Chart Navigation & Plotting · Distance — Vertical Sextant Angle
Measuring the vertical sextant angle of a lighthouse of known height allows the navigator to determine:
- AThe compass error
- BThe distance off the lighthouse✓ Correct
- CThe height of tide
- DThe set of the current
Explanation
With the charted height of the light and the measured vertical angle, distance off is found from a table (Bowditch Table 16) or formula. Combined with the object's bearing it gives a fix from a single object.
Authority: Bowditch (Pub. No. 9); Norie's/Tables
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