Chronometers

[CharlieDelta]

Bit of an odd question, but my celestial revision's got me thinking!

Any celestial calculations done on my last ship were done with GPS time corrected to UT. GPS time is, of course, meant to be very accurate.

College work suggests finding LIT, deducing ZN from that, applying to your ZT and hey presto you have UT. Then you take your chronometer time (now that you know what day and eh... half-day it's in), apply your chronometer error and get your super-accurate UT.

Now I may have been a little bit blind, but I'm pretty sure we didn't have a chronometer. So for the purposes of the nav workbook, I assume GPS time corrected to UT is ok?

What if your GPS fails?

[alistairuk]

You will have had a chronometer onboard - most likely it is at the back of your bridge and also controls all the other clocks onboard. If your on an old ship you probably have one in a little wooden box stuffed under a table somewhere.

But yes, your GPS time is correct and is what everyone uses... If your GPS fails then time is the least of your issues :-) Even with loss of satellite the clock in your GPS will remain accurate for a few days. But you can always use the pips broadcast on MF/HF every hour (can't remember the frequency) or worst case your watch!

[CharlieDelta]

Ahh, we did have a master clock in the chartroom which changed all the others, though how you'd find the error is anyone's guess.

So for nav workbook I'm ok with GPS time then?

Random other question (and I will try Googling it too!), but are there any decent books that explain "fixing in real life for dummies". I can get my head around sun/run/sun but any more than that and I'm a bit confused!!

[gadget123]

Random other question (and I will try Googling it too!), but are there any decent books that explain "fixing in real life for dummies". I can get my head around sun/run/sun but any more than that and I'm a bit confused!!

Have you tried nav basics?

[Delts28]

Just don't go by a pc's time. My laptop has drifted 40 seconds in the past two weeks. If it updates by internet then it will be fine, but I doubt most will. (GCNS halls blocks the port for updating, grrr).

[ETwhat?]

If you can plot a sun position line and move it forward to get a fix. your doing more advanced navy than getting a fix from 3 stars at one time. although obviously the timing is harder. i found doing sun and moon fixes was a good stepping stone as you don't have the same time pressure. tom cunlif does a celestial nav for yachts and that's pretty good although does skip over a few points

[YoungMariner]

If your sailing deep sea, you MUST MUST MUST ensure that you have an accurate timepiece onboard, whether your set your watch the GPS and ensure it remains accurate or whether you take the chronometer and complete the chronometer log regularly.
Losing GPS is not the end of the world; DR's, EP's and some Celestial Fixes will get you to your destination as long as you have an accurate gyro, an accurate sextant and an accurate timepiece and/or a record of errors and corrections for those items.
If you can't do Celestial Nav and feel confident as a navigator, what are you other than a button presser!

We have 4 equivilent 3rd Officers onboard at the moment, and all of whom are being tasked to conduct a voyage later this year purely on DR and Celestial Fixes, all three watches. Whilst the senior watch officers will monitor the track from the chart room. From knowing very little, these guys could fix their position to within 5 cables. It's not rocket science!