110 A TREATISE ON DREDGES AND DREDGING 



avoiding unnecessary turns. The dredges began to work at 5 A.M. on 

 Monday and did not return to the docks until Saturday at noon, 

 working continuously day and night, stopping only for holidays or 

 repairs. The efficiency of the work at night was estimated at 90 

 per cent of that done in daytime. 



As previously stated, Gen. Gillmore used the hydraulic dredge 

 of the hopper type in 1871, thus the honor of first usin; this type 

 belongs to the United States. The following description is slightly 

 condensed from a paper by Gen. Gillmore and published in Van 

 Nostrand's Magazine, September, 1872: 



A novel device, he says, for utilizing the powers of the centrifugal 

 pump, has recently been put in successful operation by the writer, 

 in deepening the channel over the bar at the mouth of the St. John's 

 River, Florida. Upon this bar the ocean swell, which constantly 

 prevails, is of such exceptional magnitude and violence that the 

 usual method of dredging into lighters or scows, ordinarily pursued 

 in still water, is entirely impracticable. 



After futile attempts to get the bar channel deepened by contract, 

 the following plan was adopted, viz. : To provide a suitable steamer 

 and fit her out with a 9-in. centrifugal pump, two branches of 6-in. 

 suction pipe, and timber bins on deck for holding the sand pumped 

 up from the bottom. 



The steamer used, the " Henry Burden," was originally built for 

 carrying passengers and light freight, is 132 ft. long, 24J ft. beam 

 with a draft of 5J ft. and carried only 100 tons on a draft of 7 ft. 

 She is a side-wheel steamer with engines of 120 H.P., and although 

 the best that could be found at that time yet she is not exactly 

 adapted to the work required of her, on account of her comparatively 

 deep draft and small carrying capacity, which rendered it impossible 

 to prosecute work the during periods of low water. 



A No. 9 centrifugal drainage pump of the Andrews patent is 

 located on the main deck aft, about 35 ft. from the stern post. 

 Its suction and discharge openings are each 9-in. in diameter. To 

 the suction there are comx < -u <! by a 2-way branch pipe two 6-in. 

 suction pipes, instead of one 9 in. as usual, the object being not 

 only to work on both sides of the boat simultaneously, but to mnke 

 the necessary handling of the pipes as easy and prompt as possible. 



The engine used to drive the pump consists of two cylinders 

 connected upon one crank, at right angles to one another, and 10 in. 

 in diameter, each with a 10-in. stroke. St<;im is conveyed from 



