Chart Navigation & Plotting · Tides — Rule of Twelfths
According to the Rule of Twelfths, what fraction of the tidal range occurs during the third hour of a roughly six-hour rise or fall?
- A2/12 of the range
- B1/12 of the range
- C3/12 of the range✓ Correct
- D4/12 of the range
Explanation
The Rule of Twelfths distributes the range as 1, 2, 3, 3, 2, 1 twelfths over the six hours. The third and fourth hours each account for 3/12, the period of fastest tidal change near mid-tide.
Authority: Bowditch (Pub. No. 9), Rule of Twelfths
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