Glenn, there should be a ton of discussion on the Forum, and perhaps even an article or two in the Upgrades/Maintenance section on this topic. Try doing a search here.

It seems to me that fundamental to determining whether you have the proper prop diameter and pitch is having a calibrated tach. Without that you won't know what true RPM you're turning at any power setting. There is also a great artile on calibrating the tach in the Maintenance section.

Glenn,
My C36 is a 1988 hull #849. I have the same engine and I have a standard 3-blade propeller of 15in dia x 9in pitch and a 15in Maxprop set at the same pitch. You need to get up to at least 2500-2600 cruising RPM to get about 6+ knots with a clean prop and clean hull. At 2100 rpm this engine does not develop much HP. Currently I have the 15in Maxprop installed, but will switch back to the standard 3 blade this fall. The Maxprop is just too sensitive to to any hard fouling. If you can't get more RPM than 2100, the propeller pitch and or diameter may be wrong.
Hans Treu, hull 849 docked in Palacios TX

The important thing with any Universal/Westerbeke engine is that you can attain max rated RPM at WOT with a clean bottom and prop and in smooth water.

Here's exactly what it states in the advanced M-25 XPB spec sheet:
[B][I]
"Universal recommends a propeller that will allow the
engine to turn 3000 RPM underway at full throttle"[/I][/B]

If you can not get to 3000 RPM, and you've checked to make sure your tach is correct, many are off by some margin of error, then you'll need to re-pitch.

Over propping is not good for the engine..

One other point to add. 15" is the max diameter you can install, due to shaft and strut dimensions. Any adjustments you make have to be done with the pitch.

Forgot to add one thing. I believe the C-34 has used the same exact spec prop on the M-25 through the M-25 XPB and if I am not mistaken it too is a 15X9 three blade Michigan Sailor. Despite the minor HP changes the 15X9 3 blade prop seems to work.

[QUOTE=Triatica;5857]My C36 Mk1 was repowered with a 25 MXPB prior to me purchasing the vessel. Now I'm looking at the prop which seems a little smaller than I would like.

Reasoning: I have very little prop walk, it rapidly revs up and I get about 5.2 knots at 2100 rpm. Since we do a ton of motoring here in the Pacific NW, I figure I should go up to a bigger prop.

Can anyone:
1. confirm I may need a larger prop to match this engine
2. offer the [I]complete spec[/I] of a fixed 3 blade that I could fit that might be more suited to the engine?[/QUOTE]

Glenn,

If you don't have a 15x9 and want to try one before buying, I have a 15x9 fixed blade at Elliott Bay Marina that you are welcome to try. Emerald City Diving can install it with the boat in the water. Let me know.

Bruce