(07-17-2018, 04:23 PM)Rumata Wrote: Joe, thank you. Yes, this small problem is a little bit tricky. If you would use all the shots , then you would get kind of ambiguous fix. And I'm wondering: if I wouldn't know the right answer, I would definitely stay with my first fix. Sure, I did everything as I supposed to do. My point is: if one makes a few shots within a very short interval, does he need to make an average LOPs or what the criterion? The difference in results maybe 10-12 miles. And if he does not have any other means to verify his fix. But , I'm just wondering. Again, thanks for working that problem in a right way
If you notice, Rumata, at the left-lower side of the last plot sheet, I made a note of how far the boat traveled in the 8 minutes of time between the sun and moon shot - she traveled less than a mile. Even at this scale one mile is not a big deal. Pencil error can be greater than that.
I can only answer your question by saying that with time you will develop a sighting technique that you will learn to ALMOST trust. I have developed my own proforma sheet that I trust about 90%. I like to use it but I still make mistakes.... as you just witnessed. I also use to assign a reliability factor or confidence factor to my observations so that if the weather is up I know that my shots are not that good and I shouldnt rely heavily on them. Have you read the story about the Edmund Fitzgerald? They had radar and RDF and visuals of a lighthouse and still hit bottom. She sank with all crew lost.
On a big ship in uneasy weather you might see 4 or 5 seamen taking observations all at the same time, then they average their readings to increase the reliability of the data. It would be easy to see which observation was really out of line with the others and throw that one out. Taking 3 observations at one minute intervals and averaging them out would be a good way to increase the reliability of your data; much like the technique used to find local noon. I didnt even think to average your sun and moon shots - I was more interested in reducing all the shots individually to check my proforma. I may go back to your data for another try... :)
There is a reason why Loran then GPS now dominate the navigation problem - they are more precise and reliable than sextants. If they did not have precision we wouldnt use them. At sea using a sextant can be fun, but I wouldnt use one to find my slip at the docks. You dont need a sextant for coastal navigation.
Have fun
joe