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post #22 of Old 09-06-2012
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Re: Free or low cost GPS navigation software?

Originally Posted by skygazer View Post
One year later........... I had a strange experience last Saturday. I was sailing in Casco Bay (Maine, lots of rocks and ledge), running up close to two small rocky islands, and deciding whether to run between them (narrow, shallow) or around the outside of the outermost one (deeper, lots of sea room).

I looked at my Garmin and it showed my boat already outside the outer island, quite a distance from my actual position - it was a clear evening with plenty of light, sun just setting, full moon about to rise - good visibility. I checked several times, the Garmin - normally extremely accurate - was showing the completely wrong position for my boat. Since I was checking for depths, I could have gone very wrong if I wasn't relying on a paper chart and visuals, with the Garmin as a helper. When I rounded the outer island and tacked into it's lee and onto my anchor, the position was shown correctly.

So while the chart on the Garmin was accurate, my position as shown was totally inaccurate for a short while.

Glad it wasn't foggy!
Similar experience with my (less than one year old) Garmin one month ago. It taught me two things. Never rely on it alone and only sail into anchorages after dark that you already have a track for. Depth sounder showed 24 feet of water and my bow hit a rock which was about 30 feet long and 18 inches out of the water. My spot light wasn't working. My keel didn't touch bottom as there was lots of depth right up to the rock. The rock was not on the chart or not in the correct location, in fact after checking the area with the same gps on my buddies boat it this whole area is not accurate on the charts when it comes to depth and land locations. I paid over $3k for this particular unit. I have sailed into some tricky spots before and the plotter was very accurate but not this time and it cost me a haul out and some fibreglass repairs. I lost all faith that I had in my new unit. I was also sailing on a friends boat around the San Blas Islands in Panama last Feb. (his chartplotter was Raymarine, not sure what charts were loaded) and there was a whole Island that was not on the charts! We were night sailing and got lucky that time.

1977 38 foot C&C Mark 1
Hull #92
Sailing the Exuma Islands, Bahamas
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