I have a 14 foot flat bottom boat with a 433cc Yamaha mounted to it. I know the prop that is on there, not sure of size, is too small from the readings i have done. I have taken it on the water and it is slow. I know the boat will not act like a real air boat should due to the design of the hull, but i want more speed. Eventually, when i finish working on my Lake Buggy, i will have ideas to retrofit this motor into a wooden hull air boat made by me. Can anyone get me in the ball park with what size prop i need for a 433cc snowmobile motor that is mounted direct drive? I plan on using it in a 14ft alumacraft flat at this time. Thanks for any help you can give.

Unfortunately those motors don't do well running direct drive. They are designed to make their power at higher rpms so a reduction drive is needed to get them in the best operating range to turn a prop efficiently.

thanks for the info, that is what i am looking for. Any suggestions on what reduction i should run and where to buy one at? I am looking at putting this engine in a new boat, but i want to do it right and not rush into anything. I appreciate any advice you can lend.
Casey

I don't have any experience with 2 strokes. You may want to check out the 2 stroke forum here. It may have been coverd if not start a new thread there and I'm sure one of the guys running a 2 stroke can help you.