LADDER OR ELEVATOR DREDGE 71 



above deck, while the latter are constructed with towers 75 and 

 even 80 ft. high. As a rule, nearly all the ladder dredges either 

 of the hopper type or those in which the material is dumped into 

 scows, have low towers. High towers are employed on dredges 

 used in narrow canals and rivers, which dump the dredged material, 

 by gravity, through a long inclined conveying tube, the material 

 being used for filling lowlands along the shores of the rivers or 

 forming the levee or dykes of canals. 



When the buckets, filled with the dredged material, reach the 

 top of the ladder and revolve around the driving tumblers they 

 discharge their contents into a large box in communication with 

 an inclined chute. Both the box and the chute are covered in order 

 to prevent the material from splashing on deck. With low towers, 

 located at the center and dumping material into scows, there are 

 usually two chutes so as to load scows located on each side of the 

 dredge. By a system of chains and pulleys the chutes may be called 

 into service one at a time or simultaneously, at the will of the operator. 

 The inclination of the chute depends upon the quality of material 

 to be dredged. Mr. Webster gives the following inclinations for 

 the various materials: 



Soft mud 1 in 10 



Soft clay 1 in 12 or 14 



Hard clay 1 in 14 or 16 



Fine sand and water 1 in 20 to 25 



Power is conveyed to the driving tumbler by endless chain and 

 sprocket wheels, by belt connection and by direct action of the 

 engine through a system of cog wheels. The method of turning 

 the driving tumbler by an endless chain and sprocket wheel works 

 very well in loose soils, but in rock and hard soils the sprockets have 

 a tendency to break easily. The method of transmitting the motive 

 power to the dredging machinery by means of a belt connecting 

 the flywheel of a horizontal engine with a system of cog wheels 

 acting directly upon the driving tumbler works well in loose soils, 

 but in tenacious material the belt has a tendency to slip. This can 

 be partially overcome by an attachment fitted with a tightener 

 pulley, which can increase or decrease the tension of the belt. Such 

 an arrangement has given satisfactory results except in dredges 

 working through rock. Another manner of conveying the power 

 to the driving tumbler is by a system of gear wheels acting directly 



