Quote Originally Posted by HeyCharlie View Post
I took my car GPS ( garmin nuvi) on boat in a couple of small lakes, just to see how it worked. It did Fine. when driving car, it shows streams and small ponds just like they are. You would think boat GPS would do as well! ( maybe because I have lifetime updates?)
It's not the GPS that isn't doing the job, it's the mapping software. The GPS you have in the boat does the same job as the one in your car (and vice-versa). That's just a GPS receiver getting a fix of your location from satelites and then displaying your location on a "map". If the mapping software you have installed (i.e., Navionics chart, basemap, etc.) doesn't have a certain area mapped (as with the Portsmouth lakes on our Lowrance or Humminbird plotters) you will only see blank, featureless land. You can still mark waypoints so you can go back to them when you want to, they will show that you are on land (since the lake most likely won't even show), but as far as showing the shoreline, depth, etc. you are out of luck, unless you can make your own map.

Mike