What is a "stiff" prop?

[1pooldoc]

I keep reading about a prop being "stiff" or "stiffer" than another of the same pitch. What exactly is a stiff prop? Is it the rake angle that makes it "stiff"? More cup? Some inexact property that can't be defined? And how does it enter into prop selection? How does the avg. Joe know what is a stiff series or make of prop? Lots of questions I know but lets see what happens.

[21XDC]

Stiff means harder to turn the rpms as other props in the same pitch. Can be pitch progression, cup, rake, diameter or any combination.

A 25P that turns similar rpms to most 26-27P is considered stiff.

TXP
TXP-OT4
Hydromotive
Fury3

Are some props considered stiff in pitch

[utinator]

The Razor-4 is another one. That one is very stiff. The Razor-3 is a little stiff. The Solas Scorpion is another one.

[1pooldoc]

So only real way to know is to run props of different makes of same pitch to see which spins most rpm or less rpm on given setup. Example: I have a vmx 25P powertech spins 56-5800 with me and usual load ran a tempest 25P A45 and it spun up to 6200 and dropped almost 10 mph. By this example the vmx is much "stiffer" than the tempest of the same pitch? So, to get to 60-6100 with either I have to go probably to a 24 vmx or 26 tempest. Question is should either way increase top end or kill it?

[21XDC]

Every propeller runs best at a different height. Unless you have found the sweet spot height with each prop, You are not comparing them properly.

It sounds like your A45 tempest has been poorly repaired in it's past history.

[1pooldoc]

What would be neat is if some of you guys with a ton of knowledge/experience of tendencies of different props could write a book or something as a reference for the rest of us still feeling our way to the best setups.

[21XDC]

Too many variables with different boats, motors, gear ratios, motor height and setback, loads, elevations, props of all sorts, etc...