5
tons per day only. In this case it was the same ship, same boilers, same
engines, same propeller, and same men, the only difference being the
addition of a third cylinder and the increase of pressure.
So far all the trials had been made with two crank engines; so it was now
decided to construct another set of engines for 150 lb. pressure, having
a crank to each cylinder. These engines had cylinders 201/2 inches, 33
inches, and 58 inches diameter by 36 inches stroke, and were fitted into
the screw steamer Rosario, whose dimensions are 275 feet 3 inches between
perpendiculars, 34 feet 3 inches beam, and 19 feet 2 inches depth of
hold, 1,862 tons gross, and the deadweight capacity 2,550 tons. In March
last year she was loaded with 2,530 tons deadweight, and did the voyage
to Bombay at an average speed of 8.6 knots on a consumption of 10.5 tons
per day of South Yorkshire coal, and burnt on the voyage 347 tons. This
result is superior to that of the Draco when the size of the ship is
taken into account, but is not so much so as might have been anticipated
from the increase of pressure and the rate of expansion, which was 14.4
in the Rosario and 12 in the Draco. Another set of engines was made from
the patterns of those of the Draco, but with the high pressure cylinder
20 inches diameter, steam at 150 lb.
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