A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Mark Coady
Date: 2017 May 25, 10:27 -0700
One thing that has appeared to me after considering my overabundent worry over goofy things happening with observations and refraction.
Most of the things I saw that might muck things up a bit on sights...well....somehow looked like they might muck things up.
One of the duties of the navigator is to assess the quality of his inputs before making decisons regarding his potential errors in positon, or using the information to update his place on the chart.
I scanned many photos and also recall various real personal observation situations where I saw peculiarities. In each case I would say there were clues. Indistinct haze, heat lines, broken edges, poor horizon resolution,weather conditions, etc.....
If it looks clean and crisp like a perfect late september day....its probobly ok.....if it looks odd...maybe it is odd.. (not that I claim expertise on every oddball thing, no sir)
In thinking big picture...If someone gives me my dream boat and I sail off into the sunset with my sextant, I would note on my sights any issues noted that might impact the quality of each. Anything from horizon quality to I couldn't hold the thing steady because I was getting beaten about.
The whole idea is I can weight my inputs based on their percieved reliability. If my trail of sights has a flyer in it, and it happens to be the one with crappy observation conditons noted, I can sleep easier when I toss it in favor of the bracketing pair that were noted as good or better.
I realized that when I do celestial for my own skill set and knowledge, I tend to focus on one or two sights in an afternoon and expect every sight to be just wonderfully accurate and a proof of concept.
If I am navigating for real world positioning, it's a little different....just like dead reckoning in poor vis..I am taking an observation or sight in a continuous chain of updating navigational information, with the understanding I'm working often in less than ideal conditions, and have to value weight each input based on a judgement of quality. The more inputs, the better I log the quality estimate on the inputs, the more likely I am to have a quality result.
Doing local stuff in my little dive/fish boat, I constantly crosscheck my visual observations agianst radar to paper chart to GPS map to sounder constantly. If all five inputs sync....good.....if my mental pentagulation (or whatever it is..LOLOL) goes funky...pull stick back and figgure out whats going amuck. So far so good, the bottom is dent free, even skirting some really tight dive spots or rescuing lobster traps in the rocks.
I find that for example that distance perception at night is often poor, so that radar vs paper chart vs GPS map provide a strong check for this problem. Notice I said paper chart. No one will ever take away my hardcopy. I don't leave home without it.
"The greatest hazard I face in navigation is me"