No, I learned cel-nav but never actually used it, so I lost the skill and am in process of relearning. Now though I have some rather nice software to crunch the numbers. Lots of different programs available.

We used it every 4 hrs when in the Carribbean Sea along with 1 Loran-C line (33,000's) broadcast from Raymondville, Tx.

CelNav is definitely a use it or lose it type of skill. I laid my last celnav fix in 1999.

It's definitely a perishable skill, but as long as the basic principles don't change (math & celestial geometry), it's always a good fall-back. In this day of possible EMP events, the US Naval Academy reintroduced celestial navigation after having eliminated it from the curriculum in the 90's iirc.

I use a (plastic) Davis Instruments Mark 3 Sextant in the backyard to shoot sun and moon using a small dish of water to function as an artificial horizon. It's good practice.

That's a good practice! Don't neglect the problem solving steps. That's what I've forgotten.

Crunching the numbers has always been the hard part. Taking a sighting is relatively straightforward if you have a horizon. Apps available can pull the almanac data and crunch numbers. There are way too many ways to screw that up without constant practice. I've got apps or .exe's on a number of devices -- iOS, Android and PC. They all work, the math is very mature.

I'm learning CelNav too (a bit stalled at the moment, but need to get back into it).

I don't see the utility of using apps. Seems to me that the point of CelNav these days is as a backup when everything goes to hell. Meaning that your device with the app on it will be a paperweight. GPS will be gone. Atomic clocks will be gone. So you need to me able to do the math manually. And you need a long term almanac to look up the data.

Sure, have an app to crunch the numbers while the app's host device still works, but know how to do the math manually for when the device fails. But if you're going to be depending on an app, why not just depend on GPS in the first place and forget about learning CelNav altogether? GPS is more accurate, much quicker, and far easier than CelNav.

The one thing I haven't figured out, is how to you have a long term accurate watch/timepiece that doesn't depend on outside technology and batteries? How do you verify it's accuracy and reset the time when appropriate? If you know your precise location you could use that to reset the time on your watch by working the numbers backwards. But if you don't know where you are to a precise degree, and you don't have a trustworthy time reference ... that's where I'm lost in what to do.

You would have to invest in a certified chronometer that is either an automatic or manual wind. Those type of watches are COSC-certified (COSC is Contrôle Officiel Suisse des Chronomètres, the Official Swiss Chronometer Testing Institute). There are many brands that send a few of their models through the testing.

My $.02.

Yeah, while small type errors are significant to GPS, how much time error is significant to cel-nav?

As I understand navigating port-to-port, 5 minutes (of arc) accuracy is acceptable. What would that translate to in time? For those who haven't seen it: Longitude (the movie)

I've been reading about Lewis and Clark and then about John C. Fremont and recall something like they reset their watches using something obscure like - observing when the moons of Saturn or Jupiter (not sure which) disappeared around the planet. THAT time would not be subject to uncertainty in your own position (much).

Kind of astonishing what they accomplished with what little they had.

My celestial nav class in NROTC was reducing some given sightings as we were far inland and the instructors said we couldn't get a proper horizon to learn the sextant (that or they just figured it wasn't worth the trouble)

Once in the fleet, we had to confirm the sextant was still onboard - annually. (submarines)

note: we are now doing sextant training onboard.