You may want to consider the feathering prop option. We had a two blade folding prop on 23' sloop we sailed across the top of Oz a few years back and found it took a fair wack of power in reverse to throw the blades open - which is always a white knuckle experience in a small crowded marina!
Mico our 33' Alajuela cutter had a 2 blade fixed prop which, together with the fact her new 39hp engine had been bolted directly to the engine beds, caused the whole boat and our tooth fillings to vibrate something terrible.
We have a 2/3 full and deep, integrated keel and at the top of it's rotation, when the blades aligned with the vertical stock of the keel we experienced significant loss of thrust and the subsequent cavitation.
After refitting Mico's engine with new engine mounts
and switching to a 3 blade Hydralign feathering prop, she's now as smooth as silk
- although we nearly came a cropper when we first reversed out of our pen after putting her hard into reverse as we used to have to do with the folding prop only to discover a feathering prop is equally effective in reverse as it is in forward
Hydralign are a Sydney based company and have a wide range of feathering options at really competitive prices. Mico has an aperture rudder and they were very helpful in matching a prop to suit.