NavList:

David McN, you wrote:
"Yes, I have GPS but I assume it will fail soon enough so I go prepared."

I feel there are enough good reasons to do some basic celestial even without "emergency preparedness" but let's go with that line of thinking for a minute... :)

There's a whole spectrum of ways in which (your) GPS might fail. From less problematic to more, on the GPS "user side":

• Your primary nav system (generally referred to as "the GPS") has a software fault and can no longer display your position on charts
• Your primary nav system won't boot up, is "bricked", dead, etc. but you still have full power for other electronics and handheld electronics
• GPS nav system is dead, but you have minimal power and handheld electronics are available for brief periods
• All on-board electronics are dead except a backup in a Faraday cage of some sort
• All electronic devices including backups and handhelds are fried

A related spectrum:

• Electronics including nav system are working properly, but the GPS position makes no sense (spoofing?)
• Electronics are fine but natural EM phenomena have overwhelmed the GPS and other GNSS signals
• Your electronics are fine, but the (US) GPS system has been hacked and is down for a day
• Your electronics are acting strangely and all GNSS (GPS etc) satellite constellations are offline.
  (Maybe Russia invading Ukraine and China invading Taiwan simultaneously? Maybe next week or next month??)
• GNSS satellites are down... Radio comm is dead... Light ash has been falling all day around you. Ash deposits on deck glow at night.

On the "user side" spectrum, at the low end, I would apply my standard advice: the best backup for a GPS is another GPS. Bring a cheap handheld GPS unit, and keep it somewhere safe and dry. Certainly paper charts or at least a short list of latitudes and longitudes of key points should be available on paper so you can get to safety if your main electronic charts are unavailable. Let's also hope you have a smartphone with excellent GPS/GNSS capability stored safely in a (sealed, waterproof) Faraday cage.

If all electronics are down and even your backups have been fried, then you're in a position where you might be forced to rely on celetial primarily. As Geoffrey Kolbe has pointed out, you may want more than one timepiece. You may also want to assume that radio time checks will be unavailable since the sort of EM insult that could kill your electronic navigation systems would probably knock out a modern radio, too. The "chronometer" has been the weak link, the mysterious "high tech", more delicate than a smartphone, since the earliest days of modern navigation almost 250 years ago.

If we're further down the spectrum (now the second list), and there is an active assault on the US GPS system or maybe just a colossal case of human error, it's possible that GPS could go offline. In that case, can your nav system work with other GNSS constellations? Most modern smartphones can access several without any effort on the end-user's part. If there's a geomagnetic storm that overwhelms GPS signals for two days, you might turn to celestial. Then again it could just as easily be cloudy for 48 hours. Your best backup in either case is practiced skill with dead reckoning... and patience.

At any point on this spectrum of calamity, you would surely benefit from a cheap "scientific" calculator. There are many models that are solar-powered and durable even in difficult conditions. For my celestial navigation classes I recommend the CASIO fx-260 solar calculator (apparently sold only in the US) which can survive after being dunked in saltwater (and yes, I've tested this!). A calculator can save you lots of paperwork. You could live without sight reduction tables and traverse tables etc. At minimum you would have an alternative in case you discover that your carefully stowed tables are missing a page, for example.

Finally, at the extreme catastrophe end of the spectrum, if global thermonuclear war has broken out, you may have other things to worry about. Celestial navigation might have one final role here. Carry a short list of latitudes and longitudes for small, quiet islands far from the rest of civilization... Someplace nice to watch the world end. :)

Frank Reed