DIPPER DREDGES 165 



ber of points of special interest, but its two prominent features are 

 the following: First, it is powerful enough to dredge solid beds of 

 soft limestone rock without blasting, and second, loss of time and 

 money due to the renewal of worn and broken main cables is greatly 

 reduced by the use of a drum which enables 500 or 1000 ft. of cable 

 to be held in reserve instead of using and renewing cables of the 

 regular working length. 



The hull is of steel, 116x40 ft. and 13 ft. deep, with two steel 

 trusses 24 ft. deep extending the entire length. The trusses are 

 built of 12-in. channels and I-beams. The boom is of steel construc- 

 tion, 60 ft. long, stepped into a steel casting at the bow and supported 

 by four cables 2J in. diameter leading from the top of a 40-ft. A frame 

 stepped on top of the anchor slides. Two of those cables take the 

 strain and the other two act as safety cables. The boom is swung 

 by a pair of 2-iii. cables on a 24-ft. turntable or swinging circle with 

 arms extending on each side of the boom. These cables are wound 

 on a 40-in. drum, compound geared to a pair of separate engines, 

 with cylinders 10 X 14 in. These engines are set on the hurricane 

 deck and this arrangement gives the cables a straight head from 

 the drum to the swing circle. The dipper handle is 54 ft. long from 

 back of dipper, and weighs 15 tons; with a 5-ft. dipper it will 

 excavate to a depth giving 30 ft. of water. The sheaves for the 2J- 

 dipper cable are 8 ft. in diameter and are of built-up construction; 

 the hub, 3 ft. long, is of cast iron, bushed with a bronze, which runs 

 loose on a 9-in. shaft. The spoke section is a steel casting, keyed to 

 the cast-iron hub; the rim is also a steel casting and bolted to the 

 spokes. 



The dipper is handled by a horizontal engine of 250 H.P. capable 

 of exerting, through the gearing, a pull of 200 tons upon the 

 dipper cable. The engine has two cylinders, 16x20 in., and, as in 

 many large dredges, cables are used instead of chains. The engine 

 drives the differential cable drum, 4 ft. and 6 ft. diameter, through 

 compound gearing, requiring 19 revolutions of the engine to effect 

 one revolution of the drum. 



The cable drum is of special design, invented and patented by 

 Mr. W. S. Edward, having as its principal feature an extension for 

 about 800 ft. of cable in addition to the 200 ft. working length, 

 so that a single cable 1000 ft. long is carried; with the ordinary 

 arrangement the dredge would have a hoisting cable about 180 ft. 

 long, and when this was broken the entire cable would have to be. 



