Chart Navigation & Plotting · Special Bearings
The 'bow-and-beam bearings' technique uses relative bearings of 45° and 90°. At the beam bearing, the distance off the object equals:
- AHalf the distance run between the two bearings
- BThe distance run between the 45° and 90° bearings✓ Correct
- CTwice the distance run
- DThe vessel's speed in knots
Explanation
Because a 45°-90° geometry forms an isosceles right triangle, the distance run between the 45° (broad on the bow) and 90° (abeam) bearings equals the distance off the object when it is abeam.
Authority: Bowditch, American Practical Navigator (Pub. 9), special bearing techniques
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