I am trying to understand the issues around blade planform on a feathering prop. A quick survey of the offerings shows a wide variety of ideas in blade planform, they can't all be optimum. Many of them seem to be copied from ordinary fixed blade planforms, but there are many outliers like Kiwiprop and Autostream. Even folders come in a wide variety of shapes, many of them have the typical elliptical blade, but many also have a very square tip. To a first order, the thrust is proportional to the 4th moment of area of the blade, that argues for the area to be distributed more towards the tip. Also, a sailboat prop operates at high slip rates, high rpm, and low water speed rates, all of which seem like they affect what would be optimum. When you ask a prop shop guy (or even a manufacturer) they seem to shrug their shoulders and say they don't know.

I am trying to solve a persistent vibration problem with my boat, a medium level of vibration throughout the operating range. I have had some suggestions from the manufacturers reps that it might be "prop phasing" or the frequency of blade passage being too close to the engine firing frequency. I am wondering it if is worth the gamble to buy another prop to see if it makes a difference. There appears to be no shop that has a prop anywhere near this spec on the shelf to try out (19 or 20 x 15 saildrive) so no try-before-I-buy. The blade issue comes up because I would be going from a 4 blade to a 3 blade, most of the charts say its too much disk load, but the charts do not account for blade planform in any way, and as I said, they are all over the map.