GPS info

With the recent news of people hitting islands at night while navigating with their GPS I thought I would share a little knowledge about GPS with everyone. This may or may not be news to some of you, but I offer it with the hopes that maybe someone else will be spared a tragic accident.

The Military controls the GPS satellites. They control the signals and the strength eminating from theses satellites. They also have an offset programmed for civilain use. This ofset changes frequently and the variance is anywhere from 3 feet to as much as 100 yds. They do this so that a civilian GPS unit cannot be used as a navigation system to hit a target with a missle. Only our military has access to the dead on accuracy of the real deal GPS signals.
So please heed the warning your unit gicves you when you power it up and do not rely on it as your sole source for navigation especially at night on bodies of water you are not intimately familiar with.

The error you are discussing is called Selective Availability. Selective availability is not used today. Any errors in a GPS are from poor satalite readings. GPSs are general much more accurate than 10 yards. They do have the ability to re-establish the selective availability errors if they deem it necessary.

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The GPS includes a feature called Selective Availability (SA) that introduces intentional, slowly changing random errors of up to a hundred meters (328 ft) into the publicly available navigation signals to confound, for example, guiding long range missiles to precise targets.

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SA was eventually “discontinued”; the amount of error added was “set to zero”[13] at midnight on May 1, 2000 following an announcement by U.S. President Bill Clinton, allowing users access to the error-free L1 signal

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This information is from: http://en.wikipedia.org/wiki/Global_Positioning_System

Good info, Regardless, Wade Still has a very good point. Remember also that your map chips only reflect the water level at the time the chip was made, so if the water level of a particular body of water would rise or fall the map chip will show the shorelines incorrectly as well.
Be safe at night, no fish is worth risking your life for!