Help with sextant advice

[tomfl]

I am considering getting a sextant to learn how use one. Not sure how to set my price point. There seem to be some cheap plastic ones by Davis. Next tier would likely be a used one on ebay likely from one of the India ship breakers. Some folks say there are really good deals on high end ones, but you need to be careful about how legit the sellers are. Probably don't wanna go above $US1,000 and really $US500. But the under $US100 plastic ones may provide the best bang for the buck.

I have also looked in the classified here and seen some deals in the past. Thing is I am not sure how good a used sextant would be. Any advice or links to how to start off welcome.

[psk125]

Went through same balancing act earlier this year. Plastic ones work - probably better than antiques- but it appears that you can never really tell if you're getting better results (improving your skills) because the error inherent in the tool is always messing things up one way or another. The really good Freibergers and Weems & Plath etc. are really expensive. Not needing a professional piece of equipment I went with a second-hand Astra IIIb on Ebay, with the hope that it would enable me to improve more but not break the bank. The Davis is perhaps half as expensive, but can provide results that are better than half as good, so the cost/benefit equation is tricky. There are good online postings that discuss the pros and cons. Good luck!

[SeanPatrick]

The Davis plastic sextants are fine for learning - and even for actual position checking. You just have to be aware of their flaws and be ready to deal with them ... constantly. The index error (basically the amount the sextant is out of proper adjustment) varies quite a bit with these sextants - and in a seemingly random fashion. They are much more sensitive to temperature changes and "less-than-gentle" handling than a metal sextant. I even discovered that I could change the index error on a Davis Mk.15 by how tightly I held the handle. Best practice when using one of these sextants is to check the index error between each sight - something you don't have to do with a metal sextant.


On the other hand, plastic sextants are much lighter than metal ones. This means you can hold them up to your eye for much longer than a heavier sextant. (It also means they are more susceptible to being blown around in the wind.) And they are much less expensive, meaning that if you just want to take a few sights every now and then for fun or if you decide celestial is not for you, then you haven't wasted too much money.



Used sextants are almost always a crap shoot. Unless you can examine it in-person and you know what to look for, you just have to trust that the instrument has been cared for properly - and that it has all the parts. That's not to say that you can't get a perfectly good used sextant online. I know people who have done just that on sites like eBay. But it's a gamble anytime you can't inspect it first. You may get a complete, working sextant right out of the box. You may get one that is missing a part or two that is not vital or can be fairly easily replaced. Or, you may get an instrument that has been dropped, is losing silver from the [cracked] mirrors, is missing vital pieces or is in some other way totally incapable of performing its intended function. Who knows?



Personally, I would recommend you get a Davis to learn the basics and don't worry about being super accurate at first. Then, if you decide you want a better instrument, I'd get the Astra IIIb*. It's half the price of some other sextants and it is indeed a very fine instrument. But, if you really want a nice Plath or Tamaya ... go for it!



*My avatar is an Astra, but I am not affiliated with Celestaire in any way.

[El Pinguino]

If you are serious about learning and using I would suggest a Freiberger from India... (or elsewhere)

Excellent sextants.... the ones coming out of the Indian breakers' yards were most likely supplied to ships built in the 90's and have possibly never been used in anger... probably less risk of damage than buying a high end one from a private buyer...

There seem to be a number (3?) of Indian dealers who have the sextant market covered and have 100% good feedback on the 'bay....

NB .. this advice is worth just what you payed for it...

[Benz]

I learned with a plastic Ebbco, and could get accurate results in some cases. But when I first laid hands on an Astra, it was an eye-opener. Literally, since the optics were several orders of magnitude better. For learning sun shots, plastic is OK--you're never gonna lose the sun. But star shots at twilight really benefit from the better lenses. Also the heft of the metal sextant helps stabilize it in your hand--the plastic ones are more jouncy, which can make you lose the star pretty quick.

[thomm225]

Just to get an idea and to see if you will stay with it, the Davis Mark 3 plastic sextant is a fun first choice and at around $50, you can't go wrong.

It has been called an Emergency Sextant for use if your instruments sudden fail.

https://www.starpath.com/catalog/accessories/1840d3.htm

[steamgoat]

Agree,a plastic one is fine ,I crossed the Atlantic with one many years ago. Learn to use it,if you like it you can then upgrade.

[psp2psp2]

Please have a look at my video of using a Davis sextant in passage, we were surprised at the results and I think you will be too.

https://youtu.be/MWqg57G52aY

myageofsail.com

[psp2psp2]

https://youtu.be/MWqg57G52aY

Me using a Davis sextant mid-Atlantic. I was interested at the results!

[captmikem]

Originally Posted by Benz

I learned with a plastic Ebbco, and could get accurate results in some cases. But when I first laid hands on an Astra, it was an eye-opener. Literally, since the optics were several orders of magnitude better. For learning sun shots, plastic is OK--you're never gonna lose the sun. But star shots at twilight really benefit from the better lenses. Also the heft of the metal sextant helps stabilize it in your hand--the plastic ones are more jouncy, which can make you lose the star pretty quick.

Benz,
Not trying to stir thing up here but I disagree with you. I say this from experience as I was second officer for many years and took thousands of sights which the ship relied on.

I always used a telescope for the sun and moon as it magnifies it greatly and you can define the lower or upper limb precisely.

I normally took the telescope off for star and planet sights as a point of light is just a point of light. Easier to find without a scope. You can preset your HS to the star (easy if you use HO 249) or, I would see the star I wanted, hold the sextant upside down and bring the horizon up to it.

As for sextants, I have used a number of them, my favorites are Freirberger (small, light, and durable), Plath, Tamaya.

I have a plastic one but have not used it much so I can not say anything about it. But, I would suggest to the OP, a lot of folks want to learn celestial, get started then kind of fade out. I think a plastic one would be a good start, then if you find you really like it, invest in a good used sextant as it will give you better sights and confidence. Also, I think it was Bowditch who said it takes a thousand sights before you can accurately start relying on your sights. This number seems large but is not. I always shot a body 3 times and averaged the time and the sight to reduce errors, when you are shooting half a dozen stars in the morning, any planets up, 10am sun line, noon sight, 4pm sun line, and evening stars, you quickly reach that number.

Good luck, and if you can find Mary Blewitt's book it will help you a lot.

M

[Stewie12]

I would go with a cheap Davis too. We bought one in Gib was insurance before setting off across the Atlantic. 3 days south of the Canaries our masthead amplifier for the satnav got taken out by lightening. Out came the Davis for the rest of the way. My sights were accurate to about 30 miles north and south, but that was good enough to get us close to Bardados. Have to admit our next purchase was a good sextant, but we never used it.

[Paul Howard]

I used a Davis Mark 25 sextant extensively and still get it out occasionally.
By 'zero-ing' the sextant before taking a sight, you will find any error and that can be added or subtracted to the sight altitude.
These are reliable pieces of equipment.
Zero and find the index error by setting the index arm to zero, and the micrometer setting as well to zero. Look at the horizon and turn micorometer setting back and forth to make the horizon split in the two mirrors. Turn the micrometer until the two horizons line up and make a note of the amount either plus or minus from zero and make that calculation with every sight taken at that time. This might change in different temperatures, so I always made it a practice to check the index error before every sight.

[robert sailor]

Originally Posted by Paul Howard

I used a Davis Mark 25 sextant extensively and still get it out occasionally.
By 'zero-ing' the sextant before taking a sight, you will find any error and that can be added or subtracted to the sight altitude.
These are reliable pieces of equipment.
Zero and find the index error by setting the index arm to zero, and the micrometer setting as well to zero. Look at the horizon and turn micorometer setting back and forth to make the horizon split in the two mirrors. Turn the micrometer until the two horizons line up and make a note of the amount either plus or minus from zero and make that calculation with every sight taken at that time. This might change in different temperatures, so I always made it a practice to check the index error before every sight.

I support using a Davis 25. Take care of them, keep them in their case..never leave them out in the sun and you will get very good results. I used one full time for over 3 years and got excellent results. You can spend a lot more money on a sextant that will not do any better than a Davis 25. Good luck with your purchase.

[alan2]

Plastic sextants are viable basic learning tools. You simply have to recognize their limitations. Supposedly, people have crossed oceans using plastic sextants to navigate. That said, the Astra IIIB seems a good instrument, though I'm far removed from expertise regarding such things. Supposedly, it is or was the sextant used at the Merchant Marine Academy which might be a good recommendation.

[meirriba]

Check for pre-owned Tamaya. I think they give the best cost/benefit ratio.