NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Ian McCrum
Date: 2025 Nov 13, 07:21 -0800
[references 2024 thread here]
The author of the design reckons it's good to 6'. Or rather, the scale is readable to that. It seems to be the most popular 3D printed design with over 2,000 downloads from Thingiverse (https://www.thingiverse.com/thing:6464051). The cost is less than a pint of beer so considerably cheaper than a Davis type (£75+)
If you search for 3D printed sextants then some have done comparisons with proper sextants and found errors of maybe 4' (one had a maximum of 13')
When I crossed the Atlantic I had two sextants (my own plastic Davis type, bought for £21 in 1974 and one that came with the boat). Of course we had 5 GPS devices on board without counting the mobile phones of the crew. My tries with the sextant got me within 2' which was good enough.
Even 6' is good enough if it puts you ten miles away from dangerous bits...
You'd need to experiment with varying temperatures, particularly if the sextant is built in PLA, the usual filament that 3D printers use. PETG is probably a better choice. Keep PLA away from long exposure to intense sunlight.
It is amazing what a £150 to £250 printer can make for under £10.
