Bad Elf makes a "puck" that makes the ipad2 gps capable. I just bought one from ebay for 85 $. Im a big fan of the navionics charts, have been using them on my iphone for quite a while.
Since buying a navionics chip for my chartplotter was going to be 200 or more it was actually cheaper for me to buy the puck, navionics app for the ipad and a ram mount. I am just waiting for the ram mount to arrive to get everything rigger up but already am happy with the setup.
Yak