Seabed Plow Capable of Over-the-Stern Release and Retrieval in Any Boulder Clearing, Trenching and Backfill Configurations

Abstract

A seabed plow capable of over-the-stern release and retrieval is usable in any of boulder clearing, trench cutting and backfill modes. In its boulder clearing mode, the plow uses its skid in torquing configuration followed by moldboards to push boulders out of the path to be trenched. In the trench cutting mode, the plow uses the skid in the same configuration with its share and moldboards for initial trench depth and the same share and moldboards with moldboard extensions for increasing trench depth in subsequent passes. In the backfill mode, the plow uses its skid in trench-straddling configuration following a blade with a passage designed to discharge fragmented spoil directly onto the pipe being covered. Thus, a single plow can be reconfigured for all modes for release and retrieval to and from a relatively small vessel without use of heavy lifting equipment.

What is claimed is: 
     
         1 . A seabed-plow chassis, comprising:
 a. a substantially unitary, elongated member, comprising:
 1. a substantially linear longitudinal axis; 
 2. a bottom surface; 
 3. a first end disposed at one end of the substantially linear longitudinal axis; and 
 4. a second end disposed at an opposite end of the substantially linear longitudinal axis; 
   b. a skid mounted to the first end, the skid configured to support the first end of the elongated member above a seabed and to push boulders outward from a path traveled by the skid;   c. a tool mounted to the elongated member towards the second end and extending outward from the elongated member, the tool comprising a curved portion; and   d. a tow connection connected to the first end.   
     
     
         2 . The seabed-plow chassis of  claim 1 , wherein:
 a. the first end of the elongated member defines a leading edge of the seabed-plow chassis;   b. the tool is mounted to the second end of the elongated member in a trailing relationship to the skid; and   c. the curved portion of the tool comprises a moldboard configured to clear boulders pushed by the skid further outward from a path on the seabed as the skid leads the tool along the path.   
     
     
         3 . The seabed-plow chassis of  claim 2 , wherein the moldboard further comprises:
 a. a first moldboard extending from a first side of the elongated member; and   b. a second moldboard extending from a second side of the elongated member opposite the first side of the elongated member.   
     
     
         4 . The seabed-plow chassis of  claim 1 , wherein:
 a. the first end of the elongated member defines an aft end of the substantially unitary, elongated member;   b. the tool further comprises a blade operatively connected to and spanning a predetermined portion of a bottom edge of the curved portion of the tool, the blade comprising:
 1. a rear apex; and 
 2. a passage at its rear apex; 
   c. the curved portion of the tool is sized and oriented to span a predetermined dimension of a trench, the curved portion of the tool further configured to cooperatively interact with the blade to sequentially collect, funnel inward, and release spoil lying outside of the trench downward into the trench as the blade and the curved portion of the tool lead the skid along the seabed; and   d. the skid is configured to straddle the predetermined dimension of the trench.   
     
     
         5 . The seabed-plow chassis of  claim 1 , wherein the skid further comprises:
 a. a crossbar mounted at the first end of the chassis, the crossbar comprising a first end and a second end;   b. a first skid post connected to the first end of the crossbar;   c. a first ski connected to a bottom of the first skid post;   d. a second skid post connected to the second end of the crossbar;   e. a second ski connected to a bottom of the second skid post.   
     
     
         6 . The seabed-plow chassis of  claim 1 , wherein the tow end further comprises:
 a. a tow bar extending laterally from the first end of the elongated member; and   b. a set of pulling line connection pulling points symmetrically arranged along a length of the tow bar.   
     
     
         7 . The seabed-plow chassis of  claim 1 , further comprising a first transition surface extending between the skid and the tool, the first transition surface contoured to selectively pivot about a fulcrum on a stern of a vessel. 
     
     
         8 . The seabed-plow chassis of  claim 7 , wherein:
 a. the fulcrum comprises roller; and   b. the first transition surface contour comprises a set of continuous, symmetrically opposing longitudinal axis points aligned with the substantially linear longitudinal axis of the elongated member, the set of continuous, symmetrically opposing longitudinal axis points defining a contoured path adapted to maintain contact with the roller as the first transition surface crosses the roller.   
     
     
         9 . The seabed-plow chassis of  claim 7 , wherein a vertical longitudinal cross-section of the first transition surface is concave. 
     
     
         10 . The seabed-plow chassis of  claim 7 , wherein the bottom surface comprises the first transition surface. 
     
     
         11 . The seabed-plow chassis of  claim 7 , further comprising a transition attachment mated to the bottom surface, the transition attachment further comprising:
 a. a transition surface comprising the first transition surface; and   b. a non-transition surface on an opposing side of the transition attachment from the transition surface, the non-transition surface configured to allow the transition attachment to mate to the bottom surface.   
     
     
         12 . The seabed-plow chassis of  claim 7 , further comprising a second transition surface extending between the skid and the tool. 
     
     
         13 . The seabed-plow chassis of  claim 12 , wherein the shapes of each of the first and second transition surfaces and the weight of the elongated member are configured to cooperatively resist roll of the tool about the longitudinal axis of the elongated member. 
     
     
         14 . The seabed-plow chassis of  claim 12 , wherein a longitudinal vertical cross-section of each of the first and second transition surfaces is concave. 
     
     
         15 . The seabed-plow chassis of  claim 12 , wherein:
 a. the fulcrum comprises a roller; and   b. a path defined by a set of continuous symmetrically opposite points of each of the first and second transition surfaces is contoured to maintain contact with the roller as the tool crosses the roller.   
     
     
         16 . A method of performing a function subsea using a plow which comprises a seabed-plow chassis comprising a substantially unitary, elongated member comprising a substantially linear longitudinal axis, a bottom surface, a first end disposed at one end of the substantially linear longitudinal axis, and a second end disposed at an opposite end of the substantially linear longitudinal axis; a skid mounted to the first end, the skid configured to support the first end of the elongated member above a seabed and to push boulders outward from a path traveled by the skid; a tool mounted to the elongated member towards the second end, the tool extending outward from the elongated member and comprising a curved portion; and a tow connection connected to the first end comprising a set of pulling line connection pulling points symmetrically arranged in relation to the longitudinal axis of the chassis, the method comprising:
 a. propelling the plow on a deck of a vessel toward and across a fulcrum on a stern of the vessel;   b. connecting a pulling line to a predetermined pulling line connection pulling point of the set of pulling line connection pulling points;   c. releasing the plow into the sea;   d. allowing the plow to rotate about the fulcrum as the plow crosses the fulcrum and is released from the fulcrum into the sea;   e. lowering the released plow at a tow-line end of the pulling line toward the seabed via the pulling line;   f. positioning the plow bow-forward in the direction of an initial seabed path;   g. propelling the plow along the initial seabed path;   h. using the tool to perform a subsea function subsea; and   i. if a wider seabed path is desired,
 1. repositioning the plow bow-forward in a direction opposite the initial seabed path direction and on a further seabed path along one of the two sides of the initial seabed path; 
 2. once so repositioned, propelling the plow along the further seabed path and using the tool to perform the subsea function subsea; and 
 3. repeating steps (i)(1)-(i)(2) until the desired seabed path width is achieved. 
   
     
     
         17 . The method of  claim 16 , further comprising:
 a. raising the plow at the tow-line end toward the fulcrum on the stern of the vessel at another end of the tow line; and   b. pulling the plow across the fulcrum onto the deck of the vessel.   
     
     
         18 . The method of  claim 16 , wherein the chassis further comprises a first transition surface, the method further comprising placing the first transition surface and the fulcrum into contact as the first transition surface crosses the fulcrum during release of the tool into the sea from the vessel and during retrieval of the tool from the sea onto the vessel. 
     
     
         19 . The method of  claim 16 , wherein the plow comprises a boulder clearing plow, the curved portion of the tool further comprises a moldboard, and the function further comprises clearing boulders from the seabed path, wherein:
 a. the method further comprises using the skid to push boulders outward of the initial seabed path traveled by the skid; and   b. using the tool to perform the subsea function subsea further comprises using the moldboard to clear the boulders from the seabed path by pushing the boulders from the seabed path to one of the starboard and port sides of the plow.   
     
     
         20 . The method of  claim 16 , wherein the plow comprises a backfill plow, the curved portion of the tool further comprises a moldboard, and the tool further comprises a blade operatively connected to and spanning a predetermined portion of a bottom edge of the curved portion of the tool, the blade comprising a passage at its rear apex, wherein using the tool to perform the subsea function subsea further comprises backfilling spoil into a seabed trench present within the seabed path by:
 a. propelling the blade to travel in a predetermined direction on the seabed along the initial seabed path;   b. collecting spoil along the sides of the trench as the blade travels;   c. funneling the collected spoil toward a rear apex of the blade; and   d. allowing the funneled spoil to be discharged through an opening in the blade apex into the trench.   
     
     
         21 . The method of  claim 20 , wherein a pipe is disposed in the trench, the method further comprising:
 a. allowing the funneled spoil to be discharged through the opening in the blade apex onto a top portion of the pipe in the trench; and   b. fragmenting the discharged spoil before the discharged spoil reaches the pipe.   
     
     
         22 . The method of  claim 20 , further comprising leveling the spoil after it is discharged into the trench.