Methods for installing or removing and replacing a segment of a mooring line

Abstract

Disclosed are methods for replacing a used wire rope segment or for installing a new wire rope segment in a mooring line useful for mooring a floating vessel such as a floating storage and offloading (FSO) vessel. The methods utilize platforms adapted to be mounted onto anchor handling vessels (AHVs) for severing the used wire rope segment and connecting the new wire rope segment thereon.

What is claimed is: 
     
         1 . A method for removing a used segment of a mooring line located on a seabed and replacing the used segment with a new mooring line segment used for mooring a floating vessel, comprising:
 a. positioning at a first location above a first end of a mooring line segment to be removed an anchor handling vessel having a platform adapted for receiving and securely holding a mooring line retrieved from the seabed;   b. attaching a lifting line having one end secured on the anchor handling vessel to the mooring line;   c. retrieving the mooring line from the seabed to the platform using the lifting line;   d. placing and securing the mooring line on the platform;   e. severing the mooring line on the platform to form a first mooring line severed end and a first segment severed end;   f. attaching a first end of a temporary line wound on a temporary line reel on the anchor handling vessel to the first mooring line severed end;   g. navigating the anchor handling vessel to a second location above a second end of the mooring line segment while simultaneously winding the mooring line segment to be removed onto a used mooring line reel on the anchor handling vessel and laying down the temporary line onto the seabed;   h. securing the mooring line on the platform at the second location;   i. severing the mooring line at the second location to form a second mooring line severed end and a second segment severed end;   j. winding the second segment severed end on the used mooring line reel;   k. connecting a first end of a new mooring line segment wound on a new mooring line reel on the anchor handling vessel to the second mooring line severed end on the platform;   l. navigating the anchor handling vessel to the first location while simultaneously winding the temporary line onto the temporary line reel on the anchor handling vessel and laying down the new mooring line segment onto the seabed;   m. at the first location, connecting a second end of the new mooring line segment to the first mooring line severed end on the platform; and   n. lowering the mooring line including the new mooring line segment to the seabed.   
     
     
         2 . A method for installing a new mooring line segment in a mooring line on a seabed used for mooring a floating vessel, comprising:
 a. positioning at a first location an anchor handling vessel having a platform adapted for receiving and securely holding a mooring line;   b. placing and securing a free end of a first mooring line lead on the platform;   c. at the first location, connecting a first end of a new mooring line segment to the free end of the first mooring line lead on the platform;   d. navigating the anchor handling vessel to a second location while laying down the new mooring line segment onto the seabed;   e. connecting a second end of the new mooring line segment to a free end of a second mooring line lead on the platform; and   f. lowering the mooring line including the new mooring line segment to the seabed.   
     
     
         3 . The method of  claim 1 , wherein prior to severing the mooring line in steps (e) and (i), the mooring line is secured on either side of the location of the severing and a predetermined tension is ensured in the mooring line. 
     
     
         4 . The method of  claim 3 , wherein the mooring line is secured on either side of the location of the severing by engaging the mooring line with a first stopper and a second stopper controllable by hydraulics. 
     
     
         5 . The method of  claim 3 , wherein the predetermined tension is ensured by controlling the distance between the first and second stoppers. 
     
     
         6 . The method of  claim 2 , wherein prior to connecting the mooring line in steps (c) and (e):
 each of the first and second mooring line leads is secured by engaging the mooring line lead with a first stopper controllable by hydraulics; and   the new mooring line segment is secured by engaging the new mooring line segment with a second stopper controllable by hydraulics.   
     
     
         7 . The method of  claim 1 , wherein the lifting line is attached to the mooring line by a remotely operated vehicle. 
     
     
         8 . The method of  claim 1 , wherein:
 the mooring line segment to be removed is a used wire rope segment between a first chain segment and a second chain segment of the mooring line;   the first location is above a juncture of the first chain segment and the used wire rope segment and the second location is above a juncture of the used wire rope segment and the second chain segment; and   the mooring line is severed through the first chain segment at the first location to form the first mooring line severed end and the first segment severed end; and   the mooring line is severed through the second chain segment at the second location to form the second mooring line severed end and the second segment severed end.   
     
     
         9 . The method of  claim 2 , wherein:
 the first mooring line lead is a first chain segment of the mooring line attached to a floating vessel;   the second mooring line lead is a second chain segment of the mooring line attached to an anchor;   the first location is above the free end of the first mooring line lead; and   the second location is above the free end of the second mooring line lead.   
     
     
         10 . The method of  claim 1 , wherein:
 the lifting line is secured to a block suspended from an A-frame on the anchor handling vessel.   
     
     
         11 . The method of  claim 1 , further comprising:
 as the mooring line segment to be removed is wound on the used mooring line reel, passing the mooring line segment over guides on a curved deflector plate on the anchor handling vessel located adjacent the platform to assist the winding of the mooring line segment to be removed.   
     
     
         12 . The method of  claim 1 , further comprising:
 as the mooring line segment to be removed is wound on the used mooring line reel, passing the mooring line segment over rollers mounted on a chute on the platform to protect the mooring line segment during the winding of the mooring line segment.   
     
     
         13 . The method of  claim 1 , further comprising lifting the mooring line off the seabed with a winch wire prior to attaching the lifting line to the mooring line. 
     
     
         14 . The method of  claim 1  or  claim 2 , further comprising monitoring the lowering of the mooring line using a video camera. 
     
     
         15 . The method of  claim 1  or  claim 2 , further comprising:
 a. prior to lowering the mooring line, adding or removing lengths of mooring line to achieve a desired tension in the mooring line. 
 
     
     
         16 . The method of  claim 1  or  claim 2 , further comprising:
 as the new mooring line segment is laid down from the new mooring line reel and onto the seabed, the new mooring line segment is passed over guides on a curved deflector plate on the anchor handling vessel located adjacent the platform to assist the laydown of the new mooring line segment. 
 
     
     
         17 . The method of  claim 1  or  claim 2 , further comprising:
 as the new mooring line segment is laid down onto the seabed, the new mooring line segment is passed over rollers mounted on a chute on the platform to protect the new mooring line segment during the laydown of the new mooring line segment. 
 
     
     
         18 . The method of  claim 1  or  claim 2 , wherein:
 the ends of the new mooring line segment are connected to the first and second mooring line severed ends by inserting connectors between the ends of the new mooring line segment and the first and second mooring line severed ends. 
 
     
     
         19 . The method of  claim 18 , wherein the connectors are selected from the group consisting of shackles and H-links.