DREDGING FOR INDUSTRIAL PURPOSES 237 



steel bar links pinned at their ends so as to allow them to work 

 around the tumblers. Roller bearings are fitted along the ladder 

 at intervals to insure uniform support to the train of loaded 

 buckets. The material is cut out and carried up the ladder and 

 dumped at the top tumbler. The empty buckets are returned 

 toward the bottom without support so that the empty train in 

 motion hangs suspended between the top and bottom tumblers. 

 The sand and gravel are separated by a moving screen, which is 

 so arranged that the coarse gravel may be loaded on one side of 

 the dredge and sand on the other. 



The machinery used in the non-propelling type of dredge 

 usually consists of boiler and engine equipment of sufficient power 

 to operate the conveyor system and provide power for capstans, 

 syphons, etc. The transmission of power to the ladder is generally 

 made through chain gears and the raising and lowering of the dredg- 

 ing end of the ladder is performed by a lifting device operated by 

 power from the main engine. Steam capstans are provided for 

 handling the barges and for changing location by using the mooring 

 lines. In the propelling type of ladder dredge the boiler equipment 

 must be of sufficient capacity to operate both the dredging and 

 propelling machinery. The latter consists of the usual stern wheel 

 equipment, which of course is entirely independent of the dredging 

 apparatus. 



The Grab-bucket Dredge. The use of the grab bucket or clam- 

 shell in sand dredging for commercial purposes is very limited. This 

 type in the relatively shallow rivers cannot be operated as econom- 

 ically as the other types discussed, since its speed is much lower and 

 the nature of its operation necessitates elaborate details for the 

 screening of the sand or gravel. However, as illustrating a novel 

 method of using the grab bucket, attention is called to the figure 

 showing such an apparatus for digging gravel direct from the river 

 bed. The apparatus travels along the broad gauge track on the 

 river bank and the cars to be loaded are run under the machine. The 

 grab bucket travels out on the overhanging arm, and on being filled 

 is carried back and the gravel dropped into the cars. 



Method of Handling Sand. In transporting the sand or gravel 

 from the dredge to the unloading station, two types of carriers 

 are used, the decked barges and the open-hold barge. In the Missis- 

 sippi River sand business with the centrifugal dredge, the decked 

 type is exclusively used, while in the upper Ohio district where 



