Chart Navigation & Plotting · Piloting — Vertical Sextant Angle
A lighthouse charted at 200 feet high shows a vertical sextant angle of 0°24'. Using the relationship distance (nm) = 0.565 × height (ft) ÷ angle (minutes), what is your approximate distance off?
- A2.4 nautical miles
- B4.7 nautical miles✓ Correct
- C9.4 nautical miles
- D1.2 nautical miles
Explanation
0.565 × 200 ÷ 24 = 113 ÷ 24 ≈ 4.7 nm. A measured vertical sextant angle of a charted object of known height gives an instant distance-off line of position (a circle of position centered on the object).
Authority: Bowditch, American Practical Navigator (Pub. No. 9), distance by vertical angle
Practice the full Chart Navigation & Plotting 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 Chart Navigation & Plotting questions
- Piloting — Vertical Sextant Angle
You measure a vertical sextant angle of 0°30' to the top of a lighthouse charted as 113 feet high. Using distance(NM) = 0.565 × height(ft) ÷ angle(minutes), how far off is the lighthouse?
- Chart Basics
On a Mercator chart, one nautical mile is measured using the:
- Chart Basics
The principal advantage of the Mercator projection for navigation is that:
- Chart Basics
Charted depths (soundings) on a U.S. chart are referenced to which tidal datum?
- Chart Basics
Vertical clearances of bridges and overhead cables on a U.S. chart are normally referenced to:
- Distance, Speed & Time
A vessel makes good 12 knots. How far does it travel in 20 minutes?