Chart Navigation & Plotting · Tides — Rule of Twelfths
With a tidal range of 6 feet (6-hour rise), how much has the tide risen 2 hours after low water by the Rule of Twelfths?
- A3.0 feet
- B1.0 foot
- C1.5 feet✓ Correct
- D2.0 feet
Explanation
After 2 hours the tide has risen (1 + 2)/12 = 3/12 = 1/4 of the range. One quarter of 6 feet is 1.5 feet.
Authority: Bowditch (Pub. No. 9); NOAA Tide Tables
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