Look in the warbird section for pictures and you will find plenty of pictures of both 3 and 4 blade props, even some two blades on trainers. The Northrop XB35 had contrarotating 4 blades on the same shaft. That being said, also drum up the rotation speed of these multiblade props. They are often not even one tenth of the speed of a model engine so it strengthens Dr.Wogz statement that the trailing blade of multiblade props has to overcome the turbulence of the preceeding blade
so the fewer blades you have the more clear air. There was guy in about 1946 or 7 that put a single blade on a 65hp continental on a Piper Cub. It had a counter balancing weight opposite the blade on the hub. He easily proved that it was more efficient. What he couldn't overcome was the fact that the uneven pull on one side of the crankshaft knocked out bearings in about 1/3 the time of a normal 2 blade.