The Offshore Voyaging Reference Site

Q&A Which Sextant To Buy…If At All



AAC Member Terje asks [edited for brevity]:

We are planning to go full time voyaging in 2016 and although we have two GPSs aboard, my wife, who is the navigator, would like a sextant and so I’m planning to give her one for Christmas. Do you have a recommendation for the sextant I should buy?


An interesting question. I have to confess that I have not thought about sextants, or had my Zeiss Freiberger (made in the former East Germany) out of the box in 15 years, but it certainly served me well, back in the days before GPS. If you could find one of those secondhand it might be a good choice.

Does anyone else have a recommendation for Terje, or an opinion on the sextant he links to above? Please leave a comment.  Those with first hand, realworld, at sea, celestial navigation experience only please.

Buy Why?

Of course there is a larger question here. And at the risk of stirring up a lot of sturm und drangwhy buy a sextant at all? I wonder if you could not find things to spend the money on that would be of more use in getting you out there (and keeping you out there) voyaging.

Or to put it another way, is your boat already equipped with every single item that costs UKP800 (the cost of the sextant you link to), that is more likely, in this day and age, to keep you safe than a sextant? The point being that optimal gear acquisition to get out cruising is all about balancing risk and prioritization—no one ever has it all.

Yes, I know that GPS can die, or be disrupted by sun spots, or whatever, but really how likely is that? And more to the point, how long is the system going to be down when you consider how reliant the whole world is on it? And the Russians even have a backup, which an iPhone—an iPhone, for crying out loud!—can receive.

More Required

And even if you have a sextant aboard, if the unthinkable happens, will you have that year’s almanac and an accurate set chronometer? If not, you will be limited to finding latitude only.

Perhaps even more to the point, will you remember how to use the sextant and work out the sight? I’m not saying you won’t, but it is important to keep in mind that a sextant is only one part of being ready to navigate by celestial.

One caution, if you do decide to go without a sextant, make sure you have a really good navigation backup system in place.

My Take on Sextants

Me? Although we still carry my sextant since we already have it, I spent way too many years hanging on for dear life, trying to snap a sight of a momentarily appearing disk, while trying to avoid getting a wet ass, or worse still a wet sextant, to want to go back to those days.

Not to speak of the gut-corroding anxiety of approaching the killing north reef of Bermuda (before the beacons were there) on a 36-hour old doubtful sun line. Oh yes, then there was the fun of trying not to woof my cookies while sitting at the chart table working the sight.

And you all thought I was an old fashioned curmudgeon who would love sextants—have to keep you guessing.

A Hobby?

Having said all that, if your wife wants a sextant because she enjoys practising celestial navigation, then go for it.

What I’m saying, I guess, is that sextant navigation is now, like SSB radio or, for that matter, my addiction to photography, a hobby and not something we actually need to go cruising.

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David e Bell

If I may amplify one point, like any other backup or emergency device, if you don’t use it regularly and often, it won’t be operational when you really need it. If you are going to carry it, use it often enough in real circumstances that you are comfortable using it. Having it sitting in a locker is not enough.

Daria Blackwell

We have a Japanese Tamaya and a Celestaire Astra IIIB, both of which we bought used on eBay. We found both to be quite accurate for noon sights. We had always intended to learn celestial but then GPS arrived and we never got past noon sights. We picked up a StarPilot handheld celestial computer at a garage sale which has all the information you need to calculate sight reductions. It is now available as an app for iPhone. We’ve played with it but never used it to actually navigate. So technically, we should be able to find our way without electronics. But, like you, we haven’t taken the sextants out of their boxes in years. The sextants are in great shape but we’re rusting away. So whether we could get back in shape in a hurry is questionable.

We have two dedicated navigation systems onboard, as well as a laptop that has navigation software and a GPS mouse, and we have Navionics on our androids now with satellite GPS, as well as a handheld GPS. Yet we know how vulnerable we are. Our previous boat was hit by lightning twice. Once as a discharge nearby which caused intermittent problems. The second time a direct hit blew a hole through the keel the size of a watermelon. (and yes, we had a lightning diffuser/attractor on the mast). Thankfully we were not onboard at the time. Everything was fried onboard, including the handhelds. We had to replace all wiring and all equipment. With climate change, electrical storms are increasing in both frequency and intensity. So, we now keep the handhelds in the oven (Faraday cage) if there are electrical storms nearby.

American GPS satellites are falling out of the sky and the iPhone/iPad will not be permitted in Russia as of January 1 because the Russians have passed a law forbidding cloud storage. Will then the Russian GPS be off limits to foreign iPhone users? I don’t know the answer.

So we’re keeping the sextants on board. Always good to be prepared for Armageddon. 🙂 Just to be sure to be sure.

Marc Dacey

Predictably, I own a Walker Log, too, along with an Astra IIIB, a Freiberger and a Davis 25 (my son’s). As for a Faraday cage…it’s the whole boat…

Francis Livingston

Hi John – your points are well made – if one is going to learn celestial navigation then one must have all the ancillary tables and equipment and experience as well – an article at last year (2016) reported that the US Navy has returned to training their officers in celestial navigation which says something about their confidence in GPS navigation if/when nations start hurling rocks at each other again – and lest we forget – there was Carrington Event of 1859 – a massive solar flare that wrecked havoc on the rudimentary planetary wiring of the time – a number of articles I have read suggest a repeat is really only a matter of time – that we have been very lucky so far – and that we are almost totally unprepared to deal with the repercussions of such an event if it occurs – happy thought that – so perhaps learning and practicing celestial navigation isn’t so crazy after all

Pat Kelly

I learned to do celestial navigation when I was a medical officer on a U.S. NAVY ship in 1967-68. There was not a whole lot for a doctor to do with 500 healthy sailors. So I used to do rounds of starts morning and twilight and noon latitudes with the Navigator and his Chief petty officer. And we used to work the sights by hand (no calculators then) and compare our fixes with LORAN C which was just coming into use then. Actually, it was fun (sort of). Fast forward 47 years and I still do sights when I’m single-handing, drifting along with little wind and nothing else to do. (Of course I have GPS units – 2 of them) I still have my old Tamaya and Plath sextants, get time signals from WWV and use a Celesticomp calculator (my rotting 74 year old brain can’t handle working the sights by hand on paper anymore) and keep my fixes within 1/2 mile compared to the GPS. The navigational self sufficiency has always appealed to me. There’s something “Thoreau-sian” about it (whatever the Hell that means!)

Richard Moore

It’s terrifying to hear that lightning can do that much damage, when you say it blew a hole through the keel and even fried hand held devices not even connected to the boats electrical system!

Makes me consider a completely Monel sailboat, Hull deck, structure and mast! basically the boat is a faraday cage same way a car is…

Stuff is also happens to be stronger tougher and more ductile than steel and pretty much immune to all corrosion other than sitting in direct contact with mud containing sulfides which is easily avoidable…

Building a boat out of it is easy as building a steel boat, welding Monel is almost identical to welding steel and just as easy, no difficulty like with aluminium welding…. So easily repaired by yourself just by carrying the welder and some monel sticks….

Speaking of welding it, you weld all the deck fittings, also monel directly to the deck, no troublesome chainplates buried in fibreglass…

Much stronger and resistant to fatigue than stainless steel and last nigh on forever

The extra cost of the materials is smaller than expected too, as the material costs are rather small in comparison to the total cost of construction and outfitting, and even pay themselves off in less than a decade from the vastly reduced maintenance costs…

Self cleaning when sailing at speed so no need for antifouling paint, just a quick scraping while still in the water if you spend too many months stationary in a particularly foul warm water harbour…

Look up the Asperida, quite the incredible boat only let down by the fact they built the decks and mast from wood but the original monel hull itself is still in fine condition today 56 years later and good for another 50 years by estimates.

Richard Moore

Just a correction to above, after checking up on the sheer electrical magnitude of lightning strikes from Matts post on the subject, even in a metal boat just the sheer amount of current flowing generates such strong magnetic fields that it can induce voltage and current through metal objects within said magnetic field… Which can include the traces in circuit boards…

So grounded Faraday cages inside the hull are still needed to protect stored backup devices…

Another note is a surprise, I assumed that Monel was a reasonably conductive metal alloy being around 34% copper, one of the best electrical conductors and around 63% Nickel, a moderate electrical conductor often used as a inter cell connector in the construction of Lithium Ion vehicle battery packs…

Both good conductors on their own, but a terrible conductor together… It amazes me the effects alloying can have on the physical properties of metal…

Electrical Conductivity of these metals….

Copper 100 %IACS

Nickel 22 %IACS

Monel Nickel Copper Alloy 3.4 %IACS

So may still require a copper cable suitable to carry the full force of a lightning strike from the top of the mast to the sea, taking into consideration that the current may need to be spread over a larger area than just having the end of the copper cable terminating in contact with the hull to avoid a “Spot Welding” effect that may damage the hull

Though figuring that out would be up to an actual engineer

Also, I was thinking of the wrong alloy to begin with as the Asperida was built from copper-nickel alloy UNS C71500

70% copper 30% nickel, still only around 4.6 %IACS in electrical conductivity

Still, that is the alloy that was used and Proven, so that’s the alloy that should be used in sailboat hull construction, cheaper too as the Asperida was only 11% more expensive than it would have been with a steel hull!

And even better than I remember the hull paid for itself within 5 years compared to steel based on the maintenance steel would have required in comparison…

Pretty incredible.

Richard Moore

KastenMarine also extols the virtues of aluminium construction…

Still, never having to paint the Cupronickel hull whatsoever even under the waterline is a huge draw to me after reading through the articles concerning aluminium here on AAC….

It’s essentially a build and forget forever hull that polishes itself clean as it sails, and surprisingly light and strong when building a boat 40ft or more in length.

Marc Dacey

John, I’m wondering if you have a lead line, or mast steps to see coral heads? (I know you’re not primarily about “low-latitude cruising!)

Funny thing is that the price of a drone and installed mast steps are now about the same. Should I ditch the mast steps?

Cruising safely is about prudence and plan B and sometime plan C. I agree (and indeed, would be foolish to reject) all your valid points about sextant use, the most realistic of which is that you have to do sights consistently to maintain speed and improve accuracy. But, in the interest of seamanship resting on a broad foundation, I would ask “why *wouldn’t* you use a sextant on passage? Consider that taking and reducing a noon sight splits the “sea day” nicely; consider the mental effort of doing the (fairly straightforward) math; consider the pleasure (verifiable with GPS, I suppose) of getting a good result through analog means, and there’s a reason for maintaining the skill. At least, there is for me. The reasons I frown on instrument integration are related to the reasons I would want to maintain celestial navigational skills and practice: it gets me away from the screens, and allows me to verify via unrelated methods that what I am seeing on them is factual. I don’t know about you, but I have seen, live, a four-satellite GPS display “correcting” itself (our sailboat went from 5.5 knots to 62 knots for about four seconds, putting us closer to shore, had I not already been doing active pilotage with a sextant on its side). GPS is not a right and if the monkeys ashore are in a poo-flinging mood, it can be “detuned” without warning. The stars and sun and moon are not so easy to bugger up.

Lastly, there’s that matter of pilotage. A sextant is rather good (superior to a hand-bearing compass, at least) at determining distance off, and the angles that indicate estimated position. Throw in a watch and you’ve got speed. Devices do this as well, but there is a certain pleasure in having the analog tools to use, in my view.

Marc Dacey

Well, John, there’s a bit I didn’t mention: we will be bringing a teenaged son for whom daily sight reductions and estimated positions will be part of his math homework… I am certainly aware that even on passage, I will have many calls on my time, including all sorts of inspection and record-keeping. On the other hand, I’m used to keeping an hourly log on Lake Ontario when we go places, and I don’t know of anyone else who bothers to do that. If I’m wrong about the sextant’s continuing relevance, there are always people interested in them as objects of beauty and craftsmanship.

Nick Hallam

Before GPS (even before SatNav or Omega for yachts), I used to deliver yachts. Being poor, and sextants being heavy/fragile baggage items, I used to carry a plastic Ebbco sextant. Nothing like the accuracy of my Freiberger, but never gave me worse than 10 miles error, even in bumpy weather. PLENTY good enough for a backup, robust and simple. I used to take star sights by removing the ‘scope and using the amazing accuracy of the human eye to centre the shot – a bit like shooting over open sights. I loved that little thing and was very sad to lose it in a sinking. No, I wasn’t lost at the time….. More important for backup purposes would be to have almanac and tables produced on waterproof material. Clocks are good enough these days provided you can keep them dry and adopt the old discipline of noting the error every day and developing a simple table. You shouldn’t be more than a couple of seconds wrong across the Pacific, I reckon. Go for it! It’s a real pleasure, except for the seasickness…..

Pat Synge

Back in those good old days I used an Ebbco as well and once I had calculated and applied the (consistent) filter error it was quite accurate. The optics are fairly ordinary however and picking up anything but bright stars in good conditions was a bit tricky. I haven’t had it out of its box for years and really should give it a go.


Hi Terje,
I own and have used professionally a Freiberger sextant from the old GDR. Still in great nick after 35 years and it is still a beautiful instrument.
If you want star and planet sights (which are the most fun, accurate and rewarding), I would suggest at least a 4x magnification telescope with good aperture (mine is 40mm) to let in enough light in the dawn/dusk. This means you should be able to find enough stars/planets whilst the horizon is clear and present and give you more time to complete your set of sights plus they will be more accurate. Make sure the sextant has a flexible and comfortable rubber cup cushioning the eye-piece, otherwise expect the odd black-eye!
Buy a light instrument, (my one is 1.4 KGs) and that is perfect for me. Your sights will be more fun, particularly if you are having to wait around for cloud breaks, and you will enjoy your sextant and so use it more.
Buy in person (perhaps forgo the birthday surprise) and make sure the balance of the sextant is right for your wife – if it feels right it probably is.
Check the telescope is clear, with no internal moisture damage or frosting of the lenses, shades or mirrors. Check the mirrors and shades are all well set perpendicular to the plane of the instrument, with minimal external corrosion, and no signs of physical damage. Check the box is in good condition (ie. has it been dropped)? Does the quick release engage positively with the worm gears and does the fine adjustment screw move freely?
Then get it professionally re-calibrated if it hasn’t been done recently.
Consider an “App” like Celestial to do all the computations and sight planning for you (cheaper than buying almanacs), leaving you with the hero fun stuff.
If you really want to practise astro-navigation, you won’t regret paying too much, but you may well regret paying too little. Good luck.


The last boat I was on had two chart plotters, an iPad with Navionics, two laptops, one with open source OpenCPN and a $25 Globalsat GPS USB puck, 3 handheld GPS and ….

Gosh it was almost terminally boring.

I recently took a boat across the Pacific to NZ. Onboard we had OpenCPN, running with the GPS puck, and that was our computerised GPS system. Worked flawlessly.

However we also had a lovely Freiberger sextant. I don’t know much about them, except that this one became a much loved tool, capable of giving me reliable accuracy within 2-3nm and allowing me to try all sorts of other sights such as star, planet and moon sites, which a cheap ebco wouldn’t have allowed me to do. (I own an Ebco). The accuracy allowed me to be able to rely on the measurements and to really progress with celestial rather than treat it as a ‘lesser’ system than the computers.

I also found the whole process rather beautiful. Another respondent here has said just how busy you can be on a voyage, and investing properly in celestial nav means that you’ll be up a LOT, at times that might be out of kilter with your other roles; but it’s immensely satisfying.

It was also quite a revelation at just how ‘lost’ you can get after a mere 7 days with thick cloud. It really makes you appreciate how wonderful a GPS fix can be. I wonder if people don’t take GPS for granted a bit nowadays.

The book that really changed everything for me was ‘Celestial Navigation in the GPS age’ by John Karl. Read it before you go, don’t get the kindle version, you’ll want to take notes in the margins. I didn’t use sight reduction tables and instead used a calculator. His approach to celestial is highly practical and pragmatic, his methods fast and simple.

A cheap android app ‘Celestial’ by Navimatics allowed me to check my fixes, and when you have a lot of maintenance to do you really appreciate these short cuts. I didn’t have time to be a purist on the celestial, we had jobs to do, like keeping the boat afloat 😉 Karl recommends using GPS initially to check your sights, which allows you to improve very rapidly. After a week you’ll be getting fixes within 4 or 5 miles, and being confident you don’t need to refer to the GPS to check it.

I’m not sure that austere ‘purity’ is the right way to go here. GPS devices are so much better, cheaper and more reliable than celestial tools, but celestial brought me a much closer feel to my place on the globe, the earth’s rotation, the relative passage of my boat on the sphere. After a while you start to use it for a lot more than just getting a noon fix, like running down a line of position to approach an island missing the offshore reefs.

I’d never leave offshore on a big trip without a sextant, preferably a Freiberger; and John Karl’s book. But I’d also have a whole load of GPS devices with me too.




I’ve used a few different ones over the years, and I now am the proud owner of a beautiful Frieberger, and also still have my old Davis mk15 given to me by my grandfather as a 21st present.

If I was going to buy one simply as a backup it would be something cheap and simple like the Davis Mark 3 for $65. Used with care this will get you a reasonable fix for an emergency, but it won’t be a joy to use like my Frieberger.

I also think the little Bris sextant would be a great backup, see Sven Yrvind’s site for some details on this very clever and compact sextant.

My Davis Mk 15 has not been a success. It has about 10 minutes of backlash in the teeth that results in erratic positions and a variable index error. I had better fixes with a simple vernier ebbco sextant. Maybe mine was faulty, but it put me off the more expensive plastic ones.

I’m not convinced a sextant is essential these days, even a simple Kamel made with a piece of string and a ruler got a position line good to 30 miles one calm clear night, and should get you to the approximate piece of coast, with a simple RDF and lighthouses to then find the port.

But there is something very satisfying about getting a nice set of stars or a noon sight, and I will continue to devote precious space aboard for my sextant and tables.

Oh, and good on your wife for learning celestial, I reckon she deserves a nice quality sextant.

Erik de Jong

Hi John,

Celestial navigation is a hobby of mine, so you can’t really reason with me I’m afraid.
I use Freiberger, but I believe that any sextant that has some mass to it will do a better job than the operator him or herself can do. My only advice on choice of sextant is to stay away from the plastic ones, it is too inaccurate to even consider using one when there is more than 10 knots of wind.

One of the things a lot of sextant owners do not realize is that one not only needs to practice regularly, but also need to verify the calibration of the sextant. A slight calibration error can put you miles and miles away from where you actually are without even noticing it, it is possible to correct this by measuring the “0” before each sighting, but a miss aligned mirror does not necessarily have a constant error over the full 110 degree span of a sextant.

Almost every celestial calculation is the same, so if you intent using it, but not on a regular basis, it might help to have some calculation sheets laying around. I made mine in Excel, and I only have to fill in the blancs and in as little as 5 minutes, a calculation has been made without even having to think about it.
But to give a heads up, the calculation is not the problem with irregular use, it is the ability to measure the angles accurately, 1/60th of a degree error can in some cases correspond to 1 mile. You need to make a lot of sightings to bring the accuracy to a usable level.

But there is more use to a sextant than only celestial navigation. I regularly get a question that asks me how high an iceberg is while somebody points a finger at a huge chunk of ice. In combination with radar, it is possible to tell within 5% accuracy how large objects are. Another feature that becomes handy when sailing in poorly charted waters which have their GPS datum off, is that you can use islands, mountains, fjord widths or any other know measurement to determine your distance to that landmark. Admitted, not a use that is applicable to many cruisers as most of the worlds waters are charted properly.

Having said all this, I do agree with John that in the modern days it is better to spend your money on other gear that you might actually need.


I think this topic is related to another topic previously discussed on this website – SSB versus Iridium. Both SSB and celestial navigation are technologies that some might consider obsolete and from the stoneage. In the end this is boiling down to the question if one wants redundant systems for communication and navigation or not. While communication might be considered optional navigation definitely is not. I would require from any oceangoing yacht an alternative means of navigation. One that is independent of US- or Russian military.
I personally own a Chinese produced Celestaire Astra IIIB which I find more than adequate. Mine does not even have an index error. I usually get results within 1-2 nm from the GPS position. If you do not want to learn celestial navigation in depth get the starpilot calculator, but you still need to practice.
If you do not carry a sextant I would recommend at least an additional handheld GPS with spare batteries wrapped in aluminum foil. In this case you will still have basic GPS navigation in case of total loss of electrical power or lightning strike.
Both SSB and celestial navigation require practice and a certain understanding of physics (SSB) or mathematics and astronomy (celestial). Both are technologies that make you independent of highly complex infrastructure both on earth and in orbit.
The probability of a solar storm to wipe out all orbital infrastructure is quiet low. The possible consequences can be severe. This is classic risk assessment. You have to balance potential damage, probability of occurrence and cost.

Viv and Mireille

I’ve used a sextant quite a bit on crossings, but used a plastic (Davis) model as one worries less about dropping it or snagging it on the rigging in a heaving sea. With the simplified (air) tables and almanac, sights took very little time to calculate and plot. Although we used the sextant for ocean sailing, it also comes in handy for distance off – using a known height – and plotting fixes using the sextant horizontally to measure angles between points.
Nice to spend 800+ on a sextant, but a Davis does the job if in good working order and allowed to acclimatize on deck before use (i.e. it expands more than a metal one). It is also easier to throw into a grab-bag for the life-raft as it doesn’t need batteries and can take a beating.
But are they useful nowadays – apart from as backup? As a fundamental tool for learning and understanding navigation, yes very much so, but you can do that ashore on the beach.

Dave DeWolfe

Hi John,
I’m a firm believer in the “Joy of Sextant”. In my mind there is a certain satisfaction of being able to find out where you are without recourse to electronics. My boat (or any other for that matter) is not a Faraday Cage and my sextant is immune to anything that can trash electronics.

Mine gets used a lot because I’ve had an interest in Astro navigation since I first used one in 1966. I also teach Celestial navigation ….

As for sextants, I think the best bang for your buck (or Euro) is a new Celestaire Astra 3B standard sextant, not the professional model they propose. The standard one is all aluminum while the ‘professional’ has a bronze arc and is therefore a bit heavier.

I regard the plastic Davis Sextants as toys ….better than nothing but not much. I have several good ones and the one I like the best is the Cassens & Plath with the whole horizon mirror. They are expensive if bought new, but can be found on eBay for ~ $500-600. I always use it with a good camera neck strap and have never hurt it in hundreds of sights.

Roger Harris

Dave, Good points.

I am reminded of the following passage in John Budlong’s “Sky and Sextant: Practical Celestial Navigation”, 2nd ed. (1978), pp. 14-15: “The quality and workmanship in one of these machines is something to behold. Just having one in the house will add joy to a rainy day and a couple of years to your life; using one is an experience in precision”.

Best wishes, Roger

Marc Dacey

It appears there is still some love out there for hoary old celestial navigation, which does not imply a disdain for all things GPS or plotter. A theme mentioned repeatedly is the satisfaction of using a sextant to get within a mile or two of one’s actual position (as verified by GPS) and of the “belt and suspenders” approach of having more than one way to navigate. Good.


I wonder what they were using to navigate the yacht on the Volvo Ocean Race who hit the reef!

Marc Dacey

Faith-based navigation?

Marc Dacey

According to this article (, the Team Vestas boat was working from electronic charts that “did not carry the warning that the paper charts did that the reef was almost a mile east of its charted position”, and this sentence resonated with me: “A second system of navigation is needed, be it only soundings, to verify GPS positions. A larger margin of error is needed in areas of suspect charts with, as was recommended in the report into the Clipper grounding, different offlying waypoints for daytime and nighttime approaches.”

That second system, whether it’s a sextant, radar (which wouldn’t have worked here, likely), a hand bearing compass, a lead line or depth sounder, is key, because it’s the discrepancy that reveals the error.

Andreas Viltfjäll

Clinging on to a sextant must be the same as stuck to your old typewriter? If (if) a most of them satellites happen to fall out of the sky, if (if) you have no power aboard, no battery in your computer, no AA-batteries… I guess you are in more trouble when knowing exactly where you are. In case you missed a war or something that shuts off all GPS-system I would rather stay on my boat far out at see til the landlubbers cleared a bit of the mess up. If the only problem you have is finding ‘land’ at all, just wait a little. Soon enough there will be smell of woods, cities and birds will come. Navigating around reefs? For sure a sextant would not help you anyway… For the cost of a sextant one can do so many things to NOT get into so much trouble.


I’ve enjoyed using, and, in several Pacific crossings have had good success with, a 1940’s US Navy Mark II sextant. It’s simple, robust and I’ve had no trouble doing running fixes on the sun, or obtaining LOPs from the planets and bright stars (generally using a current Nautical Almanac). I bought the sextant for a couple hundred US$ more than fifteen years ago and, after cleaning and aligning it, used it to pass two celestial navigation classes (USPS). I’ve also used more expensive and feature rich sextants but haven’t felt a need to ‘upgrade.’ My backup sextant is the Davis Mk3 which works (~10 nm on a good day) but is not as pleasant to use as the Navy sextant and, being plastic, is finicky (eg, a lot of thermal drift in the index error).

I don’t have any deep reasons for continuing to use celestial to augment navigation. I simply enjoy taking sights, reducing them, and plotting the results.

Randall Reeves


I use the Celestaire Astra IIIB with Whole Horizon Mirror and the 3.5 x 40 monocular telescope; i.e. the basic, no frills offering.

It’s the only sextant I’ve owned/used, so can’t compare it to others, but can say 1) its aluminum casing makes it light and easy to hold in place for repeated sights; 2) the whole horizon mirror is a dream to use; 3) the standard-issue monocular is fully sufficient for sun sights, though I did wrestle (unsuccessfully, for the most part) with the stars. Re the latter, this may have had more to do with me than the monocular; I wear glasses, and the mechanics of shooting the star and taking the time in the dark turned out to be quite the challenge.

I’ve used this sextant over three, month-long singlehanded crossings. Comparing my daily sun sights to the GPS noon position and finding that I could routinely get within a mile or two of true was deeply satisfying and a real confidence booster.

Bottom line: Celestaire Astra IIIB is, in my estimation, a quality piece of kit.

Two other notes:

I would highly recommend Tom Cunliffe’s little book CELESTIAL NAVIGATION. Though I still had to *study* it (as opposed to understanding on the first read), I found explanations in this book much clearer and easier to understand than any other, and I have three other how-to guides aboard. On that note, if teaching yourself, as I did, carrying a couple other celestial navigation primers is a good idea. If you get stuck on a concept in Cunliffe, for example, reading someone else’s notes on that point can help get you closer to the required epiphany.

Also, it is not required that you have a dead-accurate back-up chronometer. I use my land-lubber’s wrist watch for longitude shots, but over days and days of shooting, have compared its time to the time broadcasts on my SSB, so I know my wrist watch’s rate of drift to a degree of accuracy that would get me home in an emergency.

Good luck and enjoy!


Richard Dykiel

FWIW I learned Celestial online at Very well done. I carry their textbook on board (for refreshers), as well as the current year nautical almanac. I try to practice sunlines as often as I can using a Davis plastic sextant.

Besides learning celestial for fun, I intend to use it as backup to GPS. I make a point of making it a pen and paper exercise entirely (no calculator). Using the NAO sight reduction tables that you get with the almanac, and using the almanac’s printed procedure.

The only thing I would change is to take a sextant with classical split mirrors. My Davis has the full mirror that works with superposition and I find it difficult to get the proper index correction on the horizon.

Bottom line, I’m happy when my sunline falls within 10nm of my GPS position, which shows I still need to improve my sights. But it’s fun and jogs the mind in a long crossing.

Richard Dykiel

I forgot to mention their book on emergency navigation, which one might find interesting:


After reeding all these comments I got the impression that some people mainly do sun sights. For emergency navigation running fixes on the sun would certainly get you home. Those people would not need a full nautical almanac. I recompiled a version of my nautical almanac so that only tables for the sun are included. This makes really compact tables. Two to three pages will be enough for most ocean passages. I also added static tables, instructions and plotting sheets. Hopefully everything needed is available now.
Downloads can be found here:
Leave a comment if anything is missing or incorrect.


Many Thanks Enno, a fantastic resource, it looks every bit as nice, and easy to use as a real Almanac. Buying them new every year is not cost effective and all the online or perpetual ones I’ve seen up to now have been awkward to use, or just ugly, or lacking info, Nice work.

For what it’s worth I use the concise sight reduction tables in the back of the almanac. Once you get the hang of them they make an easy, no calculator sight with about 9 pages from memory.

Robert B

An interesting recent development (Fall 2015). The US Naval Academy has reinstated celestial navigation training over concerns of GPS vulnerabilities and cyber threats. It was stopped in the late 90s. From what I have read it’s only a few hours training (so far) which is obviously not enough to become proficient with a sextant; however, they clearly think a non-hackable backup is a good thing.


Pat Kelly

Seems like a bad time to throw in my 2 cents when this subject has been discussed very well – except for one aspect (in my opinion): Celestial Navigation is fun. Some people do, say, crossword puzzles, I like playing with celestial navigation. In 1967, I was the medical officer on a US Navy ship. There’s not much for a doctor to do on a ship with 560 healthy sailors, so I used to do rounds of stars and sight reductions with the navigators at twilight and dawn and noon latitudes. We had Loran C but at the time it was a NAVY directive to back up the electronic navigation with LORAN C. It was always fun to see how close we could get with a sextant, chronometer, HO 211 (later 219 the 249) and calculations done by hand (no pocket calculators then either).
So I’ve always carried 2 sextants aboard my boat CYGNUS (Plath & TAMAYA) and still “practice” when there’s no wind to go sailing – drift off the #2 buoy at Mt Desert, Maine (or underway) and use WWV time ticks & stopwatch and (bowing to technology) a CELESTICOMP hand calculator (but also have Nautical Almanac and HO 249). Then check my LOP’s on the GPS. But it’s all – just for fun.

However, if some nut blasts all of the world’s electronic systems with an EMP Electromagnetic pulse) – I’m ready!!!

Marc Dacey

Pat, this has been discussed at times in terms of the mental exercise of sight reduction, along with the sense of accomplishment when one masters the skills needed to regularly obtain a verified result (and I don’t mean GPS, I mean “arrival pretty close to where you thought you would arrive”).

Less discussed is the habit of logging position, keeping DRs and the various forms of estimated positions in the absence of twice-daily reduced sights. The GPS is a marvellous thing to have, of course, and I wouldn’t leave port without it, but nor would I stop using more “analog” methods as I feel they connect me more directly with my sailing environment. These methods, of course, include CN.

Pat Kelly

Marc – agree 100%. With the availability of GPS chart plotters, many have gotten (for want of a better word) lazy. But Nav stations with chart tables large enough to accommodate NOAA charts, plotting sheets and stowage space for a set of up-to-date charts – seem to be a vanishing priority on newer boats. However, having one’s electronics go out in a pea soup Downeast fog on the rocky coast of Maine/ Bay of Fundy/NS etc. might surely convert some to that ol’ time religion.

Marc Dacey

I was lucky in the sense that I came to sailing at a relatively advanced age and before plotters were common on freshwater boats. So I learned basic pilotage and established the habit of hourly position fixes/running fixes. I’ve kept that habit and it’s served me well, as has the notion that multiple sources of navigational data are the prudent thing to have.

Roger Harris

The Astra IIIb is a decent sextant: affordable, light, and compact. While I’m not a huge fan of the shades, I really like the rough wooden box, which is quite rugged and allows storage with the index arm in a large range of positions (impossible with many sextant cases). The lighting on the drum and arc is LED, which is desirable (although in my opinion built-in illumination is more of a ‘nice to have’ feature than a necessity).

The combination of an aluminum worm and aluminum arc can result in chronic binding problems. I’ve had some difficulties of this nature with the standard Astra IIIb, but it can be handled by periodically applying a small amount of grease. The IIIb ‘Professional’ model would avoid this issue entirely, so might be worth the extra cost (I doubt the additional weight penalty would be significant).

I have very little personal experience of Freiberger sextants. They are available in three different colours, and the marine blue is quite pretty (they also offer a deluxe version of their small ‘Yacht’ sextant, in black enamel and gold plate!). Their full-sized ‘Trommel’ model is widely carried – if not regularly used! – on commercial ships … whether that reflects their price or quality, I don’t know, but it does mean that they are frequently available secondhand.

I very much like the Cassens & Plath sextants: rather heavy and expensive, but very well made and easy to use. I have a basic ‘Professional’ with 6×30 scope, and an ‘Ultra Horizon’ with 4×40 scope. The latter’s drum index corrector is in my opinion an unnecessary frill, but the polarized shades sure are nice. Illumination is not LED, so it’s a good idea to carry a spare bulb (which C&P will happily send you free of charge: post-sale service and support from this manufacturer is truly excellent).

Tamaya makes superb sextants. The optics, and general fit and finish, are first-class. They are now very expensive (even more than C&P), and I have the impression – could be wrong – that they are now manufactured essentially on a special-order basis. Secondhand is of course a cheaper way to purchase, although older sextants will typically have wooden cases (handsome, but prone to scratches, dings and similar damage); my Tamaya has one of these but I would prefer the current issue double-walled plastic, very practical.

I hope this is of some use.

Peter Mahaffey

The Freiberger is the Rolls Royce of sextants, and a beautiful instrument to use. It’s not over-heavy either. It is expensive but well worth it. As for the book . . . it’s Tom Cunliffe’s ‘Celestial Navigation’. For the chronometer, it’s well worth buying a cheap wristwatch (eg Casio) with a digital read-put, setting it to UT/GMT and keeping it permanently at the ready in the sextant box. This saves an awful lot of hassle and conversions.
May I make a point? When one searches this site for navigation things ‘celestial’, but using the term ‘astro’, nothing comes up. I’d recommend this be adjusted to include the latter (interchangeable) term in the search!

Joe Clarke

Any body know who is giving classroom instruction? thanks Joe

Charles Starke MD

Hi John
Mystic Seaport gives an excellent course in celestial, and “Celestial, by Navimatics” is an Apple App for US$20 that does fixes and running fixes and makes everything easy!
Best wishes
Charles L Starke MD FACP
s/v Dawnpiper

John Cobb

Not classroom instruction but Oceannavigator*dot*com has recently run a series of articles on Celestial Navigation. Links on their home page if interested.

Charles Starke MD

“GPS Anti Spoof” is an Apple iPhone App that tracks the height and azimuth of celestial bodies. It allows you to set your sextant to the approximate height of a body, and makes it easy to bring it to the horizon and take a sight quickly. If you use it with the App “Celestial”, sights and running fixes are expedited, and are made MUCH easier! No calculation or calculator necessary! Amazing combination.
Best wishes
Charles L Starke MD
s/v Dawnpiper

Joe Clarke

thanks for the info – fair winds!