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Old 04-02-2016, 21:14   #16
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Re: A sextant for the 21st century?

I have a little Celesticomp V calculator made in 1991. Its internal battery has never been replaced and it still works. You can shoot any celestial body at any time with a sextant and it will tell you what body you shot and compute an LOP. 2+ LOPs will output Lat/Long position. Inputs are GMT, sextant altitude, azimuth, and DR position. No soggy tables, books, or forms. This is my backup. I think the OP's idea is interesting from an intellectual perspective, but seems kinda Rube Goldberg-ish to me.

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Old 05-02-2016, 07:23   #17
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Re: A sextant for the 21st century?

With things like Google Sky Map for smart phones, I don't see why a non-GPS location app could not be relatively easily developed. It probably could do the angles itself. As to why we might need it, consider the recent Iranian capture of two US Navy boats. I'm betting they had their GPS spoofed. That's probably why the GPS units were not returned with the boats. It's also a good reason for the military to consider options. Perhaps we should too.

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Old 05-02-2016, 07:36   #18
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Re: A sextant for the 21st century?

Look for the arrival of e-loran. It's being tested now
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Old 05-02-2016, 07:53   #19
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Re: A sextant for the 21st century?

Originally Posted by A ursae minor View Post
Hello Navigators (and tinkerers)

Here and on other fora I came to realize that there are roughly two kinds of people using sextants:
1 - People who want to be able to have a back-up when all power is down
2 - People who just like maths and old-school stuff
There is a third group:
Those of us who used to use it as our primary source to find our position, and like to keep these skills. It is an art as well as a science, it takes a few thousand sights before one can reliably trust one's results. Such a skill once attained is worth maintaining.

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Old 05-02-2016, 07:54   #20
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Re: A sextant for the 21st century?

Originally Posted by Snowpetrel View Post
Often wondered if a digital camera could be calibrated to read angles accurately.

If so take a few snaps of the Sun and horizon with a smart phone, and let some app do the calcs for you.
I've wondered the same thing especially considering the density of pixels in cameras these days, measuring angles should be quite precise,
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Old 05-02-2016, 07:56   #21
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Re: A sextant for the 21st century?

I think I'm in the minority, but I think a digital blue tooth sextant is a great idea. It combines the power of computing with the raw data of the stars...a great application of hardware and software.

I have to wonder how reliable the GPS satellite system would be in case of a terror attack or war. Although there are many satellites, they work in concert. Any error would cause havoc with so many devices. I wonder if this is a possibility and what sort of reliability the system really has? Attack on the system could be via "hacker" into the system, or a more conventional physical attack on the satellites themselves.

Take a picture of the sky (stars) and get your position....that would be awesome.
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Old 05-02-2016, 08:18   #22
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Re: A sextant for the 21st century?

One simplified way of obtaining your position at sea requires only 3 things:

1. a sextant;
2. the Nautical Almanac; and
3. an accurate timepiece from which you can get GMT.

No sight reduction tables are required, and only very simple math.

I call it, "Latitude and Longitude by Meridian Transit". Usually, this means the sun, but other celestial bodies could be used as well.

The method is very simple and it works quite well.

You obtain your latitude by taking the traditional "noon sight", and apply the data from the Nautical Almanac for the sun's altitude.

You obtain your longitude by taking sextant sights a few minutes before and after the regular noon sight, and recording the sextant readings and GMT times. No corrections are needed.

Before the regular noon sight, you take a good sextant sight and record the angle (Hs) and the GMT time.

You then go on to take the traditional noon sight for Latitude when the sun reaches it's maximum altitude.

Afterwards, you reset your sextant to the same angle you measured before noon...with no corrections needed...and you follow the sun downwards until it just kisses the horizon, whence you record that GMT time.

Add the before and after times together, and divide by 2. That gives you the actual GMT time of meridian passage. Then, just enter the Nautical Almanac and look up the GHA of the sun for that exact time. The result is your longitude.

Now you've got both latitude and longitude.

The method is not as precise as taking multiple sights on multiple bodies and reducing them. But, it does get you within a few miles and, for many purposes at sea, that's quite good enough.

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Old 05-02-2016, 08:21   #23
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Re: A sextant for the 21st century?

Think you got things screwed on backwards. A whole horizon Plath will last you your entire life, will not break down nor go dead if batteries do not work, and is simple to use. Plus it can be used for a lot of other things besides celestial navigation, like checking for boat drift at anchor, or height of cliff. Then just buy a bunch of nav calculators to plug in your sextant readings and your done. Plus they keep their value.
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Old 05-02-2016, 08:23   #24
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Re: A sextant for the 21st century?

Originally Posted by boatman61 View Post
In this day and age a sextant as a back up is not needed.. all one needs is a compass and a 'proper' pilot chart..
Anyone with half an education should be able to DR a couple of thousand miles to within 50 miles of their destination if everything crashes..
Its basic geography and simple math...
I don't know how many of you have actually used a sextant under ordinary conditions offshore, (seas of 10 feet), but it can be very chalanging to get the horizon and the limb together with any accuracy. Its not bad on a ship, but on an ordinary sailboat, it can drive you to take up drinking, which doesn't help the process.🎅
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Old 05-02-2016, 08:35   #25
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Re: A sextant for the 21st century?

I figured someone would have said something by now about the OP's use of a slip stick. I have compared slide rule calcs vs printed tables and my position accuracy is far better with the tables. 4 or 5 digit precision vs 2 or 3. I guess it is all relative. A few feet error with GPS, couple of miles maybe with the tables and the slide rule will show you which ocean you're in ;-)
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Old 05-02-2016, 08:45   #26
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Re: A sextant for the 21st century?

May I take a moment to mention the Bris Sextant which is a fantastic development of sextants, developed only in the last decades.

Where a sextant can measure the angle to a celstial object, the Bris Sextant can only measure eight fixed angles. This allows for an extremely rugged and easy-to-use construction. Remember that a sextant is a very delicate object.

Citing the Wiki article:
The Bris sextant /ˈbriːs/ is not a sextant proper, but is a small, inexpensive, angle-measuring device that can be used for navigation. The Bris is, however, a true reflecting instrument which derives its high accuracy from the same principle of double reflection which is fundamental to the octant, the true sextant, and other reflecting instruments. It differs from other sextants primarily in being a fixed angle sextant, capable of measuring a few specific angles. [...] The Bris is a low-technology, high-precision, fixed-interval instrument.

Read more on the inventor's home page.

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Old 05-02-2016, 08:55   #27
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Re: A sextant for the 21st century?

I use pocketstars on a $5.00 Windows pocket PC I bought from goodwill.

If you are looking for a app that fulfills your wishes download Spyglass for your iPhone or iPad.
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Old 05-02-2016, 08:56   #28

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Re: A sextant for the 21st century?

How about a Kamel?

Who needs a piece of &@#(&$@ sextant when you can have a string with 57 knots?

The History of the Sextant
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Old 05-02-2016, 09:06   #29

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Re: A sextant for the 21st century?

The USN won't have to ask for funding, they can ask the USAF for the surplus units from the Blackbird. The USAF had fully operational "ball turret" starfinders, that could locate and identify stars--even in daylight--and calculate the plane's position from there. Decades ago. Rarely found on the surplus market, in pieces of one kind or another.
If you didn't mind the reliance on GPS, you could use the Google Sky Map feature, an app for Androids that lets you point your phone at the sky and then identifies everything you see. A little added programming and you should be able to get the phone to tell you where you are, working backwards from optical recognition on the sky view, without the GPS. Or, now that 3D accelerometer chips are a nickel apiece instead of a quarter million dollars...just have the phone running as an inertial navigation system.
Fly it on Kickstarter, see who signs up.
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Old 05-02-2016, 09:17   #30
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Re: A sextant for the 21st century?

yes, a 21 century sextant would be no bigger than an Iphone, with an artificial horizon, once your shot is taken you would just push a button for a solution. Done.


"I spent most of my money on Booze, Broads and Boats. The rest I wasted" - Elmore Leonard

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