Shameless plug that we are looking for a "new" 3 blade for ours, if anyone would like to sell theirs off
. Ill post some info from our unique engine/gear/ prop setups below for ref. But First:
Re: Flex-o-fold (or nearly any other "tech"y prop. They are putting a lot of R&D into their props. The blades on a flexofold (et al) have a different design than your standards bronze fixed prop, meaning its a bit of apples and oranges comparing the two by numbers alone. Beta is going to give you a prop rec based on a very standard prop design. When dealign with a (reputable) prop manufacturer, trust that they know what they are telling you, even if it differs from what another manufacturer says. Obviously, sometimes you get a dud, but in general, they are prescribing THEIR best fit, which may well be different from the others, by design.
SO, we bought our boat with a Yanmar 2qm mated to what I presume was the original prop 16x14 2-blade. the gear is a 1:2.15 ( I believe). With that set up we could turn about 1400-1500rmp before we'd run into fuel delivery issues, but she wasn't good for much more than 1600-1700 anyway. That would push us about 4kts (utilizing maybe 8hp?). I later repropped with a 14x11 2-blade (which I conveniently found locally with a 1" bore!) and it mated perfectly with the engine, almost a perfect load match. With that we could do about 3.5-4.0kts on flat water, but had no bite for any adversity.
We are re-powering now with a slightly older Beta 35 ( actually a lower displacement version of the new 35 which is the same engine as the 38) and will be reusing the 16x14 2-Blade to start with, though I imagine I will be over propped a bit.