Bosunof
Well-Known Member
Where can I get a recently bought secondhand sextant serviced and calibrated. I would prefer a Scottish destination but "any port in a storm" eh?
Bosunof
Bosunof
Sextant calibration and servicing
- Thread starter Bosunof
- Start date
Bilgediver
Well-Known Member
Check Kelvin Hughes in Glasgow...However I would suggest you learn to do this yourself as it is easy to upset the mirror alignement and there is no Kelvin Hughes in mid Atlantic.
richardandtracy
Well-Known Member
For DIY checks, look at the 'American Practical Navigator' or 'Bowditch' at http://www.nga.mil/portal/site/maritime/...ec24fd73927a759. See Chapter 16.
Regards
Richard.
Regards
Richard.
bilbobaggins
N/A
Hello and welcome.
Kelvin Hughes ( Glasgow ) will most probably send your precious and delicate instrument to Amsterdam, or to :
B. Cooke and Son Ltd
( Member of the Chart and Nautical Instrument Association )
'Kingston Observatory'
58/59 Market Place
Hull
HU 1RH
Tel: 01482 223454
From personal experience, they're excellent ! Give 'em a ring!
Very few orgs now offer this service in the UK, and the knowhow and specialist collimation instruments are disappearing fast.
/forums/images/graemlins/wink.gif
Kelvin Hughes ( Glasgow ) will most probably send your precious and delicate instrument to Amsterdam, or to :
B. Cooke and Son Ltd
( Member of the Chart and Nautical Instrument Association )
'Kingston Observatory'
58/59 Market Place
Hull
HU 1RH
Tel: 01482 223454
From personal experience, they're excellent ! Give 'em a ring!
Very few orgs now offer this service in the UK, and the knowhow and specialist collimation instruments are disappearing fast.
/forums/images/graemlins/wink.gif
Talbot
Well-Known Member
Agree with earlier comment on you needing to know how to do this yourself, and checking this regularly (every time you use it if it is a cheapy plastic job)
However, serviceing may go much deeper than just alignment, for example http://www.bpsc-marine.co.uk/ are the only people I know who offer a mirror re-silvering service.
However, serviceing may go much deeper than just alignment, for example http://www.bpsc-marine.co.uk/ are the only people I know who offer a mirror re-silvering service.
bilbobaggins
N/A
[ QUOTE ]
sextant serviced and calibrated
[/ QUOTE ]
I suppose one should always ask - 'First, define your terms.....'
It makes sound sense, after - or preferably before - purchasing a second-hand sextant, to have a servicing specialist check the instrument for frame distortions, collimation, residual errors, deterioration of adjustment screws and specific 'lost motion'.
Commander Bruce Bauer's 'The Sextant Handbook' remains a reliable guide to the 'Adjustment, Repair, Use and History' of marine sextants.
BTW, one quite frequently spots tales of how to cope with a broken sextant mirror i.e. DIY replacements, black varnish, pieces of DVD-ROM, etc. Should one be going 'ocean' and likely to be reliant on a sextant at some point, why on earth not carry a couple of spare mirrors, securely squirreled away?
/forums/images/graemlins/grin.gif
sextant serviced and calibrated
[/ QUOTE ]
I suppose one should always ask - 'First, define your terms.....'
It makes sound sense, after - or preferably before - purchasing a second-hand sextant, to have a servicing specialist check the instrument for frame distortions, collimation, residual errors, deterioration of adjustment screws and specific 'lost motion'.
Commander Bruce Bauer's 'The Sextant Handbook' remains a reliable guide to the 'Adjustment, Repair, Use and History' of marine sextants.
BTW, one quite frequently spots tales of how to cope with a broken sextant mirror i.e. DIY replacements, black varnish, pieces of DVD-ROM, etc. Should one be going 'ocean' and likely to be reliant on a sextant at some point, why on earth not carry a couple of spare mirrors, securely squirreled away?
/forums/images/graemlins/grin.gif
Lakesailor
Well-Known Member
I've a mate who lives in Hull and retired recently. he decided to treat himself to a nice sextant as he was going sailing for extended periods.
Cookes told him that if he bought a good used sextant they could service it and set it up, no problem. If they supplied one new or used it would already be done and if he bought an economy one it wasn't worth the bother doing a test.
I used to gaze in wonder at the gear in their windows when I lived there. They are opposite the King Billy statue which is above the toilets with marble and glass cisterns on the urinals which really did have goldfish in the tanks.
Cookes told him that if he bought a good used sextant they could service it and set it up, no problem. If they supplied one new or used it would already be done and if he bought an economy one it wasn't worth the bother doing a test.
I used to gaze in wonder at the gear in their windows when I lived there. They are opposite the King Billy statue which is above the toilets with marble and glass cisterns on the urinals which really did have goldfish in the tanks.
MASH
N/A
Unless there is serious wear in vernier screws or other moving parts (unlikely unless the sextant is VERY well used and neglected) there are only 2 or 3 of alignment checks to carry out which can easily be done yourself as suggested above. Severe errors in alignment might mean a bent frame (instrument has been dropped) but usually they are either removable or correctable in the calculations. See how the alignment is before spanding big money on a refurb, and buy a plastic spare if you are going to rely on it at sea. (why, when it is the back up to the GPS)
bilbobaggins
N/A
I suppose that's fair enough.
All who intend to use a 'sungun' in anger should be capable of checking it out, keeping it in calibration, and spotting if something has gone seriously wrong.
The three DIY checks/adjustments are for Perpendicularity, Side and Index errors - the pnemonic 'PSI' helps. Most of the 'astro cookbooks' will explain how, but it is helpful to have someone who knows show you what's meant.
Every senior yacht club will have a retired pro navigator propping up the bar, just waiting for a call to 'tweak' someone's sextant or compass. The going rate is a couple of beers per hour, and that saves quite a lot of frustration.....
Then it's a simple matter of taking your sextant to a known location with a clear view of the southerly horizon - at anchor somewhere pleasant, or a favourite beach - and get 'shooting'. Your plotted results should be within 4-5 miles of where you are, and if that is so, there's not a lot wrong with your sextant or your techniques.
Lots of practice and comparison with known positions will reduce your 'personal error' to a couple of miles, reliably.
If you cannot get your Intercepts to plot on your chart of UK Home Waters, then it's time to wake up said old pro navigator again....
Enjoi!
/forums/images/graemlins/grin.gif
All who intend to use a 'sungun' in anger should be capable of checking it out, keeping it in calibration, and spotting if something has gone seriously wrong.
The three DIY checks/adjustments are for Perpendicularity, Side and Index errors - the pnemonic 'PSI' helps. Most of the 'astro cookbooks' will explain how, but it is helpful to have someone who knows show you what's meant.
Every senior yacht club will have a retired pro navigator propping up the bar, just waiting for a call to 'tweak' someone's sextant or compass. The going rate is a couple of beers per hour, and that saves quite a lot of frustration.....
Then it's a simple matter of taking your sextant to a known location with a clear view of the southerly horizon - at anchor somewhere pleasant, or a favourite beach - and get 'shooting'. Your plotted results should be within 4-5 miles of where you are, and if that is so, there's not a lot wrong with your sextant or your techniques.
Lots of practice and comparison with known positions will reduce your 'personal error' to a couple of miles, reliably.
If you cannot get your Intercepts to plot on your chart of UK Home Waters, then it's time to wake up said old pro navigator again....
Enjoi!
/forums/images/graemlins/grin.gif
G
Guest
Guest
Replace a mirror ? Interesting. Yes you can adjust the mirrors in their frames ... but I would hazard a guess the possibility of unadjustable error would be high.
So checking a Sextant ? Theres the frame and mirror refection to show mirror out of line and frame distortion ...
There's the sighting a singloe star at zero or near so you can align horizon mirror ....
Then there's sun diameter veiwing top and bottom touches to ascertain error against Semi diameter ... or use a star superimposed reflected on true.
That gives final errors but of course all referenced to zero. An instrument specialist will be able to calibrate for a series of different settings along the scale.
Blimey years since I did the above !! Still imprinted on the grey matter ...
So checking a Sextant ? Theres the frame and mirror refection to show mirror out of line and frame distortion ...
There's the sighting a singloe star at zero or near so you can align horizon mirror ....
Then there's sun diameter veiwing top and bottom touches to ascertain error against Semi diameter ... or use a star superimposed reflected on true.
That gives final errors but of course all referenced to zero. An instrument specialist will be able to calibrate for a series of different settings along the scale.
Blimey years since I did the above !! Still imprinted on the grey matter ...
Bosunof
Well-Known Member
Thank you for all the help. I certainly have a couple of good books that sort out the testing etc but I have a stripped thread and a mistrust of the instrument as it stands. I bought it on that basis confident that I could get it serviced and put right to start with,, but asyou can see the skills levels are not readily available and certainly not locally. Our club bar is only open for an hour on Wednesday nights so doesnt encourage the lingering sailor with this sort of expertise. And I wont drink and drive to get to another!
But thank you all. It is a great help to get this sort of advice.
But thank you all. It is a great help to get this sort of advice.
G
Guest
Guest
Sorry to say that IMHO - a stripped thread would mean resign it to display use only .... to repair a thread on this - remember the thread on any part ... mirror screw, micrometer ... even the thread edge of the arc are absolute for accuracy.
