Dredging arrangement for dredging material from an underwater bottom

Abstract

The invention relates to a dredging arrangement for dredging material from an underwater bottom ( 6 ). The dredging arrangement comprises a drag head ( 10 ) and a suction pipe ( 2 ). The drag head ( 10 ) comprises a drag head body ( 11 ) which is attachable to the suction pipe ( 2 ). The drag head ( 10 ) comprises at least one moveable part ( 12, 14 ), such as a visor and a valve, which can be controlled to change the dredging characteristics of the drag head ( 10 ). The dredging arrangement comprises wire connector ( 15 ) and transferring device ( 16 ). The wire connector ( 15 ) being connectable to a wire ( 4 ) via which a pulling force can be applied, wherein the transferring device ( 16 ) are arranged to transfer the pulling force to the at least one moveable part ( 12, 14 ) to control the characteristics that part.

1 . A dredging arrangement for dredging material from an underwater bottom, the dredging arrangement comprising a drag head and a suction pipe, the drag head comprising a drag head body which is attachable to the suction pipe, the drag head comprising at least one moveable part which can be controlled to change dredging characteristics of the drag head,
 wherein the dredging arrangement comprises a wire connector, a wire controller and a transferring device, the wire connector being connectable to a wire via which a pulling force can be applied, wherein the transferring device is arranged to transfer the pulling force to the at least one moveable part, and the wire controller is arranged to exert a controllable pulling force on the wire and also functions as hoisting device for lowering and lifting the dredging arrangement towards and from the underwater bottom.   
     
     
         2 . The dredging arrangement according to  claim 1 , wherein a biasing device is provided exerting a biasing force on the at least one moveable part and wherein the wire connector and the transferring device are arranged such that the transferred pulling force opposes the biasing force. 
     
     
         3 . The dredging arrangement according  claim 1 , wherein the at least one moveable part is a visor, the visor being rotatable with respect to the drag head body about a rotational axis which, in use, is substantially horizontal and perpendicular to a dredging direction. 
     
     
         4 . The dredging arrangement according to  claim 3 , wherein the drag head comprises a biasing device exerting a biasing force on the visor such that the visor is biased in a downward direction. 
     
     
         5 . The dredging arrangement according to  claim 4 , wherein the biasing device comprises at least one of a mechanical spring, a hydraulic spring, and a gas spring. 
     
     
         6 . The dredging arrangement according to  claim 4 , wherein the wire connector and the transferring device are positioned such that the transferred pulling force opposes the biasing force. 
     
     
         7 . The dredging arrangement according to  claim 1 , wherein the moveable part is a valve provided to open and close an opening in the drag head or a lower part of the suction pipe to allow water to enter. 
     
     
         8 . The dredging arrangement according to  claim 7 , wherein the drag head or suction pipe comprises a biasing device exerting a biasing force on the valve such that the valve is biased towards a closed position. 
     
     
         9 . The dredging arrangement according to  claim 8 , wherein the wire connector and the transferring device are positioned such that the transferred pulling force opposes the biasing force. 
     
     
         10 . The dredging arrangement according to  claim 1 , wherein the transferring device comprises one or more pulleys and a transferring cable being guided by the one or more pulleys, wherein the wire connector is connected to one of the pulleys being a moveable pulley, the transferring cable being arranged to transfer the pulling force from the wire connector to the moveable part. 
     
     
         11 . The dredging arrangement according to  claim 1 , wherein the transferring device comprises a hydraulic force transmitter. 
     
     
         12 . The dredging arrangement according  claim 1 , wherein the transferring device comprises a lever which is connected to the wire connector and to the at least one moveable part. 
     
     
         13 . A dredging vessel comprising a dredging arrangement for dredging material from an underwater bottom, the dredging arrangement comprising a drag head and a suction pipe, the drag head comprising a drag head body which is connected to the dredging vessel by means of the suction pipe, the drag head comprising at least one moveable part which can be controlled to change dredging characteristics of the drag head, wherein the dredging vessel comprises a wire connectable to the dredging arrangement for lifting and lowering the dredging arrangement from and to the underwater bottom,
 wherein the dredging arrangement comprises a wire connector, a wire controller and a transferring device, the wire connector being connectable to the wire via which a pulling force can be applied, wherein the transferring device is arranged to transfer the pulling force to the at least one moveable part, and wherein the wire controller is arranged to exert a controllable pulling force on the wire and also functions as hoisting device for lowering and lifting the dredging arrangement towards and from the underwater bottom.   
     
     
         14 . The dredging vessel according to  claim 13 , wherein the dredging vessel comprises a gantry via which the wire can be guided from the wire controller to the dredging arrangement. 
     
     
         15 . A method for dredging material from an underwater bottom using a dredging arrangement, the dredging arrangement comprising a drag head and a suction pipe, the drag head comprising a drag head body which is attached to the suction pipe, the drag head further comprising at least one moveable part which can be controlled with respect to the drag head body to change dredging characteristics of the drag head, the dredging arrangement being connected by a wire to wire controller to lift and lower the dredging arrangement from and to the underwater bottom, wherein the method comprises
 a) lowering the dredging arrangement to an underwater position with the drag head positioned on the underwater bottom, and   b) dredging by dragging the drag head over the underwater bottom in a dredging direction by means of a dredging vessel,   the dredging arrangement comprising a wire connector and a transferring device, the wire connector being connectable to the wire via which a controllable pulling force can be applied by the wire controller, wherein the transferring device is arranged to transfer the pulling force to the at least one moveable part, wherein the method further comprises:   b1) controlling the wire controller to dynamically control a pulling force exerted on the wire during dredging.   
     
     
         16 . The method according to  claim 15 , wherein the pulling force is controlled dynamically during dredging in a range which lies below a lifting force required for lifting the dredging arrangement from the underwater bottom and more than a minimum force to prevent slackening of the wire. 
     
     
         17 . The method according to  claim 15 , wherein the wire controller comprises a first wire controller and a second wire controller, and wherein action a) is performed by the first wire controller and action b1) is performed by the second wire controller. 
     
     
         18 . The method according to  claim 17 , wherein action b1) comprises temporarily operating the first and second wire controllers in opposite directions. 
     
     
         19 . A method for dredging material from an underwater bottom using a dredging arrangement according to  claim 1 .