First off, 75MHz is the surface band here in the US, good call(guess?)
Mfr02, I can't disagree with much of what you said in your previous post. That said, I referred him to Radio South since they can modify and tune transmitters as well as receivers to meet FCC regulations. I'll be sending in a radio and several receivers for retuning in the near future due to that capability. IF what he wants is doable without violating FCC regs, great. The other issue that you didn't touch on is RF transmitted power. IIRC, the FCC regulations allow no more than .5 watts of transmitted power out of a non-licensed transmitter. This applies to R/C gear and CB radios, off the top of my head anyway. The biggest issue in the case of getting out between 300 and 500 meters is the amount of power available. The general rule of thumb is that an R/C system can reach approximately 402 meters over water and 800 meters in the air. With the plan being to get out passed the breakers, with an antenna just a shy meter above the water, I see major issues. When using a 2.4GHz system, the water will reflect the signal, as you know, so the signal won't get to the boat IF the breakers are over a meter high. If he goes with a 75MHz system, the signal won't be as heavily affected but it will still be attenuated due to the electrical properties of salt water. I saw several boats crash when the Spectrum 2.4 wheel radios first came out, due to reflected signals, making most avoid them. It wasn't until they had done a major redesign of the receivers that the system was finally usable for boats.