Choice of Sextant?

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crawlerm

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I'd appreciate opinions on choice of a sextant.

I've been using a Davis plastic model to learn Astro Navigation and did not have high expectations of it. Now that I know enough to work out what it should have read I discover that the readings are quite variable. I'm intending to buy a proper sextant and have narrowed the choice down to four options:-

1. A new Celestaire - made in China, modern and functional.

2. A secondhand Hughes Royal Navy three ring circa 1968.

3. A Royal Navy surplus Hughes circa 1985 (grey warpaint).

4. A Royal Navy surplus Hughes circa 1985 that has been professionally stripped and polished. This looks beautiful but I'm concerned that stripping it down will have spoiled the calibration although I'm not sure.​

My primary concern is precision as I want to get my fixes as accurate as possible but I can see the fascination in the instrument itself so ideally I'd like to have one that was worth owning. I guess the thing I'm most unsure of is how much, if at all, the calibration will have changed through time or dismantling.

Regards

BobC
 
BobC

I can only talk from personal experience as I do not know the models you describe apart from the Davis

My experience was I bought a Freiberger on eBay when I was part way through Astro, it was a fine instrument and had a professional feel to it, sturdy and in proper box with correction certificate.

The Astro course taught me about correcting errors and I had less than 1 minute of error by the time I had finished playing, I used the Freiberger for a few months at home and found it too heavy for extended use.

I then got out the Davis and corrected it and found it light and surprisingly accurate.

I then sold the Freiberger, still have the Davis, have used it twice in 2 years.

I hope that helps a bit
 
You can tweak most sextants to a level of accuracy more than sufficient for your purposes. It all depends on how much you take pride of ownership from a object.

I have a beautiful reconditioned old ships sextant from some liner or something. Lovely to look at, needs an occasional polish, but I love it.

Where the new ones win is the quality of the viewing optics.

If I was buying again, having had an antique, I would probably buy a modern one.
 
In what way are the readings variable?

Like many, I started with a plastic one, an Ebbco. I now have a CP Sailing Sextant which is a joy to own and use.

For taking a sun sight, I found the Ebbco to perfect acceptable (typically, a MP latitude within about 8 miles). If you plan to chase down those hard to find little bug*gars at twighlight you'll need better optics.

If you have any doubts about the 4 you list, don't buy. There are plenty on e-bay so bide your time until the right one comes along at the right price, undoubtedly it will.

Why do you have concerns over the one professionally stripped and polished? Any decent book on a sextant will show how to check it for errors. Why not ask for a calibration certificate? That should smoke out its authenticity and the confidence of the seller.
 
crawlerm said:
I'd appreciate opinions on choice of a sextant.

I've been using a Davis plastic model to learn Astro Navigation and did not have high expectations of it. Now that I know enough to work out what it should have read I discover that the readings are quite variable. I'm intending to buy a proper sextant and have narrowed the choice down to four options:-

1. A new Celestaire - made in China, modern and functional.

2. A secondhand Hughes Royal Navy three ring circa 1968.

3. A Royal Navy surplus Hughes circa 1985 (grey warpaint).

4. A Royal Navy surplus Hughes circa 1985 that has been professionally stripped and polished. This looks beautiful but I'm concerned that stripping it down will have spoiled the calibration although I'm not sure.​

My primary concern is precision as I want to get my fixes as accurate as possible but I can see the fascination in the instrument itself so ideally I'd like to have one that was worth owning. I guess the thing I'm most unsure of is how much, if at all, the calibration will have changed through time or dismantling.

Regards

BobC
Click to expand...
I don't think age itself has much bearing on accuracy - my sextant is 1943 US Navy and is in very good condition, though the optics are not as good as some current models. Others have mentioned Ebay - unless you bought on a pay on personal collection basis so you could see and "feel" it first I'd be dubious about this. A look at the condition of the mirrors, a quick check on perpendicularity and side errors (takes seconds) and run the arm through the arc and see if it is smooth and tight. Then if the telesope is clear and sharp it's going to be OK.
 
A modern sextant will have much better optics than the Hughes sextants you have listed and with the usual caveats I would prefer a Freiberger from Ebay, IF there is a full description and clear photographs of its general condition, including a certificate showing trivial errors, preferably less than plus or minus 20" across the arc. Freiberger yacht sextants also come up from time to time and they are typically around £100 less than the full size instrument. They are a bit smaller, lighter and perfectly adequate for practical use.

Whatever you do, don't buy a "professionally stripped and polished" sextant. This treatment does them no good and relegates them to "collectable" conversation pieces. Some of these are obviously manufactured as ornaments, some were ONCE functional and some are obvious fakes like this horror.

Other good sextants include Tamaya, Cassens and Plath, the Russian SNO-T and probably the best ever - C.Plath of Hamburg.

Good luck with your search!
 
I looked on ebay for a while, but reading up on sextants suggested the possibility of unacceptable index errors as a consequence of damage or misuse. How could I tell? A calibration certificate produced on manufacture wouldn't reflect its current status. Index errors are not amenable to adjustment. While I'm sure 99% of secondhand sextants on ebay are top-notch (the real ones, not the 'antiques' from India), the uncertainty pushed me towards a new Astra IIIb. Certified as having no index error, and a minor tweaking having removed a smidgeon of side error, it is now error free. The optics are good; if, like me, you want to practice in the back garden using an artificial horizon (dish of oil), the reflections of the dimmer stars can be problematical. It is also lighter than older models.

Whatever you choose, ownership of a fine instrument that you know how to use is a good thing.
 
Neil said:
I looked on ebay for a while, but reading up on sextants suggested the possibility of unacceptable index errors as a consequence of damage or misuse. How could I tell? A calibration certificate produced on manufacture wouldn't reflect its current status. Index errors are not amenable to adjustment. While I'm sure 99% of secondhand sextants on ebay are top-notch (the real ones, not the 'antiques' from India), the uncertainty pushed me towards a new Astra IIIb. Certified as having no index error, and a minor tweaking having removed a smidgeon of side error, it is now error free. The optics are good; if, like me, you want to practice in the back garden using an artificial horizon (dish of oil), the reflections of the dimmer stars can be problematical. It is also lighter than older models.

Whatever you choose, ownership of a fine instrument that you know how to use is a good thing.
Click to expand...

Index error can be measured accurately and is the result of the horizon and index mirrors not being parallel when the instrument is reading zero. They are, of course, adjustable and this error should be checked routinely whenever the sextant is used. It can either be left and applied to the sextant reading or adjusted out very easily.

Most sextants have been treated with great care, but a slight possibility exists that there may be damage, from, say, the instrument having been dropped. That is why it is important to carefully study the pictures and ask the seller the right questions if the description is a little vague.

Some excellent sextants can be bought from India. They are usually sold by shipbreakers and are professional instruments that will not have had much use since the advent of GPS. Check the sellers feedback! However, the shipping costs are high and they will be liable to VAT and import duty. Should anything go wrong with the transaction it won't be as easy to resolve as one bought from a seller in the UK.

The Astra is also a fine sextant.

:)
 
I have a sextant and quite proficient at its use as well.

My sextant is one of the better "plastic" ones and I get correct fixes from it; YES, I could get more accurate fixes with a top quality unit but what for???

I have 3 different GPS, complete with their own antennas.... other than WW3 starting while I am at sea what is the problem?

You can never get a great fix when you are sitting atop a rock & roll sailboat!

Just to add some lateral thinking of course. Enjoy your sextant!

GL
 
Yes - no problem with plastic sextants. It's fun trying to get a "correct" fix with one. :)

One of my sextants is a Davis Mk 3, which is about as basic as you can get, without making a cardboard one.

I like astro and my other two sextants are a C.Plath (had that one for a LOT of years) and a Freiberger Yacht Sextant. These days the Plath stays at home and the other two are on the boat. Do I need them? Almost certainly not.

I suppose if you don't get it there's no point in trying to explain it. :):)

I also own three bubble sextants, but I probably wont be taking a Lancaster or B-16 deep into enemy territory anytime soon. They are useful for checking, from time to time, that my house is still roughly in the same place.

:D
 
Sextants and errors

Hi and happy new year to the forum!

I have just given me a nice new metal sextant (such a chinese made model ordered via SVB in Bremen) for christmas ;)

It comes with certificate (saying "no errors") and a nice wooden box. As far as I was able to check it (no side errors) is very good and has good optics. It also has light for reading the scale. I think the weight is a big advantage compared to the light-weight plastic ones, but it will take some time before I can test it on board.

So far so good... My problem with this sextant is now that there was only one day with about one hour with a bit of sun (but still behind the clouds), and one very short moment when I could observe some stars. Also this worked well - I had expected it to be much more difficult to keep the star in the ocular while moving it to the horizon but: no problem and a nice clear view...

But how can I find out the index correction now? Waiting for a sunny day - ok. I do not have a horizon here anywhere, since I still live much too far from the coast. I tried with some roofs, giving me something like -9' for the correction, but this depends still strongly on the distance, as I found out. As far as I know, the correction should be made for distances close to infinity, i.e. more than 5 nm (?) - that would mean waiting for the sunny day in my case... with the milky sun we had inbetween it was not possible to measure exactly, but a first guess is +6.5' (i.e. opposite sign compared to the roof...)

So, what if I plan to use the sextant for terrestrial navigation, as well?
For some very close objects, I found that I would have to correct for something up to one degree. But is that the correct way to do it? For every coastal observation measure this correction first and then add this to the measured angle? And also add the IC afterwards? I am a bit confused... none of my books mentions these problems.

Maybe somebody knows...
 
JayBee said:
Index error can be measured accurately and is the result of the horizon and index mirrors not being parallel when the instrument is reading zero. They are, of course, adjustable and this error should be checked routinely whenever the sextant is used. It can either be left and applied to the sextant reading or adjusted out very easily.
:)
Click to expand...

You are, of course, correct. I should have said unadjustable errors, perhaps in the case of accidental damage, such as a graduation error or centring error.
 
Larida said:
So, what if I plan to use the sextant for terrestrial navigation, as well?
Click to expand...

In the absence of a Horizon, there are only two alternatives:

1. The opposite shore of a large lake.

2. An artificial horizon. I use a shallow dish of engine oil. Look through the telescope at the reflection of the celestial body in the oil. Bring the reflected sextant image down to the directly observed reflection in the oil. Placing the bottom of the sextant-reflected image on top of the directly observed oil-reflection is the equivalent of lower limb. Divide the measured altitude by 2 to get Ho. There is no correction for Dip, but take into account any index error.

To check and adjust for index error, set your scale to 0 and look at a star. Make any adjustments necessary to get a single superimposable image of the star (given the absence of any side error).
 
I doubt if it is worth while to buy a plastic sextant these days. To cut a long story short, I recently bought two micrometer sextants with excellent optics on eBay. One was an early 50’s C.Plath and one was a 1945 Tamaya. The Plath was German Navy Surplus and has hardly been out of its box and the Tamaya had a long career in P&O. Average of the two prices: £170.00
 
I had a Freiberger it worked well. Tip, to take a sun site change filters so you can turn the sextant upside down and bring the horizon up to the sun it's much quicker than the normal way. Then change the filters back to fine it.
 
crawlerm said:
I've been using a Davis plastic model to learn Astro Navigation and did not have high expectations of it.
Click to expand...
What model do you have?

I know somebody who has a Davis 15 and gets a fix to within 6 MN when measured against his GPS fix, but he uses it a lot!

I have a Davis 25 and am usually within 15 MN.

Not sure an expensive one will be that much more accurate, but am willing to be proved wrong.
 
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