The sun., 1893-07-16
THE PRorELLERs OF wAR sHIrs.
The Rersrks sb'e Results Attained by Needed
Chnnger ~ Diar,eter and Fitch.

ing features In the acceptance trials OF our
new steel vessels 10 the uncertainty which has
prevailed even among the builders themselves
as to the siEe and pitch OF tho screws which
should be employed for giving them their
greatest speed. No such lack Of knowledge is
shown In any other part Of the construction.
But as to the propellers. instances have been
recorded In THE Sun. and VIII no doubt be re-
called by readers. In which. after important
trials of vessels had been made. the pitch Of
the screws was experimentallp changed with
the result OF getting much better speed.
Some etimes the diameter IL altered instead OF
the pitch. or In addition to tho alteration OF
the pitch. This feature OF construction evil
IDENTIFY demands more study, so that IL may he
taken out OF the domain Of euesswork or ex-
pertinent. Indeed. the amount Of money often
depending on this single factor 10 steam pro-
pulsion should apparently make It for the in
terest Of constructors to possess more certain
knowledge In regard to It
In the current number Of tho Proceedings
OF the United States Naval Institute" Mr.. ]. J.
O'Neill discusses this question. He says that
n vessel Is often tried with unsuitable screws.
and then others are substituted which realize
the original anticipation: but whether sue
cess results from either alteration Of diameter
or pitch or both is alike o mystery" He sug-
Rests, therefore, that propeller OF a given
diameter and pitch be run in progressive
trials. commencing with pitch ratio Of !. and
then varying the pitch by lilo until the ratio
is l.5. the diameter remaining constant: then
reversing the process with constant pitch
and q varying diameter. This will yield ten
progressive curves which can be combined by
q system Of cross curves. showing the varla-
tions due to altering each factor and pointing
out the proper propeller for that vessel. at
it, Al
Again. II will be found that n certain propeller
among several Of equal value for speed pur-
poses 10 the most desirable by reason Of re-
aulring fower revolutions and hence less wear
and tear on tho machinery. twill further be
found that in some cases n relatively large
propeller running comparatively slowly Is the
moro efficient. while again at high speeds
smaller propeller running quickly 10 more
desirable for speed efficiency.
Among the instances cited. It Is mentioned
that the Baltimore develops fifteen per cent.
moro power on three revolutions per minute
less. than the Philadelphia. and secures an in
crease Of speed q four. niths OF q knot. Here.
an Incorrect staten ent that the two vessels are
identical in disbursement and dranGht, whereas
eass Efh he paaepR % S
2IG tons. But a SECOND Interesting example
quoted Is thai Of the New M York; which obtained
oping about il 600 Indicated horse power. On
this point Mr.; 9NeilI declares that 1T l, san
high rate OF running machin inery can be in
creased efficiency Of propulsion. and the rec
erds not hss such @a tSo
following assertion
far @ a, can b. Judged .s. I'M machinery ran 70 i'
but 20 knott. The ds.Ixned speed 70 revolution:
"na n hay: been a snmps pror with n
knots ought to have been ached On this power and
SONS warrant The a ssrt ion ts It's eihe,en, 'psed.
WIN ,ns !, - knot: and
a reduction of diameter OF propeller and increased
sisi MAKE eSiaen1 to those experienced in such mat
that higher speed than that obtained is possbe
Whether these alterstops IN !he the propellsr
experts Of the Naval Institute. who have pub
iished this essay. may be lett to discuss; but It
Messrs. Cramp. who. in that case. would have
fssH sssHsa nSs Gny % the
tried. and her. triple screws. the matter must
BE- very important Her soptraMet m M sIsed ,, Is the
that small propelers will undoubtedly DO
found best. and II these he fitted there can be
S soaS Shs des wh SnE that I
al are snas much as S9 Knots s Would svs
The three BATTLE ships Of the Indian. class are
Sso ~ thf 10
he would give larger propeller with fewer
With rs revolu!ions this great rate q run:
A larger propeller with 100 revolutions would
5s Sst for the mHchnReE gyRs
can Eo obtained. involving a premium Of 500;
10 ob;ained. he holds, with suitable Eropelers,
Knots under natural draught with the full
power rossible from her machinery weights.
his citation OF the case. OF the Bancroft. where
2,s knots wero obtained over, anticipation.
WITH rsma% 81, e so0o9G due snrsIy Il "
MISUNDERSTANDING Of the premium y the case
OF the Bancroft. which was not ,O09 rer
but som ething vastly. IessP In either case. Of
the error would not the
In regard to the Monterey. Mr. o,Nellrs views
are worth mentioning. He speaks %f her as
tainine only 1870 on trial. with 5,24;! Indicated
horse power and lol ;. revolutions" ono ON;
stronger Mr. o'Nsili says that this vessel
is only nine; knot enc. that being her eilcient
speed. and when higher speed than this Is
sought it Is at the expense Of sycry other fac
tor In the design; nanenvrnG power. steady
Still after crticlsing b or construction. he adds
that as she Is. her hnsd Are t90 large
power specified.
It will be observed. therefore. that these
views o. xpressed In the professional quarterly
are radical; Their hnsis is that tho princi-
pal factor of the machinery Is obviously the
propeller" 1t Is held that when this is as It
should he. "on the same III, placement. ships
with from Is to 20 per cert. greater protec-
ton and 80 rcr cent. greater coal supply cnn
be produced. In tho case of the Iowa the re-
SUITS possible are enormously in excess OF the
smaller ship having twice the coal sul py Of
the Indiana with protection greatly in excess
Of that vessel. can be produced" he Is
of entertaining the hest form OF propeller to he
chosen In any particular ease. l.ut thinks that
everything points to the necessity OF tank ex-
porments. In this respect being corroborRted
By Chief Constructor Wilson. who has strongly
urged tho proposed provision for an expert
mental tank.