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  #21  
Old 12-12-2012
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Re: Gps navigation advise

Quote:
Originally Posted by travlineasy View Post

Fire up your GPS/Plotter and take a close look at the ICW behind Virginia's Barrier Islands from Cape Charles to Chincoteague. I think, John, that you'll find it interesting to say the least.

Good Luck,

Gary
Sure, I have no doubt that particular area as charted bears little resemblance to reality...

However, I doubt that waterway - with a project depth of 4 feet or so, and probably considerably less in spots, and the 35' clearance of the fixed bridges over Chincoteague Bay - is included in what most people think of when they hear "Atlantic Intracoastal Waterway"... (grin)
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Old 12-12-2012
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Re: Gps navigation advise

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Originally Posted by boatpoker View Post
For those that believe in the infallibilty of GPS charts and charting. These two photos were taken from my helm within seconds of each other. I have dozens of such shots.
Yeah, I suspect anyone who's gone pretty much anywhere can offer such examples... Where was yours taken, btw?

When it happens in places known for rocks, and fog, it should really give one pause...

Damn, think of all those Newfies lying under those headstones, who might have been saved, if only they'd had the benefit of today's technology... (grin)



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Old 12-12-2012
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Re: Gps navigation advise

It has been some time since my nav training so feel free to correct any inaccuracies I may proffer. Nav 101: Charts are flat, the earth is spheroid. Within a given chart, survey work done on the datum points give good relational accuracy which puts you pretty accurately on the chart given the bearings you take. Unfortunately, the earth is spheroid (not round or oval, but actually a little bit lumpy). GPS calculates where you are on the surface of the spheroid and not necessarily the cardinal coordinates for a given chart. If your chart has been updated to WGS 84, then it reflects this and you should have a pretty accurate fix on your (newer) paper or electronic chart. If the chart has not been updated and is showing something like WGS 72 or older, then the chart may or may not be that accurate depending upon how “lumpy” that particular patch of earth is. In the US (and most of Canada and Mexico) the WAAS system is used to ensure greater accuracy in the timing measurement. However, due to the placement and orbits of the WAAS satellites, places like the arctic, coastal Mexico (and potentially the US coastlines) may have slight variations in the timing signals and hence GPS accuracy.

GPS only “replaces” the celestial part of navigation and there are tons more to learn about navigation than turning on the Garmin and setting the autopilot. How many of us have chart #1 for example? Can you calculate set and drift? Heck, most people can’t even spell “ded reckoning” correctly. Sure, Columbus discovered the New World, but a skilled navigator will make landfall where he originally intended to go.
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Re: Gps navigation advise

The wonderful thing about all the new technology that has "replaced" paper charts is that one can now get a device that displays all the information on one screen.

AIS, radar, chart plotter depth sounder, everything one needs to exactly observe not only one's own position relative to all things stationary but also to observe one's position to and the identity of the more threatening of those things moving.

There are even some of us that believe the screen on this marvelous piece of equipment will never go black, leaving one without ANY form of positional data.

The paper charts I use cannot accidentally switch off. Sure I use GPS to find the spot on the chart where I think I'm at but if I'm able to hit something then I'm also able to see it using the good old Mark 1 Eyeball.

To each his own.
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Old 12-14-2012
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Re: Gps navigation advise

Post Disclaimer: By posting the link below I am no way saying everyone should panic, run around in circles like their hair is on fire, scream like Chicken Little, go buy the next sextant they see and learn celestial nav., brow beat those that advocate paper is a necessary back up or those that say GPS is all you need. This is squarely informational for you to use as such.

How to bring down mission-critical GPS networks with $2,500 | Ars Technica
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Old 12-14-2012
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Re: Gps navigation advise

The age of expensive, bulky, quickly obsolete paper charts is obviously in decline but even if a paper chart is obtained from your chartplotter via a printer, it is still another source of information to weigh against what shows on the plotter screen. The more sources of navigation information the better. There is always an element of DR. Confirming what you are observing should have as many inputs as possible, not just looking at a digital image which COULD be wrong for one reason or another.
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