Navigation General · Tides
Low water is at 0400 at 1.0 foot above MLLW. High water is at 1000 at 7.0 feet above MLLW. Duration of rise is 6 hours. Using the Rule of Twelfths, what is the height of tide at 0700?
- A3.0 feet
- B4.0 feet✓ Correct
- C4.5 feet
- D5.0 feet
Explanation
Range = HW − LW = 7.0 − 1.0 = 6.0 feet. Time elapsed from LW (0400) to 0700 = 3 hours. Rule of Twelfths cumulative rise after 3 hours = (1+2+3)/12 = 6/12 = 0.5 × 6 = 3.0 feet. Height at 0700 = LW height + rise = 1.0 + 3.0 = 4.0 feet above MLLW.
Authority: Bowditch (Pub. 9), Ch. 9
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