Another method of taking a running fix is by doubling the angle on the bow, having in mind the properties of an isosceles triangle.

This fix requires the first bearing to be less than 45° from the bow. Assuming the course is 090° degrees and the speed is 10 knots, or 10 nautical miles per hour. We take a bearing of 060° degrees of the Charley radio tower at 0900 or 30° degrees from the bow. Now convert the compass bearings to true bearings and plot it on the chart.

We observe the Charley radio tower, and when the new bearing reads 030° degrees, or 60° degrees from the bow, we note the time, 0915. Now convert the compass bearings to true bearings and plot it on the chart.

Knowing the speed – 10 knots – and the elapsed time between the two bearings – 15 minutes –

we use the formula: D is equal to S times T divided by 60, to calculate the sailing distance between the two bearings. In our case that is 2.5 nautical miles per hour.

As we can see, the two bearings and the course form an isosceles triangle – ABC – where sides c and b are equal.

That means that the distance from the Charley radio tower, when we took the second bearing at 0915 was 2.5 nautical miles.

Using this method we have a bearing and a distance using only one object.