NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
GPS versus sextants ?
From: Peter Fogg
Date: 2002 Feb 5, 10:37 +1100
From: Peter Fogg
Date: 2002 Feb 5, 10:37 +1100
The fragility of GPS is that it is the last link of two chains, of which each link represents a complex piece of technology. One chain leads to the satellites being up there and, we trust, continuing to do their job perfectly. The other starts on board, with the availablity of clean fuel, then the motor and/or the solar panels, progresses through the alternator then the batteries via the fuses and the boat's electrical system. If any link of these chains fails then at best we are relying on batteries with finite lives. Yes sextants are fragile too, but they are a link in a chain that does not depend (once the almanac has been published! - although there are alternatives - extended almanacs are available) on complex technologies. But that's not the whole answer. Navigation is an art as well as a science. Its just our approach that is scientific. The Polynesians had their own approach, one that relied on taking a great interest in everything that was around them. Every sailor does this to some extent too, for example monitoring the direction of the swell and the wind as primary navigational guides, independant of all instruments. The Polynesians developed this approach to such a level that they could detect land over the horizon by the minute difference it would make to the swell, or the tinge of green reflected from a cloud, as just one small example. One of the many horror stories I have heard about GPS involved a 'Sports Cruiser' that went offshore and, hopefully, had a lovely time, zooming about. To go home they invoked the waypoint for their port and at 20 knots, running with flawless accuracy towards it, hit a reef. These are examples of a difference in attitude that has got nothing to do with one technology over another. > Dan- > Obviously I have some interest in celestial but when I hearon a boat in mid-ocean with only it and no backup?> that arguement against GPS holds no water. One can break a sextant quite easily, in fact I defy anyone to drop a sextant 4' to a hard deck and then use it again. Most GPSes can tolerate a similar drop, or at least a good fumble bouncing on one's feet. Most sextants can't. > If you have a sextant you need a backup, figure $500 for the first sextant and $125 for the cheap Davis backup. That's enough money for six GPSes or four GPSes plus two solar chargers, four sets of rechargeable batteries, and a gross or so or regular batteries as well. > > Sorry, but "the dog ate my navigational instrument" doesn't have any bearing on the choice of instrument, in fact it makes the GPS more "reliable" since you can carry 4-6 of them for the price of a minimal sextant with backup. As for the entire GPS constellation going down...if THAT happens the odds are that WW3 has broken out or aliens have arrived with an attitude. In either case navigation will be the least problem.