CENTRIFUGAL PUMP DREDGING IN N.S.W. CXIX. 
by a boiler 8’ 9” diameter and 9’ long. The centrifugal pump has 
& Spinner similar to the “N eptune,” but of only 5’ 6” diameter, 
the suction and delivery pipes being 16” diameter. Pontoons 15’ 
x 15’ x 2)’ spaced 22’ apart are used, as shown in Plate 11, for 
carrying the pipes to the shore, the arrangement of gimbal and 
Plain joints ensuring sufficient movement of the dredge in all 
directions for working to the best advantage. 
Usually these dredges are worked by making a series of furrows 
about 50’ in length, until the required width of channel is 
deepened, but they can also be operated by the crane jib swing- 
ing across the channel and trailing, or dragging, the end of the 
suction pipe; a special mouth piece ane affixed to suit this 
method of dredging, 
A very useful modification of the self loading sand pumps of 
Holland was adopted for deepening Coney Island and Gedney 
channels in New York Bay, where the water was too rough for 
using pontoons and pipes.! Instead of one pair of engines being 
used, as on a vessel of the “Neptune” class, alternately for 
Pumping and conveying the sand away, the dredging vessel was 
fitted with separate machinery for dredging and driving twin 
Screws ; and instead of the suction pipe looking forward and being 
kept up to its work, as in the “Neptune,” by a steam winch 
heaving in chain led to a stream anchor, there were two suction 
Pipes, looking aft, fitted with special mouth pieces for raking the 
bottom, and hung from framework fixed on each side of the vessel 
near the stern. The dredge steamed very slowly ahead dragging 
the ends of the suction pipes over the shoal to be deepened, and 
the two belt driven centrifugal pumps, working at the same time, 
generally filled the hoppers containing about 600 cubic yards in 
forty-five minutes As the work could be only proceeded with in 
very fine weather, the cost was necessarily high, averaging about 
Is. 4d. per cubic yard. 
Dredges of this kind were used in Florida as early as 1871, and 
they are still used in America for deepening bars where there is 
1 See Trans. American Society C.E., Dec. 1891. 
