RE: Receiver/servo voltage 12 Volts?
Nomadio Transceiver(receivers) handle up to around 20V without problems.
You CAN get High Voltage Servos, but you have to check with the manufacturer if they can go 12V.
I know that the Tonegawa Servos can go 12V for the Motor, but I am not sure about their electronics, but a 500oz/in Super giant Servo is likely overkill for a boat.