TILE DII`PER DRUILP is similar in its ronstruic• ties to the ordinary steam shovel. except that the platform earrving the machinery consists of a barge instead of a car. In the ordinary dipper dredging-machines a mast or .t frame is mount ed on the front end of the barge, and to support the top end of an inelinod boom whose bottom end is pivoted to a casting on the deck of the barge. so that it ran swing par tially around like boom of a derrick. Be tween the two parallel thither: of this booin is inserted a long timber carrying at its outer end a dipper or scoop open at the top and closed by a door at the bottom By means to suitable mechanism this dipper is thrust to the bottom and given a scooping motion uhich tills the dipper: the 11•X1 1(.11 is Ihr 1111,111 r, and by .‘tinging the boom to b Ile side bring it o\ el. an attending barge. When the Well holding the bottom and the ....monis of the dipper are discharged into the barge. By sitecesske of the,e opera. lion• the bottom i• excavated to such a depth as he Ti) Itoe digging thrust of the dipper, the is provided uilh vertieal timbers or spuds, which can be thrust down into the bottom and so prevent the barge from mov ing. hipper dredges are more extensively used in America than in European countries. One of the largest dipper dredges ever built was the Pan-.-Imeriean, constructed in 1899 for work on the (:rent Lakes. The hull of this dredge was built of white oak and Oregon fir, and is 136 feet long. 42 feet 3 inches beam, and 13 feet 6 inches deep. There are four spuds—two at the bow. each 4 X 4 feet, square and 50 feet long. and two at the stern, each 2 X 2 feet square and 50 feet long. These spuds are raised and lowered by power. The A-frame and boom are of steel; the A-frame is 53 feet high and the boom is 5:3 feet long and weighs 30 tons. The dipper-handle is of wood, reinforced by steel plate-, and carries a dipper holding cubic yards and weighing 16 tons. The dredge was guaranteed by the builders to take a dipper-load from the bottom at a depth of 25 feet every 40 seconds, Another form of dredge, known as the grapple dredge, is constructed much like the dipper dredge in respect to the barge, A-frame, and boom: but instead of a dipper the excavating device proper is a grapple which is so suspend ed from the end of the boom that it can be lowered to the bottom and raised with its load. One of the most common forms of grapple is the clam-shell, which consists of two parts hinged together much like the two parts of a clam shell. The mechanism which raises and lowers the grapple also serves to open and close its jaws. In operation, the grapple, with its jaws open, is lowered to the bottom, into which its weight causes it to sink partly; the jaws are then closed, and thus grasp a quantity of ma terial, which is raised and discharged into a scow by opening the jaws again. When the material
to be excavated is hard, the grapple is provided with teeth, and when so equipped it can be used to excavate loose rock. Sometimes the grapple consists of several sectors of a sphere, when it is called an orange-peel bucket. One of the largest grapple dredges ever built was designed for use in constructing the Buffalo (N. Y.) breakwater. (See BRE-AKWATERS.) The hull was of wood, 120 feet long, 40-foot beam, and feet deep, with a false how and stern to make it tow more easily, which increased the total length to 160 feet. The A-frame is 50 feet high, and the boom is 65 feet long. The bucket is of the clam-shell type, with a capacity of 10 cubic yards and weighing 15 tons. At Buffalo, N. Y., this dredge worked in water 65 feet deep, and loaded 10 or 11 stows of 400 cubic yards capacity in 10 hours.
Tu F. CONTINUOUS-CH A ix BUCKET DREDGE con sists of a hull for the support of the excavating machinery much like the hull of the dipper or grapple dredge: but the excavating mechanism is essentially different. An elevated structure on the hull carries a long girder whose top end is hinged horizontally to the top of the framework, and whose other end extends down through a in the hull to the bottom of the water. There is a sprocket wheel at each end of this girder, over which a flexible endless chain is made to run by power applied to the upper sprocket wheel. At intervals along this chain are attached scoop buckets. which of course travel with the chain. As each bucket reaches the bottom of the girder, which is in contact With the bottom of the channel being exca.ated, it scoops up a portion of the material and parries it to the top of the girder, where the load is dis charged as the bucket passes over the upper sprocket wheel. The buckets discharge into chutes leading to scows moored alongside. or to hoppers in the dredge itself. soinctinies the girder, with its chain of buckets. is arranged to pass over one or both sides of the dredge-1ml], instead of through an inside well. A continu ous-chain dredge of 1000 horse-power capacity was built during 1599 for the harbor improve ments of Vladivostok, 'Russia. This dredge has a hull 162 feet long. 33 feet beam, and feet deep. The hull is of steel, as is also the frame work carrying the girder. The girder consists of two parallel plate girders braced together by transverse struts. The sprocket at the upper end for driving the bucket-chain is quadrilateral, and that at the lower end is hexagonal. The buckets themselves have a capacity of 21 cubic feet each, and are made of plate and cast steel, with hard ened steel cutting, edges. This dredge is provid ed with propelling mechanism by which it can be navigated from port to port.