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Just got back from a week of fishing in Loreto, BCS. My Garmin 182 with the Blue Chart chip gave me a display that was from .5 to .9 miles off the actual location. It had me motoring across islands and offshore when I was on my trailer. I checked to see if my WAAS was activated and it said I was 14 feet off of actual. Any ideas of what could be causing this problem?
This does not create warm fuzzy's as far as confidence in the system yet it has not been a problem offshore of San Diego.
Did you use the keypad to move around the chart sometime during your trip? If so, the unit won't return to the default "boat center" mode until you hit the Quit button. You can tell which mode you're in by the shape of the cursor. If you see a computer-like arrow cursor, hit Quit to get back to the normal mode with the triangle cursor.
I think your problem is with the accuracy of the source paper chart. If they (many are used to produce a single Blue Chart) are lacking the electronic chart will be as well.
What I do not think is the problem is the accuracy of your GPS or of the indexing of the chart to your location (accuracy of the placement of your location on the electronic representation of the chart on the screen).
Thom
"I command thee, O fish of the ocean, rise to my bait"
My new WAAS enabled Garmin 176 GPSMAP indicates from time to time that I'm not in a canal but on the adjacent land, or that I"m not really going through the railroad bridge, but through the tracks. Since these errors are repeatable and consistant, my own conclusion is that the charts were slightly inaccurate. Inaccurate by less than 100 feet, by the way.
I can well imagine there are areas where the inaccuracies are much greater.
Comes back to that basic of navigation, it pays to use your eyeballs on everything around you and to use common sense as a prime source of navigation.
I cannot speak as to the accuracy of Bluecharts. But as for the Lowrance maps when they show me on land when I am on water or vice vera, I will download the track, display it over a USGS DRG and the track show me exactly where I thought I was.
Conclusion, listen to Thom, the accuracy problem is with the maps, not the GPS location [img]/infopop/emoticons/icon_smile.gif[/img]
Thom...is dead right. It's the chart. The GPS location is probably OK. Can be a problem in some areas like Hatteras, NC. [img]/infopop/emoticons/icon_redface.gif[/img]
Thom...is dead right. It's the chart. The GPS location is probably OK. Can be a problem in some areas like Hatteras, NC. [img]/infopop/emoticons/icon_redface.gif[/img]
Thom is right...dead right. I'm sure you GPS location is correct but the map source is a 'little' off. Try Hatteras Inlet, NC. A little local knowledge helps. This can be a problem. [img]/infopop/emoticons/icon_redface.gif[/img]
Garmin 182 bluechart problems 
