Tazewell Republican. [volume] (Tazewell, Va.) 1892-1919, 1904-06-30
SPEED OF MOTOR ENGINES
Some That Drive Propeller Screws OF
Fast Atlantic Liners Exceed
Two Miles a Minute.

It requires some study to ascertain
the precise speed required in an engine
that drives the. fast autoboats that
pillow through the water at the rate OF
50 or rs miles an hour, and having as
certained the figures one is almost in
clined to disbelieve them, although 1t
Is said they cannot lie. To attain the
speed named, says an authority, the
propeller wheel revolves from 500 to
1880 times in minute. When the
number of revolutions is stated one
rarely comprehends what 1t means.
In boat of high power the propeller
will be 20 inches in diameter. This
means that It's periphery is little over
six feet,
If this screw revolves at the rate OF
1850 times a minute the outer edge
of the blades of the propeller Is cut
ting through the water at the rate OF
Just one and third miles a minute.
These propellers are not fiat. II
they were they would have no pur-
chase on the water and the boat would
not move an inch To give them a
grip on the water each blade is twisted
slightly, like a spiral, and this twist
increases the stretch of the blade be-
yond its circumference by about IA,
so that what marine engineers call
the helicoid path Of the propeller
would be very nearly two miles in
minute.
This remarkable speed Is produced
by motor that is only % inches wide,
40 inches long and II inches high. 1t
develops a horse power Of about 90.
The propellers which drive the fast
Atlantic liners are about As feet In cir
conference. The tip Of the blade will
cover about a mile and a fifth each
minute when revolving at full speed.
The cruiser Minneapolis, which Is
one Of the fastest in the navy, has pro-
pellers 4S feet In circumference. They
make 1872 revolutions minute, so that
the tip of the blade when driven at full
speed Is travelling at the rate of 6,336
feet each minute, and the helicoid
path, or the distance covered by the
spiral twist Of the blade, is $50 feet
a minute. or more than mile and a
half.
The Minneapolis and the ocean
liners are driven by steam, but in the
fast autoboats gasoline is the motive
power.
II can be understood to what q
nicely the mechanism in a gasoline en-
CINE Is adjusted when it is stated that
to make 1000 revolutions a minute
means that in a four cycle engine
there are 500 sprays of gasoline forced
into the cylinder, 500 times the cleo
trio battery makes a spark and SOC
times the escape valve is opened to lei
the gas out
If there are four cylinders at work
on the same shaft, and many of the fast
boats have four cylinders, then each
operation is repeated four times. Some
motors have eight cylinders and one
is now being built that will have Il
cylinders. 1t is figured that a motor
uses a pint of gasoline per each horse
power and houd. An horsepower
motor will use a gallon OF gas
oline an hour and will cost about
16 or IT cents an hour to run
A "a horsepower motor will take
three gallons an hour, which will
make the cost about so cents an hour
There is a motor boat being bull
that is to have a 500 horsepower
motor. This motor will consume
about 60 gallons of gasoline an hour
and If run for ten hours a day viii
cost more than $50 a day.