J
Jose Venegas
I started my search for a feathering prop in the assumption that it would reduce drag under sail, and maintained efficiency under power. After much research on the net and the phone, I am still not convinced about the second point. As it turns out, feathering props such as Maxprop, Autoprop and Autostream, in order to minimize drag under sail, have blades with constant pitch, that is they have flat blades. Autoprop has blade profiles with some curvature and adjusts its pitch to maintain an ideal angle of attack at varying RPM and boat speeds. However, it does not have twist on its blades. As far as I know, propellers need to have twist in their blades to accommodate the higher speed of the blade at increasing distance from the shaft. Has any body seen an airplane or water propeller without twits in the blades? In a flat blade, the pitch angle is the same close and far from the shaft, making the relative angle of attack of the water over the blade different than the orientation of the blade except in one point. This should result in a loss of efficiency under power although I don’t know how by how much. I realize that for sailing, a feathering blade with twist (if there was such a thing)would result in additional drag compared with a flat blade, but I feel it would still be a lot less than that of a fix prop. Does any body knows of a feathering, or folding, prop that has twist in the blades? I know that even airplanes with adjustable pitch props, such as turbo-jets, come with some twist in their blades.