Chart Navigation & Plotting · Tides — Rule of Twelfths
By the rule of twelfths, during the first two hours after low water the tide rises what fraction of its range?
- A1/12
- B3/12 (one quarter)✓ Correct
- C6/12 (one half)
- D2/12
Explanation
The rule of twelfths gives hourly rise as 1, 2, 3, 3, 2, 1 twelfths over a 6-hour cycle. The first two hours rise 1/12 + 2/12 = 3/12, or one quarter of the range.
Authority: Admiralty/NOAA tide practice; rule of twelfths
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