Grab Dredger

Grab dredgers are commonly known as Mechanical dredgers. 

Mechanical dredgers come in a variety of forms, each involving the use of grab or bucket to loosen the in situ material then raise and transport it to the surface. 

 

Grab Dredgers come in 2 categories:

 

1. The first category of grabdredgers are those which come with clam shell grab - see detail. 

They are usually associated with river deepening where a grab (Clam shell grab) or bucket is deployed and attached to a crane or crane arm and the crane is positioned on the bank of the river or area to be reclaimed or deepened. The spoil collected is either dumped ashore in the area of the crane swing or into vehicles to be removed from the area. 

 

2. The second category of grab dredgers are those which work alongside a suction dredger dumping spoil into a hold whereby discharge is by a bucket arrangement. 

 

These units are associated with river and estuarial channel deepening and dredging in restricted areas such as marinas, locks etc. 

The Grabs are either fixed onto a barge or the barge has a designated crane fitted. These crane barges are normally dumb barges although some are self propelled. Some have anchors at each corner to be deployed to fix the location and some have spuds for securing the barges position. 

These spuds are heavy pike-like structures which can be dropped into the sea bed by the dredger. 

 

 

The usual method for disposal of the spoil is by lighterage barges which are filled and towed away from the dredge site. The self propelled grab barges often have their own holds with through hull hoppers for discharge although these are ineffective once moved from the site and have mainly been phased out. 

 

Spoil discharge methods are numerous and each can be incorporated into the vessels dredging unit. 

 

In each case the dredge barge either has its own power plant and for the smaller units a grab / bucket crane on a dumb barge would mean the crane has its own power.