Navigation General · Tides
Using the Rule of Twelfths, how much of the total tidal range occurs during the SECOND hour of a rising tide?
- A1/12 of the range
- B2/12 of the range✓ Correct
- C3/12 of the range
- D4/12 of the range
Explanation
The Rule of Twelfths states that tidal rise/fall is not uniform. The distribution per hour is: 1st hour = 1/12, 2nd hour = 2/12, 3rd hour = 3/12, 4th hour = 3/12, 5th hour = 2/12, 6th hour = 1/12. So the 2nd hour = 2/12 of the range.
Authority: Bowditch (Pub. 9), Ch. 9
Practice the full Navigation General bank
Free spaced-repetition quizzing across 2190 USCG exam questions — it schedules your reviews so the ones you miss come back until they stick.
Related Navigation General questions
- Tides
The chart datum used on NOAA nautical charts for depth soundings is:
- Tides
The vertical difference between Mean High Water (MHW) and Mean Lower Low Water (MLLW) is called the:
- Tides
The total tidal range at a port is 12 feet. Using the Rule of Twelfths, how many feet does the tide rise during the THIRD hour after low water?
- 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)?
- Tides
A vessel drawing 14 feet needs to cross a bar charted at 10 feet (MLLW). Low water is 0.5 feet above MLLW. High water will be 5.5 feet above MLLW. How much additional height of tide above low water is needed before the vessel can safely cross with 2 feet of under-keel clearance?
- Tides
What is the height of tide formula for finding actual depth of water at any time?