Chart Navigation & Plotting · Distance — Dipping a Light
A light's charted height is 100 feet and your height of eye is 36 feet. As you approach, you will first see the light 'dip up' at a distance of (using 1.17(√H + √h)):
- A13.69 NM
- B11.70 NM
- C18.72 NM✓ Correct
- D23.40 NM
Explanation
Dipping distance = 1.17(√100 + √36) = 1.17(10 + 6) = 1.17 × 16 = 18.72 NM. Observing the exact range at which a light first appears on the horizon gives a distance-off line of position.
Authority: Bowditch (Pub. No. 9), Dipping Distance
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