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Old 27-01-2011, 20:41   #31
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Apparently they can block whoever they want too.Read this....
Intentional degradation of the satellite signal - Selective Availability (SA) is an intentional degradation of the signal once imposed by the U.S. Department of Defense. SA was intended to prevent military adversaries from using the highly accurate GPS signals. The government turned off SA in May 2000, which significantly improved the accuracy of civilian GPS receivers.
more info., Garmin | What is GPS?

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Old 27-01-2011, 21:08   #32

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conspiracy theories will abound... but, there is no doubt they are doing something intentional... if there was a problem and or they were working on a solution they would tell us...

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Old 27-01-2011, 21:09   #33
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Yon can buy a jamming device made in China for $40.00 and its run on your cellphone. Just think, you could screw someones GPS up as you sailed by.

Here's another website.

If you're not concerned by now, do a google search on GPS jamming.
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Old 27-01-2011, 21:15   #34
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Originally Posted by Bergovoy View Post
conspiracy theories will abound... but, there is no doubt they are doing something intentional... if there was a problem and or they were working on a solution they would tell us...
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Old 27-01-2011, 22:35   #35
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The Chinese military have been test jamming GPS for a while now. A lot of munitions have GPS guidance on them so I guess the Chinese feel it is in their interest to perfect the GPS jamming process.
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Old 27-01-2011, 22:55   #36
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Originally Posted by joey69 View Post
.......... There are no subscription fees or setup charges to use GPS.
Very generous, but IMHO a huge mistake. They should have put say a $10 license fee on every GPS reciever sold. Wouldn't hurt consumers in the least, and when you think of the numbers of recievers out there now, including mobile phones and car GPS's the system would probably be making money, rather than costing it.
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Old 27-01-2011, 23:16   #37
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Originally Posted by North26West80 View Post
This question this post presents (navigation without GPS?) seems like a fair question and so far the responses are more about denial that this could happen. Hmmmm.
N26W80, exactly. My point was that there has been a slow creep of acceptance of electronics as foolproof and never can fail over the years, and I wonder how many go back to the basics.

It was nice to see that after we eliminate all the conspiracy theories, that at least some suggested old fashion hardcopy paper charts and compasses still were viable.
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Old 28-01-2011, 00:25   #38
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If its true its time to blow the dust of the Sextant, Compass and paper chart.
For this very example, none of us should sail any distance where we arent capable of traditional navigation. Be it Pilotage for an inshore trip, Coastal Nav for a port hop or Celestial for blue water.

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Old 28-01-2011, 04:43   #39
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I have a sextant but have not mastered it, yet. On the bucket list.

Intentional or not GPS failure is a possibility. It could be human intervention, a solar storm of sufficient magnitude, or a life cycle failure of some satellite component.

IIRC the new generation birds are some 3 years behind schedule and GAO has published a report saying the system stability is at risk due to the Air Force not being able to manage the procurement contract.

Imagine that!
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Old 28-01-2011, 05:14   #40
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read the fine print

From Panbo

If you read the Advisory carefully you'll see that whatever is being tested -- which sure seems like jamming to me -- will apparently be more effective at high altitudes than at the levels most of us travel...No source I can find is predicting problems at ground level
There is no threat of major outage for boaters. There is no conspiracy, no planned gov't takeover of your vessel while you're away. You may experience "unreliable" signals within a small area of the ocean.

From latest Dist 7 LNM:
Discussion about alternatives to GPS are great, because there is always a chance that your own unit will fail, or your power source will fail, but interjecting conspiracy theories to debate the pros and cons of relying on GPS really doesn't move the discussion along.
"When one is willing to go without, then one is free to go." - doug86
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Old 28-01-2011, 05:40   #41
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As far as I'm concerned GPS is a lot like Heroin.... easy to buy and use but sooner or later it creates a dependancy in the majority of users.....
Take it away and watch people fall apart....
“I do not exist to impress the world.
I exist to live my life in a way that will make me happy. ”

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Old 28-01-2011, 06:10   #42
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GPS is the best invention since bottled beer; but prudent navigation mandates confirmation with all other systems on board: compass, paper charts,where the sun rises annd sets,your eyes,ears annd brain, all that with experience and good seamanship will carry the day without panic when any one system
(excepting the brain) shuts down.
For those who cannot take thier eyes off the chartplotter, it is helpful to remember that the sea is usually blue,green or grey (good) ; land and reefs usually brown (bad).
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Old 28-01-2011, 06:24   #43
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Follow the oil slick.
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Old 28-01-2011, 06:37   #44
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My Backup Navigation Plan--step 1.

My backup to GPS starts with a compass and accurate deviation chart. You'd be amazed how accurately you can navigate with just a heading (preferably held by an good autopilot), and if you have never swung your compass, you'll probably be surprised by the errors. 10-15 degrees error on some headings and zero error on others is not unusual and tiny changes in the compensator magnets can skew this all over the place.

Fluxgate compasses are better and worse--the worse being where they tend to get mounted and the flux altering stuff that tends to be stored and unstored nearby.

I have swung my compass using a sundial like device I invented to use the sun as a accurate reference direction. I've been able to adjust the compensators to get all directions within 6-7 degrees which isn't great, but of no consequence because I have a compass deviation chart that I can lookup course and get the compass "steer" value accurate to with one degree or better. I have a thirty year old analog autopilot but with a little finesse it will hold an average heading to better than one degree which I have verified by GPS and other means.

Like I said, my sundial compass calibrator is of my own invention and a bit complicated, but very accurate. I made it many years ago but since then I've seen similar things published in magazines and on the internet. Google it and you'll probably find something. There are ways of doing this with GPS now and I'll probably use that in the future.

Holding course within one degree may not sound realistic for a boat, but I'm here to tell you that I've been doing it for many years and GPS has verified the results. If you can stay on course within one degree, that's keeps you within 106 feet of course centerline per nautical mile.

Of course, this is under favoriable conditions and leeway and especially current can skew these results considerably and must be factored in amoung other things.
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Old 28-01-2011, 06:47   #45
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A Sextant? Really? GPS unreliable? Yes, occasionally the government can screw with GPS signals and cause a minor inconvenience, or a relatively rare electrical failure of some sort can take out your receiver, but a sextant can be taken out by a cloud. If you use it sunrise, sunset, or noon sights you get a position fix three times a day on your best days (ones with no clouds). Even then it somewhat depends on the skill of the user. What does a sextant user use between sights? DR and Pilotage. Besides, unless you’re anchored or tied to terra firma somehow, a sextant only tells you where you were, not where you are, because by the time you get the calculations done you aren't there anymore. I would much rather deal with an occasional GPS difficulty, than be done in for days at a time by a cloudy sky. They seem to happen much more often than GPS or electrical problems.

Perhaps a sextant is somewhat useful on a major crossing where one might be out of sight of land for days or weeks at a time and a complete on board electrical failure might take out the GPS system permanently. In reality, a sextant is used to correct DR plots, not to tell you where you are or where you’re going. Even though I use GPS a lot, I always know where I am and the compass courses and estimated times of the various course changes along my route. If the GPS goes out along with all my backups, I'll still get very close to where I intended with just a compass and a watch.

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