DEAD RECKONING NAVIGATION
Here's how it worked:
First of all, the navigator had
to collect some articles to make
a system which could "dead-reckon".
Among these items were: a long
rope , an hour glass , and a piece of wood or log
. The
navigator also needed a compass
and a log book to record his
navigational findings. The rope
was knotted every 4 to six feet
along its length. The log (piece
of wood) was tossed into the sea
after it had been tied to the
end of the rope. The rest of the
rope was piled on the ship's
deck.
The Process
From arithmetic, we know that
distance traveled in a selected
direction is determined by
multiplying speed by the time
the vehicle travels at the
chosen speed. If a car has a
steady speed of 30 mile per hour
for a period of two hours, it
has covered a distance of 60
miles (30 miles per hour
multiplied by two hours comes to
a 60 mile distance) in the
direction the driver chose to
drive. In order to determine the
car's position after a number of
hours, the driver would need to
record on paper the speed,
direction, and time the vehicle
traveled at a steady speed prior
to changing speed or direction.
Each time a change in direction
or speed occurred, the driver
must record the new speed,
direction, and time in his
log.
This is the process Columbus
used to navigate. A compass
determined the direction the
ship moved in the water. Speed
was measured by throwing the
wood float attached to a long
rope overboard. At the time the
float entered the water, an hour
glass was turned so that the
sand began dropping into the
empty lower portion of the hour
glass. Knowing the length of the
rope which trailed behind the
ship during the time it took for
the hour-glass's sand to empty
into the bottom portion of the
timer enabled the navigator to
measure both the speed and
distance traveled. While not
very precise compared to a car's
speedometer, the process was
done in a regular fashion so
that the recorded measurements
often achieved up to 90 percent
accuracy.
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