You would need about 20 definite facts of running , Acceleration from a stop. Time to get on plane. Current prop specifications. GPS speed. Accurate tachometer. Different boat loads at all speeds. Do you FORCE people to sit so the boat is always balanced in all directions ? Or do they sit where they want to ? And a lot more.
Regarding the Fishing, if you are fishing just beyond the Dock, even a 20hp would probably be fine. But if you have to get up on Plane to get to the Fishing, then very close to, or the Max would be wise
