Shen,

You're way off about two bladed and folding. I have a single prop mono
hull and I use both a fixed Martec and at times a Martec Folding, Both
13x13. They both walk. The Folding much worst than the fixed, due the
the need of higher RPM's initially to open the blades

Jeff I don't have the answer of why you don't walk but I would suspect
it has to do with the Saildrives. Walking occurs on bare props. The
Saildrives have cavition plate and shaped housing forward and shedges
below which control the water flow to aid forward and stern direction

You, my friend, are BLESSED with a vessel that goes forward and back in
a straight line. Give thanks!!

"I'LL DRINK TO THAT!"

Ole Thom