Not always true. I have devices with GPS which not only relies on a network for getting ephemeris data for the satellites, but they can't function without it. I

Not always true. I have devices with GPS which not only relies on a network for getting ephemeris data for the satellites, but they can't function without it. In other words, they don't even try to get ephemeris data through the GPS signal. So, if there's no network, it doesn't work. One of my devices is even a tablet without a SIM card, it only has wifi.. so if I'm near a cafeteria with wifi I can get a fix, and keep it for a while, but without it it's totally stuck. Forever. In any case, as others have said, in the ocean a cellphone is useless for navigation. At least use a standalone satellite navigator. And learn to use paper maps and a sextant, it's actually a lot of fun.