hour at a cost of 1.725d. per cub. yd. with coal costing 40s. per ton.
If coal had been available at the ordinary rate in England of 20s. per
ton, the cost of the dredging and delivery would have been 0.82d. per
cub. yd. for wages, coal, oil, &c., but not including the salary of
the superintendent.

An interesting example of a shore delivering dredger is a light
draught dredger constructed by Messrs Hunter & English for the Lakes
of Albufera at the mouth of the river Ebro in Spain (Plate I. fig. 6).
The conditions laid down for this dredger were that it should float in
18 in. of water and deliver the dredged material at 90 ft. from the
centre of its own hull. In order to meet these requirements the vessel
was made of steel plates 1/8 in. thick, and longitudinal girders from
end to end of the vessel, the upward strain of flotation being
conveyed to them from the skin plating by transverse bulkheads at
short intervals. The dredger was 94 ft. long, 25 ft. wide, and 3 ft.
deep, and the height of the top tumbler above the water was 25 ft.
When completed the dredger drew 17 in. of water. The dredgings were
delivered by the buckets upon an endless belt, driven from the main
compound surface-condensing engine, which ran over pulleys supported
upon a steel lattice girder, the outer end of which rested upon an
independent pontoon. This belt delivered the dredgings at 90 ft. from
the centre of the dredger round an arc of 180 deg. The dredger
delivered 125 cub. yds. per hour of compact clay at a cost of 1.16d.
per cub. yd. or 0.86d. per ton for wages, coal and stores. Another
method of delivering dredgings is that of pneumatic delivery,
introduced by Mr F. E. Duckham, of the Millwall Dock Co., by which the
dredgings are delivered into cylindrical tanks in the dredger, closed
by air-tight doors, and are expelled by compressed air either into the
sea or through long pipes to the land. The Millwall Dock dredger is
113 ft. long, with a beam of 17 ft. and a depth of 12 ft. The draught
loaded is 8 ft. It contains two cylindrical tanks, having a combined
capacity of 240 cub. yds., and is fitted with compound engines of
about 200 i.h.p., with a 20 in. air-compressing cylinder. The
discharge pipe is 15 in. diameter by 150 yds. long. The nozzles of the
air-injection pipes must not be too small, otherwise the compressed
air, instead of driving out the material, simply pier