Abstract:
A system or apparatus and method for retrieving cable from water during marine operations is provided that reduces damage to the cable from pulling forces during the retrieval. A pulling device distributes the forces and stresses all along the cable components. In one embodiment, the pulling drive comprises a pulling drum powered by a clutching system or by a hydraulic torque conversion system set to slip or stall at a selectable force value. The apparatus may use a see-saw action to maintain the forces below damaging levels. The system may be adapted for deploying cable in marine operations as well.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to cable handling systems, particularly systems for deploying and retrieving electrical and fiber optic cables. Most particularly, the invention relates to marine seismic cable deployment and retrieval systems for use in conjunction with a marine vessel. 
     2. Brief Description of Relevant Art 
     In many fields of endeavor, there is an on-going requirement to place packages of sensing equipment of various types across the earth&#39;s surface and on the seafloor. Such equipment is commonly intended to be used at one location for a period of time and then transported to a different location for further use. However, precisely deploying and later retrieving such equipment without damaging the equipment can be difficult. Operations in water, especially oceans, bays, and surf zones, can be especially problematic. The equipment commonly sinks into muddy and sandy sea beds and tends to suffer stress damage when removed. 
     Seismic cables can be especially difficult to handle because they are typically made of multiple components such as electrical conductors, fiber optics, and stress supporting members all bundled together and covered with a protective jacketing material. Handling or pulling the cable causes these components to slip and move with respect to one another. Tension applied to the outer jacket pulls the jacketing material which then pulls on the inner components of the cable. This distribution of stresses applies differing stress values and elongation amounts to the different components of the cable. Even cables where the stress members are embedded into the outer jacket have such a stress distribution, although to a lesser degree. Propagation of stress through a cable&#39;s components changes and deteriorates the components and consequently reduces the cable&#39;s useful life. 
     In water, the platform or vessel used to deploy and retrieve the cables often contributes due to the action of the water. Pulling cable up from a sea bottom and through sea bottom material is stressful to equipment in the cable, but simply pulling the cable through water is also stressful. Typically the cable will be curved in the water, extending downwardly from a platform and curving to a horizontal position along the sea bottom. The curve&#39;s length and shape will depend on the rate of retrieval, the depth of the water, the amount of cable sunk into the sea bottom, and the value of the applied pulling tension. The curve of the cable inevitably causes portions of the cable to be pulled sideways through the water, creating vortexes in the water, cable strumming, and drag on the cable, and adding further to the stresses on the cable. Such pulling tensions can exceed the strength of the cable, causing it to break. Similarly, tensions caused by pulling of the cable due to heaving of the vessel on ocean waves and swells can exceed the strength of the cable, causing it to suffer elongation damage and even break. The cable strength is commonly only a tiny fraction of the applied forces that potentially may be applied against the cable. 
     A need exists for systems and methods for deploying and recovering cables that reduce the destructive forces against such cables, particularly when the cables are distributed along a sea bed or in water. 
     SUMMARY OF THE INVENTION 
     The present invention provides a system, method and apparatus for retrieving cable from the water during marine operations and is especially advantageous for use with floating vessels. The invention may be utilized for deploying cable in marine operations as well. 
     According to the method of the invention, the retrieval of the cable is conducted while monitoring and adjusting the pulling forces on the cable so as to reduce or prevent damage to the cable from such forces during the retrieval. A pulling device that distributes pulling forces and stresses among the cable components is used to pull the cable for its retrieval. The device may employ a see-saw action, that is, a pulling and playing back of the cable, to maintain the forces below the damage point for the cable. 
     A preferred embodiment comprises a pulling drum capable of pulling the cable by wrapping the cable around the drum, thereby distributing pulling forces across the components of the cable. The pulling drum may be powered by a drive motor with a regulatable torque drive for adjusting the forces on the cable. Alternatively, the drum may be powered by a clutching system or by a hydraulic torque conversion system set to slip or stall at a selectable force value. Any means for powering the drum may preferably allow payback of the cable to lessen forces on the cable if needed to avoid damage to the cable. Preferably the apparatus or system will also have a front-mounted damper arm with an adjustable tension range positioned in front of the pulling drum to dampen stress on the cable, particularly stress caused by the movement of the water. 
     The retrieved cable is preferably stored in a storage area that will avoid tangling or twisting of the cable. The storage area preferably includes a cage within which the cable is stored, with the attachments preferably positioned or stored on the outside of the cage. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1(   a ) is a schematic of the pulling drum and damper arm of one embodiment of the system of the invention wherein the damper arm is in a raised position. 
         FIG. 1(   b ) is a schematic of the pulling drum and damper arm of the embodiment of the system of the invention of  FIG. 1(   a ) but with the damper arm in a lowered position. 
         FIG. 1(   c ) shows a system for regulating drive torque. 
         FIG. 2(   a ) is a side view of the cable storage assembly of one embodiment of the system of the invention. 
         FIG. 2(   b ) is an exploded side view of the cable storage assembly shown in  FIG. 2(   a ). 
         FIG. 2(   c ) is an exploded top view of the cable storage assembly shown in  FIG. 2(   a ). 
         FIG. 3  is a schematic of one embodiment of the system of the invention in use retrieving cable wherein the system comprises the pulling drum and damper arm shown in  FIGS. 1(   a ) and  1 ( b ), the cable storage assembly shown in  FIGS. 2(   a ) and  2 ( b ) and a powered drum for carrying cable from the pulling drum to the storage assembly. 
         FIG. 4  is a schematic of one embodiment of the system of the invention shown in  FIG. 3  but in use deploying cable. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     According to the invention, a pulling device is provided that allows cable to be retrieved from water and sea beds without damage or fouling from the pulling process to either the cable components or attachments to the cable, even though such attachments may be wider than the cable itself. Cable components may include, for example, internal stress members, protective jackets, electrical and fiber optic conductors and insulating layers. Attachments to the cable may include, for example, sensor packages and other electrical or fiber optic equipment. 
     The pulling device distributes pulling forces and stresses among preferably all of the cable components, most preferably substantially equally among all of the cable components, including internal stress members of the cable and external jacketing material. 
     In a preferred embodiment, referring to  FIGS. 1(   a ) and  1 ( b ), the pulling device comprises a pulling drum  10 , rotatably mounted on a preferably firm, stationary or relatively level or horizontal mounting base plate  12 , which is typically affixed to a platform or marine vessel  38 , as shown in  FIG. 3 . As the pulling drum  10  is rotated, the cable  20  is pulled up to accomplish the cable retrieval process. Sufficient compressional forces to distribute pulling forces among all the cable components, and sufficient frictional forces to retrieve the cable  20 , can normally be achieved by wrapping the cable  20  around drum  10  less than a full circumference, as shown in  FIGS. 1(   a ) and  1 ( b ), although cable  20  may be wrapped around drum  10  a plurality of times. Because of the compressive force between the pulling drum  10  and the cable  20 , the pulling forces on the cable will be transmitted internally within the cable to each component of the cable, thereby substantially equalizing the pulling forces on each component of the cable. Drive torque may be applied to the drum  10  by any available means known to those of ordinary skill in the art, such as electric motor, shown schematically in  FIG. 1(   c ), or hydraulic, or mechanical means, for example. The cable tension may be monitored by monitoring the position of the damper arm or the drive power applied to the drum, and the drive torque applied to the drum  10  regulated in response to the measured tension to control the force on the cable  20 . Alternatively, the drive torque may be regulated or adjusted through a clutching system or hydraulic torque conversion system  59 , shown schematically in  FIG. 1(   c ), that may be set to slip or stall at a selected force value (i.e., an amount of force that should preferably not be exceeded to ensure no damage to the cable, most preferably with a margin for error built into the value). As shown in  FIG. 1(   c ), clutching or hydraulic conversion system  59  comprises motor  54  which applies power to drum  10  through clutch or torque converter  56 . The drive torque may be set to stall at a selected force by drive torque control  58 . In either case, if the tension or force on the cable  20  continues to exceed the selected force amount, the drive torque means will stall so that drum  10  will initially discontinue forward rotation, and if stalling is not sufficient to prevent further increases in the tension on the cable, the system will allow drum  10  to rotate in the reverse direction, and the cable  20  to pay back out to lessen the tension or force on the cable  20 . As the extreme tensions relax, the system will resume retrieval of the cable, i.e., the drum  10  will resume forward rotation. The swing of the damper arm also functions to limit tension. In very high wave action, the alternate pulling in and playing out of the cable according to the invention to prevent the maximum applied tensions from being exceeded can produce a “see-saw” action. 
     Referring again to  FIGS. 1(   a ) and ( b ), in a preferred embodiment of the invention, a front mounted damper arm  30  is positioned in front of the pulling drum  10  and preferably substantially at the entry point of the cable from the water onto the retrieval vehicle, which may be a boat or other floating vessel or platform. The damper arm  30  performs a dampening function, to compensate for vessel movement, to keep the tension on the cable  20  within a consistent range. With increasing pull force, the damper arm  30  will tilt downwardly, to reduce or counteract the increasing tension in the cable. The tension forces required to pull the damper arm  30  down increases with the arm&#39;s travel distance. The tension range of damper arm  30  is preferably adjustable so as to handle an assortment of cable tension requirements within the mid point of the arm travel. Shock absorber  34 , extending between damper arm  30  and mast  36 , and shock absorber  26 , extending between damper arm  30  and base plate  12  (or vessel  38 ) function to substantially isolate cable  20  from sudden vessel movements. Mast  36  may be attached to mounting base plate  12  or vessel  38 , by standard mounting means known to those of ordinary skill in the art. 
     The damper arm  30  is preferably mounted so that the damper arm  30  can rotate about a rotation point  32  on mounting base  28 , which is also rotationally mounted on base plate  12  so that mounting base  28  can swivel horizontally. Accordingly, damper arm  30  can provide a “following” action with respect to the cable  20 . That is, the damper arm  30  preferably moves or swivels as the floating vessel containing the damper arm  30  drifts in the water due to wind and water current forces, so that the damper arm points in directional alignment with the deployed cable  20 . The damper arm  30  also preferably contains alignment devices comprising rollers or sheaves  22  and  24  to align any attachments or components attached to the cable with the cable to aid the cable&#39;s passage through the roller system comprising drums (or sheaves)  10  and  70 . 
     A preferred embodiment of the invention further provides a storage system for the retrieved cable (or for the cable prior to deployment). In one embodiment, the storage system provides for the storage of the cable and any attachments to the cable in a holding area, preferably or typically including a cage, with the attachments preferably positioned or stored on the outside of the cage, for easy access if desired or needed, with the cable storage being controlled so as to prevent fouling and tangling of the cable and attachments with one another. 
     Referring to  FIGS. 2(   a ),  2 ( b ) and  2 ( c ) for a preferred embodiment of such a storage system, in which  FIG. 2(   a ) is an assembled view,  FIG. 2(   b ) is a side view and  FIG. 2(   c ) is a top view. The storage system comprises a cage  40 , preferably substantially circular or oval, whose outside perimeter  42  has a plurality of vertical slots  41  extending from the top edge of outside perimeter  42  at least part way down the side of cage  40  so that the cable  20  may exit the cage through one slot  41  and re-enter at another such slot. The slots enable a cable with one or more attachments  7  (as shown in  FIG. 3)  to be brought outside the cage  40  at the approximate location of the attachment so that the attachment may be positioned or hung on the outside of the cage  40  and the cable then returned or allowed to re-enter the cage for continuation of the cable storage process. 
     Inside cage  40  is another smaller cage  50 , preferably also circular or oval, and preferably centered on the same point as the cage  40 , so that a raceway area or path  46 , shown more clearly in  FIG. 2(   c ), is formed between outside perimeter  42  of cage  40  and cage  50 . The top of cage  50  is preferably a cone  51  having a base or bottom perimeter preferably substantially coextensive with the perimeter of cage  50 . This conical shape facilitates storage of the cable  20  by enabling the cable that is being stored to slide down the cone  51  into the raceway area  46 . Attached to the top of cone  51  is another, smaller cone,  53 , preferably rotatably mounted on cone  51  and attached or associated with a drive motor so that cone  53  can rotate on its central axis about the top of cone  51 . An arm  60  preferably protrudes from the cone  53  and is preferably attached to cone  53  so that said arm  60  rotates with cone  53  to sweep around above cone  51  to catch and move any suspended cable toward the cone  53  so that the cable will be directed and deposited in the raceway area  46 . Most preferably, the cable will be deposited in layers in raceway area  46 . 
     As shown more clearly in  FIG. 3 , as cable  20  is being retrieved, cable  20  travels from drum  10  and around powered guide roller  70 , from which cable  20  is allowed to fall toward smaller cone  53 . Cable  20  is caught by guide arm  60 , which sweeps cable  20  around smaller cone  53  and cone  51 , so that cable  20  slides down cone  51  and is deposited in a circular pattern within raceway  46  between outer cage  40  and inner cage  50 . Guide roller  70  is supported above small cone  53  by support arm  62 , as illustrated in a first side view in  FIG. 2(   b ) and in a second side view (orthogonal to the first side view) in  FIG. 2(   d ). Support arm  62  is supported from mounting base plate  12  or vessel  38 , by any ordinary means known to those of ordinary skill in the art. 
     In an alternative embodiment, arm  60  might have its own means for rotation and be independent of any rotation of cone  53 . In such embodiment, arm  60  would not be attached directly to cone  53 . 
     Referring to  FIG. 3 , guide roller  70 , comprising a powered drum, preferably delivers the cable  20  from the pulling drum  10  and deposits the cable  20  vertically above the peak of the cone  53  so that the rotating arm  60  will cause the cable  20  to be deposited around the cage  50  in raceway  46 . Depositing the cable  20  in this manner allows the cable to lie down unstressed and to be deployed back out of the cage  40  in the same manner and direction so as not to impart any residing twist into the cable when so deployed. Thus, when the cable is pulled back out of the storage area, the cable has no twist stresses that need to be removed during the re-deployment. 
     Preferably, the opening between cages  40  and  50  to raceway  46  will be sufficiently narrow to inhibit the entry into raceway (pathway)  46  of any attachments  7  on cable  20 . Preferably, perimeter wall  42  will have a lip  44  extending from the wall  42  which, in combination with the edge of cone  51 , will serve to catch or stop the entry of attachments  7  into raceway  46 . Most preferably, such attachments  7  will bridge the entry space into raceway  46  and the cable will be directed by lip  44  into raceway  46  while the attachments remain held above the raceway  46 . The attachments  7  may then be automatically or manually pulled to the outside of perimeter wall  42  where they will preferably be positioned in a holding bracket (not shown). Preferably, a portion of cable  20  associated with the attachment  7  will be pulled through a slot  41  to the outside of perimeter wall  42 , along with the attachment. After the attachment  7  is positioned outside the perimeter wall  42 , the associated cable may be returned manually or automatically to pathway  46  via another slot  41 . That is, the cable exits from the raceway  46  with the attachment  7  via a slot  41 , and returns back into raceway  46  by way of another slot  41 . 
     Referring to  FIG. 4 , the cable  20  may be redeployed from storage cage  40  into the sea by running the cable from the raceway  46 , up and out of the raceway  46 , back up and along cone  53  and over the drum  70 , which may now be set or used in either a freewheel or a powered mode. The cable may then be passed over any other required supporting drums until reaching the area for deployment into the water. 
     Often for re-deployment, the weight of the cable and its drag in the water are sufficient forces to pull the cable out of the raceway  46  and over the side of a floating vessel transporting the cable. When such weight is not enough to effect the re-deployment or it is desired to deliver excess cable into the water faster than can be achieved by the vessel&#39;s forward speed alone, the drum or roller  70  may be powered to pull the cable up and out of raceway  46 . 
     The foregoing description of the invention is intended to be a description of preferred embodiments. Various changes in the details of the described systems, apparatuses and methods may be made without departing from the intended scope of this invention as defined by the appended claims.