Evening star. [volume] (Washington, D.C.) 1854-1972, 1898-10-01
THE SPEED OF A SHIP.
HOW IL is Measured and Descriptions
of the INSTRUMENTS
fr'm the Navy and Army Illustrated.

fr"m the Navy and Army Illustrated
How 90 you ascertain the speed OF a
Nessel?" is question frequently addressed
TO naval men, and an explanation WILL
therefore. probably be Of interest TO many
readers. There are several methods. the
commonest and most ancient being by the
use OF the log" This instrument consist.
of three parasitic logship. the line and the
marks. The losship is n piece of wood
ABOUT half an inch thick, and shaped like
quadrant with a piece of lead let n
round the circular edge TO make il float
perpendcularly in the water II is slung
by lines at each angle, the three lines be-
ing Joined together about two feet from
the logship. Two of the lines are securely
liked 10 the ship" and the other has a
bone peg at the end, which. being pushed
INTO mole IN the ship temporarily fastens
1t there. From the point OF iuncture az tha
three lines a sufficient length is measured
generally about one hundred feet To take
me loEship well clear OF the ships wash
ms is called the STRAY line" and is mark
ed with piece Of bunting From the buut-
ing Is measured a. feet inches and the
line marked hero with a piece Of leather
1hen another "a feet inches IL measured
on ana marked with two knots: then an
Other space the same length and marked
with three knots; and so on as far as seven
knots. Halfway between each batch Of
K'cts 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 800 seconds Cnumber of seconds I'm an
hcur), % seconds dength OF saudglassD
$3.50 feet number Of feet in "A nautical
milel: length OF line required-which works
out to ~ feet inches
To use the log four persons are required.
two men to hold the reel on which the
line Is wound: the Quartermaster. TO hold
the glass; and tie midshipman of the
watch, to heaye the log. TIE last-namel
puts the peg firmly in the logship. and
then gathers three or four coils Of line in
his hand. sufficient to admit of the log
snip being thrown well clear of the ship.
He asks, Clear glass. quartermasters''
Clear glass slr!' comes the reply. and
overheard goes the lugship and line tina
reel rapidly revolving. Presently the MILDLY
leels the piece IF bunting passing through
his hand, and he gives tAe order Turn ="
The quartermaster turns the glass and
atches the sand. while che 'reeler'' holds
the reel well over his head so as to give
the line fair play. When the sand has run
out stop cries the quarterma Ste- The
nidshlpman era SOS the line, assisted by the
other ree!er and looks for the nearest knot,
hiding a single one close to his hand Then
the line Is hauled in, and four knots ap-
pear, which signify that the ship is going
Tour and 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 a shin
is going over four knots a fourteen-second
double
shown by the knots on the line.
Another method in use is the patent log
This is altogether mechanical. and consists
Of long cylinder with clockWork inside
il, and four fins on the outside; il is towed
astern of the ship by A line made fast To
a swivel in the head of ii. As il is dragged
through the water the four fins make IL
reVolve, actuGting the clockwork inside
which registers a series of dialS the
number of knots run. This log has To he
hauled in every time one wants to read it,
But there is another kind where the fan IS
tcwed astern, and the dial is a fixture in
the ship. This is called a ''ckerub."
These logs are not always accurate, and
are constantly verified when near land by
cross-bearings. That is the hearings Of
two well-known points taken and the
position so obtained is marked on the
and the reading on the patent log. After an
interval has elapsed the position OF the
ship is again taken by cross-hearings when
the straight line joining the two places on
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 of the ma
chine
To finish, here is patent log yarn. as
told by an old messmate i give IL in his
own words: When in the Crocodile in the
Red sea, just after taking the reading one
night at O'Clock. the quartermaster re-
ported, Shark taken the paten Mt log, sir"
l got another one over at once. At 9::g
next morning We stopped for half an hour.
To amuse the ladies tried for and caught
a shark. on opening him we found our
patent log, and" he added. gravely,
strange to say, it registered the same as
the one in use. The line had damned be-
tween his teeth. the fan working all the
time he followed the ship. He had swum
lust 122 40 miles