please help!!!!

[raggamuffin]

I just bought a four stroke yamaha 100 HP.looking for the right size prop????i have a 25 ft highbow Mexican skiff. I carry people for fishing trips .boat is pretty light.I wanna know what would b the best size prop and pitch .please help ....boat is a arcos Mexican skiff.anyone kno lemme kno ur opinion...I have more details if u need answers bout things .boat is used in Caribbean salt waters .thanks ...and does anyone know the life span of a four stroke 100 HP yamaha ?

[rodbolt17]

prop size will be correct when it can turn 5700-6000 RPM with the load THAT day.
life span depends on engine fresh water flushing after saltwater use.