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Day Skipper - Part 6
- The rule of twelfths
 There
are various ways of establishing the height of tide at any time between
high and low water. The rough-and-ready method is the rule of twelfths.
This presumes that the height of tide rises or falls by 1/12th of the
range in the first hour, by 2/12ths during the second hour, 3/12ths during
the third and fourth hours and then 2/12ths in the fifth hour and 1/12th
in the sixth hour. Although this is not the most accurate way of establishing
a tidal height, it is satisfactory if you are not working to the nearest
centimetre.
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