A bigger, heavier boat, to go as fast or faster than another, will need more power. Since a battery is an energy store, and power is the rate of using energy, more power = faster use of energy, or shorter run time with the same battery.
The radio transmitter takes information from the channel controls (sticks, knobs, buttons, whatever) places it into a stream, then transmits it. Some modern sets, not just 2G4 ones, have the capability of modifying the behaviour of the data. In older basic sets, this happened in real time, the data was transmitted serially.
The receiver takes the data signal that has been transmitted.and distributes it around the output channels. Old (pre 2G4) sets looked for the "end of frame" indicator, then started working on the new frame when it arrived, distributing the data contained within each segment from the frame to the appropriate output pin. With modern digital systems, there is scope for the manufacturers to introduce lots of confusion.
In simple radios, the behaviour is much as before, Data that starts at a stick on the transmiter winds up appearing at a pin on the receiver telling the servo plugged in there to assume the same position as the stick. If its an ESC, the ESC throttle response does the same.
If the radio signal blanks out, the ESC switches off (i.e. no input, no output), servos stay put.
Enter clever radios. Depending on make, model, and instructions, you gets lots of extra features, or, as the experienced say, "extra ways to mess up". Fail safes are a good example. The generally safest for a boat is to stop the motor. With a normal boat ESC, that means either no RX output OR an RX output pulse of 1.5mS. Some modern clever RXs fail safe to what a plane ESC regards as "stop the motor", about 1mS. Unfortunately, to a boat ESC this means "go as fast as you can, backwards". Generally, ESCs just do as they are told. Some parameters can be changed if a programming card is available or if you are very good at counting beeps while reading the instruction sheet.
Not much specific help there, but hopefully enoug accuracy to help you think along the right lines until someone with specific knowlege turns up.