I was talking with my Dad the other night about props, and found we had some questions about some of the basic variables involved. Your basic prop has two main variables- diameter and pitch. When calculating your theoretical max speed, you only need to know pitch- diameter doesn't come in to it at all. My understanding from reading the boards is that a bigger diameter prop is more efficient- it will slip less- but takes more HP to turn at a given speed. A bigger prop will also generate more lift (so I've read).
Obviously, you can play with these variables to tune the boat. A smaller prop might have more slip but allow you to spin faster and get in a better part of your power curve, and thus go faster. There are also lots of smaller variables involved, such as material/thickness of the blades (and how much the prop bends under power) and cupped blades (more effective pitch) and cleaver props (generates lift). Last, there are things like burning the prop on launch and other dynamic effects.
Mainly I'm interested in the basics of the main two variables- diameter and pitch. It seems the new thinking is towards smaller diameter props- a lot of recommendations for 11" and even smaller props, even with the same diameter. Can anybody give us the real scoop on this?