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+--- Thread: Sale on Davis Mk3 "Lifeboat" sextant (/showthread.php?tid=240)
Sale on Davis Mk3 "Lifeboat" sextant - PeterB - 04-30-2022
April 30, 2022
Here is a link to a popular and reputable supplier of celestial navigation equipment having a sale on the simple but remarkable Davis Mk3 Lifeboat sextant. I have no affiliation with the seller or Davis whatsoever other than to have purchased a few items from each of them over the years.
These simple MK3 instruments are perfectly adequate for real navigation. They make a great first sextant due to their simplicity and low cost -- yet you can do some real navigating with them and expect perfectly acceptable results. IMHO they are a better choice than the more expensive plastic sextants that are made to look like "real metal sextants." Those fancier plastic sextants are notorious for never holding their adjustment from one shot to the next in a round of sights which only frustrates beginners. The humble Mk3 doesn't suffer from that shortcoming.
If later on you decide to treat yourself to a "fancy metal sextant" you will still keep your MK3 forever because The MK3 is also great for backup; emergency; teaching; and for use on days when the spray is flying and you would prefer not to expose your fancy metal sextant to a salt water dousing.
In fact even if you already own a "fancy metal sextnat" you should consider buying a Mk3 as a backup for those reasons stated above. I did and I am very happy I did so.
On the other hand if you decide that celestial navigation is not for you, you will be able to sell the MK3 used for about what you paid for it. Or you can just give it to a friend or stash it in the ditch bag. It is a rare "fancy metal sextant" that sells as used for about its original purchase price because people are wary of any unknown history of the instrument and possible hidden defects.
As for myself I started out with an (expensive) fancy metal sextant and turned my nose up at the MK3, although it was suggested to me to start with that model. Many years later (and a few more "fancy metal sextants" in my collection) I bought a MK3 used. I can't say enough good things about it. It is one of my favorite sextants. Sure, I'm not going to do lunar distances with it, but I can get position accuracy to within 2 nmi fairly regularly -- and as I said, no worries about eager students dropping it or salt spray ruining it. In fact just recently I was able to bring down Venus in daylight for practice with the MK3 when my fancier Tamaya failed due to a much smaller field of view.
I love this thing even if it is humble and simple. I will keep mine forever for the reasons stated above, and if it gets somehow destroyed I'd buy a replacement in a minute. I think you would love it too if you would give one a fair try. In fact the biggest down side to the MK3 is the ribbing you are likely to get about your "inadequate" or "toy" sextant from wanna-be navigators and arm-chair pirates who simply do not know any better. But after you go out and do a round of sights with it you will be convinced that they are only displaying their lack of experience.
I have seen it stated in reviews that occasionally the non-adjustable horizon mirror may not be perpendicular to the frame. To check for perpendicularity of the horizon mirror cut about 2mm off the corner of a paper business card at a 45° angle and gently present the card to the mirror as you would a carpenter's square. You need to cut the corner off the business card because there is a tiny plastic ridge at the base of that mirror where its mount meets the frame and you must create clearance for this ridge. If your horizon mirror is not square you must request a replacement instrument -- it can not be adjusted. Meanwhile expect to see some of the frame in the right hand side of the horizon mirror even if it is properly perpendicular to the frame. That is normal.
https://www.celestaire.com/product/davis-mark-3-sextant/