James Turner, Yachtmaster Ocean and retired instructor, explains how to choose the best sextants and clears up some common misconceptions.
In the mid 1970’s I sailed a small boat from the UK to Tahiti, crossing the Atlantic, Caribbean and Pacific. My primary navigational instrument was a plastic sextant, the timing of which was provided by a bedside quartz crystal alarm clock, itself a very recent invention.
My shipmate had a very expensive metal sextant. We navigated separately but compared midday positions each day and were always within four nautical miles of each other.
I know from my merchant marine apprenticeship that if two officers were targeted from the bridge of a tanker, a stable and high platform compared to a yacht, and were within seven miles of each other, they would get full marks .
In the 1970s there was no GPS and even the earlier Transit satellite system, which averaged one fix per hour, had not yet been invented, so for long-distance sailing a first class sextant, along with the knowledge to use it, was essential .
Four mile accuracy is perfect for ocean cruising. It gets you to the right Caribbean island or Pacific atoll with no hassle.
metal or plastic?
If you’re looking for a good sextant, whether for mastering the art, as a backup on a blue water cruise or to compete in the Golden Globe Race, there’s a choice of metal cased instruments ranging from £600 to £3,000, and a plastic sextant from Davis, which costs up to £350. There’s your first choice. It was easy for me.
The accuracy of a metal sextant has often been cited as a reason for spending the extra money, but in my experience the inaccuracy inherent in having a low “eye level” (your height above sea level) on a roller deck are two traits we endure on sailboats, whatever sextant we buy – negate any advantage in instrument accuracy.
One argument that strongly favors plastic sextants over metal sextants is their light weight. I know from bitter experience that when you rely on celestial navigation it’s the law of the sod that creates an overcast sky, so you spend ages standing in the shrouds, arms wrapped around the rigging, sextant at the ready, and waiting for that 30 second gleam of sun that’s all you’ll see for a couple of hours.
The difference between a heavy metal instrument and a light plastic instrument on your shoulders in this situation is immense. In summary, plastic sextants cost less, weigh less, and are reasonably accurate. Now let’s take a look at some of the best sextants available on the market today.
4 of the best sextants
Ebbco Standard and Ebbco Special
Back in the 70’s there was a brand of crude plastic sextants called Ebbco. Two models called Ebbco Standard and Ebbco Special.
If you can buy one on eBay in good condition, any model is good for sun and moon sightings, but the telescope optics have never been good enough for stars and planets. The telescope on both was awful and best without. Both models had a micrometer and vernier scale.
The main difference was that while the Standard had the scale molded into the plastic, the Special had color then applied so the numbers and arc markings stood out and were much easier to see.
Does it matter? Well, as you learn you’ll probably get three sights each time, but that matters less when you’re more experienced because you just know when you’ve got a good sight.
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Manufactured in the USA, the Davis sextant comes in three models, the Mk3, Mk15 and Mk25.
The Davis Mk3, which costs just under £100, is truly a classroom instrument and is good for standing on the pier and studying, but as it doesn’t have a micrometer – just the main dial with a vernier scale – it’s extremely limited.
I would go so far as to say “don’t use this for navigation”. It also has a very limited selection of umbrellas and is not suitable for shooting stars and planets due to a plastic telescope.
However, if you want to get started, learn the art of solar gazing, and don’t want to spend a fortune, that’s fine.
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The Davis Mk15 is the first of Davis’ two “serious navigation” sextants. It features a traditional split screen with three horizon and four sun hoods, making it easy to use in all lighting conditions.
There is also a 3x magnification telescope for stars and planets. The main scale is easy to read, as are micrometers and vernier scales. Priced at around £280, this is the most popular choice for serious navigators.
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The Davis Mk25 features an all-view screen, curiously dubbed the “Beam Converger,” where the celestial body is superimposed over the horizon glass.
This is inherently easier for a beginner to master, but as a seasoned navigator used to traditional split screen, I don’t see it as an advantage.
The other main benefit of the Mk25 is the lighted bow, which is brilliant when you’re shooting stars, which you do at dawn and dusk when the stars and horizon are visible.
Time is of the essence when targeting stars, and the built-in light helps a lot. You might think that using a headlamp would be just as good, but it’s not, it’s way too bright and will cloud your vision for the next sight. It will cost you around £350.
If you want to take advantage of the built in light but with split screen you can buy the Mk25 plus a replacement mirror set for a Mk15.
It’s an expensive route, but for those who prefer split screen, it’s an excellent solution.
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Conclusion: what are the best sextants?
Having crossed a few oceans with the Davis Mk15 I have to say it’s my absolute favorite for best sextant but having the light on the Mk25 is a great feature and it’s not very expensive. If you’re just starting out, you’ll no doubt find the Davis Mk25’s Allview mirror a huge asset.
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