You will definitely will see a decent speed improvement under sail with a
folding prop

no, you won't. folding props only hve value for racing boats, where 2 seconds
a mile means the difference between 2nd place and 6th.

According to MIT tests, a folding prop means a savings of a mere 170 pounds
drag at 5 knots (or 40 pounds drag at 2-1/2 knots, or 10 pounds drag at 1-1/4
knots) over a --------- three ------------ blade prop. ***Much*** less with
compared to a two-blade, and even less compared to a two-blade rotated verticle
behind the keel.

Wanna guess just how much powered is required to pull 170# at 5 knots?