[AugustH]

Using the iPad wifi version with a Verizon MyFi (wireless wifi router) on the northern Chesapeake this weekend, I could not get a gps position. The iPhone gave me position with the wifi, but seemed better with the edge or 3G connection.
Oddly, location services came back on the iPad for a while when I was tied up in Rock Hall, then disappeared again, both while using the myFi.
Checking online I found references to a service called skyhook that registers the ip address as mobile or something, but the references were from some time ago.
And the fact that the blue bubble on the iPad can follow me all over the place in my car but not in my boat is confusing.
I tried it with innavx, charts and tides, and google maps and the inboard map app. None of home like being on the water as far as I can tell.
What am I doing wrong?

You're not doing anything wrong. The Wi-Fi version uses multiple wi-fi hot spots with known locations to give an estimate of your position. It's not a GPS fix. When you're out on the boat, you have no known wi-fi locations to get the estimate. The same thing would happen if you had the 3G model but were out of cell tower range - the A-GPS in the iPad won't give a location if it can't find a cell tower first. This happens to me on the iPhone when it shows me that I have no service.

I've read reports that the iPad camera connection kit includes a USB port that seems able to accept much more than just a camera. It may be possible to plug a USB GPS unit to the iPad, but since I don't have an iPad I can't verify this.