Props?

[Gene]

Thinking about getting a 3 bladed prop for my Catalina 27 with a Universal 11 HP and 1:2 transmission. The existing 2 blade is a 12RH 11. The boat is on the hard and I have never ran the engine to determine max rpm. Have asked a local prop shop for a recommendation and he came up with a 12*9. Michigan Wheel came up with a 13*9. Those of you with diesel 27's and 3 bladed props, what do you have and what is your experience?

 

[Ron]

Prop sizing

From all I've read on the subject you need to balance a number of factors.1. Diameter -- this is generally determined by the designed-in relationship of the shaft to the hull. Consult Catalina or your boat manual for the proper diameter. If your 2-blade prop was original equipment from Catalina, stick to that size. A larger diameter may not hit the hull, but it could adversely interact with the water flow and result in poorer performance (or worse).2. Pitch -- this factor has a close relationship to your engine rpm/torque range AND your transmission ratio. Best to consult either Catalina or the engine manufacturer.4. Blade area -- narrow blades have less drag, but wider blades deliver more pushing-power against the water. Again, consult Catalina, the engine mfr, or a compentent prop-shop for advice.Unless you have lots of time

 

[Bob Camarena]

If it was up to me

If it was up to me, I'd forget the 3-blade prop. The two blade prop should be plenty on a C-27 with an 11 hp Diesel. Why add all that drag for a small advantage in some conditions. I can see where you might gain something when bucking a headwind in choppy seas, but that's about it. Trading that off against the drag penalty while sailing doesn't make sense.