Blundell Harling Portland Course Plotter

The Portland Course Plotter, used on RYA navigation courses: 360 x 130 mm (14¼ x 5 inches), with a moulded compass disc that turns on a brass pivot over a fixed grid in the base.

A bright blue arrow points along the course, so you don't lay off the reciprocal by mistake. The edges are graduated for measuring tide and boat speed, the grid makes it easy to plot a latitude and longitude from the GPS, domed feet let it slide across the chart, and raised fins on the disc turn easily with cold or gloved hands. Instructions are included.

How to use the Portland plotter

To lay off a course, set the disc to the course, put the edge through your position with the arrow pointing the way you want to go, and turn the whole plotter until the grid lines up with a meridian or parallel; then draw along the edge. To read a course, lay the edge along the line with the arrow pointing along it, turn the disc until its grid lines up with the chart, and read the course at the index.

About Blundell Harling

Blundell Harling, of Weymouth in Dorset, has made scale rules, drawing instruments and navigation plotters for more than 75 years. The Portland Course Plotter takes its name from the Isle of Portland, across the harbour.