A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Greg Rudzinski
Date: 2016 Apr 13, 20:26 -0700
Ebay has provided an Ebbco Special plastic sextant at a very reasonable $30. This version of Ebbco has better quality mirrors than the standard model and is the model to get. As expected on older Ebbco's the filters were bad. The best fix is solar film. See this old post on how to do it.
Another worth while modification is the addition of a sight tube. For this an old mag light was cut down and taped to fit the scope mount. See attached image. Arc error corrections were determined by comparing horizontal angles against a metal sextant then checked at the beach for repeatability. This method seems to work.
See the attached artificial horizon data that compares the calibrated Ebbco Special against the Cassens & Plath and calibrated Davis MK 3. I made it a fair fight by taking all sights on all sextants with a sight tube. Index errors were checked by x4 or x3 power scope.
The plastic sextants can get the job done if you put the time in to dial them in. I still prefer and recommend the metal sextants but if weight and space is an issue then plastic may be an acceptable choice aboard a small craft.