Starpath Chart Tutorials

Measuring true course with a string plotter...
This is a method found useful for many paddlers and other small craft operators that have little room for tools or surfaces to use them on.

Drill a hole (if needed) in the center of a 0-360° protractor and insert a string about 18 inches long. Tie knots at both ends and use as illustrated.

For some applications, the center of the protractor can be placed on your position or other reference mark, but in other examples, as the one shown here, the center is offset so the string can pass through both points of interest.

The edge or some other vertical or horizontal lines on the protractor must be aligned with some straight lines on the chart, but it is rearley a problem to make this orientation. The bearings or directions are read from the protractor where the string crosses the scale. These directions will always be true directions which must be converted to magnetic if used with a compass, which is the usual case.

Video Notes
There is no video here, just slides.

Slide 1 shows general use of the tool, aligning the protractor with some vertical or horizontal reference and stretching out the string to read a direction.

Slide 2 shows the alignment and the string in more detail. In this example, the plotter is used to measure the course from a plotted position to the pass between two islands.

Sldie 3 shows the string crossing the protractor scale and going through the plotted position. The true direction of this course is 307 T. If the local magnetic variation were 20° East, then the magnet course would be 307 - 20 = 287 M.

The compass conversion rule is "correcting add east," where "correcting" means going from Magnetic to True. We are going the other way, so we subtract. If there is ever any doubt about this, just go to a compass rose and draw a line from center to either true or magnetic course and read the "converted course" from the other scale on the rose. In short, a compass rose is just a graphic table of compass conversions, from True to Magnetic or vice versa.

This type of string plotter could be called "Sutherland plotter," named after kayaker Chuck Sutherland who, to our knowledge, is the inventor of this idea for a measuring device.

Starpath Inland and Coastal Navigation Course True direction using a string plotter
Measure Distances • Short distances with the miles scale • Short distances with the latitude scale • Long distances in steps Measure Directions • Magnetic direction using parallel rulers • True direction using Weems plotter • True direction using a string plotter Plotting positions and courses • Using Lat - Lon scale • Plotting COG from a plotted position • Using the Starpath card plotter method
Measuring true course with a string plotter... This is a method found useful for many paddlers and other small craft operators that have little room for tools or surfaces to use them on. Drill a hole (if needed) in the center of a 0-360° protractor and insert a string about 18 inches long. Tie knots at both ends and use as illustrated. For some applications, the center of the protractor can be placed on your position or other reference mark, but in other examples, as the one shown here, the center is offset so the string can pass through both points of interest. The edge or some other vertical or horizontal lines on the protractor must be aligned with some straight lines on the chart, but it is rearley a problem to make this orientation. The bearings or directions are read from the protractor where the string crosses the scale. These directions will always be true directions which must be converted to magnetic if used with a compass, which is the usual case. Video Notes There is no video here, just slides. Slide 1 shows general use of the tool, aligning the protractor with some vertical or horizontal reference and stretching out the string to read a direction. Slide 2 shows the alignment and the string in more detail. In this example, the plotter is used to measure the course from a plotted position to the pass between two islands. Sldie 3 shows the string crossing the protractor scale and going through the plotted position. The true direction of this course is 307 T. If the local magnetic variation were 20° East, then the magnet course would be 307 - 20 = 287 M. The compass conversion rule is "correcting add east," where "correcting" means going from Magnetic to True. We are going the other way, so we subtract. If there is ever any doubt about this, just go to a compass rose and draw a line from center to either true or magnetic course and read the "converted course" from the other scale on the rose. In short, a compass rose is just a graphic table of compass conversions, from True to Magnetic or vice versa. This type of string plotter could be called "Sutherland plotter," named after kayaker Chuck Sutherland who, to our knowledge, is the inventor of this idea for a measuring device.
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