I have a 1994 with three bladed prop. Can get 3200 full out. Surveyor ran it up to that during sea trial. I keep it at 2200 to 2800 when cruising.
I'm third owner and don't know if prop is original or not. Engine is M35A.

'85 3-blade, and I can get it to about 2800 max under load.

I have a 15" max prop 3 blade and have it pitched for 3100 rpms at wto in gear. Wto in neutral is 3200.

I have a 15" x 10" 3 blade fixed on my boat with the M25. At full throttle in gear I get 2700-2800 rpm and in neutral I get 3000rpm. I know that that prop is slightly over pitched for my engine but it's nice having the power.

So what is your pitch?

Prop 15" diameter, Pitch 10".

Chris, you state you like the extra power of being over proped?
Your engine will not develop more power at lower RPM, the manual calls for a propeller that will give full 3200 RPM for the M25 to achive maximum power. Being short 500 RPM will not develope more power, cruise speed may be up somewhat but, if pushing against a headwind or current you will not develope all the HP your engine is capable of at 2700. You will never get a skier up at that RPM.

As Steve F and others well know, most higher performance propeller-driven aircraft have had variable-pitch props so that you can match the pitch to the load and other conditions. You get the best of both worlds (except for the weight, expense, and complexity of the mechanism).

In boats, having a fixed-pitch prop means it will not be ideal except at one set of conditions. A slight over-pitch will often mean lower RPM needed for a given boat speed in the mid-cruising range, which can be good. But try to push to the max power and it can't get there, meanwhile overloading the engine.

The Autoprop (and some others) supposedly self-adjusts its pitch to the load for pretty efficient results. Motor-sailing is a great example where a portion of the boat speed is provided by the sails, so the ideal efficiency is a mid-low engine RPM with a higher prop pitch. Of course, then the question of running a diesel under too low a load comes into play.

Not that anyone asked... ;)

I know that I am losing some powere from not reaching full rpm and I am planning on having the prop re-pitched the next time the boat is out of the water. As far as speed under power goes I have been cruising at 2000rpm with an average speed of between 6 and 6.5kts even when I had 25kts of wind on the nose. At full throttle in flat water I am getting almost 7.8kts out of the boat but at that speed the engine is overloaded, which is why I am planning on having it re-pitch to 15"x9".

As far as my comment of extra power is concerned, I am putting more power to the water as compared to the prop that was on the boat when I bought it which was a small 2 bladed folding prop.