1/2 lb. of coal per horse
power hour.

The Intrepid, enlarged to a 24 knot boat, for the same length of
voyage of 3,000 miles, would be 650 ft. by 100 ft., 40,000 tons, and
about 45,000 horse power. So now we are nearing the Messrs. Thomson
design in the Naval Exhibition of the five-day steamer, 231/2 knot
speed, 630 ft. by 73 ft., and 30,000 to 40,000 horse power.

No one doubts the ability of our shipbuilding yards to turn out these
monsters; and on the measured mile, and for a good long distance, we
shall certainly see the contract speeds attained and some excelled.
But the whole difficulty turns on the question of the coal capacity,
and whether it is sufficient to last for even five days or for 3,000
miles. Every effort then must be made to shorten the length of the
voyage from port to port; and we may yet see Galway and Halifax, only
2,200 miles apart, once more mentioned as the starting points of the
voyage as of old, in the earliest days of steam navigation. In those
days the question of fuel supply was a difficulty, even at the then
slow speeds, in consequence of the wasteful character of the engines,
burning from 7 lb. of coal and upward per horse power hour. Dr.
Lardner's calculations, based upon the average performance of those
days, justified him in saying that steam navigation could not pay--as
was really the case until the introduction of the compound engine.

It is recorded in Admiral Preble's "Origin and Development of Steam
Navigation," Philadelphia, 1883, page 160, that the Sirius, 700 tons
and 320 horse power, on her return voyage had to burn up all that old
be spared on board, and took seventeen days to reach Falmouth. An
interesting old book to consult now is Atherton's "Tables of Steamship
Capacity," 1854, based as they are upon the performance of the marine
engine of the day. Atherton calculates that a 10,000 ton vessel could
at 20 knots carry only 204 tons of cargo 1,676 miles, while a 5,000
ton vessel at 18 knots on a voyage of 3,000 miles could carry no cargo
at all. Also that the cost per ton of cargo at 16 knots would be
twenty times the cost at eight knots, implying a coal consumption
reaching to 12 lb. per horse power hour. It is quite possible that
some invention is still latent which will enable us to go considerably
below the present average consumption of 2 lb. to 11/2 lb. per horse
power hour; but at present our rate of progress appears asymptotic to
a definite limit.

To conclude