Calder on drag (MC1's Question)
Calder doesn't offer any specific formulas or numbers but says most folding and feathering props will "greatly reduce drag when under sail, so it is ironic to see their proliferation at a time when less and less time is spent under sail" (page 201).
He goes on to rank two-bladed folders as best for sailing (least drag) and worst under power; feathering props, like MaxProp, as having a bit more drag and as being almost comparable to fixed props in forward and better in reverse; and variable pitch props, like Brunstons, as having more drag than feathering but "significantly improved performance under power throughout a boat's speed range" (202).
And, to give credit where credit is due, the citations above are from Nigel Calder's Cruising Handbook, International Marine/McGraw Hill, Camden, ME, 2001.
I couldn't find anything much more specific about drag in that section of the book, but Calder's comments on the sailing side of the issue would seem to have face validity. If one looks at the underwater profiles of the props, it would seem logical as to which would create the most drag under sail.
PSC 40 -- #46