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Join Date: Oct 2012
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Re: 2 vs 3 blade prop
I've had 3 props on my Pearson 28-2, so I feel like I can make a pretty fair comparison.
The first prop was a 2 blade Michigan Sailor. It was the stock prop on the boat. It worked pretty well, but had big flat blades that seemed inefficient. Diameter and Pitch were 16x10. I used this prop for only 3 or 4 months, so I don't have a strong opinion on it. I've kept it as an emergency spare.
The second prop was a 3 blade Campbell Sailor. I upgraded to this prop because the blade design is much improved, it has a foil shaped cross section that provides more bite, and a smaller blade that provides less drag. In fact my 3 blade CS prop had less blade area than my 2 blade MS prop. I went with a 3 blade prop because it was supposed to allow the motor to run more smoothly since the blades aren't coming in and out of the turbulence behind the keel at the same time. In retrospect I don't think that made any difference on my boat (a fin keel with tons of room between the keel and prop) and I should have purchased the cheaper (and less blade area) 2 blade prop. Diameter and pitch were 14x8. That sounds like it would be under pitched, but the blade profile gave that smaller diameter and pitch prop more bite than the original.
My newest prop is a 3 blade feathering prop (it is a Featherstream). I wanted better sailing performance, and this prop has made a huge difference in drag when sailing in light air. I considered 2 blade or 3 blade options, but Featherstream only makes 3 and 4 blade props so I bought the 3 blade one. This prop is 16" in diameter and has the equivalent of 9.5" of pitch.
The Campbell Sailor motored a little better than the Featherstream in forward. It seemed like I could go about half a knot faster without overdriving the motor. The Featherstream has less prop walk in reverse because the blades flip over and drive in a more efficient way. Both have a helpful amount of prop walk for steering in tight areas.
I don't think 2 blade vs 3 blade makes a difference on my boat, but I could see it making a big difference on a full keel boat where the prop is mounted in an aperture between the keel and rudder.
If I were buying another fixed prop it would be another Campbell Sailor in 2 blade. Since I love sailing and don't really like motoring I'm much happier with my feathering prop. My CS prop is now pushing around the boat of another Sailnet member.
To me it sounds like Frogwatch's original prop was incorrectly spec'd. Selecting prop pitch has an element of luck to it. One advantage of feathering props is that the pitch can be changed pretty easily when the boat is hauled out. The ideal pitch for a diesel engine has you moving near hull speed at about 75-85% of the engine's max RPM (where the engine is near the top of the torque curve). For my Yanmar 2GM20F that means I want the boat to move around 6 knots at about 2700-2900rpm. With the Featherstream it is more like 5.5 knots since the prop is not as efficient when motoring.
I'm no longer participating on SailNet.
Last edited by Alex W; 08-12-2014 at 12:36 PM.