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bletso · 10-05-2016, 03:36

Backlash can be accounted for by always bringing the body with the index arm from the same direction. Get it close and let the body drop / rise to the horizon. Of course when zeroing the sextant, have the index arm movement in that same direction. It is more tedious, but it will eliminate the error reading.

Snowpetrel · 10-05-2016, 03:40

Just looked it up. We were somewhere in the red sea or gulf of Aden, so probably nearer 12-20 N not 35 N. So the altitude would have been much lower. I do remember it being hard to keep both the horizon and the star in view. Anyone tried some of these emergency nav techniques?

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Mithril Bham · 10-05-2016, 07:47

I took a course from Starpath in Seattle years ago. They recommended a Chinese product above all others for the price. I have been racking my brain but can't remember the brand. I'm sure you could email them and get the info.

barnakiel · 10-05-2016, 13:29

Then there is also this kind of sextant:

https://en.wikipedia.org/wiki/Bris_sextant

Invented by Sven Yrvind. Cost zero if you have some glass and some glass glue. Very accurate too.

b.

SeeLevel · 10-05-2016, 16:01

Quote:

Originally Posted by magellanyachts

I took a course from Starpath in Seattle years ago. They recommended a Chinese product above all others for the price. I have been racking my brain but can't remember the brand. I'm sure you could email them and get the info.

That would be the Astra IIIB: Astra IIIb Sextant
PJ

Snowpetrel · 10-05-2016, 16:18

Quote:

Originally Posted by barnakiel

Then there is also this kind of sextant:

https://en.wikipedia.org/wiki/Bris_sextant

Invented by Sven Yrvind. Cost zero if you have some glass and some glass glue. Very accurate too.

b.

Hi Barnicle, have you made one? I had a play with the idea, it seemed to work, at least I got a bunch of regularly spaced suns. But I didn't use the proper glass, and just sticky taped it together. Never heard from anyone thats used one. But the concept is brilliant.

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lesterbutch · 10-05-2016, 17:43

I hear some of the folks saying there is no need to use a sextant anymore because we have GPS and their right, but some people like to develop their skills using manual methods instead of electronic. This is also good, as it keeps our heritage alive and often its just fun to do it the old way!

SeeLevel · 10-05-2016, 21:26

Quote:

Originally Posted by Snowpetrel

Yep, love my Freiberger! Its a real work of art.

I also have a Davis mk 15 which, although it was my grandfathers sextant that he gave to me for my 21st birthday, its sadly never given consistant results. There is about 12' of play in the micrometer on the plastic worm teeth that make it very difficult to use. You have to set the index error for both ways, then try to remember which way the micrometer was turned last.

I found I got much better results with an old vernier ebbco.

Any idea where replacement mirrors can be purchased for Frieberger?

Snowpetrel · 10-05-2016, 22:29

http://www.robertwhite.com/cgi-local...g=rw_celestial

Maybe worth a try? There is also info about making your own online. Though it would be hard with the round horizon mirror.

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barnakiel · 11-05-2016, 07:22

Quote:

Originally Posted by Snowpetrel

Hi Barnicle, have you made one? I had a play with the idea, it seemed to work, at least I got a bunch of regularly spaced suns. But I didn't use the proper glass, and just sticky taped it together. Never heard from anyone thats used one. But the concept is brilliant.

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No. I have not. But I will have one for our (touch wood) fall passage to the West Indies.

There is an extensive info on Sven's homesite. You get very accurate suns, at intervals, you are busted a cloud flies over just when your interval comes ;-(

Given that sight does not have to be taken daily and that you will have at least two takes on the rising sun and two on the falling one, this should work as advertised.

I have one other, equally simple method to test too but I have not implemented it yet. But I am 99% certain it may work. If it works, I will post results on the forum too.

Cheers,
b.

Littlechay · 11-05-2016, 10:38

What material did you gentlemen use for the filter in your experiments?

Many people talk of using welding shield glass, but the density used for arc welding is too dark and you can't see the horizon let alone there being any chance of seeing the moon through it.

Maybe a density that is used for gas cutting or brazing? I've been going to make one for some time but been unable to find a filter glass.

Cheers

bletso · 11-05-2016, 12:09

I believe you can use a #7 shade, #11 is indeed too much. I will post when I get one

btrayfors · 11-05-2016, 13:06

Quote:

Originally Posted by SeeLevel

Awesome, thank you for these helpful replies! Now for a bit of shopping.

btrayfors, I'm in no hurry so perhaps you can let me know how much $ when you are ready to sell, if that works for you.
PJ

Thanks very much for your interest, but the sextant has already been sold.

Bill

El Pinguino · 11-05-2016, 15:45

It is possible to get mirrors re-silvered.

A quick scan of recent posts.

I would stick with sewing machine oil.

Plath/Freiberger/Astra/Tamaya all good sextants.

First thing for me would be the quality of the optics and that is hard to judge unless you get to test all of them side by side... I do know that Plath is excellent and Freiberger very good. My Inglis Smith yacht sextant.... fair.

Second issue is weight . Plath is heavy , Freiberger quite light, by memory Tamaya v heavy , never handled an Astra.
Some like a heavy sextant as easier to hold steady in a breeze, the more petite females amongst us may prefer the lighter Freiberger.

There is a dutch sextant out there , Observatoor??, owned one for a week... sold it on. Very high build quality but freaky internal filters in the scope which I did not like at all....

Thats it.