A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Greg Rudzinski
Date: 2017 Nov 24, 08:54 -0800
If you use Pub 249 vol.1 seleted stars then you can make short work of a three star fix and not get sea sick ;-) The stars marked with the black diamonds will have the best azimuth spread so no worry on the cocked hat just use the center of the triangle to plot your error circle. The optimal three star fix does have the advantage of canceling systematic errors which is a benefit not to be ignored. The disadvatage of Pub 249 vol.1 is that it needs replacing when the epoch expires (every 9 years). Old ones are still useful for star selection and twilight pre-calculating but not accurate enough for calculating intercepts.
From: Bob Goethe
Date: 2017 Nov 24, 07:45 -0800
Gary, Greg, thanks so much for your feedback on this. It appears that once you have taken a couple of LOPs, deriving a third LOP doesn't really add much useful information. So two point fixes it is for me!
I see that Bowditch (2017), Section 1805, page 304 doesn't refer to a three point cocked hat at all...but rather recommends 5 or 6 LOPs to reduce random error in a fix. But there is zero chance that I am going to work out 6 LOPs for a celestial fix while I am on a small boat.
First, I am going to become horribly seasick while looking at columns of small numbers in tables trying to get six LOPs. And second, although I want to get a celestial fix, I also want to be on deck enjoying the sunrise. Man does not live by spherical trigonometry alone.