The Pacific commercial advertiser. [volume] (Honolulu, Hawaiian Islands) 1856-1888, 1870-12-03

1 SulD- VIC N1AAAOG ohAh NHN
as a means for reducing the figures as a common
basis. One feature in favor of screws Is the dimIn-
ished space occupied by their machinery, and IN order
to make a fair comparison between them and side
wheelers thew must be allowed the benefit of this adj
vantage. The most just basis for comparison Is FUR
nished by their freight capacity. Their earnings are
determined primarily to this, even as their expenses
are determined primarily by their consumption OF
coal and thus the net results ascertained by reduc-
ing the consumption of coal to the capacity OF freight,
will give the relative practical efficiency OF the two
classes of steamships. The ChSuncey Is 4 taVoraoie
example of her class, being fast, and a moderate con-
sumner Of coal The Efbe viii carry Luz tons OF
general cargo ; the Chauncey, 400 difference zUO
tons or IA per cent. The former burns as we have
seen 81 pounds per mile ; the latter Adj pounds
Reducing this IA per cent. il shows a consumption
for a freight capacity Of 200 tons, OF 49, pounds OF
coal per mile,-or II pounds more than the Etbe, or
% per cent. To show how serious a difference TINS
is, suppose it applies in the case OF the emma steam
ers. The freight capacity OF those ships Is, IN a1do
! ton to their Goals, about l 700 tons with 600 to 500
tons of cargo they burn 50 tons of coal per day, ana
make 9 knots loaded full, [ think we safely say
that they would, at the same speed burn DO tons. Il
ship of the Elbe'S class with equal capacity, but run
ming II knots an hour instead of 9, would consume
less than 50 tons. Here is n difference OF 50 per
cent. in speed and 10 per cent. in coal, or a total OF
in practical efficiency of AZ per cent. The difference
here is greater than that against the ChaUncey, be-
cause the China ships are less efficient than the latter.
With one-half larger tonnage, and less than ond-hal1
larger freight capacity, they have engines OF the same
power, and are thus not only nearly one-thlrd slower,
but Il dOubt) cannot be driven by any amount OF
coal-G. c. at any safe steam presSure) up to equal
speed.
1t is, however, hardly necessary to go into
minute comparisons to exhibit the economical adj
~vantages of screw steamers over the paddle the
fact that nearly all the ocean steam companies in
the world, including the Cunard, p. o., West
India, as well as the French and German COM
-o,Io. 40 49,, ~ J;-. rotb;nr also 10 aDou,b
1t is interesting, however, to examine the reasons
for this great advantage, and they are obvious.
When a paddle boat is deeply laden with coal
and cargo at the commencement OF the voyage,
and therefor requires more power to drive her,
the paddle is too deeply immersed to be cfhcient,-
the forward portion of the floats are pressing the
water Town and the after portion are raising it
up. The screw on the other hand works with
more effect the more deeply it is immersed.
Again, in rolling each paddle is alternately too
much in, and too much out of the water. The
screw in rolling preserves its efficiency nearly I'M
altered. In pitching alone, the paddle has the
advantage of the screw but inasmuch as a yes
sci at sea rolls with all seas, but only pitches in
a head sea, the average gain is vastly in favor of
the screw. A screw boat can carry sail with a
side wind and be heeled over, without affecting
her propelling power-whiIst a paddle boat under
the same circumstance has one wheel too much
in the water and the other too much out, and the
efficiency of both are seriously compromised.
Masts and sails therefore in n paddle-wheel boat
are Comparatively ineficient-as the chances of a
side wind are double those of a wind aft.
Further, the engines of a screw boat are neces-
sarily smaller and lighter with the same power
than the engines of a paddle boat, because from
the nature of the propeller in one case, a short
stroke and rapid revolutions with the assistance
of the screw or inclined plane, is used instead of
a long stroke and direct acting propelling instru-
ment at the wrong end of the lever. This smaller
and light machinery is an enormous advantage,
as it means less first cost and more room for
cargo-or the same carrying power and more
speed. To sum up, the paddle-wheels and paddle
boxes are heavy and cumbersome, they are in way
of the sails and of everything else, they hold the
wind going head to it, the guards get struck by
seas, and altogether they are in comparison with
the screw propeller, a barbarous, unsightly and
inefficient means of propulsion in the open ocean.
The advantage of iron over wood for any vessel,
and for a steamer in particular, has been thor
oughly proved. The most obvious one is that by
the best known method of combining the mate
rails in either case, n large saving in weight in
two steamers of the same capacity, can be effected
by using iron, SO that the wooden steamer has
always got her OVID extra weight to propel besides
her cargo she therefore must inevitably either
go slower, or carry so much less cargo than the
iron one. A wooden steamer, therefore, with
the additional enormous disadvantage of paddle
wheels is simply hOrs de combat with an iron
screw steamer, in anything approaching a fair
contest in other respects, and they can only be
kept running in preference, at a heavy extra
expense to somebody.
Iron screw steamers now make some of the
longest ocean voyages. There is a regular line
from Liverpool to Valparaiso, via the Straits of
Magellan. In India and China they are fast TAX
ing the trade from sailing vessels, as they have
done in the Atlantic. In the ports of the Medi-
Black Sea, and Baltic, and in English
ports, besides the regular lines, ocean screw
cleaners are usually TO be found for charter for
any part Of the world, Just as sailing ships are.
On the Clyde. the Tyne, and the Mersey, they
are built ana launched, half a dozen at a tide,
some TO order. some for sale, and the latter sell
dom remain long on hand
One Of the most important improvements in
some of these recent boats is the double-cylinder
engine, or combined high and low pressure, as in
the El6e, mentioned above; and by which a great
saving in fuel is effected. By means of these en-
gines, with other recent improvements, a steamer
the size of the City of Melbourne or Wonga
Wonga, for instance, could be run at the same
speed as these boats and save some ten tons of
coal a day, which, in a passage of say 20 days
would allow them to take 200 tons more cargo
than they do at present. -Four. hundred tons
more cargo on the round trip at so per ton
and the cost of say 300 tons less coal,
would be equivalent to a handsome subsidy.