The mirror. (Stillwater, Minn.) 1894-1925, 1916-09-14
Logs and Their Operation
An Interesting Explanation of the Uses
of Ships Log
By Mr.. J. M.

whenever the speed is to be deter
mined. The taffrail log is the type
of patent log most commonly used.
The dials and shape of this type of
log vary with the different makes;
but they are all constructed on the
same principle. A rotator in the
shape of screw propeller or fan,
is towed behind the ship. In NOV
ing. through the water rotary
motion is set up, which is in turn
communicated to the towing line.
This line is connected with small
shaft on the recording apparatus
attached to the ships rail. The
dials of some patent logs have
three hands which register the
tenths, miles, and tens of miles.
Others read like a revolution coun-
ter, while still others have a dial
similar to that of a clock. Another
type of patent log is called the
harpoon log. Logs of this kind
are claimed to be. more accurate
than the taffrail type. In the har-
poon log, the rotator is connected
directly to the recording appar-
atus, and the whole is towed
astern. The great drawback in
using logs of this type is, that in
order to read the dial, the log must
be hauled in; again the log may
become out of order and the fact
not discovered until the log has
been brought on board for read
ing. Strange as it may seem,
sharks and other denizens of the
deep, sometimes try to make
meal of the rotators being towed
by ship.
The patent log is also used when
a ships position is to be fixed when
near the shore. In a case of this
kind, a bearing is taken of some
prominent object on the shore, and
the patent log is read; the ship
holds straight course up or down
the coast as the case may be, and
when the amount of the first bear
ing of the distant object has been
doubled, the log is again read;
the distance run between the taking
of the first and second bearings is
equal to the distance between the
ship and the object observed.
In foggy weather when vessel
is nearing land, the log and sound
ing gear are both brought into use.
The approximate position of the
ship is fixed on the chart and a
sounding is taken with an armed"
lead, which when hauled up brings
with it specimen of the bottom.
The log is then read and the ships
course by compass is noted, after
a certain interval the process is re-
peated, and is continued until sew
eral soundings have been taken;
the course and distance between
each sounding as we'll as the char
acter of the bottom having been
noted, line is drawn between each
successive sounding, correspond
ing to the course and distance run,
and the diagram is compared with
the chart for the locality in which
the ship is thought to be. Calcu-
lations of this kind are seldom ever
in error, and by their use, a ships
position may be fixed very accur-
ately.
From the foregoing, it will be
seen that there are other uses for
the log, than as speed Indicator.
The patent log, however, has its
faults; it may become damaged by
oopoip ~ into of with 1ri fin r
logs, or may become fouled with
seaweed. In high speed ships, the
rotator has a tendency to jump
from the water, and by so doing,
not recording the correct speed or
distance travelled by the ship.
This tendency to leave the water
is sometimes overcome by what Is