3 blade prop question.
The facts (let's keep SD happy)
Early 70's Tartan 30 with 3 cyl 18 hp diesel. Fin keel, skeg hung rudder, properly sized and pitched 2 blade prop in place. The engine on this boat sits on the keel, the shaft exits aft the keel and the prop is RIGHT there. No strut, no exposed shaft, just prop with the zinc aft of the prop. Forward is fine, sailing is good as the shaft is marked in the bilge and the prop can therefore be aligned with the keel verticaly.
The problem. Reverse is a mess. The boat will go where it wants, period. In an adverse wind or current the boat is almost uncontrollable. You can push the tiller any way you want, until you get a good speed up it does not matter.
The question. Would a good folding 3 blade prop help. The issue is NOT speed or efficeincy, it is control in reverse at low speed.