Scientific American Supplement, No. 717, September 28, 1889 | Page 8

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a steam hammer, when the
decided difference of the granules near the circumference from that in
the central part conveyed to me that it was weakened by treatment I
have referred to. I think more material should be left on the forging,
and the high finish with a little cold water should be discontinued.
Doing away with the outer bearing in rudder post is an improvement,
provided the bearing in the outer end of screw shaft in the stern tube is
sufficiently large. It allows the rudder post to have its own work to do
without bringing any strain on the screw shaft, and in the event of the
vessel's grounding and striking under the rudder post, it does not throw
any strain on the screw shaft. It also tends to reduce weight at this part,
where all the weight is overhung from the stern of the vessel.
* * * * *

EXPERIMENTAL AID IN THE DESIGN OF HIGH SPEED
STEAMSHIPS.
By D. P.
The achievement of one triumph after another in the matter of high
speed steamships, and especially the confidence with which pledges of
certain results are given and accepted long before actual trials are made,
form one of the most convincing proofs of the important part which
scientific methods play in modern shipbuilding. This is evident in the
case of ships embodying novel or hitherto untried features, and more
especially so in cases where shipbuilders, having no personal practical
experience or data, achieve such results. This was notably illustrated in
the case of the Fairfield Co. undertaking some five years ago to build
and engine a huge craft of most phenomenal form and proportions, and
to propel the vessel at a given speed under conditions which appeared
highly impracticable to many engaged in the same profession. The
contract was proceeded with, however, and the Czar of Russia's
wonderful yacht Livadia was the result, which (however much she may
have justified the professional strictures as to form and proportions)
entirely answered the designer's anticipations as to speed. Equally

remarkable and far more interesting instances are the Inman liners City
of Paris and City of New York, in whose design there was sufficient
novelty to warrant the degree of misgiving which undoubtedly existed
regarding the Messrs. Thomson's ability to attain the speed required. In
the case at least of the City of Paris, Messrs. Thomson's intrepidity has
been triumphantly justified. An instance still more opposite to our
present subject is found in the now renowned Channel steamers
Princess Henrietta and Princess Josephine, built by Messrs. Denny, of
Dumbarton, for the Belgian government. The speed stipulated for in
this case was 20½ knots, and although in one or two previous Channel
steamers, built by the Fairfield Co., a like speed had been achieved, still
the guaranteeing of this speed by Messrs. Denny was remarkable, in so
far as the firm had never produced, or had to do with, any craft faster
than 15 or 16 knots. The attainment not only of the speed guaranteed,
but of the better part of a knot in excess of that speed, was triumphant
testimony to the skill and care brought to bear upon the undertaking. In
this case, at least, the result was not one due to a previous course of
"trial and error" with actual ships, but was distinctly due to superior
practical skill, backed and enhanced by knowledge and use of
specialized branches in the science of marine architecture. Messrs.
Denny are the only firm of private shipbuilders possessing an
experimental tank for recording the speed and resistance of ships by
means of miniature reproductions of the actual vessels, and to this fact
may safely be ascribed their confidence in guaranteeing, and their
success in obtaining, a speed so remarkable in itself and so much in
excess of anything they had previously had to do with. Confirmatory
evidence of their success with the Belgian steamers is afforded by the
fact that they have recently been instructed to build for service between
Stranraer and Larne a paddle steamer guaranteed to steam 19 knots, and
have had inquiries as to other high speed vessels.
In estimating the power required for vessels of unusual types or of
abnormal speed, where empirical formulæ do not apply, and where data
for previous ships are not available, the system of experimenting with
models is the only trustworthy expedient. In the case of the Czar's
extraordinary yacht, the Livadia, already referred to, it may be
remembered that previous to the work of construction being proceeded

with, experiments were made with a small model of the vessel by the
late Dr. Tideman, at the government tank at Amsterdam. On the
strength of the data so obtained, coupled with the results of trials made
with a miniature of the actual vessel
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