Propeller Sizing... any rules ?

[tomille3]

Hi
I try to understand the pro question

I would like to know if there is a rule for the Propeller sizing , depending of the use we want for the boat ...

I mean when the engine go to is rpm range we consider that the propeller is the right one ....

Now lets imagine we have the right propeller but we want more speed .
So we'll increase the pitch size but this will affect the RPM ...so we'll have to reduce the diameter ? Is that correct ?

I read that for 2" less on the pitch we increase about 200 Rpm the prop rot(average, depending the prop brand...)

So my question is :
1) To keep the right motor rpm , for each inches more on the pitch how many inches should be remove from the diameter ?



Is there any rules for that ? Beetwen the pitch and diameter ..?

I don't know if I'm so clear ....

[briscoe]

Read Prop Recommendation thread on pg 5

Moonlighter has an excellent response to similar question. Scroll down to pg 5. Very excellent info.
Regards,
Briscoe

[Moonlighter]

I think I know what you are getting at, and it is:

How does diameter come into the prop selection process? Most of the discussion is about changing pitch in order to get a prop that is right for your use, rather than talking about diameter as the variable to get the performance you want.

Good question. One that I dont know a hell of a lot about, it will be interesting to see where this goes.

I will toss a thought out there - i think diameter may have more to do with load carrying and lift than it does with revs.....

We need a prop guru like Ken from propgods !,,

[Harper]

Of course, one COULD put a jet drive on the motor and not worry about all that stuff