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THE AMERICAN DREDGERS ON THE PANAMA CANAL.
New York, February 14, 1885


OUR engraving represents one of the great dredgers now in use on the Panama Canal. The contract for the ten miles of marsh work, beginning near Aspinwall, was taken by Slaven Brothers, of this city; the great machine is believed to be the most effective of anything in the same line. It was built under the patents of Messrs. H. B. Angell and H. H. Lynch. The machinery of the dredge is mounted on a scow one hundred feet long, sixty feet wide, and twelve feet deep. There are eight engines, arranged in four pairs, for operating the machinery. The main engines are for driving the buckets which do the digging, and are of 250 horse power, having Myers' adjustable cut-off. The belt from the engine runs to the top of the bucket tower to a pulley eight feet in diameter, which drives compound driving gear, connected with the upper tumbler shaft, which is ten inches in diameter. This shaft moves a thirty-six inch square drum, over which the buckets pass when they dump their load into the hopper. The bucket tower is forty-five feet high above deck. There are thirty-eight buckets, with a capacity of one and a half cubic yards each. From sixteen to eighteen buckets full of dirt per minute are discharged into a hopper attached to a cast iron elbow near the top of the tower. This elbow is five feet four inches in diameter where it connects with the hopper, and thirty-six inches in diameter where it connects at the lower end to the discharge pipe, which is attached to the elbow. This pipe is made of boiler iron and is one hundred and fifty feet long. The distance the mud falls, the position in which it strikes, and the inclination of the discharge pipe give the mud a velocity of from 1,300 to 2,000 feet per minute through the pipe, according to the kind of material which is being dug and discharged. The discharge pipe is supported by a derrick which stands on the scow. Water is pumped into the hopper by a pair of ten inch pumps from the canal through a seven inch pipe which passes through the bottom of the boat and extends to the hopper, at top of bucket tower. A second pair of engines of thirty horse power raise and lower the ladder that supports the buckets; they are attached to a drum for that purpose. There is a hinged joint in the ladder outside of the derrick, for the purpose of operating one section of ladder independent of the other. A half inch cable connects the drum to the outward end of the lower section by two bails. The endless chain to which the buckets are attached is made of horseshoe iron 1-and- 1/8 inches by 9 inches. Another pair of spud and gypsy engines of thirty horse power is used for raising the spuds and feeding the buckets. The dredger rests upon the spud, upon which it can be revolved without stopping the dredging buckets, thus enabling the operators to dig from side to side at will. A chute connects with the hopper, and is boarded on the sides to prevent the mud or water from falling upon the deck. The fourth pair of engines, also of thirty horse power, is connected to a windlass for snag pulling. The engines are all supplied with steam from one set of three boilers, and will require only about two tons of coal each day. Six men, including a superintendent, run the entire machine. Capacity of the dredger, 1,000 cubic yards per hour.

The cutting of the canal is to be 100 feet wide at the bottom, 185 feet at the top, and 27½ feet deep.

A correspondent of one of our city papers, resident in New York, who has just returned from a visit to the works of the Panama Canal, writes:
The canal is an assured fact. The French seem thoroughly to understand the work before them, and have made admirable preparations to cover all contingencies. They take the greatest care of their employer, and their hospital service is unsurpassed in the world. A force of over twenty thousand men is a good many to handle, and, of course, entails a lot of red tape, but that seems necessary, especially with Frenchmen. But they have a grand chief in M. De Lesseps, and have now a splendid working staff in M. Diggler and his officers.

I was very anxious to see the Scotch dredger at work in the harbor of Colon, but it was not in operation during the eighteen days I was there. [For engravings and description of this dredger see SUPPLEMENT 491, April 5, 1884.] I was disappointed, as I wished to compare it with our mammoth American dredgers. It cost, I understand, £50,000, and is considered very good for deep-sea dredging, but for actual work I saw nothing there to compare to our American dredgers. I went on board and saw the latter work on many different occasions, and was highly satisfied. The principle is unique and very ingenious. The tower is iron, 75 feet high; the buckets and chains are of steel, and each bucket will and does take up 1½ tons of earth each lift. The spud, on which the dredge rests and revolves, enables it to take a sweep of 15 meters wide, and each move of the spud moves her forward 18 feet, so that, like a mowing machine, she cuts a swathe (to use a farmer's expression) 45 feet wide, 18 feet long, and 9 feet deep on each movement forward. They work perfectly, and it is indeed a grand sight to sit, as I have done, for an hour or two at a time, and watch them working. Rotten coral, roots, stumps of small trees, etc., all come up with the dirt, and make no difference. Of course where rock is struck, or hard coral, or an old petrified monarch of the forest, blasting has to be done by the canal company ahead of us. Otherwise, after the ground is cleared of vegetation, trees, etc., we simply start in and eat—literally eat—our way through with absolutely no other preparation whatever, no men on shore working ahead or any other way. What we take out goes through the dredger's own discharge pipe on to the bank, and forms practically the bank of the canal proper. We have now cut from the sea (the harbor of Colon) three and a half miles of the canal by one machine, and some ten miles up we have two other machines entering from the Chagres River, cutting their way back to meet the first machine. A fourth machine leaves here to-morrow, and will join the others by the middle of January, while eleven more are building, and will follow, one each six weeks or so, until all are fairly at work. Our contract is for 30 million cubic meters, and will probably lead to half as much again, as it is conceded by the canal company and every one in the isthmus that nothing like our machines has been seen or used anywhere. One instance of their capacity I saw myself. A Suez dredger was put to work at a certain spot. After fifty days she was withdrawn, and one of ours took its place, and did in five days as much as the other had done. Our machines cost about $125,000 (say £25,000), and require about 20 men to work them.


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