The Nautical Sextant

Most of the early Tamaya sextants and clones had the same design of battery switch, but I haven’t seen a modern one with two AA batteries for some time. I would expect Tamaya, in common with other makers, to have stuck with a simple design that was easy to overhaul at sea. This is what one of mine looks like:

Electricity flows from the positive battery contact clip through a short length of wire to the switch contact. Pressing the switch button causes the plunger, seen as a screw head, to bridge the gap to the other switch contact, allowing electricity to flow through a wire, poorly seen in the area of the switch, to the lamp. The circuit is completed via the frame to the negative battery contact ( and yes, I do know the electrons flow in the opposite direction).

Apart from bits breaking off, the battery going flat or the lamp burning out, what can possibly go wrong with such a simple arrangement? The short answer is “Anything that breaks the circuit”, but I’ll confine myself to the switch to begin with.

The switch contacts can get dirty or corroded and the same goes for the battery clips. The latter are easy to see and to get at to clean, so check those first. Even if they look fine, it does no harm to freshen them up by rubbing the contact areas with fine, e.g. 240 grit, emery paper. The switch contact areas are easy to get at. Simply remove the two screws that hold them to the handle and clean the undersides where they make contact with the plunger. While you’re at it, press the push-button in to prevent it from rotating and unscrew the plunger, taking care not to lose the spring that lies under the push-button. The head of the plunger, simply a shouldered screw, can then be freshened up too. Once the switch contacts have been removed, this is what you may see:

Note the bare copper wires that, given a chance, oxidise to a black, non-conducting colour.  You can freshen these up too, but a better course is to replace the short piece of wire with new, tinned wire (a piece of 15 A fuse wire will do) and to tin the end of the wire to the lamp with solder if you have a soldering iron and can use it. The other improvement you can make is to put the wires where you can see them, on top of the switch contacts rather than hidden underneath them, like this:

As a refinement, with a sharp knife cut a gasket from neoprene sheet to protect the contact area from salt water:

Assembly is the opposite of disassembly, except for placing the wires on top of rather than under the switch contacts. When replacing the switch plunger, take care not to overtighten as you screw it into the the push button. If you are too rough, you may split it and will then have to go shopping for some Araldite. The spring belongs underneath the button.

If replacing the battery and lamp and overhauling the switch doesn’t restore function, the fault most likely lies in the wire between the battery handle and the lamp, and it is most likely to break at the lamp itself. But that’s for another day.

You can read about other types of lighting systems as well as gain a knowledge of the detailed structure of your sextant(s) by buying my book The Naked Nautical Sextant and its Intimate Anatomy. Read what Trevor Kenchington has to say about it in “Inside the book”.