Re: 2 blade prop vs 3 blade
With engines that small, in the applications they are usually used, there will not be much difference at all.
If you look at the blade or the hub there will be two numbers stamped there--usually. The first is diameter and the second is pitch, like 8 1/2 X 8 1/2. The three blade has more blade area so usually the pitch or possibly the diameter is reduced a bit to load the engine the same as the two blade. With more area and less pitch the prop is more suitable to drive heavier boats than the two blade.
A two blade prop also usually gives a bit more vibration than a three blade.
IN THE OLD DAYS, and on larger engines, the two blade prop was used in racing applications because each blade is slightly more efficient than each blade of a three blade prop---theoretically. It's also easier doing only two when you are doing custom or hand work on the racing prop.
Nowadays, that conventional wisdom is out the window. You see racing engines with 3, 4, 5, and 6 blade props. It all depends on what the owner was willing to spend.
