186 A TREATISE ON DREDGES AND DREDGING 



with a high tower dredge in the excavation of Suez Canal, taken from 

 Spoon's Engineering Encyclopedia will serve to illustrate this method 

 of transporting the debris from the dredge to land. 



At Suez the ladder dredges were provided with high towers and 

 discharged their contents into an extra long chute. See Fig. 59. 

 The length of the chute from the center of the dredge was 230 ft. 

 with an elliptical cross -section 2J ft. wide and 5 ft. high. The 

 height of the upper tumbler of the ladder was 48 ft. above the water. 

 Two centrifugal pumps supplied water to facilitate the discharge 

 of the spoil. To support the chute for its entire length a latticed 

 cantilever beam was constructed which rested both on the dredge 

 and on an iron pontoon which was placed about one-third of its 

 length from the dredge. Two uprights which stiffened the chute 



FIG. 59. Ladder Dredge with Pipe Conveyor. 



were not fixed to the pontoon, but rested on beams placed longi- 

 tudinally on the pontoon. A horizontal hinge coupled the chute to 

 the dredge and allowed its inclination to be altered. To permit 

 changes in the inclination of the chute, the uprights which supported 

 it were made telescopic. The chute was lifted by two small hy- 

 draulic presses worked by hand. 



Observations made on the passing of difficult materials through 

 chute showed the following results. Only fine sands were excavated 

 and they passed easily down a chute inclined 1 in 20 or 25 if mixed 

 with a quantity of water equal to about one-half their own bulk. 

 When the chute has an inclination less than 1 in 25 the water sepa- 

 rates from the sand which is thus deposited all along the chutes in 

 layers of continually increasing thickness. The addition of a larger 

 quantity of water does not seem to make the chute more effective, 

 and it is necessary to stir the sand with a shovel. When the sand 



