to lift the cable  26  from the sediment  28 , yet avoids applying large axial tension directly on the cable  26 . 
         [0021]    In the present example, the line  20  may be coupled to the cable clamp  24  using a one way motion elements such as a ratchet  22  or similar device to limit motion of the line  20  to one direction therethrough. As the line  20  is tensioned, the line  20  moves through the ratchet  22 . The other end of the line  20  may be coupled to a third floatation device or buoy  16 . As the tension on the line  20  is increased, the third flotation device  16  may be pulled beneath the water surface, depending on the weight of the sediment  28  covering the cable  26 . The tension on the line  20  may continue to be applied until the third buoy  16  moves proximate the ratchet  22 . The system may then be allowed to remain in such condition. During such time, the buoyant force exerted by the third buoy  16  will tend to lift the ratchet  22  and the connected cable clamp  24 , thus lifting the cable  26  from the sediment  28 . Lifting of the part of the cable  26  coupled to the clamp  24  may be considered completed when the third flotation device  16  becomes visible at the water surface. 
         [0022]    In using the present system, the cable clamp  24  is affixed to the exterior of the cable  26  at a location proximate the water surface, typically from a vessel (not shown). The line  20  will be fully extended so that the cable clamp  24  may move freely along the exterior of the cable until it reaches the portion of the cable  26  resting on the water bottom or proximate part of the cable  26  buried under sediment  28 . As will be further explained below with reference to  FIGS. 2 through 5 , a locking device in the cable clamp  24  may then be applied so that the clamp  24  is no longer free to move along the cable  26 . At such time, the line  20  may be tensioned as explained above, such that in combination the buoyant force of the second flotation device  16  and the third flotation device  18  apply lifting force to the cable clamp  24  to urge the cable  26  from under the sediment  28 . 
         [0023]    An example locking device for the cable clamp  24  is shown schematically in  FIG. 2 . The locking device may include two or more first wedge segments  24 B made, for example of plastic such as one sold under the trademark DELRIN, which is a registered trademark of E.I. DuPont de Nemours &amp; Co., Wilmington Del. The first wedge segments  24 B may define a serpentine opening  27  for receiving the cable  26  therein. The first wedge segments have a generally tapered exterior surface  24 H configured to cooperate with a corresponding interior surface  24 J of second wedge segments  24 A. The first  24 B and second  24 A wedge segments may be disposed in a housing ( FIGS. 3 and 4 ), such that when longitudinal force is applied to the first wedge segments  24 B, they interact with the second wedge segments  24 A to laterally compress against the cable  26  in the opening  27 . Thus, the cable  26  is no longer free to move within the opening  27 . A serpentine opening such as shown at  27  may be preferable to a straight opening in some examples because the force exerted by pulling on the cable clamp ( 24  in  FIG. 1 ) may be distributed over a longer axial segment of the cable  26 , thereby reducing risk of damage to the cable  26 . The cable in the serpentine state will apply the loading force to the center components of the cable superiorly to that of the straight cable in a clamp. The distribution radial of the forces between the outer jacket (not shown separately) of the cable  26  and to the center components (e.g., electrical conductors) with better prevent damage to the cable  26 . 
         [0024]    The housing is shown in  FIG. 3  at  24 C. The housing  24 C may be a generally closed structure made from high strength material such as steel or aluminium. The housing  24 C may include a serpentine opening  24 D in one face thereof to enable affixing the cable clamp ( 24  in  FIG. 1 ) onto the cable ( 26  in  FIG. 1 ). The opening  24 D may be positioned to correspond to the opening in the second wedge segments ( 24 B in  FIG. 2 ). The wedge segments ( 24 A,  24 B in  FIG. 2 ) may be inserted into the housing through an opening  24 K in the longitudinal end of the housing  24 C as shown in  FIG. 3 . In some examples, clamps, doors or baffles (not shown in  FIG. 3 ) may be used to cover all or part of the opening  24 D after insertion of the cable  26  to ensure that the clamp  24  remains affixed to the cable  26 . 
         [0025]      FIG. 4  shows a side view of the assembled cable clamp  24 . The first wedge segments  24 B can be seen protruding from the longitudinal end of the housing  24 C. A cam mechanism  24 F is functionally coupled to a pull handle  24 G. The pull handle  24 G is coupled to the line ( 20  in  FIG. 1 ). When tension is applied to the line ( 20  in  FIG. 1 ) and thus to the pull handle  24 G, the pull handle  24 G rotates the cam mechanism  24 F to longitudinally urge the first wedge segments  24 B into the housing  24 C. As the first wedge segments  24 B are so urged, they interact with the second wedge segments as explained with reference to  FIG. 2  to cause the first wedge segments  24 B to tightly grip the cable ( 26  in  FIG. 1 ). A top view of the cable clamp  24  showing the cam mechanism  24 F is shown in  FIG. 5 . 
         [0026]      FIG. 6  shows a cut away view of one example of the ratchet  22 . A sheave  22 C and an insert  22 D may be disposed in a housing  22 B such that a path or channel for the line  20  may be defined. A plurality of sprags  22 A or similar one way locking features may be affixed to the interior of the housing  22 B such that the line  20  is free to move in the direction indicated by the arrows, and is substantially stopped from moving in the opposite direction. 
         [0027]    As explained above with reference to  FIG. 1 , when the system is deployed, the cable clamp  24  may be affixed to the exterior of the cable  26  and allowed to slide along the cable  26  to the water bottom. The line  20  may then be tensioned. Such tension will lock the locking mechanism in the cable clamp explained with reference to  FIGS. 2 through 5 . Continued tension on the line  20  will cause the line to move so that the third buoy  16  is moved toward the cable clamp. Buoyant force of the third buoy will eventually lift the cable clamp with the cable attached. 
         [0028]    The foregoing process may be repeated by releasing locking mechanism on the cable clamp, releasing the line and allowing the cable clamp once again to slide to the water bottom. Alternatively, a plurality of additional cable clamps, lines and ratchets may be attached to other parts of the cable. 
         [0029]    A cable retrieval device according to the invention may increase efficiency of retrieval operations and may reduce risk of damage to devices disposed on the bottom of a body of water as contrasted with methods know in the art that include only pulling on an axial end of the device on the water bottom. 
         [0030]    While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.