New Digital Sextant, would you?

[Gary Fox]

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 drop sextants anyway..personally I can definitely see them catching on, although I haven't checked the price because I can't afford one..

 

[scruff]

I have a ebbco sextant at home. In lockdown 1 I used it in conjunction with an app called 'astro calculator ' on my phone.

Taking a sight using a saucepan of water as a horizon I got within about 5 miles of my houses' actual lat long.

Would I buy a sextant with the app built in - no. I would definitely use the free app on my phone though in real life tho! Quite looking forward to using the sextant on the boat, see if I can get as accurate a result on a moving world.

 

[neil_s]

For it to be a useful advance on the normal sextant, I think it needs to do the 'Sun - run - Sun' and then calculate your fix for you, too. Like you, though, I don't think I will be checking the price!

I have also been doing a few bowl of water sights to keep my hand in! The trick with the Ebbco, I found, was to do five sights in quick succession and then average the results.

 

[Gary Fox]

For it to be a useful advance on the normal sextant, I think it needs to do the 'Sun - run - Sun' and then calculate your fix for you, too. Like you, though, I don't think I will be checking the price!

I have also been doing a few bowl of water sights to keep my hand in! The trick with the Ebbco, I found, was to do five sights in quick succession and then average the results.

Good point about sun,run,sun.

 

[Daydream believer]

I have also been doing a few bowl of water sights to keep my hand in! The trick with the Ebbco, I found, was to do five sights in quick succession and then average the results.

& where does that put you? in the lounge, the bathroom or the pub down the road?
i suspect to many, one of these would make them feel the same as they did when the first GPS came out
First question being "How much?"
Then the next comment being " But of course I always use my graduated board with bit of string and a weight, as I prefer to navigate the conventional way"

 

[capnsensible]

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

Well as long as it's not raining.

For me, the point of doing Astro is to take on the challenge. Not for everyone of course.

 

[jwilson]

Astro is now most of the time a nice harmless time-consuming hobby, orvery occasionally a "break glass in emergency" backup for when all the electronics have gone down - and this can happen even in modern boats if you apply enough salt water below decks.

As a hobby the electronics takes away a lot of the amusement, and as an emergency backup the electronics are probably a lot ore vulnerable to salt water in extremis than a "waterproof" GPS. I once had a "waterproof" GPS half dismatled in a boat oven drying out after it and almost everything else electronic stopped working through water down below. My sextant and tables kept working, as did two quite cheap Casio digital wristwatches. Even if both watches had died I'd still have had latitude.

 

[penberth3]

Not me. Can't see any point in adding electronic gadgets to a simple reliable instrument.

 

[Skylark]

I wouldn’t want one. There’s something very pleasurable about the whole process of celestial navigation. A quality sextant is a joy to own and use. I enjoy reducing a sight and keeping a record in a navigation log. On my last crossing I ran a manual log, in parallel with the plotter, of course, for 17 days /2,800m until landfall. It’s very satisfying and is a stimulating activity during a passage.

 

[lustyd]

Some interesting points here, and I wouldn't be surprised if the image is an old april fools joke or similar. We need to bear in mind though that the military prefer astro navigation as it's much harder to interfere with, so the really big missiles use stars rather than GPS. It's different but it works, and with a computer it's no harder. We also need to remember that GPS only works at all on the planet, so I'd expect more emphasis on astro over the coming century as space really kicks off properly. We now have a somewhat viable space tourism industry, and a definitely viable space freight industry. Inter-planetary mining operations are not far off, and launching a satelite is now within reach of most businesses.
What I would like to see, though, is something using a phone camera to image the sky and find a position. With all of the information of various sensors and imaging it should be possible for a modern phone to get a position without GPS.

 

[TernVI]

My first attempt at astro was using my lodger's girlfriend's theodolite which was somewhat electronic.
After several beers and some wine, we deduced that the moon was going around the earth at a believable rate.
And at exactly midnight, the darkness was indeed, directly overhead.
Happy days!

 

[Tanqueray]

If only they had fitted it with Thunderbolt / USB3 ports you could connect it to the GPS, mount it on a Gimble in your cabin and stay in bed.

 

[Uricanejack]

Not sure what the point of it is.
Im sure a cell phone app could do all the number crunching.
you could even duct tape the cell phone to a regular sextant if you wanted.

 

[Stemar]

Not sure what the point of it is.
Im sure a cell phone app could do all the number crunching.
you could even duct tape the cell phone to a regular sextant if you wanted.

Your cell phone would also give the lat/long before you've got that toy out of its box. Yes, GPS is vulnerable, but I can't help thinking that if GPS gets turned off for more than a few hours, knowing where you are is likely to be irrelevant because where you're going probably isn't there any more

 

[Graham_Wright]

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).

 

[lustyd]

The reflection is the same angle as the original, so basically you get twice the angle and half it from what I've read

 

[Skylark]

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).

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.

 

[Topcat47]

NO! I keep a log, based on gps readings and maintain a plot on a paper chart when offshore. Thus if anything goes wrong I can continue using dead reckoning. Eventually if I"m "lost" I'd not want to use an "electronic " sextant as I'd want an old school navigation method that didn't rely on wriggly amps as a last resort.

 

[Gary Fox]

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.

A nice simple and clear explanation

 

[Gary Fox]

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).

From Nigel Rennie: