A grab or mechanical grab is a mechanical device with two or more jaws (sometime clamshell-shaped), used to pick things up or to capture things. Some types include:
Roundnose grab
Clamshell grab
Orange-peel grab
in Dutch and German they are called poliep grijpers/ Polypengreifer = "polyp grabs".
There are different ways of open/close the grabs:
electro-hydraulic / diesel-hydraulic
mechanical by rope(s) (1-rope, 2-ropes, 3-ropes, 4-ropes)
Grabs can be used for:
dredging
bulk handling (e.g. loading/unloading ships)
salvage (e.g. ship-wrecks, oil)
seabed sampling[1]
History
The mechanical grab,[2]: 21 specifically the clamshell grab,[3] was invented by the PersianBanu Musa brothers and described in their Book of Ingenious Devices in the 9th century. It was an original innovation by the Banu Musa that does not appear in any earlier Greek works.[2]: 21 The grab described by the Banu Musa was used to extract objects from underwater,[2]: 44 and recover objects from the beds of streams.[3]