Your vessel is underway and approaching an overhead obstruction on Lake Superior. Given the following information, determine the clearance between your vessel and the obstruction. Highest point on vessel: 74 ft. Lowest point of obstruction: 126 (LWD) Monthly lake level: +2 (LWD) International Great Lakes Datum: 600.0 (182.88 meters)
Official USCG Answer & Rule Citation
Correct Answer: Option D — 50 feet
Vertical clearance is calculated by taking the obstruction height above Low Water Datum (126 ft), subtracting the monthly lake level rise above LWD (+2 ft), yielding an actual clearance of 124 feet above the water. Subtracting the vessel height (74 ft) leaves a 50-foot net clearance.
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