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Old 26-01-2011, 16:27   #1
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What Clock to Choose for Celestial Navigation ?

I have my chartplotter and PC full of software and charts now, and several GPS'es. But I have noticed that the GPS system sometimes have a little downtime. So even if it is improbable that the system goes down for longer time, it can't hurt to learn celestial navigation.

The problem is that I already have a sextant and tables from Astronav. But not an accurate clock that works outside the GPS system.

After what I have read, 4 seconds wrong mean one nautical mile wrong. on longer journeys that mean a very accurate clock.

So what type of clock do you use? Is it possible to buy a time piece that is a bit less expensive? Or do I need to spend 3-6000$ on a clock?
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Old 26-01-2011, 16:40   #2
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Keep buying Timexes until you find one that is accurate. Or go for broke and spend 80 bucks on a radio controlled G Shock. Any time you can get a celestial fix within four miles you're doing better than I ever have.
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Old 26-01-2011, 17:16   #3
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You don't need an exceptional clock, almost any quartz wrist watch will work just fine. You'll need a HF radio to get WWV or WWVH time ticks to verify it's accuracy. Set the watch and check it for a week against WWV and that will give you the rate of deviation of the watch. Just calculate the amount of change from the last time you set it to WWV and add or subtract to get the actual time. Most celestial nav. worksheets have provision for correcting time. I prefer a digital watch but sailed to French Polynesia and back with a then state of the art analog quartz clock. Always found land about where I expected it. Ah for the good old days of DR ad celestial!!! We were always lost, it was just a matter of how lost.

The satellite self setting watches are wonderful if you are where they can read a satellite. Hawaii is one place that they don't work and suspect most of the oceans near the equator aren't covered by satellite. The watches still work fine if you know the rate of deviation when they can't correct their setting via satellite.
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Old 26-01-2011, 17:20   #4
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Timex with Indiglo. That was always my favorite for Celestial Nav. It keeps accurate time and it's easy to read in the dark (95% of the time you need it). And it's cheap. I have a watch that is a certified chronometer, but it doesn't have a light!
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Old 26-01-2011, 18:57   #5
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If you wear a digital watch, it will keep more accurate time, as the crystal stays a consistent temperature.

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Old 26-01-2011, 20:16   #6
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Not sure if they are still made this way, but I used Casio digital watches that were adjustable. The cheapest ones didn't include this but in the $30 and up watches if you open the back there is a small screw (actually a potentiometer) that you can turn to increase or decrease the speed of the watch. I had one that I got close enough that it gained only half a second per month.

Alternatively, buy any digital watch and rate it ie. test it against a standard like WWV, establish the number of seconds it gains or loses per day and add that correction daily to know the exact time.
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Old 27-01-2011, 11:09   #7
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You can check the accuracy of your timepiece, without an HF radio,
here ➥ The official US time (NIST & USNO)
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Old 27-01-2011, 11:25   #8
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I wear a Rolex Submariner, but when I practice CN I use a far more accurate $30 Casio wristwatch (with dual time zone to display both GMT and local).

As stated, any watch / clock will do as long as you are able to set it by the WWV via an SW receiver just prior to taking a sighting.

Another option is a cheap digital stopwatch. Hack on the WWV (start the stopwatch at a given time) then calculate the hack and stopwatch time.
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Old 27-01-2011, 11:35   #9
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Originally Posted by Prerequisite View Post
Timex with Indiglo. That was always my favorite for Celestial Nav. It keeps accurate time and it's easy to read in the dark (95% of the time you need it). And it's cheap. I have a watch that is a certified chronometer, but it doesn't have a light!
Agreed, my Timex with Indiglo is accurate within 10 seconds a month. Just make sure you change the battery about every 5 years. Paid $25 at Walmart.
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Old 28-01-2011, 00:48   #10
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<< You don't need an exceptional clock, almost any quartz wrist watch will work just fine. You'll need a HF radio to get WWV or WWVH time ticks to verify it's accuracy. Set the watch and check it for a week against WWV and that will give you the rate of deviation of the watch. >>

That's it. In this digital age, you don't need an expensive chronometer. I did most of my cruising withn 99 cent digital watches. I left and returned with 5 watches. All were good. Also I had 3 plastic sextants. Before doing a round of sights, I would check the watches and adjust the sextant to zero index error, then shoot and compute. WWV was always strong and clear all over the world using any kind of short wave Radio. The most important thing is to note the time of the sight without delay. This is where a wrist watch is better than a cronometer. After you rock the sextant back and forth to find the low spot, or the high spot if doing an Upper Limb sight, then twist your wrist, look at the watch, subtract a half second and you have the time of your sight. With the sextant error set to zero, and the exact time of the sight, there are minimal corrections to apply and thus mimimal error to the resulting LOP.

I like the feature of dual time zones. I had all five watches set to GMT so that I could enter the pages of the Nautical Almanac without time conversions. This was good for navigation but could lead to confusion when trying to figure the local time.

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Old 28-01-2011, 01:42   #11
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Slocum managed very well with an old clockwork timepiece, so the accuracy of a digital watch should be more than sufficient. Keep three and compare, then keep at least two in a metal box (faraday cage) so that you can still do your astro after a lightning strike.
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Old 07-04-2011, 14:17   #12
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Re: What Clock to Choose for Celestial Navigation ?

ah but Slocum boiled his chronometer :-) not sure if my Seiko would appreciate that sort of treatment, but at 2s gain/month I can still shoot the sun accurately. the trick is to check it with a time signal.
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Old 07-04-2011, 14:44   #13
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Re: What Clock to Choose for Celestial Navigation ?

Doesnt matter what watches. Short wave radio or two a must.

accuracy with a sextant within a mile? On a small craft? With a plastic sextant? ROFL!!!
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Old 07-04-2011, 14:54   #14
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Re: What Clock to Choose for Celestial Navigation ?

Slocum did latitude sailing. When he needed a fix, he used shots of the moon in relation to other celestial bodies. The moon shots didn't require a chronometer or did finding latitude. The problem with Lunar Distances is they are very very tricky to shoot accurately and prone to error even for an experienced mariner. Slocum apparently had the technique down. Lunar Distances soon fell out of favor once reltatively cheap chronometers came on the scene in the early/mid 1800s and the lunar tables were dropped from Bowditch around 1900. Relatively cheap chronometers came into use at about the same time that Lunar Distance tables for finding Longitude were published. Slocum used his one handed alarm clock just to get a rough idea of time of day, not for navigation.

If you are interested, there is a very readable book called Longitude that recounts the efforts to find Longitude. The Brits offered a prize that ran into the millions of dollars in today's money for the first accurate system to find longitude. There was a lot of intrigue, outright politicing, skulduggery, and downright single minded labor and sacrifice in trying to win the prize.
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Old 07-04-2011, 14:58   #15
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Re: What Clock to Choose for Celestial Navigation ?

You don't need an accurate clock onboard....I know this sounds wrong. What you need is an accurate source of time from WWV or GPS and to know the error of your onboard clock. It is important to know your onboard clocks error and rate of change so you don't need WWV or GPS if that ever goes down. Ideally you want three clocks onboard whose error and rate of change you track and record.
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