i have a gaggle of phone GPS apps i was trying out on a trip to the canadian provinces last summer. some paid apps like navigon but really a whole host of others. all seemed to work when i was on land. but when i took the ferry from nova scotia to maine i noticed they all left the marker for location at some small distance odd shore and did not pick up again until outside of the coast of maine. somehow i am thinking i don’t understand something about how GPS works or about how phone GPS works. just thinking here and imagining that the roof of the ship prevented reception but this would not account for the fact that it worked fine until we dot some distance away from shore. what am i missing?