Re: prop 4 blade or 3 blade
I'm going to quote from a Propeller book I bought ... 'How many blades? Surprisingly, the ideal is one. A single blade does not have other blades disturbing the water flow ahead of it. Obviously this couldn't be balanced so 2 blades is the logical answer. Sailboats and high speed powerboats frequently use 2 blades but this is usually a problem for most boats because the diameter would have to be large to get the required blade area so 3 blades have proven to be a comprimise between balance, blade area and efficiency. 4 or more blades are useful for 2 reasons - firstly their extra blades create more total blade area with the same or less diameter but the four blader would seldom be as efficient as the three blader because the closer blades create additional turbulence. Another reason to use more than 3 blades is less vibration because more blades per revolution of the prop creates a higher frequency [of pressure waves] and lower frequency vibrations are more noticeable and annoying.' ... I hope that helps?
