52 A TREATISE ON DREDGES AND DREDGING 



are full lifts its suction pipe or its ladder and proceeds to sea to 

 dump its load. This style of dredge is not well adapted for mate- rial 

 or soil that does not settle or precipitate in the hoppers. 



When scows or barges are used the ladder dredge is well adapted, 

 especially for hardpan or similar material. In Europe this machine 

 is used on all kinds of work both wet and dry. It was used exclusively 

 on the Suez Canal and also on some of the European canals, and in 

 open channels, when large quantities of earth have to be excavated 

 over large areas it is well adapted, as it gives a true and level bottom. 

 This type of machine is not easily affected by tides or currents, and 

 although it will excavate more cubic yards per horse power than any 

 other type, yet for working in confined places, and under trying 

 circumstances, and for power, speed and general adaptability it 

 will not compare with the dipper dredge so generally used in America. 



A great advantage of the dipper type is in economy of labor. It 

 is able to handle boulders, stumps and other obstructions, owing to 

 its great strength and power, and to the fact that it is held to its 

 work by means of powerful spuds. This machine has a great range 

 of adaptability, as it will dig at depths of 40 ft. or more, load scows 

 or cast material upon the bank. 



This dredge, as well as the grapple or clamshell dredge, depends 

 upon the operator for its speed. Everything being equal, a skilled 

 operator will excavate more material than a less experienced man. 

 Thus it is important that the operator's work be made as easy as 

 possible and all levers should be located conveniently and be easily 

 controlled. Grapple dredges cannot excavate as hard material 

 as a dipper machine, but they can work at a greater depth. Spuds 

 and anchors are used to hold the dredge in place in the same manner 

 as with a dipper machine. 



Hydraulic dredges are especially adapted to excavate homo- 

 geneous material in large quantities, when the pipe line is not over 

 3000 ft. long. With a greater length of pipe a large per cent of the 

 power is absorbed by friction in the pipes. Clay material shows 

 less wear on the pipe than sand, and a larger per cent of solid mat erial 

 is carried when clay is excavated. The most important point is 

 the cutter or agitator. The simplest agitator is a bird-cage affair 

 used on small dredges for sand. Revolving first in one direction 

 and then in the other the sand is stirred up enough to become mixed 

 with water and the suction from the pump lifts the sand and water. 

 As fast as a hole is made in the sand, the mass of sand keeps caving 



