Grab Dredger / Clamshell
It is a stationery dredger, being moored, anchored, or on spud poles. The dredging tool is a grab normally consists of two half shells that are operated by wires or (electro) – hydraulically. The grab can be mounted on a dragline or on a hydraulic excavator or the backhoe type of excavator.
New innovations resulted in the modification of grabs such as the (top) open grab, (top) closed grab,and watertight grab. Grab dredgers are used at harbours, while the dragline type dredgers are usedfor deep water projects. Dredged material is then loaded into the barge.
Grab dredges, also known as clamshells, exist in pontoon and self-propelled forms. The latter usually includes a hopper within the vessel. The pontoon type grab dredger again comprises rectangular pontoon which is mounted to a revolving crane that is equipped with a grab.
Dredging operation involves the lowering of grab to the bottom, closing the grab, raising the fieldgrab to the surface and discharging the contents into a barge; or appropriately onto an adjoining bank. The size of this type is determined by the capacity of the grab bucket which can carry between 1.0 and 20 m3, depending on the horse power of the crane.
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