NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Averaging sights on commercial vessels
From: Trevor Kenchington
Date: 2004 Oct 7, 16:55 +0000
From: Trevor Kenchington
Date: 2004 Oct 7, 16:55 +0000
Alexandre, I don't have anything like Doug's depth of experience but I did start working offshore on government research ships, as part of the scientific party, before GPS appeared. (In 1987, we had what we we were told was the first civilian GPS unit in Australia -- $50,000 worth!) Never, in a total of perhaps 6 months at sea spread over 25 or 30 years, have I seen anyone take a sextant observation (though the captain of each ship has always had a sextant on hand). Outside of Decca or (later) LORAN-C range, we always used SatNav. I don't know whether that was more or less precise than celestial but it certainly was a whole lot easier and the unit maintained continuously-updated DR positions between satellite passes, which would have needed at least a pair of navigators committed to the task if the electronics hadn't done the work. (Research ships don't do a lot of steaming in straight lines, so maintaining a DR plot wouldn't be easy.) The one time that the SatNav failed, somewhere in the Tasman Sea, we set course to the northward and, after several hours at 10 knots, made landfall on Cape Howe by radar at 50 or 60 miles range. No need to break out a sextant for that trip. Decca and LORAN-C were, of course, far more precise than celestial. Omega (a low-frequency, global alternative to LORAN) was likely less precise, though more convenient. It never seemed to catch on, presumably because it was overtaken by SatNav. Trevor Kenchington You wrote: > Dear Doug, > Thank you for your explanation on how Cel nav is practiced > on modern merchant vessels. > I suppose they took it much more seriously in the pre-GPS era > that is 20 years ago. > A Russian manual (for merchant mates) of early 1970 recommended > 5 observations per day if conditions permit. > And averaging 3-5 altitudes for each observation. > > As I understand, before GPS, Cel Nav was the most precise > available method of determining position in the open sea, > superior to radionavigation. -- Trevor J. Kenchington PhD Gadus@iStar.ca Gadus Associates, Office(902) 889-9250 R.R.#1, Musquodoboit Harbour, Fax (902) 889-9251 Nova Scotia B0J 2L0, CANADA Home (902) 889-3555 Science Serving the Fisheries http://home.istar.ca/~gadus