Navigation General · Tides
At a port with a tidal range of 18 feet, low water is at 0600. Using the Rule of Twelfths, what is the height of tide above low water at 0800 (2 hours after low)?
- A1.5 feet
- B3.0 feet
- C4.5 feet✓ Correct
- D7.5 feet
Explanation
Rule of Twelfths: 1st hour = 1/12, 2nd hour = 2/12, total after 2 hours = 3/12 = 1/4 of range. Height risen = (3/12) × 18 = 4.5 feet above low water.
Authority: Bowditch (Pub. 9), Ch. 9
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