Chart Navigation & Plotting · Piloting — Geographic Range
A light has a charted height of 121 feet and your height of eye is 16 feet. Using geographic range = 1.17(√H + √h), what is the geographic range?
- A21.06 NM
- B12.87 NM
- C17.55 NM✓ Correct
- D13.69 NM
Explanation
Geographic range = 1.17(√121 + √16) = 1.17(11 + 4) = 1.17 × 15 = 17.55 NM. This is the distance at which the light is above the horizon for your height of eye; the light is only seen if its nominal (luminous) range is also adequate.
Authority: Bowditch (Pub. No. 9), Visibility of Lights
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