174 ENGINEERING FOR LAND DRAINAGE. 



dining-room, and sleeping-berths for the accommoda- 

 tion of the working force. 



Another style is the drag-boat dredge, which be- 

 gins operations at the outlet of the ditch and completes 

 the work as it goes up-stream. The excavating 

 machinery is similar to that just described, but it is 

 mounted compactly on a boat about 7 feet deep, the 

 sides having an angle of forty-five degrees and a bot- 

 tom as wide as may be desired. Some are made as 

 narrow as 4 feet on the bottom. The machine is 

 moved forward by means of a wire cable which is an- 

 chored a few hundred feet ahead of the boat and at- 

 tached to a winding drum placed underneath the deck 

 of the boat. When it is desired to move the boat for- 

 ward, the drum is set in motion, which winds up the 

 cable and moves the boat forward. Little or no water 

 is required for the successful operation of a machine of 

 this kind. The ditch can be dug with any desired side 

 slope, and the grade can be followed accurately by 

 means of guides set ahead of the work in accordance 

 with the survey. It will be noticed that the float 

 dredge must have water to work in and begins at the 

 upper end of the ditch and proceeds down the stream. 

 The drag boat requires no water except to supply the 

 boiler, begins at the outlet and propels itself up-stream. 

 The first is adapted to large ditches where the water is 

 plenty. The second is used most successfully for 

 smaller ditches, where the water supply is small during 

 the operating season. 



The excavated earth Is dropped on either side of the 

 ditch, leaving a clear berm of from 6 to 8 feet as de- 

 sired. The efficiency of these machines for doing this 



