Some important trials of the new machinery of the screw steamer Ohio,
belonging to the International Navigation Company, have recently taken
place on the Clyde. The Ohio is an American built steamer measuring
343 ft. by 43 ft. by 34 ft. 6 in., and of 3,325 tons gross. She has
been entirely refitted with new engines and boilers by Messrs. James
Howden & Co., Glasgow, who also rearranged the bunker, machinery, and
hold spaces, so as to give the important advantage of increased cargo
accommodation obtainable from the use of their improved machinery,
which occupies considerably less space than the engines and boilers of
the same power which have been replaced. The new engines are of the
triple expansion type, and the boilers, which are designed for
supplying steam of 150 lb. pressure, are worked on Howden's system of
forced draught, which combines increased power with high economy in
fuel. The object of the owners in refitting the Ohio was to test the
capability and economy of this system of forced draught on a
sufficient scale to guide them in dealing with steamships of the
largest class and great power.
In the refit of the Ohio the boilers were designed to work with a very
moderate air pressure, this being sufficient for the power required by
the contract. The combined power and economy, however, guaranteed by
Messrs. Howden & Co. for the use of their system of forced draught was
higher than has hitherto been attempted in any steamship, and
sufficient, if attained, to prove the large reduction that could
safely be made in the number and size of boilers for the use of the
system, and the quantity of coal required to produce a given power.
The contract for the refit of the steamer required that 2,100
indicated horse power (which was the maximum power of the engines
removed) should be maintained during the trial on a consumption of
1.25 lb. of coal per indicated horse power per hour. Originally the
boilers of the Ohio, from which this power was produced, were three in
number, double ended, 12 ft. 6 in. in diameter by 17 ft. 6 in. in
length, having each six furnaces 3 ft. in diameter, or eighteen
furnaces in all, with an aggregate fire grate area of 300 square feet.
The new boilers, fitted with the forced draught, are likewise three in
number, but single ended, 13 ft. in diameter by 11 ft. 2 in. in
length, having each three furnaces 3 ft. 3 in. in diameter, or nine
furnaces in all, with an aggregate fire grate area of 112 square feet.
Air for combustion is supplied to the boilers by one of Messrs. W.H.
Allen & Co.'s fans, 5 ft. 6 in. in diameter, driven direct by an
engine having a cylinder 7 in. in diameter with stroke of 4 in. The
boilers removed had two stoke holds across the ship, one fore and one
aft of the boilers, while the new boilers have only one stoke hold on
the after side. The engines removed have cylinders 57 in. and 90 in.
in diameter by 48 in. stroke, while the new engines have three
cylinders 31 in., 46 in., and 72 in. in diameter respectively, with
piston stroke of 51 in.
During the trials the coals were weighed out under the supervision of
the officers of the company, who also took the record of speed and
other data. After running down Channel for a considerable time, the
trial on the coals weighed out began, and lasted 4 hours 10 minutes,
during which time 10,885 lb. of Welsh coal were burned, the trial
ending with the same revolutions of engines and the same pressure in
boilers with which it began. The mean indicated horse power,
calculated from the mean of seven sets of indicator cards, taken
during the trial, and the mean revolutions per minute, found by
dividing the total revolutions recorded on the engine counter by the
minutes in the period of the trial, amounted to 2,124, thus making the
consumption 1.23 lb. per indicated horse power per hour, and the power
per square foot of fire grate almost exactly 19 indicated horse power.
While testing the indicated horse power and consumption of coal, the
steamer ran to and fro between the Cloch and Cumbrae lights, and also
made several runs on the measured mile at Skelmorlie, from which the
mean speed of the vessel was found to be 14.12 knots per hour. The
remarkably high results obtained were most satisfactory to the
representatives of the owners, and a large party of experts on board
congratulated Mr. Howden on the successful fulfillment of the onerous
guarantees undertaken.--_Engineering._
* * * * *