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Old 29-12-2009, 23:26   #1
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Trust Your Eyes, Not the GPS

I just saw this on one of our national news channels. I think it applies to boating as well.

CTV News | Couple stranded after GPS sends them down backwoods
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Old 30-12-2009, 02:46   #2
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What a thing! 50km down this road! Didn't they just ask if this could be right?

We are often asked, in the last two or three years particularly, if 'we have satnav on the boat?" We started off by saying, well. we have 3 GPS and chart plotters, but it's not quite the same. Now we just laugh and say yes. Just not in the car. (We don't own a car.)

In a useful reminder, my mother's place is incorrectly plotted on the satnav by her postcode, so any delivery involves lots of explaining about using your eyes and following landmarks!
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Old 30-12-2009, 07:24   #3
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We bought parents a tom tom. Had to chuckle, it told them to take a left and get on the ferry in southern central wisconsin. No water or ferry for many miles around.
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Old 30-12-2009, 07:34   #4
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Yet another reason to have a quality magnetic compass.
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Old 30-12-2009, 07:37   #5
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I had a similar experience (or nearly so) when I used a GPS on a drive from Maryland to Indiana a few weeks back. The GPS continually gave nonsensical backroad routes despite being selected for "main roads only." I gave up trying to use it and trusted the maps instead. Good thing.
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Old 30-12-2009, 08:00   #6
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This situation is not limited to just automotive GPS systems, I rememvber reading an article a few years back where a cruise ship allowed their integrated GPS system to steer the ship onto a shoal that was clearly marked on the charts.
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Old 30-12-2009, 08:58   #7
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Quote:
Originally Posted by Roaring Girl View Post
What a thing! 50km down this road! Didn't they just ask if this could be right?
There is no one to ask in this section of the country! Remember the story of the couple and their baby who were stranded in the snow several years ago? 200 miles between towns is not uncommon. Ranch houses are sometimes ten miles from the main road. School age children live in town with aunts and uncles during the school year. Several Indian Reservations dot the area. Yes, everyone has cable TV, Internet, Cell phones, indoor plumbing(most), etc.

GPS never gives the safest route, only the shortest.
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Old 30-12-2009, 09:05   #8
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GPS

Many times I have had the chartplotter show my position to be up on dry land. Don't have one in my car so not familiar with them, but if you rely totally on the GPS in the boat, your gonna get in trouble.
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Old 30-12-2009, 09:13   #9
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I've found that over 10 years of use my GPS has never given me a false longitude or latitude position. My eyeball triangulation is far less accurate.

I've sometimes received incorrect waypoint information or entered it incorrectly myself, but that's not a matter of trusting the GPS, that's a matter of human error. It's the human error that I tend to back up, not the position.
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Old 30-12-2009, 09:21   #10
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Many times I have had the chartplotter show my position to be up on dry land. Don't have one in my car so not familiar with them, but if you rely totally on the GPS in the boat, your gonna get in trouble.
Car GPS uses Maptech or Google.

Some chartplotters use charts that were surveyed in the late 1700's.

One chartplotter, I saw several years ago, of the entance to SF Bay, uses two charts, one with the water depth in fantoms the other in feet, with no warning!
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Old 30-12-2009, 15:34   #11
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I must be allergic to chartplotters...

Quote:
Originally Posted by nautical62 View Post
I've found that over 10 years of use my GPS has never given me a false longitude or latitude position. My eyeball triangulation is far less accurate.
I learned on my first charter. Brand new spiffy chartplotter. Showed a way to get through Boca Grande shoals (north side) My first mate kept on running to the front of the boat and saying "there's too much sand there" I got tired of the critique and announced that I was going there because the chartplotter said so. Sure enough- we hit sand.- Sure sand drifts I thought....
Since then, I have had the chartplotters put me in the wrong bays, oceans and on land. I would be west of the riprap and the chartplotter would have me on the east- the list could go on and on.
Bottom line: Its a navigational aid.
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Old 30-12-2009, 17:20   #12
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Makes you wonder about things like this

Woman, 47, killed in boat crash | Townsville Bulletin News

Woman killed in late-night boating crash | Townsville Bulletin News

I have seen boats come in here at full noise at night, no nav lights or markers whatsoever here.

cape capricorn - Google Maps

Same here. The lagoon and entrance is fairly riddled with coral bombies and a long way from help, but boats come and go at night, presumably putting all faith in that GPS, which, I thought were out by about 10 metres, which is about how wide the entrance is.
fitzroy reef - Google Maps
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Old 30-12-2009, 18:04   #13
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GPS are electronic devices and have only been around for a short period of time. Man has navigated the seas for thousands of years using their eyes and their brains. Do the math.
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Old 30-12-2009, 20:13   #14
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I have never had a GPS give a incorrect position. The Chartplotter overlay on the other hand is only as accurate as the original chart it was copied from. Many of these charts are based on very old surveys and may be as much as a mile off. GPS and or a chartplotter are simply another tool to navigate with. They should be used in conjunction with other sources and are a huge aid to navigation.
George
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Old 31-12-2009, 15:28   #15
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Once, a few years ago, both my GPS units told me I was in the middle of Trincomali Channel when I knew I was peacefully anchored in Princess Cove on Wallace Island, about 3/4 of a mile away. Never did figure out why.
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