I assume the pitch is the same on both (23) and I assume the material is the
same (I hope SS for this application).
The smaller diameter is to compensate for the extra blade surface of the 4
blades vs 3. This will allow you to maintain the correct rpms on top
end/wot.
Otherwise you would see a drop in rpms and speed or you would have to go to
a lower pitch which would still mean a drop in speed.

The 4 blade will be a better prop for this application assuming my
assumption above is correct.

--
Tony
my boats at http://t.thomas.home.mchsi.com

"Short Wave Sportfishing" wrote in message
...
I had a discussion with a friend this afternoon about props and he was
trying to parse the difference between a 14 1/2 x 23 three blade and a
13 1/2 four blade for the same outboard. Apparently, he was told he
will get much better trim response on a 20 ft CC with a four blade,
but the size difference is to prevent the prop spinning on the hub.

As I'm not much of a prop guy, I really couldn't answer that question
although we batted around some ideas.

Anybody say which would be better for, say, a 225 Johnson?

Later,

Tom