The joy of sextant

David Barrie first heard the word sextant as a nine-year-old watching Mutiny on the Bounty in a darkened cinema.

Marlon Brando screamed: “We will never leave here without it!” — but the ship sank with the precious instrument still onboard.

Haunted by the image of Brando leaping into the flames to try to rescue the device, young David asked what a sextant was — and why it mattered so much.

Later, as a 19-year-old crossing the North Atlantic in a 35ft sloop, he would find out for himself how the small device helped sailors track their way across vast oceans using the positions of the sun, moon and stars. He also discovered that the sextant had changed history.

In Sextant: A young man’s daring sea voyage and the men who mapped the world’s oceans (William Morrow), Barrie tells of how the instrument saved the lives of navigators and played a pivotal role in their ability to explore and chart the globe. The Briton made his 1973 transatlantic crossing just as the technology was being developed that would mean using a sextant was no longer the only way to fix a position out of sight of the shore.

Many older seafarers lament their younger colleagues’ inability to look at the sea and sky and read the natural signals, particularly at times when screen-based electronic navigation instruments can fail.

Barrie says GPS has made life easier and safer, but has shortcomings. It is vulnerable to interference that can easily jam it, or to “spoof” signals that can convince it that it is somewhere it’s not. Charged particles entering the atmosphere can also fry the circuitry in GPS satellites.

“Of course the most robust alternative to GPS is the good old sextant. It doesn’t even need electricity! But to navigate reliably with a sextant requires practice,” Barrie says.

The saddest thing about GPS is that so few people are acquiring the skill, he adds. Perhaps his book can persuade a few to take up the art again.