I find what erps posted a little more convincing. The point I was making previously centers around reliability. The only item subject to failure, in celestial navigation, is the chronometer, and if it is a wound chronometer, that is extremely unlikely. Damage to the sextant is either repairable (mirrors) or correctable at sea. To be of any use, one must periodically check their sextant's accuracy and this is done at sea. A sextant that has taken a fall can be checked and compensated for. Precision instuments, such as sextants and chronometers are not judged on their perfection of measurement, but their consistency. A chronometer that gains a second a day is just fine. One that is erratic is junk. A sextant with fifty-five seconds of error is fine; we apply it to our sight reduction. We even have a correction for user error! Some navigators will be "off" by a number of seconds than another using the same instrument! We tabulate this through consistent practise, shooting from known positions, and comparing with other mates.
The rest of the "system" is most reliable due to it's lack of dependence on human factors.
GPS is subject to human and mechanical error. Multiple units on board reduce, if not eliminate, receiver error. That is, if you are taking fixes with both units at the same time. If you are not, how will you know there is an error, your unit doesn't tell you it's on the fritz. So you really need three units, just to verify one unit! Geostationary satellites aren't. At 28,500 miles they are 1/10th the distance of the moon, the least accurate celestial body. Small errors in a satellites position will result in inaccuracy of a large sort-we rely on humans to monitor this. Your receiver does not tell you if they are.
GPS relies on
radio waves, which are much more subject to interference than are light rays. We've already discussed the political errors posible in
GPS, ie...the Feds pull the plug. I'm not saying that any of these things are even likely, but they are possible sources of error or lack of position finding. CN is inherently error free and so it is more reliable.
There are some misconceptions on the practise of celestial navigation. One of the biggest is the need for more than two bodies at am/pm stars. Two are all that are needed for an experienced navigator, preferably close to 90 degrees apart. In poor conditions, we pre-calculate our altitude and azimuth, and instead of a slow, exact shot; we take a snap-shot. Actually, experienced navigators take a snap-shot even in good conditions because they are experienced. It does take practise, in stable conditions, to get good at this. But we learn to drive a car in the day and in the dry before we try the snow too.
When one's electronics fail, for whatever reason, you're lost and if CN is an art-form try dead-reckoning for days on a sailboat. With a sextant alone, no chronometer, you can parallel sail, as did Columbus and the ocean navigators prior to accurate time keeping. The knowledge of latitude alone is a huge benefit to the ocean navigator. With merely an ocean chart, he can determine whether he'll make land at Bishop Rock or Gibralter. The navigator with broken electronics has only the snow on deck to tell him he's closer to Bishop Rock than the Gib!
Now as to your ascertation that anyone going to sea without
GPS is unsafe. This is just not true.
Radar is a far more useful electronic device than
GPS. Offshore, I am happy if I know within a couple of miles of where I am at. And, if I can't get a fix for a couple of days that's OK too. Traditionally, the only fix logged was the noon fix, a running fix of the sun and perhaps Venus. All of the trouble is when I get near land and
radar is far superior to any other form of navigation, other than gyro-stabilized bearings, in that instance.
In my twenty years at sea, it was not at all uncommon to encounter yachts with far more sophisticated navigational equipment than what was on the bridge of my ship. The difference was, that when the electronics went on the fritz, we sailed on in confidence of finding our destination.
Celestial navigation is an art, and while frustrating to some, it is not an archaic art. As navigators, professional and amateur alike, we must always evaluate our position based on the best information available. And, if little is available, we must go back to the fundamental "this I know to be true" and pilot our vessel accordingly. The sea demands it.
I would be remiss if I did not state that I have the utmost regard for Camaraderie and his posts. I make a point of reading them whether they are on a topic of interest or not. I am also sure that he is a consciencious and good navigator. But others read our posts, and I feel that our differences, while perhaps philosophical, could lead others into a false sense of security and not exercise the due diligence that Camaraderie has.
Best regards,
Guy
Note to self: Learn to ride a horse, but don't nned to buy one 
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