Dredging arrangement comprising a biasing device

Abstract

The invention relates to a dredging arrangement for dredging material from an underwater bottom ( 6 ). The dredging arrangement comprises a drag head body ( 11 ) and a visor ( 12 ), the visor ( 12 ) being connected to the drag head body ( 11 ) and is moveable with respect to the drag head body ( 11 ) over a predetermined range. The biasing device ( 60 ) is provided in between the drag head body ( 11 ) and the visor ( 12 ) exerting a biasing force on the visor ( 12 ) over a biasing portion of the predetermined range, the biasing portion being at least 25% of the range.

1 . A dredging arrangement for dredging material from an underwater bottom, the dredging arrangement comprising a drag head body and a visor, the visor being connected to the drag head body and being moveable with respect to the drag head body over a predetermined range, wherein a biasing device is provided in between the drag head body and the visor exerting a biasing force on the visor over a biasing portion of the predetermined range, the biasing portion being at least 25% of the range, wherein the predetermined range is adjustable and defined by mechanical stops. 
     
     
         2 . The dredging arrangement according to  claim 1 , wherein the biasing portion is at least 40% of the range. 
     
     
         3 . The dredging arrangement according to  claim 1 , wherein the biasing portion is at least 60% of the range. 
     
     
         4 . The dredging arrangement according to  claim 1 , wherein the biasing portion is 80% or 100% of the range. 
     
     
         5 . The dredging arrangement according to  claim 1 , wherein the visor is rotatable with respect to the drag head body about a rotational axis, the predetermined range being a predetermined rotational range, the rotational axis, in use, being substantially parallel to the underwater bottom and perpendicular to a dredging direction. 
     
     
         6 . The dredging arrangement according to  claim 1 , wherein the biasing device exerts a force on the visor such that the visor is pushed into a downward direction. 
     
     
         7 . The dredging arrangement according to  claim 1 , wherein the biasing portion of the range is an upper portion of the predetermined range and the visor moves freely in a remaining lower portion of the predetermined range. 
     
     
         8 . The dredging arrangement according to  claim 1 , wherein the biasing device is adjustable to set the biasing force being exerted. 
     
     
         9 . The dredging arrangement according to  claim 1 , wherein the biasing device comprises a spring device, the spring device being loaded in the biasing portion of the range such that the spring device exerts the biasing force on the visor. 
     
     
         10 . The dredging arrangement according to  claim 9 , wherein the spring device comprises one or more torsion springs. 
     
     
         11 . The dredging arrangement according to  claim 9 , wherein the spring device comprises one or more coil springs. 
     
     
         12 . The dredging arrangement according to  claim 1 , wherein the biasing device is mounted between the visor and the drag head body or a lower end of a suction pipe. 
     
     
         13 . The dredging arrangement according to  claim 1 , wherein the biasing device is connected to the dredging arrangement via a force transmitting construction. 
     
     
         14 . The dredging arrangement according to  claim 13 , wherein the force transmitting construction is adjustable to set a moment of force exerted on the visor by the biasing device. 
     
     
         15 . The dredging arrangement according to  claim 13 , wherein the force transmitting construction is adjustable to set the predetermined range. 
     
     
         16 . The dredging arrangement according to  claim 1 , wherein the biasing device is arranged to exert the biasing force resulting in a moment of force acting on the visor which is, averaged over the biasing portion at least 50% of a gravitational moment of force acting on the visor as a consequence of gravity acting on the visor. 
     
     
         17 . A dredging vessel comprising a dredging arrangement for dredging material from an underwater bottom according to  claim 1 , and a suction pipe connecting the dredging arrangement to the dredging vessel. 
     
     
         18 . A method for dredging material from an underwater bottom using a dredging vessel comprising a dredging arrangement, the dredging arrangement comprising a drag head body and a visor, the visor being moveable with respect to the drag head body ( 11 ) over a predetermined range,
 wherein the method comprises
 adjusting the predetermined range through the use of mechanical stops; 
 lowering the dredging arrangement to an underwater position with the drag head positioned on the underwater bottom, 
 dredging by dragging the drag head over the underwater bottom in a dredging direction by means of a dredging vessel, and 
   wherein the dredging arrangement comprises a biasing device provided in between the drag head body and the visor exerting a biasing force on the visor over a biasing portion of the predetermined range, wherein the method comprises
 adjusting the biasing device to set the biasing force being exerted. 
   
     
     
         19 . The method according to  claim 18 , wherein the biasing device is connected to the dredging arrangement via an adjustable force transmitting construction, and the method comprises,
 adjusting the force transmitting construction to set a moment of force exerted on the visor by the biasing device.   
     
     
         20 . (canceled)