, 1898-11-14
THE SPEED OF A SHIP
METHODS BY WHICH ITS KNOTS PER
HOUR ARE MEASURED.

METHODS BY WHICH ITS KNOTS PER
HOUR ARE MEASURED.
An Interesting Description of the
Mechanism, and Use of the LOG, with
= Truthful Red Sen Shark Story At
tachment.
"How do You ascertain the speed Of
q vessel?" is a question frequently ad-
dressed to naval men, and an expIana-
ton will therefore probably be of inter
est to many readers. There are several
methods, the commonest and most an
cient being by the use of the clog"
This instrument consists Of three pats
the logship. the line and the marks.
The logship is u piece of wood about
half an inch thick and shaped like a
quadrant, with a piece of lead let in
round the circular edge to make it float
perpendicularly in the water. 1t is slupg
by lines at each angle, the three lines
being Joined together about two feet
from the logship. Two of the lines are
securely fixed 70 the ship and the other
has a bone peg at the end, which, being
pushed into a hole in the ship. tempo.
rarily fastens it there.
From the point of juncture of the three
lines a sufficient length is measured,
generally about 100 feet, to take the
logship we'll clear of the ships wash.
This is called tho "stray line and is
marked with a piece of bunting. From
the bunting is measured Al feet 8
inches, and the line marked here with
a piece of leather. Then another "a feet
3 inches is measured off and marked
with two knots, then another space
the same length, and marked with
three knots, and SO on as far as seven
knots. Halfway between each batch Of
knots one single knot is made. The log
line is then ready for use.
The space between the knots is found
from the simple little rule of three sum:
As 8, 600 seconds number Of seconds in
an hour), 2S seconds Qength of sand
glass;, $3.50 feet (number of feet in a
nautical mile) length of line required
which works out to 4? feet 3 inches.
To use the log four persons are re-
~quired--two men to hold the reel III
which the line is wound; the quarter.
master. to hold the glass, and the mid
shipman of the watch, to heave the log.
The last named puts the peg firmly in
the logship and then gathers three or
four coils of line in his hand, sufficient
to admit Of the logship being thrown
we'll clear Of the ship. He asks, CLEAR
glass, quartermaster!"
bTton. class ca. ~ p,,,CS tha roy1y,
and overheard go the logship and line,
the reel rapidly revolving. Presently
the MILDLY feels the piece of bunting
passing through his hand, and he gives
the order, "Turn." The q~uartermaster
turns the glass and watches the sand
while II ''reeler" holds the reel well
over his head. so as to give the line fair
play. When the sand has run out
"Stopi" cries the quartermaster.
The midshipman grasps the line, as
sisted by the other %reeler. and looks for
the nearest knot. finding a single one
close to his hand. Then the line is haul
ed in, and four knots appear, which
eignify that the ship is going four and
a half knots through the water. The
jerk Of the line draws the peg from the
logship, which now floats on its fiat
side and is easily hauled in. When n
ship ia going over four knots. a Ia sec.
ond glass is used, the speed being double
that shown by the knots on the line.
Another method in use is the patent
log. This is altogether mechanical and
consists of q long cylinder with clock
work iEs;de it and foul fins on the u
side. 1t is towed astern of tho ship by a
line made fast to n swivel in the head
of it. AS 1t is dragged through the wa
ter the four fins make it revolve, actu-
ating the clockwork inside, which regis
ters on a series Of dials the number Of
knots run. This log has to be hauled in
every time one wants to read it, but
there is another kind where the fan is
lowed astern and the dial is a fixture
In the ship. This il called a "cheruh.
These logs arc not always accurate.
and are constantly verified when near
land by cross bearings-that is, the
bearings of two we'll known points are
taken, and the position so obtained IL
marked ON the chart, the time Of obser-
walton being noted and the reading on
the patent log. After m interval has
elapsed the position of the ship is again
taken by cross bearings, when the
straight line joining the two places OH
the chart will show the direction of the
course steered and its length the distance
run. A comparison with the readings
by patent log will give the error O 'the
machine.
To finish here is a patent log yarn,
as told by an old messmate. Igive it in
his own words: "When in the Crocodile
in the Red sea, just after taking the
reading one night at 8 o'clock. the
quartermaster reported. Shark taken
the patent log, sir!' l got another one
over at once. At 80 next morning we
stopped for half an hour. To amuse the
ladies I tried for and caught a shark.
On opening him we found our patent
log, and" he added gravely, "strange
to say. it registered tho same as the one
In use. The line had damned between
his teeth. the fan working all the time
he followed the ship. He had swum
Just l22 7-10 miles. Navy and Army
illustrated.
ssThe Dirty Dozen"