Chart Navigation & Plotting · Tides — Semidiurnal Interval
At a port with semidiurnal tides, successive high waters are separated by approximately:
- A6 hours 12 minutes
- B24 hours 50 minutes
- C12 hours 25 minutes✓ Correct
- D12 hours 00 minutes
Explanation
Semidiurnal tides have two high and two low waters each tidal day. The tidal (lunar) day is about 24 hours 50 minutes, so successive high waters fall roughly 12 hours 25 minutes apart, and each day's corresponding tide arrives about 50 minutes later than the day before.
Authority: Bowditch (Pub. No. 9), Tides
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