There are numerous small jobs for the boat that can be done away from it, in some spare time. One of these was the cleaning and servicing of the sextant that was included in the sale of the boat. It was mounted on the cabin side above the navigation area and as can be seen from the photo (click to enlarge) on the right it was dirty and had corrosion on the brass minute arc. The sextant is a Simex Mariner made by Tamaya but has no correction chart, case or accessories, but as we all know that one day all the electrics will fail and I will need it to find my way home. There was a book on the boat "The Sextant Handbook: Adjustment, repair, Use and History" by Cmdr. Bruce A. Bauer, USN (ret.) Second Edition 1992 (ISBN 0-07-005219-0) which together with a "Sextant Test and Adjustment" work instruction I found on the web (click here) encouraged me to have a go at servicing it myself.
The first order of business was to get it home, easier said than done as I don't think it had been taken down for many years. Careful use of a drift and hammer eventually freed the locking arm and I wrapped it carefully in a jacket to protect it on the way home. Once home I commandeered the dining table as a worksite and began work - well almost. I must admit some trepidation at taking on this task as if I stuffed it up it would either cost me a couple of hundred to get it serviced or worse a new sextant. I spent the next few nights cruising the online forums and visiting the library before I realised that I just had to get on with it.
The sextant was so dirty that I took it outside and using a can of compressed air from my camera bag blew most of the dust off. Then using soapy water and a well wrung out cleaning cloth I wiped away the years of accumulated grime from the frame. I then removed the scope and shade and gave them a clean using the same process. Then using the lens cleaner and cloth I use for my glasses I cleaned the mirrors, shades and scope lenses. The silvering on the mirrors was in perfect condition and the shades and lenses were like new.
I tried to unscrew the cap for the battery compartment on the handle but it was corroded shut. Fearing that there may be corroded batteries in the handle I removed the endplate the cap screwed into to check inside. No batteries, no corrosion, but I still can't remove the cap - I'll have to think some more about how to solve this problem - any suggestions?
The next step was what concerned me the most - the corrosion on the arc. The arm would not move easily when I used the clamp release and I was not game to try the vernier at this stage. I tried amonia on a cotton bud but had limited success in removing it. My daughter asked why I had not used one of the scratch free Scotchbrite pads we use on the non sick cookware to avoid damaging them. I removed one of the stop screws on the end of the arc and cleaned the area behind it as a test and it worked. Fifteen minutes later the arc was smooth, the scale was intact and readable and I could move the arm using the clamp release. To clean the teeth I used a new toothbrush (small cost for such an important job) and a weak amonia solution which seamed to work quite well. I cleaned the vernier and worm screw with soapy water and the toothbrush, followed by a rinse with clean water and a blow dry with my can of compressed air. I moved the arm to one end of the arc and applied two drops of watch oil (bought from a hobby shop) to the worm screw and wound the vernier through the full arc. The action was very smooth and there seemed to be no play which meant it could now be reassembled for testing.
Next: Testing and Adjustment
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