Saturday, 26 March 2016

Second hand metal sextant

I learnt celestial navigation on an RYA Yachmaster Ocean course in the 1980s, from a woman who lived in rural Oxfordshire and whose name I am sorry I cannot recall. She had many ocean crossings under her belt and had a wonderfully un-mathematical way of understanding the mathematics and an incredible ability to recognise navigational stars as they peeped out from between clouds perhaps by knowing where they should be and their colour and magnitude but with out the need for constellations as a guide.

Davis Mark 3
My first sextant was a Davis Mk 3, a very cheap plastic vernier sextant while much better than it looks (it looks like a toy) it is not very accurate. A few years ago I bought a Davis Mk 25 and could find my position on dry land to within about a nautical mile by sun sights. Better than that if I averaged five sights and used liner regression. My problem with the Mk 25 is that it seems to need alignment every time I use it. I like the "beam converger" which means you can see the sun and the horizon superimposed across the full width of view.

Mark 25
Eventually I decided to buy a "proper" metal sextant. I bought a Tamaya MS-2L for £275 on ebay. It was made in 1984 and as far as I can tell has sat on a merchant ship unused all its life until the ship was broken up in India and it fell in to the hands of a dealer. Its certificate says it has a fixed error of 0''.  It has a 7x35 monocular scope and I added a zero magification sight tube from Celestaire.   . It comes in a very practical protective plastic case. I am still getting used to using it. For example it is much heavier and taking a series of sights in rapid succession and you feel the weight. Also it takes some getting used to using the monocular as it is harder to find a star. As expected though it stays in adjustment unlike the Davis.

I understand that modern new Chinese Astra sextants are excellent value and in particular lighter, but a good Tamaya is probably the best value to be found second hand. 

I look forward to trying my new one at sea!

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