The iPad2 w/o 3G does not apparently have a gps receiver. At the dock, my iNavX iPad app worked great, but unbeknownst to me it is using my dock wifi router as a location
I ran into the same thing. My boss gave me an iPad 3 WiFi and I found out the hard way that it does not have GPS. So I returned it for a 3G version. Contrary to what some think, you do not need cell reception for the GPS to work. In fact, I turned off the cell reception and only used the GPS, which is as accurate as any GPS chart plotter. To that end, I use iNavx, iSailor, and iRegatta as navigational aids. I later turned on the cell capability and hotspot feature so that I could have my laptop access the internet. But I will stress that 3G is not
needed for the GPS to work.
We generally keep the iPad below deck but on deck, in a ziplock bag, it's an extremely versatile navigational tablet. The power draw isn't that bad when plugged in and the battery lasts.
I would not buy a Bluetooth GPS receiver as Bluetooth sucks battery like crazy. And I hate external stuff flying around the cabin.