Coastal Skipper and Yachtmaster Quiz · Position fixing
The angle on the bow to the lighthouse has doubled, from 30° at 1000 to 60° at 1030. How far is the yacht from the lighthouse at 1030?
Seen from above: a yacht on a straight course from left to right, shown at 1000 and again at 1030. A lighthouse lies ahead and to one side of her track. At 1000 the line to the lighthouse makes an angle of 30° with her course. At 1030 it makes 60°. The 1030 line to the lighthouse is drawn in gold with a question mark. Caption: speed 6 knots, no tidal stream.
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3.0 miles. When the angle on the bow doubles, the distance off at the second bearing equals the distance run between the two bearings. She has run 30 minutes at 6 knots, which is 3.0 miles, so the lighthouse is 3.0 miles away. It only holds on a steady course, and the run must be distance over the ground.
