If you change the torque curve of the motor by changing the camshaft, etc you may have to change the prop pitch.
If you get carried away with the cam selection you may loose 10hp @3000.
Big cams trade low end power for more top end power.
3000 rpm is mid low rpm.
Larger cams need more compression ratio. and tend to enhance power at higher rpms. Don;t get carried away.
If you really want more engine power, you need to improve the induction and exhaust system (porting, larger valves, better intake, exhaust etc) to go along with a new cam.
(the cam is part of the induction, exhaust system, it all has to work together)
if the engine then makes a good bit more power @3000 rpm and the prop must run at 3000rpm (limit) then the prop will need to be changed (pitch, diameter).
You'll need a accurate tach and a radar gun to evaluate your boat's performance change after moding the motor.
Many of the cam companies have high perf cams for this motor even if you don;t see it in the catalog. Call a few of them for tech help.
They have probabily dealt with this before. You are surely not the first to want to cam up your air boat.