Thorny subject: Sextant and GPS era

[ZULU40]

just possible someone else is interested in this

'Interactive Spreadsheets for Celestial Navigation'

Interactive Spreadsheets for Celestial Navigation

[double u]

the higher the body in the sky, the more difficult it is to take the sight (just try it!)
furthermore the sun "lingers" a short while at max alt - so lotsa fun with this system!
4 sec error= 1'longitude

[ZULU40]

Originally Posted by double u

the higher the body in the sky, the more difficult it is to take the sight (just try it!)
furthermore the sun "lingers" a short while at max alt - so lotsa fun with this system!
4 sec error= 1'longitude

thats why more numerous recordings help
but even if you had just one sight, its a help
you have to operate the boat to those circumstances

[RaymondR]

I have an expensive big-ship brass sextant left over from the blacksmith days of navigation which I am going to mount in my saloon as a decorative conversation piece.

With US, Russian, European and Chinese satellite constellations and McDonalds giving away receivers with hamburger purchases the tables, sextant, chronometer, skills retention thing as a contingency against GPS withdrawal is just too much bother.

[Otia]

Originally Posted by Flagman101

Hello, last week-end I got unwillingly into a thorny discussion with an other boater about Sextant and GPS.

So anyways this post is not to argue the necessity or not of knowing how to use a Sextant.

What I'm looking for is actual accounts of sailors, getting lost or in trouble because they're GPSs broke down and did not know how to navigate without a sextant.
Actual bleue water sailors.
I have never heard a single story about that.

I did experience a GPS failure. That's why I have a backup
BTW I also have a battery powered GPS backup; just in case...
I also have Navionics on an iPad, but in case of a catastrophic situation it would not yield enough autonomy. I think its a good idea to put a small GPS unit with batteries in a waterprof bag, like in your ditch bag, before a voyage to cover for the situation where the boat would have taken on water and you'd be left without power from your boat batteries.

[El Pinguino]

Originally Posted by Flagman101

........

What I'm looking for is actual accounts of sailors, getting lost or in trouble because they're GPSs broke down and did not know how to navigate without a sextant.
Actual blue water sailors.
I have never heard a single story about that.

Two words

Wolfhound

Bermuda

[jackdale]

2.5 years ago I was delivering a catamaran from South Africa. I knew there was a sextant on board and had decided to see what I could do - I had the publications I needed. Just before departure from Cape Town, I was in a bookstore and spotted The Sextant, by David Barrie. One line in the book convinced I had done the right thing in getting reacquainted with celestial navigation::

"It is time to rediscover the joys of celestial navigation, not merely as a safety net, but because using sextant to find our way puts us in the closest possible touch with the natural world at its most sublime."

If you have not read the book, I highly recommend it.

[jackdale]

Originally Posted by captmikem

ZULU40

Yes, an accurate noon sight with accurate time can be used to get an approximation of longitude. it was used in the 1800's when accurate timepieces became available. It is just not used nowadays as much more accurate sights are available. That is why a noon sight is also called a latitude sight.

M

I use the arc of time to determine / estimate longitude on a noon sight. It can be done, so why not do it.

[ZULU40]

Originally Posted by jackdale

I use the arc of time to determine / estimate longitude on a noon sight. It can be done, so why not do it.

sure
you can take a first sight recoding the time and not moving the instrument
and catch the sun again on its way back down recoding the time

the point of noon is exactly between the two sight times
but if you screw up, your chance is lost or approximate at best

[double u]

imho the only doable way! just one cloud at the time of the second sight (sic!) & nada!

[ZULU40]

and now for something completely different

the Bris sextant

https://www.youtube.com/watch?v=pm79kH2BBMY

[james247]

Originally Posted by Jammer

If your entire electrical system is toast, the experience of others would show that the GPS is the least of your problems. Besides, on passage, everyone carries handheld battery GPSs, and spare batteries, or has those things in the lifeboat.

Sure do. If you are actually doing things carefully you fill your
R log every hour lat long wind speed dog etc. And mark the gps position on a chart. Nice to have a point certain every hour. And if it doesn't look logical then. Something might be wrong and you only took an hour to realise this. Sailing cruising is a discipline.

[james247]

Originally Posted by ZULU40

depends on the instrument and the user, otherwise about 1 NM



shouldnt take much longer than a few seconds



then you use dead reckoning



the easiest and most crucial are the primary sights, noon, sunrise and sunset

Standing on a wharf you can do better then one mile. Standing on the deck of a 40footer in 3 m of the 5 miles would be exceptional

[james247]

Originally Posted by Dockhead

Fair enough.

Note that I never said that celestial is useless. Not by any means! I just said that in most cases it would not be a disaster to fall back on DR. If I'm trying to find Ireland crossing W to E, I would be quite OK with DR, for example.

And as Zulu40 said, there are ways to find islands without position data. Columbus found the Azores, after all.

Try doing recognition of coast or islands in the Red Sea or the gulf of carpentaria.
You can be 40 miles off the Azores and see them.
Dead reckoning gets better with practice and a gps to check it

[james247]

Originally Posted by double u

they didn't use charts???

This whole issue of being at one with the ocean is interesting. After leaving the land for about 10 days I pick up a whole lot of sixth sense knowledge. Is it bound in my Dna lost in some chasm of my brain. Does anyone else know of the type of experience I refer to. I expect in Viking times Portuguese and other naval explorers they would have know the time from the star locations. Understood the weather from sea direction sky conditions .
Is this knowledge printed in our brain somehow