New prop same pitch different brand less speed

[Buckhoule]

Hey guys,
I have a 1989 maverick with a 115 merc, I ruined my 12 3/4 x 21p mercury black Mac prop last week, I ordered a 13 1/4 x 21p turningpoint hustler prop. I figured I would get about the same speed, both are aluminum and the same pitch and only 1/2” different in diameter. With the old prop I was getting 5100rpm and 45mph, with the new prop I’m at 5250 and only 39mph what gives?

[21XDC]

All props have different shapes, cup, geometry and produce different "Lift" ... Pitch is only a small part of a propeller.

[billnorman1]

The 1/2 inch in diameter makes a huge difference. Do the math. I'm running a 23.5 pitch 3 blade on a 200 Suzuki but a 16 inch diameter. That same prop would have to be about a 27 pitch 4 blade if it was 14 & 1/4".