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Navigation Station |
Nautical Clocks (Page 3)
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Speed in Knots
The speed of a vessel at sea is reckoned by knots, each knot being equal to
a nautical mile (6,076 feet), which is slightly longer than a mile measured
on land (5,280 feet). Six nautical or geographical miles are about equal to
seven statute English miles, so that a ship making 12 “knots” an hour is
actually traveling at the rate of 14 statue miles per hour. The following
explanation from an old training manual tells how a ship’s speed came to be
measured in knots:
“ The speed of a ship is ascertained by means of the log-line, which is a
cord knotted at equal distances of 51 feet; 120 of these lengths are equal
to a geographical mile. At one end of this line the ‘log’, which is a piece
of flat, light wood, generally triagular in shape, weighted along one edge,
is attached, much in the same way as a boy fastens his kite to the string,
so that it floats vertically, with it’s flat surface presented to the ship.
When thrown overboard, with the line allowed to pass over the stern freely,
the log meets with so little resistance that theoretically it remains
stationary. The number of knots in the cord being equal to the number of
half minutes in an hour, it follows that as many ‘knots’ of the line as pass
over the stern of the vessel every half minute, so many geographical miles
or knots are being ‘made’ by the ship in an hour.” |
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