[Bushwacker]

Brian - You have to know both pitch and diameter before you can predict what a given prop will do. Most props I've seen from a given manufacturer go up in diameter when you drop down in pitch with same material. On my old 115, OMC offered a 13 x 19P, a 13.25 x 17P, and a 13.75 x 15P. With Michigan, the 4B aluminum Vortex I started with was a 14"dia. x 20" pitch. The equivalent SS 4B Apollo was a 14.125 dia x 20" pitch, so with the same power input they could evidently turn the same rpm with a little more diameter due to less drag from thinner blades on the stainless prop. When going from 3 to 4 blades, the equivalent 4B props seem to be smaller in diameter, but you're still picking up quite a bit more blade area with the additional blade.

Suggest you check the various websites, such as Merc and PowerTech. Don't know what Yamaha has. On these websites you can plug in boat weight and type, motor, and max speed & rpm with an existing prop, and it'll recommend various props optimized for different conditions, such as max acceleration (water skiing), cruise efficiency, or top speed. I suggest you get more data with a heavy load and T-top before you lock in on a prop. Might also see if you can find a dealer that will loan used props to try, or come to one of the SeaCraft gatherings! Most of the guys probably have spare props they'd let you try! Denny