Re: Difference between a 3 and 4 blade prop
There's a lot more to it. First keep in mind that generally speaking - very generally - a 4 blade runs at a higher X dimension than a 3 blade. And that's if you're comparing the same manufacturer and style. So that brings you to the next question - are you talking about an outboard or an I/O? It's a lot easier to raise the height on an outboard than an I/O.
If you're talking about an I/O there are 4 blade props made specifically to run deeper in the water.
Props have different lift abilities. If you're running a 3 blade with built in bow lift, and that's what your boat needs, you don't want to replace it with a 3 or 4 blade that has tail lift.
Again speaking generally, if you replace a 3 blade prop with a 4 blade of the same make and style it'll run a little higher X dimension. That should put the rpm back where it should be (assuming the 3 blade set up was correct) and give you everything the 4 blade is supposed to do.
