How to use a Chart Compass Rose to quickly plot your position

Establish the position of the centre of a convenient Compass Rose on your paper chart, and enter the co-ordinates as a waypoint in your Chart Plotter.

You can then configure the Chart Plotter to continuously read of the distance and bearing to the ‘Rose’ waypoint.

All you now have to do is regularly read off the bearing and distance from the waypoint reported on your Chart Plotter. To do this, you first need to convert the bearing to the reciprocal of the one read from the plotter. This is because the plotter is telling you the direction from your boat to the compass rose waypoint. You want to know the bearing from the compass rose on the paper chart to your boat.

There is an easy way to work out reciprocals in your head:

If the bearing is more than 200 degrees, subtract 200 and add 20.
For example, Plotter reads 270°. Subtract 200 = 70. Add 20 = 90°

If it is less than 200°, add 200 and subtract 20.
e.g. Plotter reads 16°. Add 200 = 216. Subtract 20 = 196°

Using this simple method avoids mistakes.

Next, use a ruler to measure the distance shown by the plotter using the latitude scale (left or right side of the chart). Then, using the compass rose, mark the position of the boat on the chart by placing the ruler at the correct angle and draw a line from the centre of the compass rose through the reciprocal of the bearing angle read from the plotter. Measure along the bearing line to get the distance using the chart´s latitude scale.

You should repeat this every half hour or so. With a little practice, this can be done in a few seconds. See (Figure 1).

A neat trick of using the co-ordinates of a Chart Compass Rose on your Chart Plotter to quickly plot your position and bearing underway

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