NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Francis Upchurch
Date: 2015 Jul 16, 22:21 -0700
The original 1714 longitude prize set the target as 30' arc (or 2 minutes time) after 3 months trip to Jamaica.
Ironically, I doubt whether H4 would have saved Sir Cloudsley Shovel and HMS Association.
Thick fog around the Scillies would probably have prevented sun sights (with backstaff accurate to say 5-10'?) and their charts were miles out anyway!
The Brown-Nassau accuracy 5-10' was thought good enough for US Naval flying in 1944.
I still think in a bouncing boat in a seaway, the sextant readings may be the biggest source of error.
How accurate is a bubble sextant in a pitching,rolling and yawing plane ?
If I was close to Scillies and the fog descended (has happened to me), I would want GPS+chart plotter to a few meters to avoid the rocks, then I would still be scared stiff! Back in the 80's with no Decca, just RDF, we just turned round and headed out to sea to wait for the fog to lift. 30 miles is fine out in the deep blue water yonder, the biggest danger probably being run down by a ship who doesn't see you on his radar!
The joys of sailing!
Best wishes
Francis
