Davis Mark 3 Plastic Sextant

Instruction manual included. Sextant weight is 6oz, shipping weight is 2 lbs.

$49.00   ...item# 1840d3



Davis Mark 3 Plastic Sextant
This product when purchased here includes a complimentary Elibra ebook copy of How to Use Plastic Sextants—with Applications to Metal Sextants and a Review of Sextant Piloting by David Burch. The ebook must be read from a Windows PC. A serial number is provided at the time of sextant purchase. More info.


A forerunner of this instrument was developed for emergency use during WWII, called the "Lifeboat Sextant." This is the least expensive sextant in the world that will provide dependable accuracy adequate for actual ocean navigation. With good procedures you can obtain some 5 to 10 miles position accuracy routinely, and better with practice, providing you follow the careful procedures outlined in the book above, which is also included in our cel nav course materials.

All replacement parts (even the screws!) are readily available. Note that there are no optics nor telescope and the vernier can only be read to the nearest 2', so obviously one needs to take multiple sights and average them to obtain good LOPs and the fixes themselves must be made from 3 bodies properly selected.

This sextant is popular as a back-up or learning sextant, but aside from these celestial applications, it is actually the sextant of choice for inland and coastal piloting. Using the sextant horizontally, you can find your position on a chart much more accurately than you can by other conventional piloting techniques such as compass bearing fixes. See related note on Plastic sextants index page.

In short, even if you never plan to sail offshore and need celestial navigation, we still strongly recommend this device for inland and coastal piloting. Without GPS or radar, this is your most powerful tool for finding and keeping track of position in sight of land — or lights.

There is an optional hard plastic carrying case available from Davis Instruments for this for $25; it is the same one used for the Mark 15 and Mark 25. For years, however, we have just used a Rubbermaid No 4 food container (shown here) for the job. They may have changed numbers. See also this tupperware item_number=P10107637000. These are waterproof and float to boot, and has room for pad of wateproof paper, pencils, plotting sheets, watch and long term almanac, small compass, etc. In short, when underway, this container becomes an emergency nav kit.

These are great instruments and a joy to use for piloting. It is actually difficult to imagine how these techniques seem to have faded away. Some time around 1950, they were not even covered in Bowditch any longer. From the 1800s to 1930s leading navigation texts devoted entire chapters to the subject. We preserve and elaborate on these methods in our course materials, since the simple design of the Mark 3 makes these sights very much easier than they are with conventional sextants.

Compare Plastic Sextants.

11/22/13 

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