Queensland State Archives posted a photo:
A grab dredger picks up seabed material with a clam shell bucket, which hangs from an onboard crane or a crane barge, or is carried by a hydraulic arm, or is mounted like on a dragline.
This technique is often used in excavation of bay mud. Most of these dredges are crane barges with spuds.
Description source:
Wikipedia
View the original image at the Queensland State Archives:
Digital Image ID 12423