don't have one but I understand you can purchase an external GPS antenna ($30.00) and the Navionics chartplotting program works well. A good thing about the GPS antenna is that you can keep the Ipad out of the weather. If you don't have an Ipad, it might be comething to consider for your backup as it does so much more.

But,,,,,, and it's a big one, I don't have an Ipad, only did some research on it.