Page:The New International Encyclopædia 1st ed. v. 06.djvu/523

* DREDGE. 453 DREDGE. timbers or spuds, which can be thrust down into the bottom and so lutveui the barye from mov- ing. Dipper dredges are more extensively used in America than in Elurojiean countries. One of the hirgest dipper dredges ever built was the I'an-Atncrican, constructed in IS'.t'J for work on the (ireat 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 G inches deep. There are four spuds — two at the bow, each 4X4 feet square and 50 feet long, and two at the stern, each 2X2 feet square and 50 feet long. These spuds are raised and lowered by power. The A-frame and boom are of steel; the .V-frame is 53 feet high and the boom is 53 feet long and weighs 30 tons. The dipi)er-handle is of wood, reinforced by steel plates, and carries a dipper holding 814 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 constnicted much like the dipper dredge in respect to the barge, A-frame, and boom : but instead of a dipper the excavating device pro])er is a grapple which is so suspend- ed from the end of the boom that it can bo 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 (X. Y.) breakwater. fSce Bre.^k water.?.) The hull was of wood, 120 feet long, 40-foot beam, and 121A feet deep, with a false bow and stem 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 tj-pe. with a capacity of 10 cubic yards and weighing 15 tons. At Buffalo, Js. Y.. this dredge worked in water 65 feet deep, and loaded 10 or 11 scows of 400 cubic yards capacity in 10 hours. The CoxTixfor.s-CnAix Bfcket Dbedge 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 wellhole 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 inter-als along this chain are attached scoop buckets, which of cotirse travel with the chain. As eacli bucket reaches the bottom of the girder, which is in contact with the bottom of the channel being excavated, it scoops up a portion of the material and carries 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. Sometimes the girder, with its chain of buckets, is arranged to pass over one or both sides of the dredge-hull, instead of through an inside well. A continu- ous-chain dredge of 1000 horse-power capacity was built during 1S99 for the harbor improve- ments of Vladivostok, 'Russia. This dredge has a hull 162 feet long, 33 feet beam, and 121-. feet deep. The hull is of steel, as is also the frame- work carrying the girder. The gii-der consists of two parallel plate girders braced together by transverse struts. Tlic 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 east 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. SucTiox Dredges are extensively used where the material to be excavated is nuid, sand, or other soft matter which can be mixed with water and pumped through pipes. The excavating ma- chinery consists of a suction pipe which can be lowered through a well or over the side or end of the hull, a centrifugal pump for sucking or drawing a stream of water through this suction pipe, and a discharge pipe through which the pxmip discharges the water thus sucked in. In operation the end of the suction pipe is lowered to the soft bottom, and partly buries its end in the material. The pump is then started, and sucks a stream of water and mud through the suction pipe and discbarges it into the discharge pipe. In most dredges of this type the end of the suction pipe is provided with revolving cut- ters or with water jets to loosen the material, so that it will be more easily drawn into the suc- tion pipe. The discharge pipe may lead to hop- pers in the dredge, or it may be extended to the shore and discharge at some point where land is to be filled in or where the waste material will do no injury. The two suction dredges built dur- ing 1900 for removing the 40.000.000 cubic yards of sand and mud in the East Channel improve- ment of Xew York Harbor are among the most perfect suction dredges of the hopjier type ever built. These dredges have hulls 300 feet long, with a beam of 52'f. feet and a depth of 25 feet. The hoppers on each dredge have a capacity of 2800 cubic yards, and occupy a space of 125 feet amidships on each side of the hull. Between the two rows of hoppers is the well for the suction pipe. Water jets are used to loosen the mate- rial. The centrifugal pump has a capacity of 75.000 gallons of water jx-r minute. The dredge is provided with its own propelling machinery. The four types of dredges which have been briefly described are often modified in their construc- tion and arrangement for special u«e?. and the features of one type are often combined with the features of another type to form n combination machine. The best descriptions of dredges are to be found in the various engineering society period- icals and the engineering papers of Europe and America.