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Old 15-02-2011, 19:48   #61
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I think it's probably more likely your gps unit will fail long before gps all the sudden becomes unavailable -- at least for the foreseeable future, though denying it could ever happen is, well, ridiculous (no offense intended).

In fact, there have been plenty of things take place over the last decade that I never thought would happen, some of which were good (our lists may differ, but I hope you get my point).

I guess it just depends on what you want to do and what you feel comfortable with. I'm certainly not going to try to convince someone to do something that may end up endangering their lives -- after all, I won't be there when s*** hits the fan.
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Old 15-02-2011, 21:27   #62
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There are several other techniques then using a sextant.
Indeed. Starting with the fact that many of us are able to use radar to observe a land mass from as far away as 24 (or in many cases, 48) nautical miles.
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Old 15-02-2011, 21:43   #63
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GNSS is here to stay , live with it. If you want a safety belt then brush up on other techniques as well. Don't justify celestial usage by suggesting far fetched GPS /GNSS failure modes.

Dave
The idea that you could convince 19 guys to hijack four jets on the same morning in the 21 century probably seemed far-fetched...you know, before it happened.

Impact of January GPS Glitch on US Military Slowly Being Revealed - IEEE Spectrum

Glitches happen. Sabotage happens. Acts of war happen, but they aren't likely in the future to look like acts of war. Guns are so passe, really, when you could damage your enemy in other ways.

GPS Jamming Devices Pose Many Threats (w/ Video)

My last sextant came from China. It's made of the finest irony.
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Old 15-02-2011, 21:47   #64
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Indeed. Starting with the fact that many of us are able to use radar to observe a land mass from as far away as 24 (or in many cases, 48) nautical miles.
Absolutely, but the prudent mariner relies on a mixture of navigational techniques to obtain decent fixes.

This implies a familiarity with a mixture of techniques beyond "one".

A lot of people with RADAR don't know how to operate it effectively. I myself have heard a skipper claim "the radar is broken" when the gain needed to be adjusted for a rain band.

A lot of people (admittedly fewer) can't easily work a compass or take a bearing. GPS is of course not to blame for this, but for those who can't or won't master basic seamanship, the beautiful little moving triangle on the plotter provides false confidence.

Mastering pilotage, CN and the other methods provides not just confidence, but competence.
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Old 16-02-2011, 04:49   #65
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Indeed. Starting with the fact that many of us are able to use radar to observe a land mass from as far away as 24 (or in many cases, 48) nautical miles.
Regardless of what range scale is available on the display, if you only have a 2 Kw transmitter you will not get returns at those ranges except in extraordinary ducting conditions.
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Old 16-02-2011, 05:44   #66
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No Celestial in not Necessary to sail off shore but neither is a life jacket. The likely hood that GPS will go down in rather slim, but lighting isn't and I personally can point to more than one boat that has been hit and lost everything electric. This year when I dragged my hand held GPS out I found it totally useless due to the fact that I had left the battery's in over the summer lay up and they exploded inside and ruined the entire unit. Now imagine you are mid ocean and this happens, no paper charts, no dead reckoning experience, what to do, radar won't help, depth sounder won't help. Due to the fact that you were counting on your GPS you more than likely have not plotted your position every hour or every watch change and now have no idea where to start your dead reckoning from even if you know how to do it.
In my younger days we did not have electronics just a watch and a compass, we threw a chip of wood over the side and timed it's passing to get our speed, took bearings off radio towers or water tanks to get a line of position or a running fix. I may never need to use these skills again but if I do they are available to me.
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Old 16-02-2011, 07:07   #67
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Well, if the GPS satelites fall out of the sky they shouldn't effect the Irridium satelites so you should be able to download How to Make your own Sextant!
http://www.google.com.au/search?hl=en&source=hp&q=how+to+make+a+sextant

Then you can point it at [whatever-you-point-a-sextant-at] and put the numbers into a On-Line sextant calulator and know you are within 5 miles of where you think you are (in St Martin that would hopefully be on the French side instead of anchored in the stinky Lagoon!).

Voila!!

Mark
PS I don't ask if people have a sextant. I certainly do ask if they have a Liquor Cabinet.
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Old 16-02-2011, 07:49   #68
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I hope those sattilites don't hit my boat when they fall....
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Old 16-02-2011, 08:16   #69
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Why not spend the time to learn it? It's not that difficult and, if nothing else, it gives one an appreciation of what "the ancients" (well, not so ancient) were able to do with a glorified protractor and some trigonometry.

I finally learned celestial this winter and am now wondering why I was convinced for so long that it was some sort of enormously complex black art. It is not.
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Old 16-02-2011, 12:29   #70
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Of course it isn't. Child midshipmen were taught it for hundreds of years in the Royal Navy. That meant learning long-form sight reductions, not the four-function easy stuff we can do today. Learning the "lunars" method must have been an utter pain, but again, every prospective lieutenant had to know it, and the Navy histories have several constructive examples of what happened to wooden ships that had poor navigators.

The only conceptual hurdle is learning how to add and subtract around a 360 degree circle without putting yourself in the middle of a continental landmass.

GPS presents so few conceptual hurdles that relying on it as a sole method of navigation cuts off the skipper from a wider appreciation of what a little boat on a big, watery sphere actually means. It's the equivalent of omitting half of the driving test because you will never go on the highway or parallel park.

The point about lightning or total electrical failure is well-taken.
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Old 17-02-2011, 12:39   #71
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"A powerful solar eruption that triggered a huge geomagnetic storm has disturbed radio communications and could disrupt electrical power grids, radio and satellite communication in the next days, NASA said.
A strong wave of charged plasma particles emanating from the Jupiter-sized sun spot, the most powerful seen in four years, has already disrupted radio communication in southern China."

I took this off of Yahoo a few minutes ago. I thought that it was of some value for this discussion.

Mike
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Old 17-02-2011, 17:02   #72
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It's a reminder. Solar wind and flare activity can damage satellites like the GPS constellation or simply by swamping their transceiver frequencies. LEO constellations like Globalstar and Iridium can be affected by the heating and expanding of the upper atmosphere to create (admittedly miniscule) drag forces.

Or, like Iridium 33, they can just collide with another satellite.(2009 satellite collision - Wikipedia, the free encyclopedia). In fact, if I had to lay money on it, I would suggest that the greatest threat to keeping satellite constellations and their ground-based systems intact was space debris.

Are satellites robust? Generally. Are they bulletproof? No. There have been several failures. Can they be jammed? Yes.

A sextant is prudent. Knowing navigation holistically (and through eyeball practice) makes good sense.
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Old 18-02-2011, 07:16   #73
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Pitty the doomsaysers were wrong again.

All satelites present, accounted for and Intact! Sir!!


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Old 18-02-2011, 10:33   #74
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That's just one flare, after a lengthy period of low solar flare activity.

Here comes the sun: Solar flares make way to Earth - The Globe and Mail

From today's paper: "NASA says the particle cloud produced by a Feb. 14 event is relatively weak, and most likely will only result in some beautiful sightings of the aurora borealis – shimmery displays of red, green and purple that are expected to light up the northern sky this week.

But Mr. O’Hanlon, who conducts research on space weather and its effects on GPS software receivers, says people who have come to rely on their GPS technology during the period of quiet solar activity may see more interference with their navigation systems as solar activity picks up.


“It’s been minimum activity, and we haven’t had to really worry about GPS. That may not be quite the case over the next few years,” he said."


Bolding mine. Hence, CN as a Plan B is prudent. Quite frankly, if you rely solely on GPS and minor/transient activities creep in due to solar activity, are you even going to notice until you hit something?


The focus on GPS as an infallible system of astounding accuracy reminds me of how Catholics used to regard the Pope and how today they assume having belts and airbags will save them from their own crappy, too-fast driving. It's not "doomsaying" to critique the notion that GPS is infallible. It's prudence. It's reasonable caution. It's seamanship.
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