EXPERT ON BOARD

ROUGH & READY CELESTIAL NAVIGATION

A sextant and the sun is all you need to find your position, says Tapio Lehtinen. It’s easier than messing around with stars and much more satisfying than GPS

When you read this, I will be somewhere in the depths of the Southern Ocean, bound for Cape Horn aboard the Swan 55 Galiana WithSecure. Supported by a crew of young Finnish sailors, I’m taking part in the Ocean Globe Race, a fully crewed round-theworld race that eschews modern technology, including GPS, to recapture the spirit of adventure of some of the early offshore races. I actually first started writing this article while aboard the m/v Darya Gayatri following my Southern Ocean rescue, initially by Kirsten Neuschäfer, when my beloved yacht Asteria sank suddenly during the Golden Globe Race last in 2022.

Modern technology is great, but there’s something about finding your position on the Earth’s surface without it that is immensely satisfying, and helps us know our place within the cosmos, rather than just on a digital screen.

While much as has been written about the noble art of astro-navigation, I hope to set out, as simply as possible, how I have navigated my way round the world more than once using little more than the sun, a sextant, a watch and an almanac.

You certainly don’t have to mess around with the stars to establish your position to an accuracy of five to 20 miles, which is perfectly sufficient in the middle of an ocean and adequate even for most landfalls. You do not need to worry about fine-tuning your sextant or understanding the spherical trigonometry or astronomical theories behind the process. The processes for forenoon and afternoon sights are fairly simple, not to mention the noon sight, which gives your latitude, which is very simple indeed. If you enjoy the process, you are free to go deeper into the theory and also to making the next step of taking sights of the moon, planets and stars.

NOON SIGHTS

The noon sight is a simple calculation and the result provides your exact latitude.

CALCULATING LOCAL NOON TIME

This is based on the longitude of your rough dead reckoning position. The sun revolves around the earth, which means 360° of longitude in every 24 hours. That means the sun moves 15° of longitude per hour or four minutes of time for each degree of longitude. That’s one minute of time per 15 minutes of longitude. Figure these out with paper and pencil and remember them by heart – it will make the calculations easier.

The sun crosses the Greenwich Meridian (000º) roughly at 1200 each day.