Evening star. [volume] (Washington, D.C.) 1854-1972, 1897-11-27

lations to the form Of the hull about the
stern where the water runs into the screws.
ana also to tell what proportionate part of
the total resistance of the model is due to
friction OF the underwater surface. what
to wave resistance and what to edd.es.
Value of the Tank.
All of these things must be taken into
consideration in determining the best form
for ship and the responding econom-
ical speed for that form; and from this
some modest notion may DE got of what
the naval architect has to provide for
and consider. In the absence of a tank he
must make the most Of the known per-
formance of other ships. and approximate
the possibilities of his intended craft as
best his judgment can. Pretty guess-work
and some wonderfully clever forethought
alone are the basis upon which our own
successful ships have been Planned far:
and one naturally wonders what might nor
have been accomplished mad we had these
absolute, practical facilities.
The models to be experimental upon will
be as nearly possible of a uniform
length of twenty feet as an even scale
proportionate to the full-sized craft will
allow. For instance. vessel 156 feet long
Will have model on an eighth scale. that
is 1871 feet long. while craft 3S3 feet long
will have a model on a nineteenth scale, or
POI feet long. They will be of pine wood
accurately cut. by a special machine. from
TIE iincS VI the proposed VeSSel ana men
carefully measured and checked before be-
ing launched into the basin. They will
then be prepared in the balancing basin
prior to starting and nicely ballasted SO as
to accurately represent the intended craft
when she is ready for her trial.
The advantages to be gained by expert
menting with such apparatus. both from a
scientific and a practical point of view are
clear.
Help to the Designer.
1t is easy to say that because a certain
vessel steamed SO fast another of similar
foim and even power will go at the same
speed under like conditions, or it is posi-
BILE to approximate closely, even when de-
parting to come extent from strict par
allel by reasoning from past experiences.
Undoubtedly many fine ships have been
designed and built. but the fact remains
that the question of speed and coal con-
sumption nave in many cases varied widely
from that expected. Perhaps, in some
cases. the actual results could not have
been foreseen or provided against in any
event, but it Is possible, even certain that
many failures could have been prevented
had the designs first been tested and proved
or disapproved by models in the manner
proposed.
1t is in connection with radical changes
of form and conditions as to power, draft
OF water. etc, and with designs wherein
the limits are closely drawn that the value
OF the basin becomes paramount. Ten
years ago. any one suggesting thirty knots
as being possible of attainment with self
propelled vessel would have been considered
visionary. Today, contracts are being
made for vessels with a guaranty of even
higher speed; and who can say what is to
be the possible limit?
For strictly commercial purposes. how
ever. where the dssiderata are maximum
speed with large carrying capacity on a
moderate expenditure of power and light
consumption of coal, the value of model
trials is of prime Importance. as they would
also be where the attainment of exception
ally high speed were the prerequisite.
HOWARD p. ELWELL.
Copyright, 1897.