Increase Prop Size?

[Borealis]

I have a 10HP Sabb diesel with the standard 2 blade 17" variable pitch prop that is manufactured by Sabb for the engine.

I wish to repower with an 18 hp Sabb with the same clutch for the variable pitch shaft/prop. (Same footprint and shaft connection.)

My question: In order to increase power and speed of the boat to match the power increase of the engine, would I need to increase the prop size?

My quandary: In order to increase the propeller size I would need to cut a larger space in my rudder/hull to make it fit. If I go with a 3 blade then I need to look at different F/R gear box and drive shaft.

[Cheechako]

No, usually your diameter is limited to 15% of the diameter clearance from the hull anyway. With the vari pitch and more HP you will likely end up fine.