A few years ago we got a B-727-200 to add to our two 727-100s. When we recieved the 200 it had no long range nav. of any kind. A bunch of us had boats, one of the guys took his hand held GPS that he had on his boat and started using it on the 200. I flew with him a few times and we used it to see how it worked in a fast airplane. It worked really good. We did NOT tell ATC that we had long range nav., but when ATC gave us a heading for a fix down the road we would use it as a back-up. It was also handy for flight planning.
One of the humorous aspects of this GPS was that because it was made for a boat the winds read out as current. Current is 270 degrees at 97kts. Anyway it worked and there was no interference with anything in the cockpit that we could tell.