The Locomotive - Lighthouse Survival Blog

122 THE LOCOMOTIVE. [August,
requires a much higher engine speed than the paddle wheel, but at first it was not con-
sidered practicable to drive the screw shaft from the engine direct, so that the higher
speed necessary was secured by gearing. Even during the Civil War a great many of
the vessels which took part used paddle wheels. Most of them built during that period
were propellers, and this has been the practice in the Navy for ocean navigation ever
since.
In reviewing the literature of the early days of steam navigation, after ocean steam-
ers had become fairly well established, it is very interesting to note the evident aim at
greater economy in the use of fuel, and there was no lack of suggestion of methods for
accomplishing this result. It is surprising to note, however, that what to us nowadays
seems the obvious way of determining the value of these methods, namely, actual experi-
ment, seemed to have little chance. The authors do not seem to have been able to
refer to any attempt to secure greater economy by higher pressures and increased
expansion, although this was a favorite subject of discussion. It is only fair to remem-
ber, however, that metallurgical operations were by no means so well developed as in
our day, and the workmanship on the machinery was also quite inferior. The difficulty
of procuring thick boiler plates which would be thoroughly reliable offered an effectual
bar to high steam pressures, and the inferior workmanship prevented high rotational
speed, two features which, we now know very thoroughly, are necessary to give economy.
With reference to the question of expansion, not only the early writers but those as
late as 1860 believed that the only limit to expansion was the practical consideration of
npt reducing the mean forward pressure so low that the back pressure would be too
large a percentage of it, thereby requiring a very large engine. Most of them seem to
have been entirely unaware of the effects of cylinder condensation in reducing the theo-
retical benefit to be derived from expansion. These older writers also seemed to have
been familiar with the indicator mainly as an interesting scientific
comparatively little use was made.
instrument, of which
The first reliable data with respect to the cost of power that I have been able to find
are given in a work which at one time had considerable vogue, called "Engineering
Precedents," by Chief Engineer Isherwood, of the U. S. Navy, published in 1858. In
1863 we come to the first volume of his " Experimental Researches." These include
records of the performance of a class of naval screw steamers built about 1854 to 1856.
The Merrimac was one of them. These vessels were about four thousand six hundred
tons displacement, three hundred feet long, fifty feet beam, and twenty-one feet draft.
The engines were of about thirteen hundred horse power working with a steam pressure
of thirteen and one-half pounds above the atmosphere, and making about forty-five rev-
olutions per minute. A record of the maximum performance in smooth water showed a
coal consumption of 4.37 pounds of coal per horse power hour. Under ordinary steam-
ing conditions at sea, when a certain amount of heat was lost due to " blowing off" to
reduce the density of the water in the boilers, as the condensers were of the jet variety
and using anthracite coal with eighteen per cent, refuse, the coal consumption was six
pounds per horse power hour.
This same work contains the record in extenso of the famous Michigan experiments,
conducted by a board of naval engineers, of which Isherwood was president, on the
economy of using steam with different degrees of expansion. The Michigan was built
in 1854, so that the machinery was of an older type than that of the frigates just dis-
cussed. It is, however, very well designed for the period in which it was built, and it
is in use today, the only change being in the boilers, which have been renewed twice in
the fifty-seven years since the vessel was commissioned. The first renewal occurred in