Props
Your best method for inproving performance is to go to a three blade prop. A two blade prop spend 50% of it's time being shadowed by the skeg and keal while a three blade prop always has two blakes exposed and digging in. When going from a two to a three blade, you must either degrees diameter by one inch or pitch by one to two inches. Many prop manufacturers will tell you never to reduce diameter because that is your sorce of power. Pitch on the other hand gives you speed. Yanmar diesel, however recomends that you do the opposite. They recomend that you go down one inch of diameter and leave the pitch alone. If you go to Yanmar on line you will find their conversion chart. Their method to me makes more sence. Remember you are already getting a 50% increase in blade area by going to a three blade. By dropping one inch in diameter, you are probably still realizing a 40% increase. But by dropping one inch in pitch, you are losing close to 10% in speed potential. Check your owners manual to make sure that you have the correct two blade and then go to the yanmar chart. I think that they will recommend a 16X11. I did this on a Paceship 26 which was underpowered with a eight HP Yanmar diesel. Big improvement!
