When To Use Great Circle Sailing?

Great circle sailing is a method of navigating a ship along the shortest navigable distance between the point of departure and the point of arrival. It is used for long ocean passages, especially those that involve crossing different latitudes. The Earth is considered a perfect spherical shape, so the shortest distance between any two non-antipodal points on a sphere’s surface is the only great circle track (GCT) passing through them.

Great circle sailing requires changing steering course at intervals throughout the passage, usually once a day. A great circle track also means that when plotting a course over a distance of 500 miles or more, it usually makes sense to travel a Great Circle route between origin and destination as it will be a shorter distance over the planet’s surface than the straight route, also known as the Rhumb Line.

A great circle can be drawn as a straight line on a gnomonic chart and then plotted as a circle on a mercator chart. The great circle route is only of significance for distances over about 600 miles, and if you are in high latitudes and want to travel east.

The chart and methods suggested by Prof. Proctor are very simple and may be readily grasped by navigators of even small mathematical knowledge. They promise to provide accurate navigation for long voyages, saving time and fuel, especially in challenging sailing conditions.

In conclusion, great circle sailing is a method of navigating a ship along the shortest navigable distance between the point of departure and the point of arrival. It is a useful technique for commercial vessels across the North, but it is not suitable for all cruising boats.