Coming to the question of the consumption of fuel, a considerable saving
has been effected in nine years, as shown in the following table:
Item. 1872. 1881.
Working pressure, lb. per sq. in......... 52.5 77.4
Heating surface per I. H. P., sq. ft.... 4.64 3.919
Piston speed, feet per min.............. 376 467
Coal burnt per I. H. P., lb.............. 2.11 1.828
This shows a saving equal to 13.38 per cent, in quantity of fuel
consumed. Mr. Marshall then read a letter from Mr. Alfred Holt, of
Liverpool, bearing on this subject, in which Mr. Holt spoke favorably of
the single-crank engine, and stated his belief that the compound system
would ere long be abandoned for the simple engine. He is endeavoring to
feel his way to using the steam in one cylinder only, and so far the
results have been encouraging, and he is now fitting a 2,200-ton vessel
on that system. He is also endeavoring to do without a crank shaft, the
forward end of the screw shaft carrying an ordinary crank with overhung
pin. This experiment also promises satisfactorily. In his opinion the
great improvement of the immediate future is to increase the steam
production of our boilers. A ton weight of a locomotive boiler produces
as much steam as six tons of an ordinary steamboat boiler.
Mr. Holt speaks of the coal account as one of the minor disbursements
of a steamer. He does not give the ratio which coals bear to the total
disbursements, but from other reliable sources Mr. Marshall found that,
according to the direction of the voyage, it varies from 16 to
20 percent.--or, say, an average of 18 per cent.--of the total
disbursements, in a vessel carrying a cargo of 2,500 tons. This will
represent to-day about £3,000 per annum, and in 1872, at equal prices,
the cost would have been £3,750--showing a saving of £750, equal to a
dividend of, say, 3 per cent. on the value of the ship. Again, the cost
of coal per mile run for such a vessel, in 1872, would have been at
least 16½d.; to-day it does not exceed 13d.