Chart Navigation & Plotting · Distance Off — Doubling the Angle
By the 'doubling the angle on the bow' method, when the relative bearing of an object doubles, the distance run since the first bearing equals:
- AThe distance to the object at the time of the second bearing✓ Correct
- BHalf the distance off
- CThe distance to the horizon
- DThe vessel's speed in knots
Explanation
When the bow angle doubles (e.g., 30° then 60°), the triangle is isosceles and the run between bearings equals the slant distance to the object at the second bearing — giving distance off without identifying the beam.
Authority: Bowditch (Pub. No. 9), distance by bearings
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