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09-09-2024, 03:49
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#1
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Moderator
Join Date: Mar 2009
Location: Denmark (Winter), Cruising North Sea and Baltic (Summer)
Boat: Cutter-Rigged Moody 54
Posts: 34,842
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Time Precision Needed for Celestial
My best sailing friend studied astrophysics as an underground and is a master of celestial nav. I'm hoping to not be too busy the next time we cross an ocean together to take his classes.
I think with the widespread jamming and disruption of GPS we are seeing these days, these skills are more relevant than they were before. I note that the US Navy has re-introduced celestial nav.
Meanwhile I was thinking about how to solve the time problem in a robust way, so that you can do celestial even after a bad lightning strike etc. which wipes out your electronics.
I was discouraged to find out that mechanical chronometers are exorbitantly expensive to service and adjust.
So I'm looking at quartz marine chronometers, like the Seiko QM-10 and QM-11, which is not that expensive and readily available.
It has electronics so would be vulnerable to EMP but maybe could simply be kept in a metal box.
The accuracy looks like 60 seconds a year, but I don't know how crystal aging affects that -- these are decades old by now.
I also don't know if that's accurate enough -- 5 seconds a month?
There are HAQ watches available which are accurate to 10 seconds a year or even 5 seconds a year, which I guess could likewise be kept in a metal box.
Or maybe it's not all that important if you reset it to GPS time once a week.
With that process, maybe even a mechanical one would be OK.
Views?
__________________
"You sea! I resign myself to you also . . . . I guess what you mean,
I behold from the beach your crooked inviting fingers,
I believe you refuse to go back without feeling of me;
We must have a turn together . . . . I undress . . . . hurry me out of sight of the land,
Cushion me soft . . . . rock me in billowy drowse,
Dash me with amorous wet . . . . I can repay you."
Walt Whitman
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09-09-2024, 04:13
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#2
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Senior Cruiser
Join Date: Mar 2003
Location: Thunder Bay, Ontario - 48-29N x 89-20W
Boat: (Cruiser Living On Dirt)
Posts: 50,790
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Re: Time Precision Needed for Celestial
Quote:
Originally Posted by Dockhead
...
I think with the widespread jamming and disruption of GPS we are seeing these days, these skills are more relevant than they were before. I note that the US Navy has re-introduced celestial nav. ...
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“Global navigation jamming will only get worse. The U.S. needs to move fast” ~ by Sean Gorman
➥ https://spacenews.com/global-navigat...eds-move-fast/
Quote:
“Jamming and spoofing attacks on GPS, and other global navigation satellite systems [GNSS], are becoming increasingly common, as geopolitical crises escalate, creating major challenges and risks for aviation, shipping, and other critical services, across the world.
Data, from GPSJam.org*, has confirmed widespread GPS/GNSS interference, across parts of Europe, and beyond, as an outcome of the war in Ukraine.
Regions affected range from Finland and the Baltics, to Poland, Romania and Bulgaria; in addition to the Black Sea, the Caucasus, and Turkey.
The Middle East is also being affected by interference, stemming from Israel and Iran’s hostile activities, in the region.
Other interference efforts, albeit at a lower scale, are also regularly occurring in areas of Pakistan, India, and Myanmar...”
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* GPSJAM: Daily maps of GPS interference ➥ https://gpsjam.org/
FAQ ➥ https://gpsjam.org/faq
__________________
Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"
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09-09-2024, 04:17
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#3
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Registered User
Join Date: May 2013
Location: Portland, ME
Boat: McCurdy & Rhodes 56
Posts: 240
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Re: Time Precision Needed for Celestial
Any quartz device will do (Casio), and digital more accurate than analog.
Earth rotates at 465.1 m/s at the equator or about 1/4 nm/sec.
Pre-gps we set the time by the time signal at WWV https://www.nist.gov/pml/time-and-fr...io-station-wwv
In case of the zombie apocalypse, Citizen has an HAQ solar version so you don't have to worry about a battery.
Your cocked hat size will most likely be driven by sea-state.
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09-09-2024, 04:30
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#4
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Senior Cruiser
Join Date: Mar 2003
Location: Thunder Bay, Ontario - 48-29N x 89-20W
Boat: (Cruiser Living On Dirt)
Posts: 50,790
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Re: Time Precision Needed for Celestial
The future of Global Navigation Satellite Systems [GNSS] may lie in a combined use of GPS and Galileo [and, perhaps, GLONASS, & Beidou]. A multi-mode system, with a second or [3RD or 4TH] constellation, effectively eliminates any common modes of failure, with GPS, improving dependability by a factor of 1,000, or more.
__________________
Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"
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09-09-2024, 06:02
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#5
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Moderator
Join Date: May 2012
Location: At sea somewhere in the Caribbean
Boat: Jeanneau Sun Fast 40.3
Posts: 6,505
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Re: Time Precision Needed for Celestial
Quote:
Originally Posted by Dockhead
My best sailing friend studied astrophysics as an underground and is a master of celestial nav. I'm hoping to not be too busy the next time we cross an ocean together to take his classes.
I think with the widespread jamming and disruption of GPS we are seeing these days, these skills are more relevant than they were before. I note that the US Navy has re-introduced celestial nav.
Meanwhile I was thinking about how to solve the time problem in a robust way, so that you can do celestial even after a bad lightning strike etc. which wipes out your electronics.
I was discouraged to find out that mechanical chronometers are exorbitantly expensive to service and adjust.
So I'm looking at quartz marine chronometers, like the Seiko QM-10 and QM-11, which is not that expensive and readily available.
It has electronics so would be vulnerable to EMP but maybe could simply be kept in a metal box.
The accuracy looks like 60 seconds a year, but I don't know how crystal aging affects that -- these are decades old by now.
I also don't know if that's accurate enough -- 5 seconds a month?
There are HAQ watches available which are accurate to 10 seconds a year or even 5 seconds a year, which I guess could likewise be kept in a metal box.
Or maybe it's not all that important if you reset it to GPS time once a week.
With that process, maybe even a mechanical one would be OK.
Views?
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Dockhead - if I recall correctly, you have an old US Destroyer clock (such as the one I have) hanging in
your salon. I would suggest if it was good enough for them during WWII to find their position, then its accuracy is probably also good enough for you. Just make sure it is serviced and adjusted regularly
__________________
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Our books have gotten 5 star reviews on Amazon. Several readers have written "I never thought I would go on a circumnavigation, but when I read these books, I was right there in the cockpit with Vinni and Carsten"
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09-09-2024, 06:18
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#6
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always in motion is the future
Join Date: Feb 2009
Location: in paradise
Boat: Sundeer 64
Posts: 19,570
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Re: Time Precision Needed for Celestial
Quote:
Originally Posted by GordMay
The future of Global Navigation Satellite Systems [GNSS] may lie in a combined use of GPS and Galileo [and, perhaps, GLONASS, & Beidou]. A multi-mode system, with a second or [3RD or 4TH] constellation, effectively eliminates any common modes of failure, with GPS, improving dependability by a factor of 1,000, or more.
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We use GPS + GLONASS simultaneously at all times and some sensors can use Galileo as a third constellation but I’m not even sure of it’s status anymore.
But for electronic warfare I think they are all taken out in one flip of the switch
__________________
“It’s a trap!” - Admiral Ackbar.
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09-09-2024, 06:24
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#7
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Moderator
Join Date: Mar 2009
Location: Denmark (Winter), Cruising North Sea and Baltic (Summer)
Boat: Cutter-Rigged Moody 54
Posts: 34,842
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Re: Time Precision Needed for Celestial
Quote:
Originally Posted by carstenb
Dockhead - if I recall correctly, you have an old US Destroyer clock (such as the one I have) hanging in
your salon. I would suggest if it was good enough for them during WWII to find their position, then its accuracy is probably also good enough for you. Just make sure it is serviced and adjusted regularly
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You remember correctly, and it's still there, but that is a deck clock, not a chronometer, so very far I think from accurate enough.
__________________
"You sea! I resign myself to you also . . . . I guess what you mean,
I behold from the beach your crooked inviting fingers,
I believe you refuse to go back without feeling of me;
We must have a turn together . . . . I undress . . . . hurry me out of sight of the land,
Cushion me soft . . . . rock me in billowy drowse,
Dash me with amorous wet . . . . I can repay you."
Walt Whitman
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09-09-2024, 06:25
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#8
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Moderator Emeritus
Join Date: Oct 2009
Location: Manchester, UK
Boat: Beneteau 473
Posts: 5,617
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Re: Time Precision Needed for Celestial
Back in the day, we kept a chronometer rate book.
Each day, the chronomter would be checked against a radio time signal, the error recorded in the book.
It was called a rate book as the advantage of the chronometer is that despite having an error, the error increased at a set rate.
If unable to get a time signal, the error could be estimate by extrapolating from the historical daily errors.
__________________
Nigel
Beneteau 473
Manchester, UK
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09-09-2024, 06:25
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#9
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Moderator
Join Date: Mar 2009
Location: Denmark (Winter), Cruising North Sea and Baltic (Summer)
Boat: Cutter-Rigged Moody 54
Posts: 34,842
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Re: Time Precision Needed for Celestial
Quote:
Originally Posted by s/v Jedi
We use GPS + GLONASS simultaneously at all times and some sensors can use Galileo as a third constellation but I’m not even sure of it’s status anymore.
But for electronic warfare I think they are all taken out in one flip of the switch
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All modern GNSS systems will use multiple constellations -- GPS, Glonass, Galileo, and now Beidu.
But so do military receivers so yes, they will all be taken out at once.
__________________
"You sea! I resign myself to you also . . . . I guess what you mean,
I behold from the beach your crooked inviting fingers,
I believe you refuse to go back without feeling of me;
We must have a turn together . . . . I undress . . . . hurry me out of sight of the land,
Cushion me soft . . . . rock me in billowy drowse,
Dash me with amorous wet . . . . I can repay you."
Walt Whitman
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09-09-2024, 06:27
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#10
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Moderator
Join Date: Mar 2009
Location: Denmark (Winter), Cruising North Sea and Baltic (Summer)
Boat: Cutter-Rigged Moody 54
Posts: 34,842
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Re: Time Precision Needed for Celestial
Quote:
Originally Posted by nigel1
Back in the day, we kept a chronometer rate book.
Each day, the chronomter would be checked against a radio time signal, the error recorded in the book.
It was called a rate book as the advantage of the chronometer is that despite having an error, the error increased at a set rate.
If unable to get a time signal, the error could be estimate by extrapolating from the historical daily errors.
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That makes a lot of sense, but that's also a lot of workload. Did you try to keep the chronometer accurate to the second? Did you check it every day?
__________________
"You sea! I resign myself to you also . . . . I guess what you mean,
I behold from the beach your crooked inviting fingers,
I believe you refuse to go back without feeling of me;
We must have a turn together . . . . I undress . . . . hurry me out of sight of the land,
Cushion me soft . . . . rock me in billowy drowse,
Dash me with amorous wet . . . . I can repay you."
Walt Whitman
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09-09-2024, 06:30
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#11
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Moderator and Certifiable Refitter
Join Date: Jan 2008
Location: South of 43 S, Australia
Boat: C.L.O.D.
Posts: 21,236
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Re: Time Precision Needed for Celestial
Quote:
Originally Posted by Dockhead
Views?
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Absolute accuracy is not so critical, what is more important is the variation of rate. A time piece that has constant rate of change is preferable to one that has a variable rate of change.
You don't need a marine chronometer, you only need a time piece that has an almost constant rate of change.
Presumably you only wish to navigate celestially for the remainder of the duration of the voyage after the electronic stuff has been fried (say a few weeks to a month or so).
You may already have a suitable time piece if you wear a wristwatch. If so, try rating it against GPS time. Do this every day for say a fortnight or month and then every month. If the rate of change is reasonably constant, then you are good to go.
Log the date that the watch was set to GPS time and if you know the average daily rate of change, then you have a very good estimate (within a one or two seconds) of the real time when the electronics were fired.
A reasonable quality quartz watch permanently mounted below decks probably rates very well; run your own test. Buy two, keep one visible and one in a tin box. Rate both, go sailing.
Use a stopwatch to time the interval between shooting the sight and going below to view the time piece and apply the known rate to the time piece to get the real time of the sight.
Of course a marine chronometer is nice if dollars aren't an issue but getting real time is not expensive if you are happy rate the time piece and reset it weekly or monthly.
__________________
All men dream: but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find it was vanity: but the dreamers of the day are dangereous men, for they may act their dreams with open eyes, to make it possible. T.E. Lawrence
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09-09-2024, 06:38
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#12
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Moderator and Certifiable Refitter
Join Date: Jan 2008
Location: South of 43 S, Australia
Boat: C.L.O.D.
Posts: 21,236
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Re: Time Precision Needed for Celestial
Quote:
Originally Posted by nigel1
Back in the day, we kept a chronometer rate book.
Each day, the chronomter would be checked against a radio time signal, the error recorded in the book.
It was called a rate book as the advantage of the chronometer is that despite having an error, the error increased at a set rate.
If unable to get a time signal, the error could be estimate by extrapolating from the historical daily errors.
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This ^^
Once the rate is established, you can confidently use the time for months by extrapolating. Historically (before radio time signals) the Chronometer was only reset in port.
__________________
All men dream: but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find it was vanity: but the dreamers of the day are dangereous men, for they may act their dreams with open eyes, to make it possible. T.E. Lawrence
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09-09-2024, 06:42
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#13
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Moderator Emeritus
Join Date: Oct 2009
Location: Manchester, UK
Boat: Beneteau 473
Posts: 5,617
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Re: Time Precision Needed for Celestial
Quote:
Originally Posted by Dockhead
That makes a lot of sense, but that's also a lot of workload. Did you try to keep the chronometer accurate to the second? Did you check it every day?
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So these were the old mechanical type chronomters, the ones which cost an arm and leg nowadays.
No, the chronomter was not adjusted, it was just left to run.
Ot was the third mates job to wind the chronomter daily, at the same time, and with a set number of turns on the key.
If he forgot, and the clock stopped, it was normally a hanging offence.
__________________
Nigel
Beneteau 473
Manchester, UK
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09-09-2024, 07:07
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#14
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always in motion is the future
Join Date: Feb 2009
Location: in paradise
Boat: Sundeer 64
Posts: 19,570
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Re: Time Precision Needed for Celestial
Quote:
Originally Posted by Dockhead
All modern GNSS systems will use multiple constellations -- GPS, Glonass, Galileo, and now Beidu.
But so do military receivers so yes, they will all be taken out at once.
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The Garmin GPS19x that I got was by default configured for GPS only. It required being configured from a Garmin plotter to enable GLONASS and that is all it can do.
I believe my B&G Vulcan was also configured for GPS only.
Maybe most GNSS sensors in use by cruisers only use GPS because that is the default configuration. I also only know of a few that can do three constellations and only if those are GPS + GLONASS + a third.
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“It’s a trap!” - Admiral Ackbar.
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09-09-2024, 07:45
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#15
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Moderator
Join Date: Jan 2010
Location: Minnesota
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Re: Time Precision Needed for Celestial
The usual recommendation on navlist and elsewhere is to use inexpensive digital watches. The Casio F91W-1 is usually recommended for this purpose because it has been produced in enormous numbers, has a long battery life, and is available inexpensively anywhere:
https://www.amazon.com/gp/product/B000GAWSDG
If EMP or lightning is a concern people put them in a tightly lidded aluminum box.
Typically The F91W-1 is accurate within several seconds a week, which can be further improved by rating. Recommendations vary. One approach is to buy three watches, mark them so they can be identified, rate them by recording the time delta vs. an accurate source over a period of time, and then use the rating to determine an accurate time aboard. Using three watches makes it possible to identify a watch whose rate has changed for whatever reason and stop using it.
Other authorities (including Starpath.com) suggest that using a single watch is sufficient.
IMO the main problem with this line of reasoning is that the rate for an inexpensive watch is going to vary with temperature, often considerably. How much this matters depends on use case, I guess.
How accurate is accurate enough time for celestial? Prior practitioners of celestial before the GPS era usually peg the practical, achievable accuracy of celestial (assuming no time error) at 3nm-10nm depending on who you ask with the 3nm claims probably involving hubris or ideal conditions or both. This is for highly skilled practitioners with higher quality equipment. A four second error in time is 1 NM at the equator. It makes sense to think in terms of an error budget. 10 seconds, 2.5 NM, would contribute to inaccuracy but still be reasonable, for example. Then you can think about how long a voyage can be between time references, with no radio time setting ability maybe use 4 weeks, so 2.5 seconds a week would be tolerable. Maybe more.
Another way to look at it is to think about how far off your latitude can be and still be acceptable during an offshore passage with a GPS outage. Trying to find the Marquesas or Bermuda would be an example, you would typically run down the latitude but if out of sight of the islands would want to be able to determine whether you're east or west of them. In reasonable weather you would be able to see the terrain from at least 20 miles away so your latitude would have to be off by 40 miles = 40 minutes of latitude = 2 minutes 40 seconds time error for you to think you're on a different side than you actually are.
Of course, time can be obtained from other sources. GPS, even if functional only briefly. WWV. Some broadcast AM/FM stations state the time at the time of the hour. Or you can shoot a lunar and get within a minute or two.
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