There are several forms of mechanical, power-operated dredges. One of the most common is the "clam-shell" dredge, consisting of a pair of large, heavy iron jaws, hinged at the back, in general form resembling a pair of huge clam shells. This with its attachments is called the grapple. In operation it is lowered with open jaws, and by its own weight digs into the ground that is to be excavated. Traction is then made on the chains controlling the jaws, which close; the grapple is hoisted to the surface and its contents discharged into scows alongside the dredge.

The dipper dredge, an exclusively American type, has a bucket rigidly attached to a projecting timber arm. In operation the bucket is lowered and made to take a curving upward cut, thus dipping up the bottom material, which is discharged through the hinged bottom of the bucket. The pump or suction dredge operates by means of a flexible pipe connected with a powerful centrifugal pump. The pipe is lowered into contact with the bottom to be excavated and the material is pumped into hopper barges or into a hopper-well in the dredge itself.

The center ladder bucket dredge operates by means of an endless chain of buckets moving over an inclined plane, which in structure is a strong iron ladder, one end of which is lowered to the sea bottom. The steel buckets scoop up the material at the bottom of the ladder, which they then ascend, and are discharged by becoming inverted at the upper end of the ladder. This dredge is the only one found satisfactory in excavating rock.