Proper prop size for 32-200, 1988 Ericson

[October]

What diameter and pitch would be appropriate for a two bladed propellor which will give maximum RPM..3600..for proper pitch and diameter...the engine has to run to its maximum and on the 25XP this is 3600 if you are running slower maximum RPM you are lugging the engine

 

[Loren Beach]

My shop manual(s) for my '88 M25XP call for a cruising rpm of 2400 to 2600, IIRC.
That's where we run it. WOT is about 3000.......
Not sure where your higher WOT rpm is coming from; maybe I'm just misreading the manual.
Ours is rpm limited to about 3K , max, in any case.

Loren

 

[October]

I am wrong...it is not 3600...it is as you say...my mistake

 

[TakeFive]

I am wrong...it is not 3600...it is as you say...my mistake

If you can reach a little under 7 knots at WOT of 3200 rpm in calm water, you have the right size prop. Typically this would be about a 15X8 for 2 blades.
Cruising range is anywhere from 2100-2600 rpm. There is usually a sweet spot where increased rpm's don't give much of a speed increase, so you may find 2200 rpm's provides a nice balance of speed, fuel efficiency, and lack of vibration. I'm happy at 5.2 knots, depending upon wind and wave direction, full water tanks, etc.

You should determine what is on the shaft now, and make sure you have enough cushion to push you to max hull speed.

-Garrett