The morning call., 1891-07-05
SPEED THROUGH WATER.
Comparison Between the Old Paddle Wheel
and The Screw,

1t is common experience with shp-owners
and ship-builders to have propounded to
them means whereby even thirty knots per
hour may be realized, and these backed up
by very elaborate calculations as proof, but
which, when investigated. are found, like
those Of well-known writer of scientific
romance. TO be wanting in some little detail,
Insignificant at first sight, but absolutely es-
sential to complete the proof, writes A. E.
Seaton III July Seribner, in an article en-
titled speed in Ocean Steamers" So far
no great departure from the existing form
of ship, nor from the method of propulsion,
has resulted in obtaining higher speed
than is common with ordinary ships OF the
same dimensions; and in nearly every case
such departures have mortified tina inyen-
tors as well as disappointed the public by
turning cut absolute failures; and there is
no good reason to suppose that fur
Their successes than have already been
attained will be achieved in any other way
than by improving the conditions that
now obtain, both as regards form of snip
and method of propulsion, inasmuch as the
physical causes which combine to retard
the motion OF vessel, and the physical
forces which are employed in overcoming
that resistance, remain to-day as they ever
were, and are, III fact, natures immutable
laws. The commercial question is also one
that presses very hardly at all times and
must continue TO do so more and more, as
will be seen later on. The Atlantic grey
hound of to-day is, i'll immersed form. sub
stantially that of the vikings craft OF more
than thousand years ago. And if we look
to nature for our study We shall find that
the SWifteSt fish are not unlike in general
form to the submerged part of ship; and
the comparison is the more easily accepted
when 1t is remembered that the fish is
wholly submerged. while the ship Is only
partially so. The one has to contend with
waves and other surface disturbances, and
must perIorce keep above the water, while
the other is free from such disturbing ele-
mentS and conditions, and pursues its course
in practically smooth water.
The primary condition for high speed is
hneneSS OF form, so that the water at the
bow of the vessel may be separated and
| thrown to one side, and brought to rest
| again at the stern and behind the vessel with
| the least possible disturbance, and the
| measure of efficiency of form for the maxi
mum speed intended is inversely as the
| height Of the waves of disturbance. a ship
| that has been designed to attain speed Of
| 10 knots Will, when moving at Il knots,
| show very slight disturbance indeed, and
III one designed for Is knots, when moving
| at this lower speed, it will be scarcely
observable; but however fine the lines Of
| ship may be, she must at every
| speed produce some disturbance, although
| it may be very slight, as the water displaced
| 10y her must be raised above the normal
| level and replaced at the normal level
| hence, at or near the bow Of ship there is
| always the crest of wave, and at or near
| the stern the hollow of one. When a vessel
| Is going at lis maximum speed. and IS prop
erly designed for that speed, the wave
| should not be very high, nor should ii eX-
tend beyond the immediate neighborhood of
the bow; likewise the wave of replacement
| should be the same at or near the stern of a
! ship, and the wake, or disturbance of
| water left behind in the track of the ship
| should be narrow.
The paddle-wheel was obviously the first
| instrument accepted by the early engineers
| as means of proI ulsion. Long after the
| experiment OF H. 3. NJ S. Rattler had de-
| monstrated the contrary the public faith in
| the visible wheel was greater in reality and
more sincere than that in the invisible
| screw; and 1t is probable that it was more
| the question OF cost than anything else
that gained the victory for the screw for
ocean and general service. The paddle
| engine is in itself heavier and occupies
more room than the screw engine; it
is as rule more expensive per indi-
| Gated horsepower; and in wear and tear
| Especially of the propeller itself-it far
exceeds the screw. 1t occupies the best
| part of the ship, and its position is
not a matter of choice, as with the
| screw engine, but Is, of necessity, at OF
| near the middle OF the ship. 1t is evident
| that a paddle steamer must require more
room, and that in moving among ships or
other distractions the liability 10 damage
the propeller is greater than with the screw
| steamer, and in the case of long voyage
| the paddle, generally worked al disadvan-
tage, as at the commencement it was too
| deeply Immersed, and at the end not
| Immersed enough for efficient working. If
| the sails were set so as to steady the vessel,
or il set in sufficient quantity to be of any
| use in quickening the speed, she was in
| clined until the lee wheel was buried" and
| the weather" wheel doing very little work,
besides there being a general tendency on
| the part of the ship to turn round, which
| had to be counteTbalaneed by the ruddrr.
| The race of water from the wheels past the
ship being at high velocity, and raised
| above the normal level, causes a resistance
to the ship beyond that due to her passage
| through the water. as in the case of screw
ship. On the other hand, tine paddle-boat is
more readily got into motion and her speed
| more rapidly arrested than is the casa with
| the screw steamer; and 1t is claimed for the
| paddle wheel-although the foundation for
| such claim is rather nebulUus-that when
at full speed the ship is prevented from tx
| cesSive rolling