Poll-Blue water. Is a Sextant Necessary?

[S/V Alchemy]

Originally Posted by sailronin

Unless you're piloting from buoy to buoy, thinking "Somewhere around here" keeps you more alert than "knowing" with in a few meters. Many boats run into trouble cutting hazards too close because they are so certain of their exact position they forget to look out the window and reality reaches up and bites them.

This was my point, better expressed. Of course, use the GPS. But take sights at noon or once per watch not only because it gives you excellent practice and keep your mind sharper, but because you are actually concentrating while keeping an arm around a shroud and experiencing the sea more or less directly.

Night sights are challenging to plot, but you can learn a lot about the weather to come if you can "see" in a familiar star's twinkle the movement of upper air. Sounds crazy until you try it, but a disturbed or fast-moving load of even clear air will make the stars appear to twinkle differently than still air.

It is too easy, with all the electronics available, to spend time offshore lolling about in the cockpit. You learn about the totality of your immediate environment. Celestial's side benefit is that it requires you in most cases to get out on deck.

[sailorboy1]

I believe that if you have a fix that the GPS will indicate almost exactly where you are.

The chart that you are using the fix with is a different matter!!!

I would guess chart accuracy wouldn't be as much of a danger if using a sextant.

[noelex 77]

It does seem ironic to me that GPS is often criticised or its accuracy. Yes it's generally much more accurate than the charts, but I don't see that a negative.

I sometimes get the feeling that if we turned SA back on some people would be happier with GPS. If we degraded the fix to 2-5nm and limited it to one fix a day they would be ecstatic

[sailronin]

The fact that GPS is more accurate than the charts has caused multiple groundings and loss of vessels as skippers inexperienced in "pre electronic" navigation put too much trust in the absolute accuracy of their GPS.
A few years ago I was coming into Golfito, Costa Rica at night. I instructed the mate to circle offshore until daylight. He objected saying that the GPS and chart plotter were accurate and he was comfortable running on them. I over ruled him and in the daylight entered the harbor, I asked him to read the position on GPS/plotter as we entered without looking out of the pilothouse. He panicked when he thought we heading over a 1/4 mile out of the channel onto the sand spit; that I reminded him is where we would have been had he tried to bring us in on GPS. He never argued with me again about eyeball vs. electronic navigation.
Complete dependance on any single aid to navigation can lead to problems. Generally the more experienced the navigator, the less likely he is to put "all of his eggs in one basket".

[Cheechako]

Originally Posted by sailronin

The fact that GPS is more accurate than the charts has caused multiple groundings and loss of vessels as skippers inexperienced in "pre electronic" navigation put too much trust in the absolute accuracy of their GPS.
A few years ago I was coming into Golfito, Costa Rica at night. I instructed the mate to circle offshore until daylight. He objected saying that the GPS and chart plotter were accurate and he was comfortable running on them. I over ruled him and in the daylight entered the harbor, I asked him to read the position on GPS/plotter as we entered without looking out of the pilothouse. He panicked when he thought we heading over a 1/4 mile out of the channel onto the sand spit; that I reminded him is where we would have been had he tried to bring us in on GPS. He never argued with me again about eyeball vs. electronic navigation.
Complete dependance on any single aid to navigation can lead to problems. Generally the more experienced the navigator, the less likely he is to put "all of his eggs in one basket".

yep, just one tool of many.

[noelex 77]

Originally Posted by sailronin

The fact that GPS is more accurate than the charts has caused multiple groundings and loss of vessels as skippers inexperienced in "pre electronic" navigation put too much trust in the absolute accuracy of their GPS..

And this is the fault of the accuarcy of GPS not the fault if a stupid skipper? Would the stupid skipper manage better with less accurate, more difficult form of navigation?

You cannot fix stupid.

Giving them a less accurate, more difficult form of position fixing, does not seem the solution IMHO.

I understand the bias. Stupid and poor navigators are more likely to use GPS alone without any knowledge of the proper principles of navigation.

This does not make the GPS technology evil or less safe.

[44'cruisingcat]

Originally Posted by noelex 77

Has a sextant and the ability to use it become no longer necessary for a water sailing">blue water sailing boat.
Sadly I think the answer is yes. I wish it was not so.

I can't see why you would wish it were still neccessary to depend on a less accurate and less reliable system of navigation!

If Magellan, Cook etc had access to GPS, do you doubt they would have used it?

[sailronin]

Not stupid, rather inexperienced. Newbies are enamored by the accuracy of GPS, not understanding that an absolute position on the surface of the earth may have little relationship to the vessels relative position on a chart. Frequently new skippers fail to enter the proper geodetic datum into the GPS thus inducing errors into the fix. This can be compounded by charts that are less accurate than the GPS (usually with errors in longitude) or that reference yet another datum.
I'm not suggesting that we would all be better off with the dithered signal; just that mariner's dependance on GPS as a single system cure all for navigation needs is misplaced faith in the real world. Rather simply stating that a knowledge of celestial navigation generally requires an understanding of plotting and pilotage which rounds out a navigator's education. I don't believe having a "sextant onboard" makes one safer, rather it is the knowledge gained in learning celestial navigation that bodes well for the safety of the vessel and her crew.

[sailorboy1]

Originally Posted by noelex 77

It does seem ironic to me that GPS is often criticised or its accuracy. Yes it's generally much more accurate than the charts, but I don't see that a negative.

99% of the time when I stop looking at my GPS/chart-plotter because of the accuracy it is because at the moment I'm MUCH more focused on something even more useful for me at that location .............. my depth gage!

I don't think a sextant would help at those times. But I don't hear of people not believing their depth gage to the point of tossing lead lines over while coming into a cove etc., which to me would be the non-modern equivalent.

[Andrew Troup]

If you have to sail routinely in parts of the world where the charts have land the right shape but in the wrong place (which is the usual problem), there's a third option apart from GPS and celestial which some of the above posters are overlooking.

Position fixing with direct reference to land features and nav markers, immunises you from chart datum problems and inaccuracies.

IOW, 'land relative' navigation methods are not affected, 'global absolute' navigation is. And of course a sextant is helpful for pinpointing 'land relative' positions.

This will not interest those who sail only in well-surveyed waters, but for those venturing far from the beaten track, it's another reason to keep those skills alive (or acquire them)

[Sailmonkey]

Originally Posted by Andrew Troup

This will not interest those who sail only in well-surveyed waters, but for those venturing far from the beaten track, it's another reason to keep those skills alive (or acquire them)

Plus it's a whole lot easier to draw two or three bearings on a chart than it is to reduce a sight

[barnakiel]

All true

and we did get

from

'is sextant necessary'

to

'gps rulez, NOT'

again!

;-)

So ... what do you guys think about R---- anchors?

b.

[Celestialsailor]

Originally Posted by noelex 77

Has a sextant and the ability to use it become no longer necessary for a blue water sailing boat.
Sadly I think the answer is yes. I wish it was not so. The sextant is a wonderful instrument to use and it is immensely satisfying, but is it necessary?

Many years ago in the early days of GPS I cruised with a very competent skipper. He expressed a desire to learn to use a sextant and since we were sailing between NZ and Tonga, it seemed an ideal time for him to learn.
Despite trying as hard as I could, I could not teach him. Mostly because his motivation was not there. He felt with a fixed GPS and a single handheld GPS he had a reasonable backup.
I spent my final day (and night) writing simplified celestial navigation instructions and sealing them in plastic bag for the emergency situation when the GPS failed.
He still cruises 6 months of the year and when we meet up for dinner, even some 20 years later, he always teases me that he still has my handwritten instructions ready for the day his GPS units fail.

The GPS system is more robust than it was 20 years ago. With cheap GPS units its feasible to have multiple backups and keep some of these sealed with their own power supply and protected by a faraday cage.

So is a sextant and the ability to use it essential for for blue water cruising?

Oh boy!!!...This is going to be a good thread! Is it necessary? Not really but nether is sailing. I mean one could take a plane or train to an exotic destination. What is necessary is the what it feeds back to you. How using one makes you feel. I have a C.Plath Navigator Classic. Only 1600 built. There is no better sextant. I love showing it to people that appreciate beautifully hand crafted, extremely accurate measuring equipment. I have a main GPS and a hand held back-up. I do not have an Almanac for the sextant and I'm wondering if I can find it online or on CD. That would be mixing old school with new school.

[Celestialsailor]

I see most of what I need is here...
The Astronomical Almanac Online -- Welcome

[Andrew Troup]

And sight reduction tables, the entire HO249* set, are also available online (for which knowledge I am eternally grateful to a member of this forum)

Maritime Safety Information

I only had some volumes in book form, covering only the latitudes I usually frequent, and occasionally would get a tad apprehensive about losing or soggifying those.

It's nice to be able to print out certain pages too, especially if trying to pass the skills on to budding celestial navigators.

*ON EDIT
actually they're the US equivalent, ie Pub 229
which as far as I can tell differ only in being arranged with the same LHA on the same page, where HO249 has the same Latitude on the same page.

The latter is a bit more convenient, as you don't change Latitude quickly in a sailing vessel, so you can stay on the same pages.
I guess the tables were intended for Air navigation, so this convenience factor was not considered in the layout of Pub 229

.... of course HO249 were also intended for air navigation, but perhaps British planes do not change latitude with such gay abandon !