Doubling the Angle on the Bow

Definition

Note the distance run between the moment an object bears at a relative angle and the moment that relative angle has doubled. The resulting triangle is isosceles, so the distance run equals the distance from the object at the second bearing. Example: with the object 30 degrees on the bow, run until it is 60 degrees on the bow; if 2.4 nautical miles were logged, the object is then 2.4 nautical miles off. It assumes a steady course and negligible current.