What is a grab or clamshell dredger?

Definition and basic structure of the dredging grab bucket
Grab Dredger and Clamshell Dredger are different names for the same type of mechanical dredging equipment, the core feature of which is the gripping of bottom sediment using a suspended grapple that resembles a clamshell when closed.

Structural composition of the dredging bucket
Grab: It is composed of two hinged bucket flaps, which are opened and closed by hydraulic or mechanical drive to grab materials such as mud and sand, rocks, etc.
Crane: Mounted on the hull or platform, it is responsible for lifting and moving the grab. Some models are equipped with an automatic positioning system.
Control system: Manual or automatic control of the opening, closing, and positioning of the grab; modern models often integrate GPS and sonar technology.
How it works
Positioning: The ship or platform moves to the work area and is fixed by anchoring or dynamic positioning systems.
Lowering the grab: The crane lowers the grab to the bottom of the water, close to the sediment.
Gripping materials: The grab is closed to pick up sediment, rocks, or other substrates.
Lifting and unloading: The grab is lifted to the surface of the water and moved to a designated area (such as a barge or shore) to unload the material.
Repeat the cycle: Continue the operation until the dredging task is completed.