Time Precision Needed for Celestial

[El Pinguino]

Originally Posted by Bowdrie

Before the U.S. bacame involved in WWII, when Gen. George Patton was commissioning his new schooner, "When and If", he inquired about chronometers.
He was told that with one he could never be sure that it was correct.
So, he ordered two.
Then he was told that with two he would never know which one was right, so he ordered three.
A good friend of mine is a collector of watches, (all makes/models/price ranges,) my joke to him is that he never really knows what time it is.

Before the coming of the radio time signal 3 chronometers was the standard on the better class of steamship.
They would be compared with each other to establish the rates... a procedure I have never had to get involved with.
Below is from the 1910 edition of Lecky's Wrinkles.

[barnakiel]

Time only required to get the lat. Hence not much of an issue in Atlantic crossings.


Well now in the Pacific there are low lanfdfalls and low obstacles ...


Given that a Casio is 15 USD and a chronometer 1k and upwards - and that there is not much in between ...


Well I am stuck with the Casios.


Cheers,
b.

[Jammer]

Originally Posted by SeanPatrick

Just remember: Joshua Slocum famously circumnavigated with celestial and "a cheap tin clock".

Indeed, mainly through DR and, it is thought, with occasional use of lunars.

And you can always recover UT (GMT) by shooting a lunar.

Within about a minute, if you're good and have the correct tables.

[Uricanejack]

Originally Posted by barnakiel

Time only required to get the lat. Hence not much of an issue in Atlantic crossings.


Well now in the Pacific there are low lanfdfalls and low obstacles ...


Given that a Casio is 15 USD and a chronometer 1k and upwards - and that there is not much in between ...


Well I am stuck with the Casios.


Cheers,
b.

Anyone can get a latitude with a lodestone or an astrolabe if you want more accuracy.
For Longitude you will need one of Harrison”s fancy watches.

[Uricanejack]

Originally Posted by El Pinguino

Hardly a 'lot of workload'. These days you don't even have to tune to WWV/WWVH on your HF. Simply look at time on watch, look at time on GPS, note difference in deck log. Maybe 5 seconds a day.
It doesn't have to be 'accurate' - you just need to know the error and the rate. And you only need to know the rate when your GPS has gone TU.
First three lines in my sight books. Chron, Error +/-, Chron Corrected.

Note to self. I must rate my two cabin clocks. I know that when I rejoined after two years absence during the covid business they both seemed to be showing something close to the coreect time.

And yes - in the old fashioned days the chron error ( or errors, fancy ships had two ) was checked daily. You would open the little hatch connecting chartroom to radio room. Ask Sparkie for a time signal. Little speaker on chartroom bulkhead would start ticking away...... tick tick tick BEEP - job done.

Yup.

Been doing my daily time check with GPS for a decade or two. Bit of a cheet but they got rod of the RO before i quite DSea 30 odd years ago.
WWV still going no doubt it is on Putins target list so if you live in Colorado and you are worried about it. Move to a mountain top in Idaho and build yourself a shelter like the rest of them.

[s/v Jedi]

On accuracy: GLONASS on average is a little less accurate than GPS but is better at high latitudes.

Galileo is much more accurate, think 3-5 times as accurate.

For time I think they will all be good enough.

[El Pinguino]

Originally Posted by barnakiel

Time only required to get the lat. Hence not much of an issue in Atlantic crossings.


Well now in the Pacific there are low lanfdfalls and low obstacles ...


Given that a Casio is 15 USD and a chronometer 1k and upwards - and that there is not much in between ...


Well I am stuck with the Casios.


Cheers,
b.

I think 'you have your hat before your cattle'.
Only a vague idea of time is required for finding your Lat.
Some semblance of accurate time is required for finding longitude.
This is why in the old fashioned days of paper charts lots of atolls etc in the South Pacific had next to them something like ( Repd to lie 3 miles West). This was due to the original discoverer having a chronometer the knowledge of whose error was a little bit in error.

[Bowdrie]

Originally Posted by El Pinguino

This is why in the old fashioned days of paper charts lots of atolls etc in the South Pacific had next to them something like ( Repd to lie 3 miles West). This was due to the original discoverer having a chronometer the knowledge of whose error was a little bit in error.

Never really got much press, but during WWII scores of the smaller vessels, like Destroyers, Destroyer Escorts, and PT boats, along with inshore supply vessels got lots of self-inflicted damage from running around at night in the relatively congested and reef strewn waters in the South Pacific.
If the shooting started a few minutes of rapid maneuvering and nobody really knew where they were.
Yeah, the new-fangled radar would (generally,) show the larger islands, but in many cases, they were using charts that had been made from the days of the Spanish American war.
Sights were being taken as often as was possible, and the nav/plotting teams were always busy.

[El Pinguino]

Originally Posted by El Pinguino

Before the coming of the radio time signal 3 chronometers was the standard on the better class of steamship.
They would be compared with each other to establish the rates... a procedure I have never had to get involved with.
Below is from the 1910 edition of Lecky's Wrinkles.

Correction to the above - they were compared with each other to ensure the rate of each one stayed relatively constant.

[GrowleyMonster]

An ordinary Casio or Timex is sufficient. Here is the trick. DO NOT reset your watch! Instead, check it once a week against the time ticks from WWV or WWVH. Slightly more dependable than setting by internet time and more accurate due to update interval and timing of the screen update than setting by your GPS unit. Back to the watch... check it weekly and record the correction to correct time. While actually at sea, try to get a time check daily. Then after a month, start calculating your rate. That is how fast it gains or loses. If the rate is consistent then from your chronometer log you can always apply a correction to watch time to get GMT.

Joshua Slocum, on at least one occasion, checked his cheap alarm clock that he used for a chronometer, using the Lunar Distance method, which will seldom be better than 10 seconds of accuracy. And he made the first circumnavigation by a solo sailor. A standard digital wristwatch will be plenty more accurate than that, once you know your last correction and the rate.

You can do what professional navigators are taught to do, and use a hack watch and subtract elapsed time from chronometer time, or do what many or most professional and accomplished amateur navigators ACTUALLY do. Bring down your body to the horizon and then take your time looking to your watch. Count "thousand-one, thousand-two..." etc and have your eyes focusted on the watch at the five second mark. Record your time, then look at your sextant for the Hs. You will be within a half second, good enough by far for small boat navigation where the accuracy of the observation is usually your limiting factor due to platform instability and raggedy horizon from being down in the waves instead of 70 or 80 feet above them like on a ship.. A one mile triangle for your fix on a small yacht is pretty excellent. Sometimes you will struggle to get it tighter than 4 miles. A half second on the time is more accuracy than you can make full use of.

Also, always complete bringing the body down to the horizon as you are on the top of a wave.

There are a few other tricks you will learn if you study and practice for very many years.

Before you bother buying a dedicated timepiece for navigation, or a sextant and tables and almanac, practice making plot sheets and keeping an accurate DR track. This is the most elemental form of Navigation and serves as a basis for picking your Assumed Position which you need to calculate your azimuth and intercept, which you use to draw your Line of Position, two or more of these, usually three, that you will advance or retard to an arbitrary time, (typically noon, LMT) for your daily fix. Your DR is of extreme importance and you can even make a sometimes surprisingly accurate landfall using only your DR. And you don't need any equipment except paper, pencil, dividers, and triangles.

[clakiep]

The influence of faulty time depends on your latitude : high latitudes low, at the equator high. You can find out your latitude with no time information, just observe culmination of sun or stars. Any mechanical chronometer will depend on temparature for correction with the respective tables for this watch. As long as a time signal trough radio broadcast is available (BBC ?) this plus a simple quarzwatch was what I used.

Capt. Claus Sâo Paulo/Brasil

[waterman46]

Originally Posted by S/V Illusion

What did Frank Worsley and Shackleton use? It was good enough for them.

I would guess they didn't use much celestial nav due to the places they sailed, where it's almost always cloudy, and had no good charts. And they might not have known much about the ocean currents in those areas either. No electronic depth sounders. Those guys had balls of steel. I suppose they would simply go slow and keep a good watch.

[GrowleyMonster]

Originally Posted by barnakiel

Time only required to get the lat. Hence not much of an issue in Atlantic crossings.


Well now in the Pacific there are low lanfdfalls and low obstacles ...


Given that a Casio is 15 USD and a chronometer 1k and upwards - and that there is not much in between ...


Well I am stuck with the Casios.


Cheers,ltitude
b.

I am sure you must have meant time is only required to get longitude.

[El Pinguino]

Originally Posted by waterman46

I would guess they didn't use much celestial nav due to the places they sailed, where it's almost always cloudy, and had no good charts. And they might not have known much about the ocean currents in those areas either. No electronic depth sounders. Those guys had balls of steel. I suppose they would simply go slow and keep a good watch.

I would suggest quite the opposite. Frank Worsley was a remarkably competent navigator and - as every navigator knows - the sun always comes out at noon.
He did manage to navigate a small boat from Elephant Island to S Georgia and the position where Endurance sank was plotted accurately enough for them to locate the wreck a few years ago.

Re depth sounders, they were still fitting versions of Lord Kelvin's deep sea sounding machine to ships well into the 1950s, I've used one with the chemical in the tube. https://www.rmg.co.uk/collections/ob...c-object-42898

Coastal? Yes, they would 'gang warily' to use my clan motto.

[Kelkara]

Originally Posted by El Pinguino

I would suggest quite the opposite. Frank Worsley was a remarkably competent navigator and - as every navigator knows - the sun always comes out at noon.
He did manage to navigate a small boat from Elephant Island to S Georgia and the position where Endurance sank was plotted accurately enough for them to locate the wreck a few years ago.

Worsely had access to two chronometers during the voyage to South Georgia ... one rescued from the Endurance, and also Shackleton's personal chronometer (Which he gifted to Worsely after the voyage). Both are currently in museums.

https://www.rmg.co.uk/collections/ob...c-object-79134
https://www.spri.cam.ac.uk/museum/sh...rticles/n999a/

During the 11 day voyage he managed to get just 3 successful sights ... from the last sight until seeing land, it was four days and 250 miles of dead reckoning ... a phenomenal feat of navigation!