SEA-GOING HYDRAULIC DREDGES 111 



the boiler to the pump engine through a 3-in. iron pipe, the usual 

 pressure carried upon the boiler being about 25 Ibs. to the sq.in. 



This pressure develops about 26 useful horse power and gives a 

 speed of about 180 revolutions per minute to the engine shaft. On 

 this shaft is a pulley 42 in. in diameter, carrying a rubber belt 12 in. 

 wide, communicating the power to the pump shaft through a pulley 

 24 in. in diameter, thus giving the pump disk and wings about 

 315 revolutions per minute. This speed with the No. 9 pump is 

 equal to the work of raising 3000 gallons of clear water per minute 

 30 ft. high through a 9-in. vertical pipe. The actual height raised 

 above the water on the St. John's bar varies with the amount of 

 sand taken on board from 10 to 11 ft. Owing to the facts that 

 the pipes are 50 ft. long with bends, are in two branches instead of 

 one and as the mixture of sand and water is heavier and more impeded 

 by friction than clear water, 300 revolutions are required to raise 

 2500 gallons of sand and water 11 ft. high through the two inclined 

 suction pipes having two turns each, discharging through a pipe 

 having one turn. 



To prevent the ends of the suction pipes being lifted off the 

 bottom by the pitching of the boat, and, as a precaution against 

 accident, a portion of each pipe is made flexible, being composed 

 of 6-in. rubber hose stretched over a coil of wire. In addition, the 

 ends are loaded with an iron frame or drag, each weighing about 

 250 Ibs., which is intended to move flat along the bottom during 

 the operation of dredging. To the under-surface of this frame, 

 directly below the mouth of the pipe, a number of teeth or knives 

 are attached to stir up the sand and aid its entrance into the pipes. 



Tackles are arranged for lifting the pipes from the bottom when 

 not dredging, or when pumping clear water to discharge the sand 

 from the bins. 



For receiving the sand, bins are located along the main deck, 

 fore and aft, on each side of the steamer's engine, each bin being 

 provided with a sliding gate over the steamer's side, which can be 

 opened anol closed at pleasure. The bottom of the bin slopes down- 

 ward toward the gates. They are filled from two open troughs, 

 one from each branch of the discharge pipe, pro vided at suitable 

 intervals with valves or gates so that the load can be distributed 

 to the bins wherever desired. 



Including the time occupied in turning the boat and emptying 

 the bins, the least average result of an entire month's work was 



