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Old 09-12-2008, 17:49   #1
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How are you keeping time for celestial nav?

Many years ago, (1953 or so) my dad took a powersquadron course in celestial. He used a wind up wrist chronometer, which was passed down to me. However its not in great shape, so I'm thinking of getting something else.

So what is everyone using to keep track of time these days

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Old 09-12-2008, 17:59   #2
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A good wristwatch. Or use the clock on your GPS
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Old 09-12-2008, 18:08   #3
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A $9.99 quartz watch keeps better time than the $1000 chronometers of old.
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Old 09-12-2008, 18:30   #4
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A $59.95 (USD) Timex quartz sailing timer/watch, cross checked daily (when underway) against WWV time signals on our SSB. Thus far--since setting the watch on Christmas day, 2006--I've not had to correct it, tho' I understand the batteries are only good for 3 years!

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Old 10-12-2008, 18:52   #5
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A $2,390 DOXA dive watch that is checked with my cell and radio everyday, it's really expensive but I think it is worth it to have a watch that will survive WWIII and is never wrong.
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Old 10-12-2008, 18:55   #6
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The watch might survive WW3 but will you?
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Old 10-12-2008, 19:03   #7
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I don't know but if I don't people in the future willknow what a watch was. =)
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Old 10-12-2008, 19:42   #8
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Old 10-12-2008, 19:46   #9
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I used a cheap Casio digital watch set to WWV when I learned. GPS did not exist back then. I would set the watch to GPS time now.
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Old 10-12-2008, 20:09   #10
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Any watch will do. The important thing is that the error rate be kept track of(checking WWV).
In the Navy, we used 3 outrageously expensive chronometers whose error rate was logged daily by comparison to WWV. I thought it was odd that we used these chronometers when my $10 Casio kept better time. The reason was reliability, particularly in the event of electromagnetic interference (nuclear explosion I supposed) they'd still be ticking if we weren't so close to otherwise survive.

By the way, I think it's great you're using celestial. Electronics fail - period. They're great for convenience, but they can't be wholly trusted.
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Old 10-12-2008, 20:25   #11
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At the maritime academy on the training ship we also had three very expensive chronometers. You nailed the reason why...complete self-reliance and a backup for a backup. If all else failed we still had these chronometers to determine longitude. We also kept a log of their error and error changes. We weren't though concerned about nuclear detonations.
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Old 10-12-2008, 22:29   #12
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i understand the time on a handheld gps is updated pretty regularly by the atomic clocks onboard the satellites its tracking , of course thats only as reliable as its batteries/power supply.
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Old 11-12-2008, 05:12   #13
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i understand the time on a handheld gps is updated pretty regularly by the atomic clocks onboard the satellites its tracking...
The GPS system's master clock is always kept within 1 microsecond of the U.S. Naval Observatory's Master Clock. Each GPS satellite has four atomic clocks on board, which are so accurate that they are almost always within 250 nanoseconds.

Unfortunately, not all GPS receivers are designed to be used as time sources. Some will create time glitches when they change which satellites they are using. Some are unable to keep a time lock with fewer then three satellites in view. Some consider their serial output a 'low priority' task and can delay time code outputs by randomly varying amounts if they are busy computing.
If you are serious about accurate time, it is important to use a GPS unit designed for this purpose.

Considering the other variables inherent in celestial nav' aboard a small boat, your digital Timex should more than suffice for a time tic.
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Old 11-12-2008, 05:55   #14
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The GPS system's master clock is always kept within 1 microsecond of the U.S. Naval Observatory's Master Clock. Each GPS satellite has four atomic clocks on board, which are so accurate that they are almost always within 250 nanoseconds.
Global Positioning System time, is the atomic time scale implemented by the atomic clocks in the GPS ground control stations and the GPS satellites themselves. GPS time was zero at 0h 6-Jan-1980 and since it is not perturbed by leap seconds GPS is now ahead of UTC by many seconds. GPS time must never be used for celestial navigation.

When doing celestial navigation I record the time for each sight with a cheap digital watch. When I am ready to reduce the sights I tune in WWV and determine the correction for the watch. This correction is applied to the times for each of the sights. This eliminates the possiblity of setting the watch to the wrong time and wondering way your position just doesn't seem to be right.

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Old 11-12-2008, 06:02   #15
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GPS Time

You should be aware that GPS time is ahead of UTC time by 14 seconds. This is because the satellites are not updated with leap seconds.

GPS, UTC, and TAI Clocks
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