Looks like you are now leaning towards fixed blade propeller. So whats wrong with a16” Variprop.
Are you looking for faster sailing speed or what is it you looking for.
Think it’s the tip vortex phenomena that cause unwanted banging on your hull that is the main objection to small tip clearance. Another reason is the wake speed further out from the hull differs greatly in the vicinity of where your top blade and the bottom blade will be, less so further out.
Of course, less blades, bigger diameter, slower speed improves efficiency. But you will gain more by going to a folding prop if you do lots more sailing.
Pitch determines wake speed and is related to slip ratio, thrust, power etc. You could I think go for a 15” if vibration has been a problem, and increase your pitch.
Has vibration been a issue?, what is the reason for the change.