Being a two-channel 27meg sort of guy, this is a bit off my patch.
If you want to remote control the moving boat, you are pretty much stuck with a radio working in the approved band. If you just want to use the PC as a replacement for the TX control sticks, then I'm sure that the major makers have models with trainer facilities where one TX can be "buddied-up" with another- whether these are OK for PC connection is not something I know about, but there might well be a converter box for RS232 or USB to whatever standard the TX wants to see on its input socket. There are certainly model helicopter flight simulators that use the TX as a control unit for the PC, but this is the wrong way round for this application.
I have seen remote control systems in the Maplin catalog that allow a PC to work a selection of remote devices, but because of range, legality and price problems I never bothered to follow them up.