The pump
is shown in Figs. 2 and 3. The fan is 2 ft. diameter, and has only two
blades, a larger number being less efficient. The faces of the blades,
where they come in contact with the sand, are covered with flaps of
India-rubber. Small doors are provided at the side of the pump for
cleaning it out, extracting stones, etc. The fan makes 350 revolutions
per minute, and at that speed is capable of raising 400 tons of sand,
gravel, and stones per hour, but the average in actual work may be taken
at 200 tons per hour. This is with a 10-horse power engine, and working
in a depth of water varying from 7 ft. to 25 ft. The great advantage of
this dredger is its capability of working in disturbed water, where the
frames of a bucket dredger would be injured by the rise and fall of the
vessel.
[Illustration: THE BRAZIN SYSTEMEM OF DREDGING.]
Thus at Lowestoft bucket dredgers are used inside the harbor, and the
Bazin dredger at the entrance, where there are sand and gravel, and
where the water is more disturbed. The dredger does not succeed very
well in soft silt, because, owing to its slow precipitation, it runs
over the sides of the hopper barges without settling.
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