Page:Popular Science Monthly Volume 32.djvu/175

Rh York," the greatest dredge probably ever constructed; built by the American Contracting and Dredging Company, and by them used at Panama. The engines of the largest Suez dredges had a force of seventy-five horse-power. Those of the "City of New York" have a force of three hundred. To run all parts of the complicated machinery, no fewer than eight are employed. The huge ladder which carries the buckets is one hundred and ten feet long; the chain to which the buckets are immediately attached, if ruptured, would reach from the top to the bottom of Bunker Hill Monument. Two discharge-pipes, each three feet in diameter and one hundred and eighty feet long, carry the earth to the banks. By means of steam-pumps, as in the case of the Suez dredges, water is forced into the bell or hopper, and the discharge facilitated. The effectiveness of this mechanism is not due solely to its construction on an enlarged scale; contrivance comes in for part of the credit, and has effected part of the result. One of the peculiarities of the American dredges may be referred to. To steady the vessel and hold the buckets against the bank, two spuds or pile-anchors are employed. In the case of the "City of New York" these spuds are sixty feet high and two feet in diameter. They pass through the hull, one on each side, and the iron chisel point at the termination of each weighs eighteen hundred pounds. This is planted in the bottom. When spud No. 1 descends, it serves as a pivot around which the dredge, carrying the bucket-ladder in operation, slowly revolves, thus traversing the arc of a circle. When No. 1 is raised, No. 2 is lowered, and serves in like manner as a center. After this fashion, planting a foot at a time, this huge digging, spouting creature, as one might term it, advances. The movement through an are is regulated by two distance-lines, so called. These are attached to windlasses, one on each side of the forward deck, the other end being attached to the shore. As one line is drawn in, the other is paid out, and by this simultaneous process the motion in curves is maintained. A high degree of interest attaches to a structure combining power, ingenuity, and complexity as these are not united in any other mechanism of the sort. Such among contrivances of the kind is the "City of New York."

With regard to the amount of excavation effected by the dredgers of the American Company, Mr. Bigelow sets it down as about double the largest output of any machine at Suez. Lieutenant Kimball, comparing the output of the later American dredges with the best at Suez, sets it down as more than double, twelve hundred cubic metres per hour, as compared with four hundred and eighty.

While in the matter of dredges Americans have contributed of late more than others by fresh devices and an increase of dimensions, the French seem to have effected like results with regard to excavators.