Sextant Adjusters

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simond1230

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Does anybody know where I can send my sextant to be checked over and adjusted if necessary? Can't seem to find anywhere!
It's an old H Hughes & Sons of London and was given to me without a certificate.
Any ideas would be greatfully received.
 
it is within the capability of the ordinary sailor to deal with the principal 4 sources of error:
perpendicular
side
collimation
index.

Do all the screws and bits move, or are they gunged up ? How is the silvering on the mirrors ? If these two items are not OK, then it will need servicing as well as adjusting. Give it a go.
 
Unfortunately, I'm up in Cumbria, nowhere near Hants, though thanks for the offer!
All the adjustment screws etc move and I've managed to get the index error right down, though I've been advised to get it professionaly adjusted so I can get a new certificate for it.
The mirrors could be in better shape, though they're not bad enough, I wouldn't have thought, to warrant replacing them.
Otherwise the sextant is in good condition. I suspect it may have been dropped or mishandled at some point in its past.
 
As another says ... if you can go through the check routines ... sighting arc via mirror and direct ... aligning a stellar object vertically and horizontally ... which will basically give you which way to adjust what ...
Then a final check to see what residual error is for correction to sights ... that is good enough. Seriously.

Ships used to have on-board Sextants that got used by all and sundry ... you can imagine some of the less than gentle handling. We never sent ashore unless seriously needing TLC ...

In fact on one ship - I had the 3rd Engineer run up new adjustment screws for a Tamaya Star Sextant ... a particularly fiddly job ... after a number of failures - the screws were so small and with lips .. that they kept breaking in the lathe when machining the lip ... he managed to succeed ... Sextant was spot on !

FYI ... calibration certificates are only valid at time and place made ... later most ignored them based on personal checks in use.
 
Refueler has the measure of it.

The certificate was only for the original leaving the factory state. Ours only went ashore after they were dropped and couldn't be brought back to form by the standard adjustments.
 
DIY is the way to go, because that's what's going to happen when you do it for real.
Google for a manual on any sextant and you will get the procedure for basic alignment, and pre-use calibration procedures. After that it's just practice practice practice. Enjoy.
 
All sextants have errors on the arc. All of them. I have a nearly perfect one but there are still small errors on it. Provided you are able to eliminate the others and end up with small errors you would just have to factor it in when using your sextant. Consult an expert in sextant correction and see what he says. I have never heard of a dropped sextant having all the errors eliminated but at least to have the very small ones that remain, workable. Error on the arc, subtract, error off the arc, add. "When its off its on and when its on its off". :D
 
I had a Freiberger that I bought used from Ebay. It had play in the tangent worm screw that was so small I did not notice it after inspecting the sextant after it arrived. When testing it out and comparing it to my old Leupold, I noticed that I was getting huge errors, but not with every shot. I used the Leupold and I didn't have errors like the sight taken with the other sextant a few minutes before. Then I noticed that there was a tiny delay when I turned the micrometer drum on the Freiberger. I turned it one way and it engaged properly but if I turned the drum the other way you could see that it didn't respond immediatley, causing the error.

If this is a sextant that you've had and used and didn't notice any problems like I described, then the adjustments the other folks suggested is good advice. However, if this is a sextant that you just purchased used, I would make sure your tangent worm screw functions properly.

Good luck

Neil
 
Institute of Navigation Quote

This thread has got me thinking about errors in sextant observations.
The following quote, originally from the Institute of Navigation in 1957, is printed in the front of my copy of Burton's Tables:

"An extensive investigation into the degree of accuracy normally obtained in the practice of astronomical position-finding at sea has indicated that the average inaccuracy in a position line produced by the average observer is 0.7', and that one in twenty such position lines may be as much as 3.0' in error."

These errors are for professional navigators working on the relatively stable platform of a ship's bridge and high enough to minimise the effects of wave height on the observed horizon.

In a yacht I would be happy to accept much larger errors, but anyway, like most other people, don't much bother and just consult the GPS.:)
 
Thanks for all your advice... I guess I the certificates are only valid when they leave the factory, then it's pointless bothering!

I'll just live with the error and fall back on it as an excuse when I mess things up!
 
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