what is the difference between 3 blade and 4 blade propellers?
Compared to 3 blades, 4-blade boat props provide better "hole shot" performance with less steering torque and less vibration at high speeds. When switching from 3 to 4-blades, generally a 1" pitch decrease is required. So, a 21" pitch 3-blade is replaced with a 20" pitch 4-blade.