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View Poll Results: Blue Water- is a Sextant Necessary?
Absolutely essential 24 18.75%
Desirable, but not essential 52 40.63%
Good fun, but little practical use these days 40 31.25%
Don't waste your money and time on this 11 8.59%
Sextants make excellent dingy anchors. 3 2.34%
Multiple Choice Poll. Voters: 128. You may not vote on this poll

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Old 31-10-2012, 06:16   #61
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Quote:
Originally Posted by noelex 77
.....quite unlikely possibilities, in non critical systems, (such as the US government shutting down the GPS system).
Anyone know if it's possible to just turn off the bit of the system we use without affecting all the other services which rely on GPS, airlines, financial systems and health services use the time signal I think as well. Probably many more.
If the whole lot goes down then a lot of stuff will be going badly wrong..
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Old 31-10-2012, 06:27   #62
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Re: Poll-Blue water. Is a Sextant Necessary?

Quote:
Originally Posted by conachair View Post
Over 50 posts but still no one has even tried to get any reliable data on what level of risk loosing GPS is for ocean cruising. "Heard of a couple of boats" doesn't cut it.

Such is the land of forums..
Not to don the tinfoil sou'wester here, but "reliable data" is unlikely to exist outside of academic journals generally inaccessible to the broader public.

I have seen on my own boat momentary "speeds" of 50-60 Kts. by the GPS, which was basically correcting itself despite having a solid 4 or 5 satellite "lock".

For some undetermined period, my GPS didn't know where it was...until it did. On the ocean, or coastally at night or in fog, I have very little empirical means (short of perhaps following a depth contour) of determining GPS accuracy or function. I wouldn't likely notice a mile off discrepancy, even though I log the LAT/LON hourly on watch.

Given the tendency to sail to the mark or the waypoint, or to allow the magic of GPS to navigate in tight places (on the usually sound assumption that it is working accurately), I prefer to exercise prudence and take GPS as a strong, but not error-free, suggestions as to where my boat and crew are.

The system is aging and can be thrown off. I navigate accordingly, and that can include a sextant. Including a sextant and not accepting GPS as the final arbiter of my actual position is just a part of prudent seamanship, in my view. Yours may vary.
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Old 31-10-2012, 06:45   #63
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Re: Poll-Blue water. Is a Sextant Necessary?

Quote:
Originally Posted by S/V Alchemy View Post

The system is aging and can be thrown off.
I think the evidence is that the GPS is getting better not worse. New and better satellites are being launched. The last one just in October.


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Old 31-10-2012, 08:51   #64
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Re: Poll-Blue water. Is a Sextant Necessary?

Quote:
Originally Posted by conachair View Post
Over 50 posts but still no one has even tried to get any reliable data on what level of risk loosing GPS is for ocean cruising. "Heard of a couple of boats" doesn't cut it.

Such is the land of forums..
The problem is that is no good way to get the data.

The only convenient way to get the data would be to look at groups of boats of boats traveling together for long periods.

You might think long distance races, but they for the most part aren't long enough, and they really aren't representative of how boats are a outfitted.

Rally's being longer would be better, but the pool of participants would not be a good representation of the average boat out cruising, self-selection prevents that.

The only other way to get the data would be to interview a lot of boats out actually cruising.
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Old 31-10-2012, 12:17   #65
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Re: Poll-Blue water. Is a Sextant Necessary?

If one data point is any use my GPS has been on virtually continuously for the last 5 1/2 years.
There has been 2 occasions i have lost or had a poor fix.
One due to a malfunction of the primary GPS. Switching to secondary GPS gave an immediate fix.
The second due to a lightning strike. Switching to the GPS, which was an old handheld stored in a faraday cage took maybe 10 mins to get a fix. ( the old single GPS units took a long time to download the almanac and get a first fix). It is still working, but has been joined by a more modern HH GPS that will get a cold fix much quicker.

Some boats do report an occasional loss of GPS fix, but every case I have seen so far is due to poor instalation, a faulty GPS, or incorrect settings.
There must be genuine cases of GPS jamming, but they are rare. GPS coverage is continuous.

To put these outages in perspective celestial navigation will give you a fix on average maybe once a day.

With care and skill you can navigate sucessfully with celestial navigation and DR, but the very best most skilfull celestial navigation is vastly inferior to GPS navigation.

Celestial navigation is easy to learn. The mystyque should be dispelled.
Someone with reasonable intelligence and some mathematical skills can be taught in a Day or couple of days.

Learning navigate a yacht safely with only a modestly reliable fix once a day requires a much higher level of skills.
I worry that many sailors that have mastered the skills to fix their position with celestial navigation and determine a DR position have not learnt the skills to sucessfully complete a voyage this way.

GPS navigation is very different to celestial / DR navigagation. Try It and see. My guess is that if you do you use it seriously many will order an extra HH GPS a metal box and some AA batteries even if you have a back up sextant and know how to use it to fix your position.
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Old 31-10-2012, 13:12   #66
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Re: Poll-Blue water. Is a Sextant Necessary?

I've lost my fix twice. Once was a bad wire on my unit. Once was in an anchorage that just "fixed" itself the next morning when I left and it came back on at the same spot where I lost it the night before.

I don't plan to ever buy a sextant, but that ony makes me part of the 8%. Could be part of a larger group, but I just don't think a sextant would make a good dinghy anchor and a good dinghy anchor will cost less!
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Old 31-10-2012, 17:05   #67
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Re: Poll-Blue water. Is a Sextant Necessary?

It's amazing how many people think MacGyver was a documental.

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Old 31-10-2012, 18:13   #68
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Re: Poll-Blue water. Is a Sextant Necessary?

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Originally Posted by Sailmonkey View Post
Really?! is it a dinghy anymore when it has it's own navigational system
Not necessarily. It might just be a camera. Or a phone. Or a watch.

Pretty soon our toasters will all have integral navigation systems.
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Old 01-11-2012, 00:27   #69
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Quote:
Originally Posted by Don Lucas
people talk talk about the GPS system going down like if that were to happen there wasn't bigger issues, like the end of the world, going on

this IF and that IF

one of those living/sailing in fear things where the fear doesn't cross over into other safety issues

sailing has been going on much longer than GPS and sextants have been around
Yeah. There's a good argument to being lost for a few months at that point...
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Old 01-11-2012, 02:40   #70
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Quote:
Originally Posted by Adelie

The problem is that is no good way to get the data.

The only convenient way to get the data would be to look at groups of boats of boats traveling together for long periods.

You might think long distance races, but they for the most part aren't long enough, and they really aren't representative of how boats are a outfitted.

Rally's being longer would be better, but the pool of participants would not be a good representation of the average boat out cruising, self-selection prevents that.

The only other way to get the data would be to interview a lot of boats out actually cruising.
I think to be honest, even talking to every ocean crossing boat out there today completely loosing a GPS fix offshore might turn out to be so rare that it would be difficult to draw any firm conclusions.
Part of the point of the previous post was that people tend to make their mind up about what the world is like without actually making the effort of trying to find out what actually goes on.
But despite that I do have a sextant. Lovely object in its' own right, and fun to learn. though with even just an ais reciever needing a gps signal its getting more difficult to enjoy the feeling of sailing offshore completely disconnected from the modern world.
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Old 01-11-2012, 03:35   #71
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Re: Poll-Blue water. Is a Sextant Necessary?

Quote:
Originally Posted by conachair View Post
though with even just an ais reciever needing a gps signal its getting more difficult to enjoy the feeling of sailing offshore completely disconnected from the modern world.

Why, can't you just turn it all off if being disconnected from the world is your goal?
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Old 01-11-2012, 05:22   #72
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Re: Poll-Blue water. Is a Sextant Necessary?

GPS will never fail! And if it does, then we have another unit held in a Friday cage.

GPS is a unique system, on so many levels:
- it has been built with parts hand made in China (no planned obsolescence),
- all technicians and engineers are still married (to the same partners),
- it denies gravity (see, it is in the orbit),
- it is protected from solar fluxes (eight layers of International bottomkote),
- etc., etc.,

So, do not listen to naysayers. Go big, go now. Yes, you can!

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Old 01-11-2012, 05:27   #73
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they also said the Titanic didn't need enough lifeboats for all the passengers...... just sayin' if necessary you could rig up an astrolabe something like that but when you can buy a sextant so cheaply that's at least good enough to get you a shore landing with 1 of the little Davis mark 3 is that it seems to me that stupid not to carry 1.
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Old 01-11-2012, 06:29   #74
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Re: Poll-Blue water. Is a Sextant Necessary?

I wonder in which direction the sun rises and sets in? Does it change? If I were to lose my GPS and were to just follow the sun what would happen? If I keep spending money for things on the boat "because it might happen" would I ever go anywhere? If I'm that worried is it smart of me to get on a boat to start with?

Just so many unanswered questions, just what is one to do?

By the by the poll at the moment says that 81.25% of responders don't feel a sextant is needed. What fools!
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Old 01-11-2012, 06:43   #75
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Re: Poll-Blue water. Is a Sextant Necessary?

Don,

The sun always rises in the west and sets in the east, unless of course you are in the southern hemisphere, where it is the direct opposite (except wednesdays and during full moons - then it's like the northern hemisphere).

O course you should note and be aware that if you travel far enough north (or south) there will be times when the sun doesn't rise for several months at a time - what will you do then? I would suggest that you make a chalk mark (or similar) at the bow of your boat sometime when you know you are sailing due north.

That way, if all your GPS's and compasses do a tube job and quit on you - you'll always know which way is north!

I mean - how hard can it be?

jus' sayin'

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