More disc area for sure - and the boat would benefit from the same I think.
Is diameter restriction the issue on the boats?
In a way, it is restricted as the motor pylon/stand is in a fixed position height-wise. I'd have to ask crispy, but I don't know how much more diameter it could handle and conversely he's already over-powering the motor by 4 cells I believe. I'm not sure what's worse - over powering the motor by a bunch or spinning the prop 1k rpm above its safe limit. Hopefully crispy comes back with some better answers than I can provide.
Edit:
16" diameter prop is the biggest he can fit.