PURPOSE:To enhance the efficiency of suction by a method in which a sending reel is horizontally set to a dredging hose near the water surface of the hull and the intermediate part of the dredging hose is engaged on a hose cradle set on the hull in a vertically movable manner. CONSTITUTION:The hull 10 is provided with a water jet pump to break up the sand of the seabed, a water pump to dilute the sand, and a dredging pump 51 to suck up the sand. In the operation of collecting sand, a dredging tower 14 is lowered, a dredger 15 is landed on the seabed, and a hose cradle 43 is lowered to an opening 11. The pump 51 is then operated to start up the operation, where a dredging hose-sending reel 65 is positioned near the sea surface, and the hose receiver of the hose cradle 43 is also lowered to near the sea surface. Therefore, the height of suction and pumping is reduced, and sand can be sucked up with good efficiency. The dredging pump 51 can thus be used as a suction pump.
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