I'm looking at buying the third prop for my boat. The boat is a Pearson 28-2, 24.5' waterline, 7000lbs dry, Yanmar 2GM20F engine with 1:2.62 gear ratio transmission.
I started with the stock 16x10 2-blade "Michican Sailor" prop that served the vessel fine for the last 27 years.
Before heading out for a lot of cruising last year I upgraded to a 14x8 3-blade "Campbell Sailer". This is the prop that I've used this most. At 2800rpm on flat water the boat goes about 6 to 6.2 knots with this prop. I've measured the engine RPM using a digital/optical tach on the engine flywheel, the engine's tach is not at all accurate.
I'm now looking for a folding or feathering prop for club racing and more recreational sailing. At the top of my list is the Flex-O-Fold. They are recommending a 15x12 prop for 2-blade for 15x11 prop for 3-blade. Since my engine, waterline length, and displacement are all very common I'm assuming that they are making a good recommendation. However compared to the other props that I've used this sounds like it would be overpropped.
8" pitch to 12" pitch is a pretty big variance! Why does it vary so much?
Maine Sail has also used both a Flex-O-Fold and Campbell Sailer as noted by his (not successful) experiment in this thread:
Folding Prop Report - SailboatOwners.com
From a little digging his Flex-O-Fold was 16x12 2-blade and his CS was 16x9 3-blade. It sounds like the Flex-O-Fold was underpropped compared to the CS:
"*Slower than 3 blade under power at same RPM"
I'm also considering a Max-Prop. Flex-O-Fold is a little higher on my list due to price (about 30% cheaper), not catching kelp when sailing, and simplicity.