Sources of accurate reference time on board ?

One of the pleasures of sailing AND the introduction of reliable GPS are that you really don't need to 'know' about time. You get up with the sun (well you do in Australia) and have sundowners (if at anchor) as the sun falls below the horizon. You have no train to catch, you eat a little bit after deciding you are hungry, fish don't know the time (so re-stocking the fridge does not need an accurate time piece.) and a few minute out in tide will not have much impact.

It all seems very old fashioned to be tied to shore based habits.

:) :)

We do need to know the time roughly as our forecasts are at specific times - but listening 5 minutes early is not an issue and they are repeated every 4 hours (and we can call up the forecast on Ch16 - anytime we like).

Jonathan
 
lw395 said:
How accurately do you want to know?
You should start by working out the consequences of 'n' seconds error.
A quartz watch can be kept on your wrist and its error tracked against R4 over a period of months.
Generally the frequency drift reduces over the years, so keep the same watch and keep it at steady body temperature for best results.
If you are only reading the watch by eye, for astro, then there is the major part of a second's error in timing your observation anyway.
If you are timing something electronically, then you can get better crystals for better long term stability (a few parts per million), or Rubidium clocks are available (potentially good beyond parts per billion).
I once designed something that was stable to about 1/100th of a second over a couple of weeks using a Rubidium clock module. That's not state of the art, just doing a job on a budget.
GPS is of course broadcasting atomic clock time, but what comes out of the receiver is much degraded, often 'only' good to a fraction of a second.
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I bet Nelson and the like with their sextants had timepieces accurate to a fraction of a second! I presume Tim is getting his ducks in a row for his long trip south, well for those of us who have done it, time never came in to the equation. Press goto on the gps and follow the arrow! Thats it!
 
Re: Sources of accurate reference time on board ?n

I started sailing when a deck watch and the time signal were the state of the art. I developed a bit of an interest in the subject. I have two quartz “chronometers” from the 1980s, both of which still work and both of which will wander off.

So far as non electronic methods go, if you want a good mechanical timekeeper for navigation look out for a Hamilton model 992B watch (say £450) or a Hamilton “Type 23” deck watch. (say £1,100) which is more or less the same movement in gimbals in a nice box.

If you want the last word in deck watches then look for a Ulysse Nardin as supplied to both the RN and the Kriegsmarine in WW2 and expect to pay £2,000 or so. All these should be cleaned professionally as soon as you buy one and should be cleaned every three years no mater what. Expect to pay £100 or so for that.

The reason I am recommending these is that they were made using Invar and Elinvar balances and balance springs and as such are free from Middle Time Error which is the great weakness of older deck watches.

A proper detent escapement chronometer, such as a Mercer, or a Hamilton Model 22, is useless in a boat as the motion will make the escapement skip, which is why you want a lever escapement deck watch.

What you are looking for is not perfect timekeeping but a steady rate of gaining or losing (usually gaining!) and you establish this by noting the error on GMT at the same time every day and plotting this without changing the hands on the watch. Then apply the correction to the time of the sight.
 
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Re: Sources of accurate reference time on board ?n

Minn said:
I started sailing......
Click to expand...

.....when the Yeoman of the Watch turned the patent hourglass over, rang that bleedin' bell, and read the taffrail log.

[quote}
.....Then apply the correction to the time of the sight.[/QUOTE]

"One pink elephant, two pink elephants, three pink elephants..."
 
Re: Sources of accurate reference time on board ?n

zoidberg said:
.....when the Yeoman of the Watch turned the patent hourglass over, rang that bleedin' bell, and read the taffrail log.

[quote}
.....Then apply the correction to the time of the sight.
Click to expand...

"One pink elephant, two pink elephants, three pink elephants..."[/QUOTE]

On a point of information, he wouldn’t have read the taffrail log as it hadn’t been invented. And he wouldn’t have counted pink elephants, he would have said “On!” to the timekeeper.

But you knew that anyway.

Why is there no pink heffalump smiley when you want one?
 
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skipper_stu said:
I bet Nelson and the like with their sextants had timepieces accurate to a fraction of a second! I presume Tim is getting his ducks in a row for his long trip south, well for those of us who have done it, time never came in to the equation. Press goto on the gps and follow the arrow! Thats it!
Click to expand...

Nelson didn't have GPS mocking his efforts at Astro, which I assume is what the time is for?
 
Four seconds of time is a minute of longitude.

So in longitude terms a second is 462 metres on the Equator.

In real life yottigation you get an intercept which might be five miles either side of where it says it is and you cross that with your DR track, which is a DR track, and you are probably within a few miles of where you think you are.
 
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"Point I am making, how accurate does the timepiece have to be to get a good fix? "


Reduction of degrees of freedom within the practical application of statistical chronometric parameters, of course.

But I expect that you knew that already.
 
When I was a cadet and 3rd Officer in the merchant navy, 34-41 years ago, sextant positions were only done out of sight of land and the reach of DECCA. It always amazed me that, of 4 sun sights, (2nd and 3rd Officers and 2 Cadets), it was the highest ranking Officers position that was taken as correct, and the others were generally considered, OK, but not quite right, for a variety of reasons.

My own thoughts were that, if 4 positions were withing a few miles of each other, (say 5 or 10 miles or so), on an ocean crossing, any of them could be the most accurate, and the chances of one being close to correct, pretty much nil... so it would have been good, and motivational, to use a junior ranking Officers position from time to time, or even on a regular basis.

I no longer know how a clocks inaccuracy, (say 30 seconds to a minute or so), affects position, but I also wonder how much it actually matters, in the circumstances when the position would be taken?
 
Minn said:
I think so. But what with the boat jumping around, incorrect counting of pink elephants, and so on, they aren’t going to be!
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Thus, given a timepiece accurate to around half a minute, time could be the least of a yachtsman's concerns, when considering the accuracy of a sun, or stars, position - and how much does it matter anyway?
 
Richard10002 said:
Thus, given a timepiece accurate to around half a minute, time could be the least of a yachtsman's concerns, when considering the accuracy of a sun, or stars, position - and how much does it matter anyway?
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Some people like to worry about these things, and it can be a useful mental exercise.

Practically, there's no point being more accurate than you need to be. Check the other thread on GPS - position to 10mm of a 10m boat, why???
 
Richard10002 said:
Thus, given a timepiece accurate to around half a minute, time could be the least of a yachtsman's concerns, when considering the accuracy of a sun, or stars, position - and how much does it matter anyway?
Click to expand...

In 1892 the United States required railway locomotive drivers and train guards to carry watches accurate to within thirty seconds a week. And they all did so. So any US “railroad grade” pocket watch, if cleaned and adjusted, can be used for navigation. Hiscock and Tilman and almost all pre-GPS long distance yachtsmen used them.
 
Page 208 of Hiscock’s “Voyaging under Sail”, showing the classic yachtsman’s noon fix.

Note the 41 seconds on the stopwatch (clicked when the sun was “on” and used to transfer time to the deck watch (a Waltham, in his case)) and the accumulated error of 3 minutes 15 seconds fast on the deck watch based on the time signal.

He was comfortably close to his DR position.

image upload no resize
 
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penberth3 said:
Some people like to worry about these things, and it can be a useful mental exercise.

Practically, there's no point being more accurate than you need to be. Check the other thread on GPS - position to 10mm of a 10m boat, why???
Click to expand...

Seems reasonable though to reduce errors the you can , without getting too carried away, so they don't add to the errors you have no control over. A cheap casio watch and log which way the time drifts for a few weeks before setting off should get time errors down to a few seconds, if you're going to do something why not make just a little effort to do it well?

The gps thread began as a link to some interesting technology, nothing more.
 
Yes.
I used to receive WWV in Europe and many other remote parts of the world.
I think it’s used by USN
With a good SW radio mine was a small Sony with an antena wire I could extend out.
Best later in the day or at night rather than in the traditional morning sight routine.
Sunset or sunrise between the transmitter and your receiver disturbs the ionosphere and affects radio transmissions.

You may find you have to vary the the choice of MHz some work better a different times of day.
This might be wrong my memory is not so good
The lower MHz at night higher MHz during the day or it could be the other way round.

I also used the world service and the time signal from Just before the shipping forecast but it’s just once an hour.
WWV is continuous

The issue with BBC is they changed to satellites to retransmission which puts a small delay in some of thier signals.
Back in the day when it came in from big transmitters and terrestrial relays I used BBC.
 
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