I need prop size help please.

[Sturgeon Tom]

I have two stainless props. One is 15 1/4 X 19 and the other is 14 1/2 X 21.
I would guess that one gives grater torque (out of the hole) and the other would be for speed?
Could anyone help me as to just what all these numbers mean for what the prop will do?
They would be going on a 225 Yamaha.
Thanks

[GSD]

pm sent------------>

[jetsled1]

The first number is the diameter, it will affect your overall rpm slightly, the second number is your pitch this is what affects your hole shot or speed, and your 15 1/4 X 19 pitch will be your power prop. or fastest out of the hole but slowest top end. The 14 1/2 x 21 Pitch will have the best top end but may be slower out of the hole. This is assuming you are able to turn the 14 1/3 X 21 at your rated max RPM for you engine. I am guessing with a 225 HP there isn't going to be a hell of a lot of difference between the two. A rule of thumb is you will affect your RPM 2-300 by each pitch jump 19-21 is one jump, and every 1" diameter will maybe change the RPM 100-150 RPM if the pitch was the same. It is best to make sure your engine is able to run close to is max RPM it is rated for at wide open throttle, then if you need more hole shot for skiing tubing etc. you could drop down one or two pitches, but you would then have to make sure you weren’t over revving you engine at wide open throttle.

[Sturgeon Tom]

I now have the information that I was looking for.
I am going to run the boat with both props and watch the RPM's and speed. I will also pay attention to the hole shot. I do have trim tabs to help that.
Thanks all.