Anchor system for offshore dynamically positioned drilling platform

Abstract

An anchor system may reduce stress on anchor cables when an offshore drilling platform weathervanes. The anchor system may hold the platform in a set position above the sea floor during drilling operations. The anchor system includes anchor cables that pass through a split bearing. Clamps may be connected to the bearing to hold the anchor cables in tension.

1 . An offshore drilling platform comprising:
 a dynamic positioning system; and   an anchoring system to couple tensioned cables to anchors, said platform being rotatable above said anchoring system.   
   
   
       2 . The platform of  claim 1  wherein the anchoring system includes a split bearing. 
   
   
       3 . The platform of  claim 2  further comprising retractable actuators coupled to said split bearing. 
   
   
       4 . The platform of  claim 2 , said anchoring system further comprising a tube coupled to said bearing. 
   
   
       5 . The platform of  claim 4  further comprising pulleys coupled to said tube to guide the tensioned cables. 
   
   
       6 . The platform of  claim 1  further comprising a winch to adjust tension on the anchor cable. 
   
   
       7 . The platform of  claim 1  further comprising a motor to rotate the bearing to account for the rotation of the platform. 
   
   
       8 . The platform of  claim 1  wherein said platform is a drilling ship having a moon pool, said anchoring system mounted in said moon pool. 
   
   
       9 . A method comprising:
 tensioning an anchor cable coupled to an anchor on the sea floor, while an offshore drilling platform is being positioned by a dynamic positioning system.   
   
   
       10 . The method of  claim 9  further including clamping the anchor cable in a clamp. 
   
   
       11 . The method of  claim 10  including enabling said offshore drilling platform to rotate around said anchor cable. 
   
   
       12 . The method of  claim 11  including passing said cable through a moon pool. 
   
   
       13 . The method of  claim 12  including guiding said cable through said moon pool using a guide that is retractable relative to said moon pool. 
   
   
       14 . The method of  claim 11  including passing said cable through a split ring bearing and allowing said cable to rotate relative to said platform. 
   
   
       15 . The method of  claim 14  including passing a cable through each portion of said split ring bearing. 
   
   
       16 . The method of  claim 14  including driving the portion of said bearing including said cables to counteract motion of said platform. 
   
   
       17 . An anchor system for an offshore drilling platform comprising:
 a split bearing including outer and inner races, a pair of openings in an inner race to allow anchor cables to pass through the inner race; and   clamps to hold the anchor cables in tension.   
   
   
       18 . The system of  claim 17  further comprising a moveable actuator mounting the split bearing. 
   
   
       19 . The system of  claim 17  further comprising tensioners to adjust tension on the anchor cables. 
   
   
       20 . The system of  claim 17  further comprising a device for rotating the inner race to account for movement of the platform. 
   
   
       21 . The system of  claim 17  including a tube coupled to said inner race, said tube having one end connected to said inner race and an opposite end including guides to guide said anchor cables. 
   
   
       22 . The system of  claim 21  including a bearing between said guides and said tube. 
   
   
       23 . The system of  claim 17 , said anchor system to receive information about movement of said platform and to use said information to drive said inner race relative to said outer race. 
   
   
       24 . The system of  claim 17  including a controller to operate said clamps and to receive information about wind and wave action affecting said platform. 
   
   
       25 . The system of  claim 17  including a dynamic positioning system. 
   
   
       26 . A method comprising:
 mounting a split bearing in a moon pool with openings in the bearing to pass anchor cables through; and   connecting clamps to the anchor cables to hold tension on the anchor cables.   
   
   
       27 . The method of  claim 26  including mounting retractable actuators to retract the bearing with respect to the moon pool. 
   
   
       28 . The method of  claim 26  including coupling said anchor cable to a tensioner. 
   
   
       29 . The method of  claim 28  including providing couplers on said cables to couple to anchors. 
   
   
       30 . The method of  claim 26  including coupling a controller system for said anchor cables and a dynamic positioning system.