On trial trips with the
steamers already named, the consumption of ordinary South Yorkshire coal
was 1.6 lb. per indicated horse power, and the consumption of water per
indicated horse power calculated from the high pressure indicator
diagrams was 1.41 in the Draco, 13.2 in the Rosario, and 13.16 with the
Finland, or taking the medium pressure diagrams, it was 12.2, 1.30, and
11.95 respectively. Twelve months ago we constructed for Messrs. Thomas
Wilson, Sons & Co., two sets of triple expansion engines of 600 indicated
horse power, one having two cranks and the other three cranks, the
engines, boilers, and propellers being otherwise exactly alike and fitted
into sister ships. The water consumed in the three crank engine is 12.93
lb., against 13.0 in the two crank, but the former drives its ship nearly
1/2 knot per hour faster than the latter does its, and when both ships are
driven at the same speed the consumption of coal in the three crank ship
is considerably less than in the other.
We have now entirely given up the construction of two-crank triple
expansion engines, because of the impossibility of equally dividing the
work between the cranks; for, although the engine when running appeared
to be perfectly balanced, the wear of the brasses of the crank having the
two cylinders was always considerably more than that of the other.
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