Dredge.
A scraper or drag-net for gathering mud, sand, or oysters, as the case may be, from the bottom.
Mud is dredged to improve the channel, sand for making mortar, oysters from their beds, for food.
A bucket or scoop for scraping mud, sand, or silt from the bed of a stream, pond, or other body of water.
Such are usually on endless chains.
See dredging-machine.
The “clam-shell” dredge used for removing the excavated material from the working-chamber of the
East River, New York, bridge caisson, consists of a pair of scoops which are hinged to an axis and close upon the load, whether a mass of mud or gravel, or boulder of moderate size.
The dredge ascends and descends in a vertical water-shaft in which the water rises as high as its natural level on the outside of the caisson.
The view shows a portion of the working-chamber through which the dredge-shaft passes, and the numerous layers of timbers which form the roof of the workingchamber and support the masonry of the pier.
The dredge is lifted with its load by the tackle above, and, being suspended above the car, the contents are dumped into the latter by shifting the points of suspension of the latter to the chains which are connected to its outer corners; this causes the scoop to gape open and spill its contents.
The car is then run down an incline, and dumps its load into a lighter alongside the caisson.
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Oyster-dredge. |
A rake and bag dragged over an oyster-bed to detach and gather the bivalves.
The dredge is towed by a sail-boat, and by hand or tackle is lifted by a lever swung from a davit, and is eased over the side by a roller mounted on the gunwale, as shown in
Figs. 1756,
1757. See net; trawl.
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Oyster-dredge. |
