PURPOSE:To simplify the structure of a grabber as well as attain the miniaturization and weight reduction of the grabber by a method in which a pair of grabbers are provided at the lower end of a strut having a drain trap inside, a control valve is opened upon touch to the seabed, and a water-pressure cylinder is driven by the pressure of sea water to close the grabbers. CONSTITUTION:A drain trap 5a is formed in a strut 5 suspended from a base ship, and the lower end of the trap 5a is closed by a stop valve 15 and the upper end is led to the lower chamber 10b of a water-pressure cylinder 10. The flow path is closed by a control valve 17. A pipeline 23 having an opening leading to sea water is connected to the upper chamber 10a and a stop valve 24 and a check valve 25 are provided in parallel. When the stop valves 15, 21, and 24 are closed and thrown down, the pressure of sea water acts on the chamber 10a all the time. When they reach the seabed then, they are pushed up by touch of an operating lever 19, the control valve 17 is opened, and water in the lower chamber 10b is discharged to the trap 5a. A piston rod 12a is extended to close the grabber 7. The operations can thus be performed without the needs for power.
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