New Digital Sextant, would you?

[Never Grumble]

I reckon it's extremely useful on a warship operating in a gps denied environment.

Back in the 80s we used to have them horrible brown calculators did all the complicated maths. I wonder how they do it nowadays?

 

[newtothis]

Consider using the sextant at sea.
You have a reading of the sun lower limb touching the horizon. This is Hs, sextant altitude.
First correction is for Index Error (which you check every day by taking a sight at the horizon. This is Observed Altitude.
Second correction is for Dip/Height of Eye. This is taken from Tables. Result is Apparent Altitude.
Third correction is for Lower Limb (could also be Upper Limb, but less likely) and parallax. This is also taken from Tables. Result is Ho, True Altitude and is the figure used in the Sight Reduction Process.

If using an artificial horizon.
Take the measured value of Hs, apply Index Error and divide the result by 2. Then apply correction for LL/Parallax and you have Ho. The correction for Height of Eye/Dip is not required.

And that, you honour, is why I use the GPS.

 

[neil_s]

I have GPS too - but I still like to fiddle about with the sextant!

 

[Laminar Flow]

A confession. I do not understand the use of an artificial horizon. A friend used the water in his pond. Bowls of water , ponds etc are (very probably) higher than a true horizon. Surely that makes a difference to the angle. Taken to the extreme, a sight taken from a satellite (bit of a problem with a bowl of water in the absence of a G force) or an aircraft must surely need a correction or are we talking about insignificant errors?
Please educate an innocent.
(I have also often wondered about using a plumb line (and adding 90°) although I realise that the centre of the gravitational pull moves around a bit).

You are not too far off there; on aircraft they used what is called a bubble sextant, essentially, a sextant, or more commonly an octant, with a built in spirit level.

 

[Skylark]

And that, you honour, is why I use the GPS.

I wouldn’t want to be without GPS either but there’s nothing wrong with practicing the fine art of traditional navigational techniques.

If you’ve never used a sextant, I’d strongly recommend that you give it a try, it really isn’t difficult and who knows, you may join the rest of us and “become hooked”.

On a long passage/out of sight of land, it is stimulating, satisfying and very rewarding.

Of course, this is a truism made by our resident, experienced sailor and trainer.

Not for everyone of course.

 

[Graham_Wright]

I knew the captain of one of the merchant ships on the Falklands expedition.

He made his passage using DR and sextant. (For obvious reasons).

 

[shortjohnsilver]

I was an RFA third officer deck in the South Atlantic aboard a commercial ship the Alvega Silver Line. The old man had me doing stars every morning and evening 8 - 4 watch. Would take quite a while to sort them out too, although I got quicker. The old man used to come up into the bridge just after eight and say “where are we then?” I would duly indicate current position distance run etc. He would walk to the back of the bridge and fire up the starlight navigation machine there and wait. The sat nav was new technology then and this was his toy. No one was allowed to use it, well, I certainly wasn’t. He’d make a note of the last and long the sat nav machine gave and come back to the chart table and compare it. Every morning this happened on passage down to the S Atlantic. He wasn’t a bad man just like to test his officers and that including me first trip third officer freshly promoted and first trip to the falklands during a war.
Thankfully my navigation wasn’t too bad and those compared positions were generally not that far off each other. He’d say, “ good, we’ll go with yours today”! Top fella really like him.
I came to love the sextant and would use it a lot.

 

[neil_s]

Good point about sun,run,sun.

Just seen it on Ocean Navigator. It can do multiple sights and sun-run-sun and it gives you your lat long. It also reads the Alt. for you. So it seems it's a 'point and shoot' position fixing instrument. Not bad! GPS is obsolete!

 

[Gary Fox]

'GPS is obsolete..'

 

[Buck Turgidson]

You are not too far off there; on aircraft they used what is called a bubble sextant, essentially, a sextant, or more commonly an octant, with a built in spirit level.

And if you were on my aircraft you would have learned quickly to check I hadn't put soot on the eyepiece lest you spend the rest of the flight looking like a panda!!

 

[Laminar Flow]

And if you were on my aircraft you would have learned quickly to check I hadn't put soot on the eyepiece lest you spend the rest of the flight looking like a panda!!

You scoundrel, you.

 

[Kukri]

Just seen it on Ocean Navigator. It can do multiple sights and sun-run-sun and it gives you your lat long. It also reads the Alt. for you. So it seems it's a 'point and shoot' position fixing instrument. Not bad! GPS is obsolete!

I think I like it. The Astra IIIB is a very good sextant, and if I don’t have to do sums, I love it!

 

[Zing]

This is a modified new-build Astra IIIB, it is in production. No consultation of tables is needed, or even a pen and paper, but you need to choose your body and time.
You check the index error and enter it into the computer, followed by the name of the planet.
Then you use like a normal sextant, bring it down to the horizon and swing to check you are vertical.
Now it gets interesting, the light button has been converted, and you press it.
The computer in the sextant will immediately give you a LOP on the screen!

Obviously this raises a few questions, I'm only at RYA Ocean Theory level so don't shoot the messenger, but would you buy one of these?
It drastically reduces the possibilities for mistakes in plotting on paper of course.
Sadly it would take away the jolly fun of peering at confusing columns of 1 millimetre high numbers in a damp book, while being flung about and wondering if your stopwatch is correct..
The robustness of the electronics is unknown, but we don't usually View attachment 108967drop sextants anyway..personally I can definitely see them catching on, although I haven't checked the price because I can't afford one..

Surely if you have electricity to run that thing you have power to run a GPS? So what’s the point? I say learn it the old fashioned way and keep paper tables or don’t bother, because when you are mid Atlantic during WW3 and the Chinese have destroyed the GPS satellite network and the nuclear bomb EMP has destroyed your electronics, how on earth are you going to get across otherwise?

 

[Kukri]

There are, I think, two points in favour of this instrument:
First, half of the battle is keeping in practice with observations. We are taught to plot our results on graph paper, but this is easier.
Second, I find that I make silly mistakes with the arithmetic. This eliminates that.

 

[neil_s]

I have the Almanac and the tables - but I also have a scientific calculator to do the reductions and I have PC based astro calculators. I enjoy messing about with all of it! As for GPS, the Furuno GPS30 I have dates from GPS only days, but how are later - Galileo enabled models going to cope now we are excluded from Europe? They don't seem to like us very much - remember selective availability?

 

[Frank Holden]

There are, I think, two points in favour of this instrument:
First, half of the battle is keeping in practice with observations. We are taught to plot our results on graph paper, but this is easier.
Second, I find that I make silly mistakes with the arithmetic. This eliminates that.

Graph paper?.... we used to dream of graph paper on the 'Cape Mail' ..... I didn't even know of or see those green US plotting sheets until I went foreign flag.
Full morning's work on 2 pages... from mate's stars ... to a 1200 posn to give to the old man ( 1st class passenger betting on the day's run was BIG in that trade ) .... two sights on the left hand page ... all the runs etc on the right...ABC tables used to calculate ITPs.... basic bit of plotting on the left as shown.

I think this instrument is ... how you say...dumb.

The electronics will be dead, deceased, the full Norwegian Blue.... while the sextant will still be going strong.

What exactly do you need to transfer from traditional sextant to computer? The Altitude? Nada Mas...... not too hard...

My money will stay in my pocket...

PS Just in case anyone thinks I am a luddite... I started using 'puters for sights in about 1990.... a program by Mike Harris published in PBO and a Sharp(?) pocket computer with 8k of memory....

Prefer paper... you can find your mistakes......

 

[Bristolfashion]

Isn't it a bit like a digital abacus? I don't really see the point of a back up for when your electronics fail that is electronic!