Method of recovering a deposit from the sea bed

Abstract

A method of recovering a deposit from the sea bed using a surface vessel ( 20 ) untethered from the sea bed and first and second suction vehicles ( 27; 30 ) which traverse the sea bed to suck up the deposit and are each connected to the surface vessel by a respective flexible riser ( 26; 29 ) along which a slurry of the deposit is transferred from the suction vehicles to the surface vessel. The method comprises moving the first and second suction vehicles to and fro across the sea bed in a plurality of lanes such that they travel substantially further than the surface vessel, turning or reversing each vehicle at the end of each lane in a manner such that the lanes are adjacent to one another to mine the deposit substantially without gaps between adjacent lanes. Only the suction vessels rest on the sea bed.

1 . A method of recovering a deposit from the sea bed using a surface vessel untethered from the sea bed and first and second suction vehicles which traverse the sea bed to suck up the deposit and are each connected to the surface vessel by a respective flexible riser along which a slurry of the deposit is transferred from the suction vehicles to the surface vessel, the method comprising:
 moving the first and second suction vehicles to and fro across the sea bed in a plurality of lanes such that they travel substantially further than the surface vessel, turning or reversing each vehicle at the end of each lane in a manner such that the lanes are adjacent to one another to mine the deposit substantially without gaps between adjacent lanes,   wherein only the suction vessels rest on the sea bed.   
     
     
         2 . The method of  claim 1 , further comprising moving the first suction vehicle across a first grid, with the first grid being covered by the first suction vehicle moving in a first lane in a longitudinal direction from a first end of the first grid to a second end, making a small lateral displacement before returning longitudinally to the first end along a lane adjacent to the first lane, and repeatedly moving in this way between the two ends, each time along a lane laterally adjacent to the previous lane until the first grid is completed;
 simultaneously moving the second suction vehicle in the same manner in a second grid laterally adjacent to the first grid, such that the lateral spacing between the first and second suction vehicles remains substantially constant throughout; and   once the first and second grids are completed, moving the first and second suction vehicles to third and fourth grids longitudinally adjacent to the first and second grids respectively and covering these in the same manner as the first and second grids.   
     
     
         3 . The method according to of  claim 2 , further comprising moving the surface vessel in a lateral direction while the first and second suction vehicles are moving in the first and second grids, and moving the surface vessel in a longitudinal direction as the first and second suction vehicles move to the third and fourth grids. 
     
     
         4 . The method of  claim 1 , wherein the small lateral displacement in the first and second grids takes place in the opposite lateral direction from the respective third and fourth grids. 
     
     
         5 . The method of  claim 1 , further comprising moving the surface vessel in a longitudinal direction and moving the first and second suction vehicles in a lateral direction. 
     
     
         6 . The method of  claim 5 , further comprising moving each of the first and second suction vehicles one on each side of the surface vessel. 
     
     
         7 . The method of  claim 5 , further comprising moving each of the first and second suction vehicles on both sides of the surface vessel. 
     
     
         8 . The method of  claim 1 , further comprising the steps of moving the first and second suction vehicles in an arcuate path substantially centred on the point where the respective flexible riser attaches to the surface vessel. 
     
     
         9 . The method of  claim 1 , further comprising moving each of the first and second suction vehicles one on each side of the surface vessel. 
     
     
         10 . The method of  claim 8 , further comprising moving each of the first and second suction vehicles on both sides of the surface vessel. 
     
     
         11 . The method of  claim 1 , further comprising turning each one of the first and second suction vehicles through substantially 180° when it reaches the end of lane. 
     
     
         12 . The method of  claim 1 , wherein each of the first and second suction vehicles has a mouth at each end and the method further comprises reversing each one of the first and second vessels when it reaches the end of the lane.