Which Sextant Is Best For A Yacht?

On a yacht, a sextant can act as a great backup in case you lose your GPS.

If you have learned how to use one, the next choice is to select the best one for your yacht. There are many considerations, but whenever I am asked which one I recommend, I always say the same.

The best sextant for a yacht is the Davis Mk15. It is a plastic sextant, making it a lightweight, cost-effective option that produces accurate enough results for any situation where you would legitimately consider using a sextant.

Davis Mk15 sextant box contents
Davis Mk15 Sextant

I accept that metal sextants could offer a slightly better theoretical accuracy than a plastic model. In the hands of a well-practised navigator though, the Mk15 produces a perfectly acceptable celestial position fix.

Celestial navigation is only used when you are away from the land and there are no terrestrial features available to give you a visual position fix. You are never going to be able to get a fix more accurate than within a couple of miles.

As such, my recommendation for a sextant on a yacht is based on other advantages offered by the Mk15, rather than on accuracy alone.

  • Lightweight and easiest to use on a rolling yacht.
  • Cost-effective and most affordable when sailing on a budget.
  • Accuracy is still comparable with other sextants on the market.

Despite my recommendation though, you should always just select the best one for your own circumstances. Other highly recommended options include the Astra IIIB, a Freiberger, or the Davis Mk3.

What to consider when buying a sextant for a yacht

In considering which sextant you are going to buy, it is worth asking yourself a series of questions to make sure you make the right decision.

Even budget-friendly models can cost a few hundred dollars, so it pays to get the one that will work best for you.

Do you already know how to use a sextant?

If you have never used a sextant before, I recommend learning as much as you can before selecting the model you want to purchase.

We can’t cover it in this post, but for a quick overview, you can learn how the sextant works in this article: How Sextants Work: An Illustrated Guide. Then you can learn how to use the sextant in this article: How To Use A Sextant: A Step By Step Guide.

Are you a beginner or experienced with a sextant?

Beginners and experienced users will have different requirements when it comes to selecting the best sextant.

For beginners, I always recommend the Davis Mk15 Sextant because it is an affordable plastic sextant that produces results that are accurate enough for practice and training. You can read my full review of the Mk15 here: Davis Mk15 Sextant Review.

More advanced users might want to consider a metal sextant, like the Astra IIIB instead. Metal sextants are significantly more expensive than plastic models. As an advanced user, however, you will know how much you plan on using it and whether the investment will be worth it for you.

What will you use the sextant for?

On a yacht, most navigators only intend to use the sextant for practice so that it can get you home if your electronics fail.

Pro Tip: I have heard of cases of lightning strikes knocking out all electronics on a yacht. Learning how to use your sextant would give you a backup in that sort of situation.

In those sorts of situations, you do not need the high performance and reliability of an expensive model. You can base your decision more on your budget instead.

Conversely, if you plan on navigating with only the sextant, across an ocean for many months, you might want to consider investing more.

Do you plan on sailing in extreme temperatures?

The main disadvantage of plastic sextants is that they are more likely to become inaccurate in extremes of temperature.

A sextant with a metal frame is more likely to maintain its accuracy in such circumstances.

You should carefully consider where you plan to do most of your sailing. Also, consider that most yacht owners only use their boats in nice weather, and only get their sextant out at sunrise and sunset.

Find Out Why: Best Times To Use A Sextant

Assuming you store the sextant in its case, inside a dry locker in your boat, even plastic sextants are unlikely to deteriorate in all but the most extreme conditions.

How much does your boat move?

Small yachts move around a lot more than large ships.

Taking sextant sights on a small yacht is a very different experience from a large vessel. It is likely that you need to balance yourself and it might be a struggle to keep yourself upright.

You will be moving your sextant around a lot to try and keep it focused on the celestial body you are trying to measure.

As such, the weight of the sextant you choose will have a big impact on your comfort when taking sights.

The Mk15 that I recommend is made of plastic, making it significantly lighter than its metal counterparts.

On a large ship, I do like to use a metal sextant, but I have a large stable bridge wing to take my sights from. I don’t need to keep my balance while swaying around in a swell.

You should carefully consider the size of your own boat and how much you are likely to move around. Would you prefer a heavier or a lighter sextant?

Are plastic sextants any good?

If you search forums or ask “experts”, you will often be incorrectly told that metal sextants are the best and are the only sort you should consider.

In fact, for all but the most extreme cases, plastic sextants are a great alternative.

Plastic sextants are good for both celestial and terrestrial navigation. Their lighter weight and lower cost actually make them a better choice than a metal sextant in many situations. Concerns about accuracy and degradation are often misplaced.

With the right care and practice, a plastic sextant can produce results just as accurate as a metal sextant.

Unfortunately, their lower cost often means that navigators take less care with a plastic sextant, resulting in greater degradation over time.

Assuming you treat it with the care and respect that a highly accurate navigational instrument deserves, a plastic sextant will last you as long as you need.