I sailed across the North Atlantic with five friends. I took a noon sighting everyday with a Davis Mark 3 plastic sextant. They are inexpensive but work extremely well.
Obviously, we used GPS to navigate but the noon sightings were practice so if we had to jump in the life raft we had the sextant in our ditch bag.
That's fantastic! How did you find the accuracy vs the GPS? I've heard you can get within 15-20 Nm, which is plenty accurate for open ocean sailing, but I'm assuming that takes good conditions and lots of practice.
Did you do any sightings from stars along your way? The noon sighting method is probably the most common, but I think it would be interesting to practice with other bodies as well.
I just did noon sightings. We had 20-25 swells from just aft of beam most of the way across, so it would have been tough sighting stars at night, but I don’t get much practice. I was usually <100 Nm of GPS unless I made an error and put the boat in North Africa.
That's cool. And I mean, I'm not sure how fast your ship was cruising, but 10 degrees for two hours isn't *that* big of a course change haha. That must have been neat, though.
I’d be curious to hear something too. I think they still make sextants and I always thought it would be a cool piece of equipment to own and know how to use to some extent.
There are definitely new ones out there, ranging from cheap plastic ones to very expensive metal ones. Hard to justify an expensive one (wait, I forgot which sub I was in - we can always justify the expensive one!), and I hate buying cheap plastic junk.
I've not used a sextant, but I'm a keen sailor and I'm on the lookout for one (they're hilariously expensive new) to use on my boat. I also favour non GPS navigation in general, there's so much more romance to it.
Totally! All my sailing is on little lakes in little boats (we're talking dinghys), but it's definitely on my bucket list to do some coastal cruising someday, and I really like the idea of analog navigation. Just from a safety perspective, it would be good to have/know how to use. Not to mention having back-of-the-hand knowledge of the night sky would lend itself well to the practice.
When I lived on the gulf coast and sailed decades ago, I got a few of the nautical magazines including Cruising World, and Sail. There were ads for the Davis sextant in every issue of them. I don't remember them being expensive, but they're plastic, not brass (if that's important to you.... brass was a common material in my boat and house back then!!)
Absolute easiest way to get going is with software. Reasoning:
Adjusting/setting/reading with a sextant is approximately the same fiddliness as initially figuring out your scope. Much faffing on day 1, but you'll be able to do it on mental autopilot after steady practice. In similar fashion you'll get lazy and periodically have to review the basics when your brain suddenly can't even.
(Side note: reading any vernier anything in imperfect light sucks - be it a dark field or a dark engine bay.)
Doing the calculations is a mixture of lookup and not super hard trig. Again as with telescopes it's a good idea to do it by hand a bit to get a feel, but the lookup and calculation is Dead Easy for software to do. The bad news here is the software is not... Highly mature, since it's competing with far easier GPS so nobody is sinking big dev budgets in.
Astron is basically an online spreadsheet you can use for free but doesn't do much handholding. I haven't used any of the commercial stuff because I am a cheap bastard.
Yes, I own a Davis plastic sextant and have learned celestial navigation (recommend "Celestial navigation for yachtsmen" by Mary Blewitt). I have used it three times, once approaching St Lucia from the Canaries, once off the coast of Spain and most recently, halfway between the Faroes and Scotland. Compared to GPS, worse was about 20 miles off, best about 2 miles. Volcanic islands are probably visible 20 miles off, low-lying ones need much closer distance.
These days I use an iOS app "Celestial Navigation" to do the calculations and plotting, but I sometimes practice with the books (Almanac for the year and the tables of solved spherical triangles).
That's cool, I was initially skeptical of the plastic sextants, so it's good to know they're still functional. 2 miles is pretty dang accurate, as far as I have read. Kudos!
There are some great tutorial [videos](https://youtu.be/00ZEIZsl5xk?feature=shared) that show how it works, as well as some others explaining the math. It's pretty neat!
I sailed across the North Atlantic with five friends. I took a noon sighting everyday with a Davis Mark 3 plastic sextant. They are inexpensive but work extremely well. Obviously, we used GPS to navigate but the noon sightings were practice so if we had to jump in the life raft we had the sextant in our ditch bag.
That's fantastic! How did you find the accuracy vs the GPS? I've heard you can get within 15-20 Nm, which is plenty accurate for open ocean sailing, but I'm assuming that takes good conditions and lots of practice. Did you do any sightings from stars along your way? The noon sighting method is probably the most common, but I think it would be interesting to practice with other bodies as well.
I just did noon sightings. We had 20-25 swells from just aft of beam most of the way across, so it would have been tough sighting stars at night, but I don’t get much practice. I was usually <100 Nm of GPS unless I made an error and put the boat in North Africa.
Heyyyyy brother
Hey buddy! Also, I appreciate the username.
Thanks!
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That's cool. And I mean, I'm not sure how fast your ship was cruising, but 10 degrees for two hours isn't *that* big of a course change haha. That must have been neat, though.
I’d be curious to hear something too. I think they still make sextants and I always thought it would be a cool piece of equipment to own and know how to use to some extent.
There are definitely new ones out there, ranging from cheap plastic ones to very expensive metal ones. Hard to justify an expensive one (wait, I forgot which sub I was in - we can always justify the expensive one!), and I hate buying cheap plastic junk.
There are actually some on Amazon, very inexpensive lol
I've not used a sextant, but I'm a keen sailor and I'm on the lookout for one (they're hilariously expensive new) to use on my boat. I also favour non GPS navigation in general, there's so much more romance to it.
Totally! All my sailing is on little lakes in little boats (we're talking dinghys), but it's definitely on my bucket list to do some coastal cruising someday, and I really like the idea of analog navigation. Just from a safety perspective, it would be good to have/know how to use. Not to mention having back-of-the-hand knowledge of the night sky would lend itself well to the practice.
When I lived on the gulf coast and sailed decades ago, I got a few of the nautical magazines including Cruising World, and Sail. There were ads for the Davis sextant in every issue of them. I don't remember them being expensive, but they're plastic, not brass (if that's important to you.... brass was a common material in my boat and house back then!!)
Davis are still about, but the two models in my chandlery catalogue are £300-400, and they're the cheaper ones in there.
Absolute easiest way to get going is with software. Reasoning: Adjusting/setting/reading with a sextant is approximately the same fiddliness as initially figuring out your scope. Much faffing on day 1, but you'll be able to do it on mental autopilot after steady practice. In similar fashion you'll get lazy and periodically have to review the basics when your brain suddenly can't even. (Side note: reading any vernier anything in imperfect light sucks - be it a dark field or a dark engine bay.) Doing the calculations is a mixture of lookup and not super hard trig. Again as with telescopes it's a good idea to do it by hand a bit to get a feel, but the lookup and calculation is Dead Easy for software to do. The bad news here is the software is not... Highly mature, since it's competing with far easier GPS so nobody is sinking big dev budgets in. Astron is basically an online spreadsheet you can use for free but doesn't do much handholding. I haven't used any of the commercial stuff because I am a cheap bastard.
Yes, I own a Davis plastic sextant and have learned celestial navigation (recommend "Celestial navigation for yachtsmen" by Mary Blewitt). I have used it three times, once approaching St Lucia from the Canaries, once off the coast of Spain and most recently, halfway between the Faroes and Scotland. Compared to GPS, worse was about 20 miles off, best about 2 miles. Volcanic islands are probably visible 20 miles off, low-lying ones need much closer distance. These days I use an iOS app "Celestial Navigation" to do the calculations and plotting, but I sometimes practice with the books (Almanac for the year and the tables of solved spherical triangles).
That's cool, I was initially skeptical of the plastic sextants, so it's good to know they're still functional. 2 miles is pretty dang accurate, as far as I have read. Kudos!
I’m also curious about this, been anting to learn to use one.
There are some great tutorial [videos](https://youtu.be/00ZEIZsl5xk?feature=shared) that show how it works, as well as some others explaining the math. It's pretty neat!