Division Eleven - Chip Log
The Chip Log is a Division Eleven newsletter. This newsletter is unclassified.
The Chip Log derives its name from one of the oldest devices used to navigate. One of the three main aspects of navigation is dead reckoning (DR). Simply put, DR is an estimate of your position, based on course, speed and time from a known, observed point. For example, if you started from a point on a flat open plain, in an automobile with the windows painted over and with a compass on the dashboard, and drove 1 mile north, 1 mile east, 1 mile south, and finally 1 mile west (provided you didn't collide with something along the way), then you should end up right where you started from, whether you could see outside the vehicle or not. If you had no odometer, to measure the distances you would need to know your speed and the elapsed time at that speed in order to determine the distance traveled. In order to determine a ship's DR position, one must be able to observe the ship's course and speed, updated frequently since the last good celestial or visual fix.
In the most ancient times, speed at sea was measured
by dropping a piece of driftwood or a small log off of the stern of the
moving ship. As the ship moved away from the wood, an approximate speed
could be guessed. Of course, one could only do this so many times before
exhausting the supply of wood aboard. This was remedied by attaching a length
of light twine or line to the log; the same log could then be retrieved
and used repeatedly. The rope tied to the log had a number of measured knots
tied in it. The speed of the ship was indicated by the number of knots passing
over the stern during a certain period of time. The unit, knot, for nautical
mile per hour, was derived from the knots tied in the rope of a log.The
entire system to calculate speed is called a Chip Log.
August
2006 - Adobe Acrobat PDF
format
September
2007 - Adobe Acrobat PDF
format
May 2008 - Adobe Acrobat PDF
format
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