Apparatus

Abstract

A trenching unit used to cut trenches in the seabed for laying pipelines or cables. The unit comprises: a jetting arm with a plurality of sections, each section having at least one nozzle; means for supplying fluid to nozzles in at least two sections; and means for separately controlling the flow characteristics of the fluid supplied to each individual section of the jetting arm. Two or more units of such apparatus can be used in tandem to extend the fluidization period of a localized area of the seabed. This is particularly useful when pipes or cables are relatively stiff. The fluidization period depends upon the distance between the units which is calculated as a function of the characteristics of the seabed and the capabilities of the individual units. The distance between the units is determined by the length of an adjustable linkage.

What we claim is:  
     
         1 . A trenching unit comprising: 
 a housing;    a jetting arm mounted to the housing, the jetting arm having: 
 a first section having at least one nozzle,  
 and a second section having at least one nozzle,  
   a first fluid supply device for supplying fluid to said at least one nozzle in said first section of said jetting arm;    a second fluid supply device for supplying fluid to said at least one nozzle in said second section of said jetting arm;    a first fluid flow controller for controlling the flow characteristics of the fluid supplied to said first section of said jetting arm, and    a second fluid flow controller for controlling the flow characteristics of the fluid supplied to said second section of said jetting arm.    
     
     
         2 . A trenching unit comprising: 
 a housing;    a first jetting arm mounted to said housing, said first jetting arm having: 
 a first section having at least one nozzle,  
 and a second section having at least one nozzle,  
   a second jetting arm mounted to said housing, said second jetting arm having: 
 a first section having at least one nozzle,  
 and a second section having at least one nozzle,  
   a first fluid supply device for supplying fluid to said at least one nozzle in said first section of each of said first jetting arm;    a second fluid supply device for supplying fluid to said at least one nozzle in said second section of each of said first jetting arm;    a third fluid supply device for supplying fluid to said at least one nozzle in said first section of each of said second jetting arm;    a fourth fluid supply device for supplying fluid to said at least one nozzle in said second section of each of said second jetting arm;    a first fluid flow controller for controlling the flow characteristics of the fluid supplied to said first section said first jetting arm,    a second fluid flow controller for controlling the flow characteristics of the fluid supplied to said second section of said first jetting arm;    a third fluid flow controller for controlling the flow characteristics of the fluid supplied to said first section said second jetting arm, and    a fourth fluid flow controller for controlling the flow characteristics of the fluid supplied to said second section of said second jetting arm.    
     
     
         3 . A trenching unit according to  claim 2  wherein the second jetting arm is arranged in parallel to the first jetting arm.  
     
     
         4 . A trenching unit according to  claim 2  wherein said first and said second jetting arms are separated by a distance which is adjustable.  
     
     
         5 . A trenching unit according to  claim 1  wherein said fluid flow characteristics comprise at least one of fluid pressure and fluid volume.  
     
     
         6 . A trenching unit according to  claim 1  wherein said first fluid flow controller comprises a first discharge manifold having at least one individually operated valve, and said second fluid flow controller comprises a second discharge manifold having at least one individually operated valve.  
     
     
         7 . A trenching unit according to  claim 1  wherein said jetting arm comprises a third section having at least one nozzle, and a third fluid supply device for supplying fluid to said at least one nozzle in said third section of said jetting arm, and a third fluid flow controller for controlling the flow characteristics of the fluid supplied to said third section of said jetting arm.  
     
     
         8 . A trenching unit according to  claim 1  wherein said jetting arm further comprises an adjustable mounting to said housing and drive means for moving said housing over a medium to be trenched.  
     
     
         9 . A trenching unit according to  claim 8  comprising an adjusting device for setting a vertical position of said jetting arm relative to said housing.  
     
     
         10 . A trenching unit according to  claim 9  wherein said device for setting a vertical position of said jetting arm relative to said housing comprises a hydraulic actuator.  
     
     
         11 . A trenching unit according to  claim 1  comprising an adjusting device for setting an angular position of said jetting arm relative to said housing.  
     
     
         12 . A trenching unit according to  claim 11  wherein said adjusting device for setting an angular position of said jetting arm relative to said housing comprises a hydraulic actuator.  
     
     
         13 . A trenching unit according to  claim 10  or  claim 12  comprising means for remotely controlling one of said hydraulic actuators.  
     
     
         14 . A trenching unit according to  claim 1  wherein said jetting arm is oriented horizontally relative to said housing.  
     
     
         15 . A trenching unit according to  claim 1  comprising an adjusting device for setting an angular position of said jetting arm within a horizontal plane perpendicular to the direction of motion, for cutting different profiled trenches.  
     
     
         16 . A trenching unit according to  claim 1  comprising a device for moving said jetting arm reciprocally in a direction perpendicular to a direction of motion of said housing.  
     
     
         17 . A trenching unit according to  claim 1  wherein at least one of said first fluid supply device and said second fluid supply device comprises a water pump.  
     
     
         18 . A trenching unit according to  claim 1  comprising a device for guiding said trenching unit along a pipeline.  
     
     
         19 . A trenching unit according to  claim 1  comprising a communications device for communicating with a support vessel.  
     
     
         20 . A trenching unit comprising: 
 a housing;    a jetting arm, said jetting arm having: 
 at least one nozzle; and  
 an adjustable mounting to said housing;  
   a fluid supply device for supplying fluid to said at least one nozzle,    a fluid flow controller for controlling the flow characteristics of the fluid supplied to said at least one nozzle;    a device for adjusting an angular position at which said jetting arm is set relative to said housing; and    a device for adjusting a vertical position of said jetting arm relative to said housing.    
     
     
         21 . A trenching unit according to  claim 20  wherein at least one of said device for adjusting an angular position at which said jetting arm is set relative to said housing and said device for adjusting a vertical position of said jetting arm relative to said housing comprises a hydraulic actuator.  
     
     
         22 . An arrangement comprising: 
 at least two trenching units; and    a link connecting the two units in tandem;    wherein each unit comprises: 
 a housing;  
 a jetting arm mounted to said housing, having at least one nozzle;  
 a fluid supply device for supplying fluid to said at least one nozzle; and  
 a fluid flow controller for controlling the flow characteristics of the fluid supplied to said at least one nozzle;.  
   
     
     
         23 . An arrangement according to  claim 22  wherein the link is adjustable to set the distance between the units.  
     
     
         24 . An arrangement according to  claim 22  comprising at least two trenching units according to  claim 1 .  
     
     
         25 . An arrangement according to  claim 22  comprising at least two trenching units according to  claim 2 .  
     
     
         26 . An arrangement according to  claim 22  comprising at least two trenching units according to  claim 20 .  
     
     
         27 . An arrangement according to  claim 22  wherein the adjustable linkage is resilient.