JohnShannon was talking about me STB.
My point of view it isn't about speed. It's about thrust at low rpms.
More blades & larger wheel equals lower rpm which is important when using an electric drive. Capta pointed out how pitch & diameter can effect efficiency of a wheel, slippage also plays into it also. My understanding is most props have roughly 50%-55% slippage.
If your prop has a pitch of 10, toss slippage into the equation you move 5" for each revolution. Is there a difference in efficiency between 2-3 blade prop when slippage is tossed into the equation? I would think so if low rpms are the objective.
Some people have claimed US Navy Destroyers have such huge props they can do 30 knots running at 300 RPM. True, I don't know.
Far as the flexfold test, maybe propaganda wasn't the correct word to use.
Without a doubt a 3 bladed fixed prop will cripple the sailing speed of a boat that has an ICE when you need to lock the tranny.
Merry Christmas Everyone
Bob