Davis started out making the mark 15 in the 1960S and it remains popular today. Made of stabilized impact-resistant plastic, Davis sextants have circled the globe for decades. Includes carrying case and Instruction booklet

3 x 27mm Star telescope and 7 sun shades
Traditional half-silver split image mirror
Made of stabilized high-impact and weather-resistant plastic ///

REVIEW

San Franciscan

4.0 out of 5 stars
Reviewed in the United States on February 6, 2017
Know why you want one and when to use it before buying
After spending a long time reading reviews for Mark 15, Mark 25 and Mark 3, Astra IIIb and other sextants, also after finishing my celestial navigation course and playing with a couple of very different types of sextants and taking sightings, I went ahead and bought a second hand but practically unused Mark 15 and decided to write this review. I will explain my reasoning below but if you are in the process of shopping for a sextant, you need to think WHY you want to have one. You may think it is obvious and the same for everyone, but it is not. I think there are at least three different categories:

1) A sextant looks so cool, I want one.
2) I am an off-shore sailor. Having GPS is good but what if it stops working because of lightning, cyber war, apocalypse etc.
3) I am into stars, I like gadgets and I am a geek of sorts. I want to learn more and have fun (or) I want to challenge myself to navigate in open ocean by only looking at the stars, I want to be a Polynesian! (Ok, maybe by cheating a bit with a sextant, Polynesians certainly didn’t have any. But you get the idea.)

Depending on where you land on this scale, your preferences could be vastly different. I personally land somewhere between 2 and 3, I call it 2.5.

If you are in the first category and want a sextant for decoration, simply stop reading here and go elsewhere. Davis Mark 15 is not for you. While it looks like a real sextant, it is plastic and unnecessarily expensive in relative terms for a decoration purpose. There are a ton of brass sextants for prices less than $50 here and elsewhere. They look good, much better than Mark 15. They will address your need better for much less. But if you decide to buy one of those $50 brass sextants, please do all of us a favor and don’t give poor reviews because they don’t work. They are not meant to work.

Let’s now look into 2nd category. But before we go much further, let’s also do a contemporariness test. It is worth to ask if a sextant is even relevant and needed for sailing these days, with multiple different services and emerging ones like GPS, GLONASS, Galileo and Beidou and abundance of cheap receivers. It is fairly easy to carry multiple (sometimes in the order of 10 including mobile phones and tablets) receivers onboard and keep them at different places, including in faraday cages (oven) for lightning protection. That said, sailors are opinionated people and they will have very different but equally strong opinions. Have a look at what they have to say. Check this poll on Cruisers Forum, a leading web forum that brings long distance sailors and cruisers together: http://www.cruisersforum.com/forums/f121/poll-blue-water-is-a-sextant-necessary-91929.html If you have time, read 15 pages of comments as well (did I say sailors are opinionated?). At best you will see many of those contemporary sailors saying it is desirable but not required. You need to make your own conclusion and decide where you land here for yourself. If you decide you are better off by carrying more GPS receivers, then you can also stop reading and start looking for backup GPS and faraday cages.

You continue reading, so you do want to have a sextant, good. Now it may be good to give some reference point for pricing. Working brass sextants sell around $2,000, aluminum ones around $600. When it comes to plastic ones, Mark 15 is around $150, Mark 25 is around $200 and Mark 3 is around $50, which is as basic as it gets. You need to decide between these three options. As you can see, it is a very wide range. It is important to mention that these are all brand new. Sextants last LONG if used properly, especially considering that they are not used that regularly. I used a sextant from 1944 and it worked like a charm. So there is a huge second hand market. Prices vary significantly but you can find a good aluminum sextant like Astra IIIb for anywhere between $250 to $300.

The question for a used sextant is not how old it is, how well it has been taken care of and whether it actually works. But there lies the problem. If you are reading this review, it probably means you are trying to learn about sextants and do not know enough already. If that is the case, how will you know if a second hand sextant is in decent shape? This doesn’t mean that there is foul play on the side of sellers, there usually is not. I have seen many sellers saying “I don’t know if this works because I am not knowledgable on sextants, I got this from my <fill in the blanks>”. And if they don’t know if it is working and you don’t know yourself, well that is a vicious circle. So be careful when you read a review here or elsewhere when someone says “Go and buy a second hand <XYZ> sextant instead of this new one as they are the same price”. While it may be a perfectly sound advice in theory for the person giving it, it may not work that well for you in practice. Also when people say they are the same price, they usually are not. I notice about 2x price difference between new plastic sextants and working second hand metal sextants.

It is also good to ask WHEN you will use the sextant. One thing important to know about sextants is they are almost useless for proper navigation unless you have other accompanying stuff. At a minimum you need to have an almanac, which changes yearly (although there are ones that go until 2050). For finding your longitude, you also need an accurate clock (you can find your latitude without a chronometer). An error of just one minute of time means 15 miles, so the clock needs to be accurate. And on top of everything you need quite a bit of practice, it is not the most intuitive thing when you do it for the first time. Obviously there are apps and computer programs that automate the calculations but again, you assume the electronics might have fried in the very first place otherwise one of the backup GPSes would work. Also it is important to think about the context here. If you were hit by a lightning in the middle of the ocean that was severe enough to fry all electronics onboard, even if you were lucky not to have a structural damage on your boat because of that lightning, I would assume you wouldn’t be continuing your regular cruise. Instead, you will head to closest port for repairs or simply go for a landfall anywhere you can. So you will need some emergency navigation skills and tools. A sextant will be handy then, even if you may not have an up-to-date almanac. If what you are concerned about is this scenario, I would highly recommend the book “Emergency Navigation: Improvised and No-Instrument Methods for the Prudent Mariner” from David Burch. For such use, I think Davis Mark 15 or even Mark 3 are good and useful to keep onboard (more on Mark 15 vs 25 below). Would having a more expensive metal sextant be better? Presumably but I personally don’t think the difference will be materialistic enough given all other suboptimal conditions. Remember, this assumes you are in an emergency and trying to do a landfall somewhere, many more things will be suboptimal and a plastic sextant as opposed to a metal sextant may be least of your worries.

And finally if you are in the 3rd category, into serious celestial navigation for fun and you are learning and plan to use your sextant frequently, then I’d look for higher end metal sextants. Astra IIIb seems to be the decent choice when you look for reasonably priced metal sextants. Used ones sell around $300 on eBay and around $600 new.

One last note on plastic sextants. If you buy a plastic sextant (or maybe before buying one), I recommend reading “How to Use Plastic Sextants: With Applications to Metal Sextants and a Review of Sextant Piloting” again by David Burch. Plastic sextants have their quirks. Many techniques in the book can also also be recommended for metal sextants but they are more important for plastic sextants. And Burch has a note on Davis Mark 15 vs Mark 25: "[...] the full mirror on Mark 25 makes the easier sights easier and the hard sights harder.". Read the book for more details on his reasoning.

To sum up, as I said I am in category 2.5 and didn’t want to spend several hundred dollars on a metal sextant. I just wasn’t sure if I would use it frequently enough. Yet I wanted to have a sextant, to get a feel of sailing by the stars like older navigators did, and to have a gateway of last resort if everything else fails, however unlikely it may be. I eliminated Mark 25 because of above comment from David Burch and eliminated Mark 3 when I actually played with one in real life. I bought a practically unused Mark 15 for half the price, and spent the delta on the books mentioned above. If you get a sextant of any sort, I highly recommend downloading and using the open source and free OpenCPN navigation application and celestial navigation plugin for it.