Distance to run made simple

A basic graph can keep you on track and simplify your decision-making at sea, says David Smith

- David Smith

There has been much said of the roles of traditional and electronic navigation techniques in recent years. For my own part I consider GPS chart plotters to be the tool to tell you where you are and where you are heading, and paper charts, along with almanacs and tidal stream atlases, are the essential tools for planning. Having spent much of my life learning navigation, not only at sea but on land and in the air, I thought I had everything needed in my navigational toolbox. However, last year I added something new.

In May my wife Sarah and I began a 2,142-mile cruise from Devon to Scotland, returning in September. We sailed aboard Mollymawk, our Pan Oceanic 38, a cutter-rigged sloop with a pilot house and eminently suited for such a voyage. An old friend joined us as far as Strangford Lough and, as a ‘superannuated navigation officer’, John showed us a little of one of the tools he used in the Royal Navy while navigating a frigate and a nuclear submarine. He learnt the basics on two navigation courses, developing them at sea, and was therefore very surprised that I did not employ what he considered to be a standard planning method. We therefore had to improvise at the beginning as I had not shipped any graph paper.

The method John showed me is very straightforward, easy to remember, and indispensable for planning any passages where there are time constraints. Essentially it is the use of a distance-time graph, familiar to anyone from schooldays and also to sailors who are ex Royal Navy, but it is certainly not part of any RYA course that I have undertaken. The real trick is that it allows you to see how a passage is progressing and gives you the information you need to make sound and timely decisions without having to think too hard.