snag sucked against the roller is forced to turn by the spiral ridges towards the horizontal position on the vertical rollers 12 at least one of the vertical rollers is force driven and provided with feed teeth whereby the snag is forced to travel in its longitudinal direction as suction retains the snag tight against the rollers when the snag end reaches beyond one of the vertical rollers even a tall snag is turned by suction so that it is forced endwise into the suction pipe via the suction end b the suction end is also provided with under pressure flaps 13 which open automatically and bring water from outside into the suction pipe 5 as a result of sudden blocking of the suction end for clearing of blockage of the suction end the suction end b also comprises a blow nozzle 14 wherethrough by means of valves 15 and 16 all water produced by the high pressure pump can be injected against the normal direction the equipment of the suction end also includes illuminators 18 and a television camera 19 besides the hull the vessel a comprises a water pump 20 hydraulic pumps and air compressor as well as electric generators the steering of the vessel is accomplished by four winches 21 whose steel.