Several ways of going about that, none of them all that simple, easy, or cheap. One method is a complete 'on-board' set up. Another is a two way set up, an 'APRS' and remote control systems 'on-board', the interpreting and guidance system not on board (next to your on the shore, typically a computer). The 'APRS' sends positional data to the computer (has to have it's own receiver). The computer 'computes' the appropriate signal to send to the boat, and the R/C radio does that sending. With the typical R/C boat, that 'split' systems seems to be a better idea, not as much stuff in that boat taking up room. But then, considering the size of some of this gear, it's gonna have to be a sort of large boat to start with
I've a little experience with the 'APRS' thingy (Automatic Position Reporting System), but none with the programming part. All I can say is Good Luck!