Roger Long wrote:
I can give you a rough answer on this if you tell me:

Displacement
Length on Waterline

I can give you a better answer if you an also tell me:

Current HP and reduction gear ratio
Prop size, pitch' and number of blades
Propeller aperture size
C
Current max RPM and speed at that RPM
Roger Long

Hi Roger:
Thanks for the reply. Yes, my QM is a raw water engine. I need to dig
out my manual for the Hurth-18 gear ratio. 2.37 may be the answer but I
need to check And this is another issue: I read the hurth18 was a
special model for the qm only. A rare pair with no parts availble. Seem
to remember a post about having to ceate a modifed flange and fit
another hurth gear on the QMs. My head hurts thinking about this.
Ill post the specs you requesed in a couple days. Thank you for
offering your time on this.
Bob