23G 



A TREATISE ON DREDGES AND DREDGING 



of boiler is used, and all these commercial dredges are of the non- 

 propelling type. 



The Ladder Dredge. For the excavation of gravel in the upper 

 Ohio and Allegheny Rivers the hydraulic dredges are not found 

 suitable owing to the fact that the material will not readily flow 

 into the end of the suction pipe and the wear on the pump and other 

 parts of the machine would be simply enormous. For such work 

 the ladder or elevator type of dredge is well adapted, and in fact, 

 almost all the dredges operated by the sand companies in the upper 

 Ohio and Pittsburg districts are of this type. Fig. 78. 



The hull used in this type of dredge is of the usual square barge 

 construction. It is built of wood with heavy timber frames, 

 thus securing great strength and stiffness. The dredging apparatus 



FIG. 78. Ladder Sand Dredge. 



is usually arranged on the side, since this results in cheap construc- 

 tion, and allows a more compact arrangement of machinery. The 

 hull is housed over and frequently quarters are provided for the 

 crew. Some of the dredges are self-propelling, the dredging 

 apparatus being fitted on the side of a stern-wheel river steamboat. 



The ladder is of very strong construction; as a rule, it is of timber 

 with steel bracing. The members forming the ladder are connected 

 by bracing, and at their upper end by a shaft which is carried in a 

 frame forming part of the hull, so as to permit the ladder to revolve 

 and change the position of the lower end. 



The top tumbler construction is of great strength, as it is here 

 that the power is applied to the conveyor system and the cutting 

 resistance overcome. The buckets forming the conveyor system 

 are usually of steel plates riveted together by a chain formed of 



