Trenching Machines And Methods

Abstract

The invention relates to a sub-sea trenching machine (16) including two cutter units (26 a, 26 b ). The cutter units are preferably chain cutter units. The cutter units are mounted to be moveable from a use position in which the cutter units are juxtaposed or spaced a limited distance apart to a stowed condition in which the cutter units are sufficiently spaced apart to allow mounting of an elongate workpiece (18) such as a pipe or cable onto the trenching machine.

1 . A trenching machine comprising:
 a body portion;   first and second arms mounted on the body portion; and   first and second trench cutter units mounted on the respective arms, wherein the arms are moveable between a first position in which the cutter units adopt a stowed position and at least one use position in which the cutter units can adopt a trenching condition.   
   
   
       2 . A trenching machine as claimed in  claim 1  wherein when the arms are in the first position, the cutter units are spaced apart and when the arms are in the use position the cutter units are relatively closer together. 
   
   
       3 . A trenching machine as claimed in  claim 2  wherein when the arms are in the first position the cutter units are spaced apart to an extent sufficient to allow passage therebetween of the an elongate workpiece to be trenched. 
   
   
       4 . A trenching machine as claimed in  claim 3  further comprising lifting means for raising an elongate workpiece between the cutter units to a position above the cutter units, when the cutter units are in the stowed position. 
   
   
       5 . A trenching machine as claimed in  claim 1  wherein when the arms are in the first position, the cutter units are in a relatively higher position and when the arms are in the use position the cutter units are in a relatively lower position. 
   
   
       6 . A trenching machine as claimed in  claim 1  wherein the first and second arms are pivotally mounted on the body portion. 
   
   
       7 . A trenching machine as claimed in  claim 6  wherein the pivot axes of the respective arms are arranged to be generally parallel to the longitudinal axis of a work piece to be disposed in the trench. 
   
   
       8 . A trenching machine as claimed in  claim 1  wherein when the arms are in a use position, the cutter units are selectively moveable relative to the arms to adopt any of a desired range of trenching conditions. 
   
   
       9 . A trenching machine as claimed in  claim 7  wherein when the arms are in a use position, the cutter units are selectively moveable relative to the arms to adopt any of a desired range of trenching conditions; and
 wherein the cutter units are moveable relative to the arms by rotation of the cutter units about an axis.   
   
   
       10 . A trenching machine as claimed in  claim 9  wherein said axis of rotation of the cutter units is orthogonal to the pivot axes of the respective arms. 
   
   
       11 . A trenching machine as claimed in  claim 1  wherein the cutter units are chain cutter units. 
   
   
       12 . A trenching machine as claimed in  claim 1  wherein in one use position of the arms, the cutter units are juxtaposed. 
   
   
       13 . A trenching machine as claimed in  claim 12  further comprising securing means operable to join the first and second cutter units together. 
   
   
       14 . A trenching machine as claimed in  claim 1  wherein in one use position of the arms the cutter units are in spaced apart relation. 
   
   
       15 . A trenching machine as claimed in  claim 1  wherein in their trenching condition, the cutter units are arranged substantially vertically. 
   
   
       16 . A trenching machine as claimed in  claim 1  further comprising supporting means configured to support the workpiece on passing through the body of the machine substantially without deformation of the workpiece from a generally linear condition, with respect to a nominally horizontal plane. 
   
   
       17 . (canceled) 
   
   
       18 . A method of laying an elongate workpiece in a trench, comprising:
 providing a trenching machine as claimed in  claim 1 ;   arranging the trenching machine over the elongate workpiece;   moving the first and second arms to their first position, if not already in said first position;   moving the elongate workpiece to a supported position within the machine; and   moving the arms to a use position in which the cutter units adopt a trenching condition.   
   
   
       19 . (canceled)