Setting the time on a chronometer - how?

[tudorsailor]

I am planning to use the sextant that I was given as a gift 2 years ago, and until now have not used! I know that I will need to know UT accurately. My questions are how accurately and whats the best way to set a digital watch to UT?
Sorry if this is a very basic question but in this I am a complete novice!

Thanks

TudorSailor

 

[coopec]

I am planning to use the sextant that I was given as a gift 2 years ago, and until now have not used! I know that I will need to know UT accurately. My questions are how accurately and whats the best way to set a digital watch to UT?
Sorry if this is a very basic question but in this I am a complete novice!

Thanks

TudorSailor

I'm interested too as I have a plastic sextant.

Apparently you could use a GPS
TIME SIGNALS _ GPS

 

[tross]

If you have a GPS unit this is probably the most accurate clock you can get ( public)

 

[GHA]

Been a while since done for real but playing recently I've just used the mobile phone, which should be near enough to UTC - exact time now - Time.is or radio pips if it's set to auto time. Or GPS is usually within a second or so. Though doesn't seem quite right somehow
Then count 3 or 4 seconds between the sight and reading the time and subtract.

 

[Stemar]

I have an Aldi or Lidl (can't remember which) weather station on board. As well as a barometer/barograph, it has a radio controlled clock that synchronises daily to an atomic clock somewhere in Germany. I doubt it's ever more than a few milliseconds out. Mine's probably close to 10 years old now, but they crop up regularly for around £20-25.

 

[lw395]

Set the chronometer about 10 seconds fast, then keep a log of differences compared to radio time signals, GPS and of course your own sun sights.
You may find it much less confusing if all the errors are in the same direction.
Then graph them and see if you have any pattern. (you may not need to physically draw the graph).
It's not (just) about having it indicate as near as possible to the correct time, it's more about knowing what the error is and having a best estimate for the errors after however many days. You can extrapolate this from your graph and maybe have some idea of how confident you are in the accuracy.

 

[VicS]

I have an Aldi or Lidl (can't remember which) weather station on board. As well as a barometer/barograph, it has a radio controlled clock that synchronises daily to an atomic clock somewhere in Germany. I doubt it's ever more than a few milliseconds out. Mine's probably close to 10 years old now, but they crop up regularly for around £20-25.

+1 for radio controlled clocks

I have several . 2 small alarm clocks. a mantel shelf clock in the lounge, a couple built into weather stations and one which when new could project the time onto the bedroom ceiling. Most came from Lidl and use the German time signal from Frankfurt. One uses the UK signal from Anthorn and one of the weather stations can be switched between the UK and German signals. The oldest is now about 20 years old .

I believe the accuracy is 1/100 second

 

[maby]

GPS or the atomic clocks in Germany or Rugby (is that still running?) are the best for ordinary mortals like us. Internet time done over a decent speed network is also pretty good - but be careful about trusting the time displayed on your PC - by default it does not synchronise with the central time servers very often.

The bips on the radio are also pretty accurate - provided you are using an old fashioned analogue radio. The digitization of DAB, Freeview, Freesat, iPlayer etc. can add errors of a couple of seconds - or more. If you have access to an analogue FM radio, try tuning both it and your Freeview (or Sky) TV to the same radio channel in order to judge the lag.

 

[Sandy]

I have a Radio Controlled Watch

Radio Controlled | Watches | Products | CASIO

Works for me and my sextant.

 

[Refueler]

The standard way to set a Chrono - is to NOT set a Chrono.

On first day its started - its set to near correct time. The Greenwich Time signal is then used to indicate how many seconds fast or slow of correct time. A book is kept that logs the time check each day at same time. This then tells you two things :

The accuracy of the indicated time
The rate of change of the indicated time to that of correct.

Why ? Simple. The Thomas Chronometer was never designed to absolutely correct time - but to be a steady rate of change time keeper. Once error is known and the rate of change of error per day ... even if you miss a day or two of time signals - you can use the tabled data to arrive at correct time.

Of course today we have so many displays of time - that the old ways are fast fading away - but a ships Chrono is still kept as above.

17 yrs I used a Sextant professionally and one thing that was soon learnt ... it was better to not use a time piece in hand with the sextant ... but to take the sight, walk to chrono counting and read the time. Jot down time and count as well as sextant reading ... go back out and take next sight. Sounds wrong - but in fact its much better as you are not fumbling around ... and count as : one banana, two banan, three banana etc. is remarkably accurate and less stressful.

 

[lw395]

I have seen radio controlled clocks set themselves to complete nonsense time when you motor up the river.
Some race officers are very keen on them, I don't trust them as I've never seen a waterproof one. I sync my Casio watch to a radio controlled clock after I've sanity checked against the GPS.
Presumably anyone using a sextant will be aspiring to sail out of reception range at some point.

 

[tudorsailor]

Thanks for all the replies. It does strike me that if one has a device with GPS that is working, then you dont need to use your sextant!

My thought in learning to use a sextant is to cope with the unlikely event that all GPS electronics are not working! Also I would need to do this to get YachtMaster Ocean

Am I correct that I could set a Casio radio-controlled watch to UT (GMT) rather than BST . Then once of radio range it will continue to keep time?

TudorSailor

 

[Refueler]

I have seen radio controlled clocks set themselves to complete nonsense time when you motor up the river.
Some race officers are very keen on them, I don't trust them as I've never seen a waterproof one. I sync my Casio watch to a radio controlled clock after I've sanity checked against the GPS.
Presumably anyone using a sextant will be aspiring to sail out of reception range at some point.

On one ship (270,000 tonne) - we had a Pateke Phillipe Chrono - electronic job as well as the analogue mechanical. The PP was capable of being corrected by radio time signal back in the early 80's when ship was built. But was disabled function by Company instruction. We kept both clocks error records ...

The PP also controlled the ships clocks around the cabins etc. as it had a slave clock below the chrono - you set that to time zone and all ships clocks altered to suit.

Boy this is memories coming back !! 12 turns of the key to wind same time each day ...

 

[Refueler]

Just to set record straight ...

UTC is not actually GMT. They are based on different standards and normally would agree - but do get out of step by slight amount over the year etc. Its a technical difference and not really of concern in practice.

 

[LadyInBed]

The bips on the radio are also pretty accurate - provided you are using an old fashioned analogue radio.

Yes, I think R4 LW still send out accurate time pips.

 

[Refueler]

Yes, I think R4 LW still send out accurate time pips.

Do they still do the Shipping Forecast after as well ?

 

[Kukri]

I would not want anyone to think I am a bit obsessed with this...



An analogue radio (NOT a digital one) will give the BBC time signal, as has been mentioned, in home waters, if you are in Internet range you have the very convenient Exact Time website and of course if you want to be traditional and have a short wave receiver there is Fort Collins, which you can get anywhere:

WWV (radio station) - Wikipedia

And of course the time signal is broadcast on BBC World Service long wave.

By the way, you don’t need accurate time for a noon latitude (or a Polaris latitude). Start with distance off by vertical angle, go on to noon latitude and then do the position line sights.

 

[Refueler]

By the way, you don’t need accurate time for a noon latitude (or a Polaris latitude). Start with distance off by vertical angle, go on to noon latitude and then do the position line sights.

Basically Latitude has never been the problem .... the problem was Longitude and one of the main reasons the Chronometer was designed and put to use.

I'm intrigued by your statement ... because the age old professional Navigator would take a series of morning sun sights and then run them up based on speed / course on the plotting chart to ships noon. At local noon he would then obtain suns highest altitude - giving him Latitude. Simple course and speed correction to ships noon and draw the line intersecting with run-up morning sights ... giving the ships position at ships noon. Marc St Helaire of course. (I used Long by Chron as a cadet just to prove I could do it - but soon preferred MsH).
Because the ship had reports to make to owners / charterers via the Master - the noon position had to be available as near to noon as possible and not based on run back afternoon work.

Not trying to be smart - just commenting based on Commercial Shipping nav work.

 

[pcatterall]

As suggested it is not important to actually set the chrono to the right time but to check it against your choice of time signal and correct as required. And ( also as advised) best to be a good 10" ahead so that your corrections will always be negative.
We used the old rugby time signal for land based astro and tried to get the readings to 1/10th of a second.

 

[Refueler]

I would have to say also that the average yacht on the open sea is going to move about a lot more than the deck of a ship. That in itself creates a large margin of error in the sight itself. I agree that minimising every error is important though. But 1 second out on time is approx 1nm ......

1nm close inshore is very important ........... offshore is about as important as ???

A good steady noon fix is about 5nm radius accuracy ... 10nm on a rough day. Stars on the other hand - which I much preferred doing is a different ball game and accuracy is much better.
I also used to practice Moonlight stars .... traditional navigation - like for my Father - was my favourite part of the job.