Selection of a prop for maximum performance for a given motor/hull/battery combination is a "black art". Conventional wisdom is that often, if the motor has more revs to give, a larger prop will not allow the motor to spin fast enough to increase speed, and may well cause the whole thing to slow down while using more current and overheating the motor. It is possible that you may need a two blade prop to allow an easy increase in RPM, and eventually, speed. Counterintuitive, but...........
Hopefully, someone with more experience in making heavy boats go fast will give some accurate advice.