The easy way to calculate course to steer

You don’t need paper charts and complex diagrams to calculate course to steer. Mark Browse explains a method that’s easy enough to do in your head

- Mark Browse

Like many sailors I have gradually drifted away from printed charts over the last few years, and have come to rely more on my tablet and smartphone than on bits of paper.

On last year’s cruise to the Channel Islands and northern France I insisted on carrying a ‘proper’ chart, but the truth is I only used it once: and that was to give my mainly novice crew an overview of the area we were sailing in.

A TRADITIONAL APPROACH

In the August 2019 edition of Yachting Monthly Bruce Jacobs made the following observation:

‘Course to steer (CTS), much beloved of RYA theory courses, is barely used in truth as the wind, current, tacks, traffic and timings are always different to the plan.’

He’s right, of course. On most shortish passages, it is enough to keep an eye on the course over the ground and make sure the boat’s heading keeps you on that track. If it doesn’t, ask the helm to tweak the course by a few degrees until it does.

On a longer passage such as a Channel crossing that lasts long enough to see the tide turn, you could theoretically still use this approach, and your ground track would show as a nice straight line, suggesting efficiency.

But this apparent neatness would come at a cost. Your distance through the water, as you battled the tide first one way then the other, would actually be longer than it needed to be. It could mean you have to make do with Pot Noodles à la mal de mer served with a seawater jus, instead of savouring