Sextant App

[jamhass]

Some years ago I put together an Excel spreadsheet that does just that, giving the point along the line of position closest to your presumed initial position.

Math part is straightforward. But to be useful, needs to have the ephemerals for each celestial body one might sight. They are readily available, but took fair amount of effort to implement.

It was all done in Excel macros and Visual Basic I am sure any decent 12-year-old could code it all in Java and port it to Android.

[goboatingnow]

Originally Posted by jamhass

Some years ago I put together an Excel spreadsheet that does just that, giving the point along the line of position closest to your presumed initial position.

Math part is straightforward. But to be useful, needs to have the ephemerals for each celestial body one might sight. They are readily available, but took fair amount of effort to implement.

It was all done in Excel macros and Visual Basic I am sure any decent 12-year-old could code it all in Java and port it to Android.

iPhone apps like iMariner will automate all the sight reduction process including embedding all the almanac tables. At least no more carrying HO volumes of sight reduction data.

[Idaho]

Thank you, everyone.

I learned celestial navigation in 1983, then sailed as crew from Panama to Noumea on a boat with only a shortwave receiver for the time signal and a sextant. No fancy Satnav or LORAN.

We typically did noon sights for position. Strangely, we arrived to every island we planned to visit without difficulty locating them.

Now I am making ready for another Pacific crossing, I bought a book to relearn the math, and my crew noticed my sextant and now want to learn how to use it.

I showed them how to shoot the sun at noon, but teaching them the math is a bit daunting. I told them there is an app for that in this more modern age.

So now I am looking for that app.

[Bowdrie]

I've still got an ancient HP-41 with the "Nav-Pac/Navigation" module, and an HP-48SX into which I wrote the equation for HC.
But yes, with known time, graphing a few sights that encompass LAN will render position with accuracy determined by operator skill.
I like HO-211 for general work.

[El Pinguino]

Originally Posted by Idaho

Thank you, everyone.

I learned celestial navigation in 1983, then sailed as crew from Panama to Noumea on a boat with only a shortwave receiver for the time signal and a sextant. No fancy Satnav or LORAN.

We typically did noon sights for position. Strangely, we arrived to every island we planned to visit without difficulty locating them.

Now I am making ready for another Pacific crossing, I bought a book to relearn the math, and my crew noticed my sextant and now want to learn how to use it.

I showed them how to shoot the sun at noon, but teaching them the math is a bit daunting. I told them there is an app for that in this more modern age.

So now I am looking for that app.

Not an 'app' whatever that may be but your crew may find this useful, written by a simple sailorman for simple sailormen.
https://docdro.id/5rFQH7g

[Rumrace]

I have a piece of software called Visual. It’s photometric software from Lithonia. There is a Visual Basic for laymen. Funny stuff.

[SeanPatrick]

The sensors in any phone, tablet, etc. available today are simply not accurate/sensitive enough to produce a reliable position fix. You might get an accurate position ... but you probably won't. The technology simply cannot currently match the accuracy of a real sextant/octant ... which is kind of ironic, when you think about it.

Don't get me wrong, I've downloaded and played around with several such apps. They're fun, and they might teach you at least a little about celestial navigation. But until the technology advances to a point where a mobile phone or tablet can accurately measure altitudes down to a tenth of a minute of arc, they are essentially useless in terms of actual navigation. As it stands, you'd probably be lucky to get within the nearest whole degree ... far too low a resolution to be relied upon for safe passage.

So, go ahead and download an app like CamSextant, or something similar. Have fun messing around with it and learning about the concepts. But absolutely DO NOT - under any circumstances - rely on such an app for an accurate position fix. At least not yet.

[ChrisJHC]

Originally Posted by SeanPatrick

The sensors in any phone, tablet, etc. available today are simply not accurate/sensitive enough to produce a reliable position fix. You might get an accurate position ... but you probably won't. The technology simply cannot currently match the accuracy of a real sextant/octant ... which is kind of ironic, when you think about it.

Don't get me wrong, I've downloaded and played around with several such apps. They're fun, and they might teach you at least a little about celestial navigation. But until the technology advances to a point where a mobile phone or tablet can accurately measure altitudes down to a tenth of a minute of arc, they are essentially useless in terms of actual navigation. As it stands, you'd probably be lucky to get within the nearest whole degree ... far too low a resolution to be relied upon for safe passage.

So, go ahead and download an app like CamSextant, or something similar. Have fun messing around with it and learning about the concepts. But absolutely DO NOT - under any circumstances - rely on such an app for an accurate position fix. At least not yet.

I think he’s looking for an app to do the calculations once you’ve taken the sextant readings (and the time of course).

[Sos]

Another thread here Celestial Navigation for Android

[Benz]

I don't understand why people think the noon sight is the easiest--sure, I get it, the math is easier than going into the HO 229 tables, and it gives you a latitude, but taking five or six shots to pin down actual Local Apprent Noon seems like so much more work than taking one sight and reducing it in the comfort of the cabin. It only takes a little practice to be able to reduce a sight quickly (I had it down to five minutes from shot to plot when I was in mid-season form), and if a running fix is kept, everything seems to shake out with reasonable accuracy.
I think that the most errors are introduced when I get sloppy about keeping my DR fix up-to-date, and it does take discipline to keep up with it. But whenever I carefully shepherd the DR, my LOPs come in pretty close.
Last of all, I think I may have gone off topic...sorry

[Sailor Sailor]

Both Weems & Plath and Tamaya sell a navigation calculator that can do this. Unfortunately, the new ones are over $1.5K. There are used ones on eBay for less than $200.

It is wise to have a backup to GPS if you are far offshore. Smartphones need to be recharged. In the event of a lightening strike, war, or some other international incident, or a rollover with extensive water damage, you should still be able to calculate your position. Everthing necessary should run on regular batteries and not require recharging. Celestial navigation is also a beautiful process to learn and to preserve. It puts you further in touch with nature, which is what sailing is all about.

My solution is currently a Davis lifeboat sextant, the current Nautical Almanac, a good quartz watch and clock, a Grundig YachtBoy 300 shortwave receiver that runs on AA batteries, along with the three HO249 volumes, and Davis worksheets for LOP plots.

With the shortwave receiver, you can pick up the WWV time broadcasts for accurate time. With a nautical almanac and sextant, and a noon shot followed by a Polaris night shot in the Northern Hemisphere, you have confirmed latitude and close-enough longitude based on zenith meridian passage and adjusted Universal Time for your position.

Here is my Grundig shortwave receiver picking up time signals from Ft. Collins, Colorado, 1,700 miles away, on 25 Mhz:

https://youtu.be/DvrirXQENn0

https://youtu.be/DvrirXQENn0

[Rumrace]

One day when your children are a little older in a social gathering at the club, some condescending pot bellied boater may belittle them suggesting they are superior due to knowledge on the sextant. It’s to compensate for some deep routed personal failure in most folks.
Have them build this toy which is accurate to 7.4” (made that up)!Sextant !
Then when the bloheart babbles they can sit in quiet confidence knows big they are not the village idiot, he’s speaking.

Reception.com.br

[Cwens]

Originally Posted by Benz

... but taking five or six shots to pin down actual Local Apprent Noon seems like so much more work than taking one sight and reducing it in the comfort of the cabin...

I've only done a celestial fix a couple of times, but I found getting an accurate shot to be a lot harder in practice than it would seem in theory. An old graybeard taught me this: Take five or six shots a couple of minutes apart, even if you aren't trying to do a noon sight. Go below, and, on a piece of graph paper, plot the elevation on the Y axis and the time on the X axis. Eyeball the dots, ignore the ones that are obviously way out of line, and draw a smooth curve to fit them. Now, you don't have to use any specific one of your shots; you can take any point along that line and plug it into the math as though it was an actual shot.

[SeanPatrick]

Originally Posted by ChrisJHC

I think he’s looking for an app to do the calculations once you’ve taken the sextant readings (and the time of course).

Ah, yes. After re-reading the OP, I believe you are correct.

I know of a pretty good Excel spreadsheet for that.

[goboatingnow]

I enjoy sextant sights. The iPhone app is handy as it saves carting the sight reduction tables around.

What I never would suggest is it’s a backup to gps. As I’ve said three are 11 GNSS capable devices on board.

I’ve done transatlantics without any need to not use gps , in fact just follow the setting sun !!

I like celestial but let’s not drown it in teary eyed nostalgia.