Century Dictionary and Cyclopedia
- n. An apparatus for lifting mud and silt from the bottoms of rivers, harbors, canals, etc. Some dredging-machines employ a single bivalve or clam-shell scoop; others a series of scoops on an endless chain; others some form of suction apparatus. The earliest form appears to have been a single box-like shovel or spoon, suspended from a crane rigged up on a large flat-boat. It was lowered into the mud, dragged along by means of ropes till filled, and then raised and emptied into the boat. Another early form is the chapelet or chain-pump, which, by means of an endless chain carrying buckets traveling in a trough, lifts mud and water, discharging them at the top into a flat alongside the machine. On this plan are now built some of the largest and most powerful dredging-machines in use. They consist of large, flat-bottomed boats, usually of iron, with a bucket-chain carrying nearly 40 buckets, each with a capacity of about 13 cubic feet. In excavating the Suez canal, the lifting buckets of some of the larger machines had a capacity of 5 cubic feet each, and the delivery was 20 buckets a min ute. For the delivery of the sand or spoil both chutes and traveling buckets were used, the spoil being, in some instances, delivered 230 feet from the dredger. The clam-shell dredger is largely used in the United States, and has the merit of ease of management, the scoop operating in a half-circle about the boat, so that a wide channel can be excavated without moving the boat. The scoop is suspended from a crane at the bow of the boat, and is operated by means of chains controlled by steam-power, two long flexible poles serving as guides for the clam-shell. In the machines employing a suction or exhaust, a tube is lowered into the mud, and the mud and water are raised by means of a revolving disk in the tube, or by the aid of a vacuum or an ejector. A large vessel on the boat, being exhausted of air, is connected with the submerged pipe, when the mud and water readily rise into the receiver. In another form of pneumatic dredger a pipe is lowered into the silt and closed air-tight, and steam is then turned into the upper part of the pipe, driving out the air. Many other forms are used.
“Over this channel a bridge led into the town, and offered the convenient support of its parapet to the crowd of spectators who wished to inhale that powerful odor at their ease, and who hung there throughout the working-day; the working-day of the dredging-machine, that is.”
“Parallel with the railway was a channel where small fishing-craft lay, and where a leisurely dredging-machine was stirring up the depths in a stench so dire that I wonder we do not smell it across the Atlantic.”
“In the Pyrrhaean Strait the clam was exterminated, partly by the dredging-machine used in their capture, and partly by long-continued droughts.”
“Of course, we all considered it lost -- all except Mr. Trelyon, who took the trouble to go at once all the way to Plymouth for a dredging-machine, and the following afternoon I was overjoyed to find him return with the lost ring, which I had scarcely dared hope to see again.”
“She would not have written so calmly if she had foreseen the passion which her ingenuous story about the dredging-machine was destined to arouse.”
“Well, I could see no reason why Captain Cook, if he made up his mind to repair his ship inland, couldn't have dredged out a channel to the place where the monument now stood, if he had a dredging-machine with him, and afterward fill it up again; for Captain Cook could do 'most anything, and nobody ever said that he hadn't a dredger along.”
“Next evening the storm went down, and by mutual consent our mud-pilot left, taking passage in a passing river-craft, with his pay and our best advice, which was to ship in a dredging-machine, where his capabilities would be appreciated.”
“_ Perhaps one of the young gentlemen would like a dredging-machine?”
“As the axle and the wheel go round, the pots on the cords are drawn over the wheel, and made to move in a circle like the buckets of a dredging-machine.”
“Sir C. Wyville Thomson found that the specimens of the fauna of the coast of Brazil, brought up in his dredging-machine, are similar to those of the western coast of Southern Europe.”
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