Course Plotters

The Portland Course plotter, is very similar adaptation of the traditional Breton plotter which was invented by Capt Yvonanick Gueret who was a Breton seafarer. Both are popular with yachtsmen however they are very rarely seen or found aboard merchant and commercial vessels where parallel rules and Portland squares are the standard equipment for chart-work navigation and plotting.

Laying of a true course using a course plotter

Both instruments are constructed in a similar fashion utilizing two simple component  pieces, a ruled baseplate and a rotating compass rose.

At this point in time the most important elements we need to concern ourselves with our the course and direction of bearing line, the rotating compass rose, and the meridians of longitude that run from North to South on a navigation chart.

In this first example we will use the plotter to measure the true course we have laid off between point A due North of The Wallet Buoy  No. 4 and  B Due North of the Wallet Buoy No. 2

Please note this is True Course between points A and B and not the course to steer (CTS) or the course made good (CMG) as no magnetic variation or deviation or set and drift has been applied.

[ Return to Videos ]