RichardS
N/A
OK but .... I would have said it was the other way around.
You can set your watch from GPS time very precisely but it might not be accurate. However, each time you set it, it will be equally inaccurate.
Richard
Use GPS time to set watch for astro navigation?
- Thread starter Prasutigus
- Start date
OK but .... I would have said it was the other way around.
You can set your watch from GPS time very precisely but it might not be accurate. However, each time you set it, it will be equally inaccurate.
Richard
JumbleDuck
Well-Known Member
Indeed, and as the NASA document to which I posted a link said, the GPS system itself sends difference from UTC to a precision of 90ns.
Lon nan Gruagach
Well-Known Member
OK but .... I would have said it was the other way around.
You can set your watch from GPS time very precisely but it might not be accurate. However, each time you set it, it will be equally inaccurate.
Richard
My bad. when I say a watch is fast, I dont mean how far ahead it is, I mean how much quicker it is at passing time.
So, I am fairly sure we have accurate and precise sorted, but fast (and I'm definitely not bringing driving into this thread) is where we diverge.
When governing a proper watch, one with a balance wheel. It is required to time the watch in 6 orientations: face up/down 12 o'clock up/down and 3 o'clock up/down Then the angular inertia of the balance wheel can be set. That is, of course, after it has been timed at different temperatures so the weights on the end of a bimetallic strip (which is part of the balance wheel) can be adjusted to allow for temperature compensation.
lpdsn
Well-Known Member
No impact at all for noon sights. When it comes to longitude however the sun will have moved over 4 minutes in 17 seconds, which could be up to 4 miles. Enough error to start with before you start adding the other errors from inaccuracies in the sights actually taken.
MM5AHO
Well-Known Member
I receive this and also the European ones most of the time (but not always). Just now, at 2125 I can hear the VVW one on 2.5MHz, (just, but enough); the 5MHz one is good (S9), but the higher frequencies are inaudible. During the day 15MHz perhaps best.
Uricanejack
Well-Known Member
I used to receive it all over the Atlantic and N Sea. Although I would often Use the BBC Near the UK.
My Radio was or is a small digital SONY ICF 7600 DS with a wire extension to add to the antenna. I suppose you could say I was a little bit of a radio nerd. Not a real amateur radio nerd, I don't do ham. I just used to like to keep in contact with the world when offshore.
I used to tune into the BBC WS Daily all over. And WWV. I even listened on Occasions' to Voice of America and Moscow neither of which compare to the BBC.
A lot of it is time of day and which frequency to try and tune in to. If there is a sunset or sunrise between you and the transmitter it can be difficult. Due to changes in the Ionosphere at sunset and sun rise. It tends to be stable during the Day and Night.
Lower frequencies tend to be better at night and higher frequency during the day.
I think WWV transmits on the 5 10 15 20 25 30 KHz. My 30 plus year old SONY kicked the bucket and I got a cheep Chinese Shortwave Radio for the boat.
I don't see good short wave radios around now. Even radio shack didn't have any.
Last edited:
anniebray
Well-Known Member
Hi Jerry.
It was good sharing Astro Nav with you at Marchwood YC. I missed the final exam because of Flu. Now on La Palma waiting for a clear night so I can get into Star finding, did not risk bringing my Sextant but do have the 2102-D device together with instructions by Starpath.
This is my first visit to La Palma which I find more attractive than Gran Canaria. I am near Tazacorte completely surrounded by Banana farms. Canaries not as warm as usual ,20 deg max so far but sunny. I'm not complaining !
Richard
It was good sharing Astro Nav with you at Marchwood YC. I missed the final exam because of Flu. Now on La Palma waiting for a clear night so I can get into Star finding, did not risk bringing my Sextant but do have the 2102-D device together with instructions by Starpath.
This is my first visit to La Palma which I find more attractive than Gran Canaria. I am near Tazacorte completely surrounded by Banana farms. Canaries not as warm as usual ,20 deg max so far but sunny. I'm not complaining !
Richard
maby
Well-Known Member
That Sony was a nice radio - I have one somewhere, but it has not been used in years and I guess the batteries have probably rotted and leaked by now - I must have a look for it!
Prasutigus
Well-Known Member
Hi Richard. Yes well passing the exam doesn't actually teach you anything, I'm still doing the same type of exercise as Jules was giving us for homework, and it's still needing intense concentration! I reduced my sextant errors down to practically zero with an hour of twiddling, which is encouraging.
Yes sextants are a bit nervewracking to risk them being flung about by Gatwick baggage monkeys..
All the best J
Last edited:
Normalfornorfolk
Well-Known Member
Confuscius he say, "Man with one clock always know time. Man with two clock never certain".
Skylark
Well-Known Member
Very true, which is why I added the rider "It could be argued that you need to carry 3 watches but that's another story".
Digital watches, in my experience, tend to be accurate, measured as no more than a few seconds drift per year. I've never known two to vary by more than a second or so over a month. As you friend Mr Confuscius points out, that doesn't tell you which one, if either, is correct. Certainly a lot more accurate than my Rolex
On a long passage, I'll still content myself to carry two digital watches as I think two are better than one.
LittleSister
Well-Known Member
Reminds me of the story told by Shane Acton, of being perplexed for ages why his sextant derived position kept jumping about. He eventually realised the minute hand on the cheap clock he was using was loose, and would fall behind on the 'uphill' journey between 30 and 60, then fall ahead between 0 and 30.
maxi77
Well-Known Member
In the Navy we used 3. The chronometer was the master and checked daily against the time signal. The 2 deck watches were checked against the corrected chronometer time. None were corrected to show the correct time rather the error was recorded daily so that the error drift could be checked and also allowed extrapolation when a time signal was missed not uncommon in a submarine.
Uricanejack
Well-Known Member
The Chronometer and the Chronometer rate book. An essential part of the traditional navigation equipment and procedure.
I don't have one on my boat. Just a nice Brass clock Quartz movement and battery. And the GPS. My Cell Phone, and a watch.
I have my dads Rolex chronometer date just. 1970 watch it still works and is still pretty good. haven't checked or kept a rate book. but its a couple of seconds a day. I don't wear it regularly which is a problem. I have tendency to break watches.
I rather liked my Seiko automatic. I went through a few of them.
I got my wife a Rolex she is still wearing 30 years later. Hers was never as good as my dads.
Over the years. I have had lots of quartz digital. I prefer a traditional analog display. They are very accurate beating the old chronometer. But The dam things irritate me. The batteries die. I have a drawer with several old dead quartz watches. Sometimes it is cheaper to by a watch than a new battery.
I have gone back to wearing an automatic watch.
So for the boats official time piece? what to use ?
My watch is to vulnerable, I will drop it, bash it into some thing, break the crystal or just loose it or the battery will run out.
Sound like the GPS is the most reliable.
I don't have one on my boat. Just a nice Brass clock Quartz movement and battery. And the GPS. My Cell Phone, and a watch.
I have my dads Rolex chronometer date just. 1970 watch it still works and is still pretty good. haven't checked or kept a rate book. but its a couple of seconds a day. I don't wear it regularly which is a problem. I have tendency to break watches.
I rather liked my Seiko automatic. I went through a few of them.
I got my wife a Rolex she is still wearing 30 years later. Hers was never as good as my dads.
Over the years. I have had lots of quartz digital. I prefer a traditional analog display. They are very accurate beating the old chronometer. But The dam things irritate me. The batteries die. I have a drawer with several old dead quartz watches. Sometimes it is cheaper to by a watch than a new battery.
I have gone back to wearing an automatic watch.
So for the boats official time piece? what to use ?
My watch is to vulnerable, I will drop it, bash it into some thing, break the crystal or just loose it or the battery will run out.
Sound like the GPS is the most reliable.
Prasutigus
Well-Known Member
I also like analogue watches to wear, but I'm going to keep a couple of digital watches in my sextant box, and maybe it's possible to attach a watch to the sextant itself.. that's done by the makers of some top-end sextants, but not my humble Freiberger.
