Topic: Nacionics, GPS and error depth readings

[steelebob]

I have 2 Humminbird 898c and 2 Navionics Premium cards. The worst mapping errors for me I was looking for largemouth water on my console unit. The map kept tell me it was 5 feet deep, this was over 100's yards of cruising, but the HB was consistently saying 25 to 30 feet. Another time that sticks out in my mind was cruising around another lake. That time I was using both the console and bow units. I kept saying to myself, the guy who did this lake "survey"  was lazy and didn't cover the entire lake, just did some readings here and there and made assumptions about the rest of the lake. It was strange because I started to see a pattern in the errors I was getting and started to predict correctly the errors in readings that was coming up ahead in my cruising. On only one lake (out of about 20) is the map spot on.
 So are we JUST talking about map offsets? If not, what should I do in the future when I come across these situations again?