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  1. #1

    Join Date
    Feb 2006

    3 versus 4 blade Props - Why?

    Before anybody jumps to conclusions, I have searched and researched the topic. But, I need to understand why. I'm hoping this spurs a dialogue or that someone with more knowledge will chime in.

    Common subjective data is:
    - 3 blade better holeshot, better acceleration
    - 4 blade better mid-range and better top end
    - 4 blade has better gas mileage (less RPMs for the same speed versus the 3 blade)

    There are those who say the holeshot difference is slight, and those that say it is quite significant. It appears that those who claim only a slight decrease have more heavily modified skis. They probably plane out faster and fill the pump quicker, so the holeshot and acceleration difference is felt less.

    Empirical data is:
    - 4 blade gains 2+ MPH on the top end

    Without getting into root angles and blade design, I thought about the answer hydrodynamically:
    - at idle, the pump is fully loaded
    - when you hit the throttle, the impeller moves the water in the pump to the periphery
    - once on plane, and moving, the pump is fully loaded once again

    That being said, evidently the 3 blade moves more water when the pump is not fully loaded, so I took some measurements:
    - each blade on the 3 blade has 7.5 inches on the periphery of the pump, for 22.5 inches total to move water at the periphery
    - each blade on the 4 blade has 6 inches on the periphery of the pump, for 24 inches total

    So why would the 3 blade be better at moving water when the pump isn't fully loaded?

    Since the 4 blade has a higher top end, it stands to reason that it can process more water than the 3 blade when the pump is fully loaded. Curious if the 3 blade or 4 blade is more susceptible to pump stuffing? I would surmise that the 3 blade is the one more susceptible to pump stuffing.


  2. #2

    Join Date
    Feb 2006
    After more research and talking to impeller experts, I think the answer is:

    It is easier to move 3 blades through the water versus 4 blades

    And that is it. Simple. It explains the better holeshot and acceleration, and also why high horsepower skis don't notice as much of a difference.


  3. #3
    Firestomper247's Avatar
    Join Date
    Feb 2015
    Graham, NC
    I'm sure it would be easier to move 2 blades than three. Wonder how a 2 blade would perform?

  4. #4

    Join Date
    Feb 2006
    A 2-blade would have even better holeshot and acceleration than a 3-blade, but would lose a lot more on top. Probably hard to get any RPMs out of it.

    That was part of my research. 2-blade props are used on dinghy motors and electric trolling motors. Very low horsepower and very low RPMs. They would have a hard time getting going with a 3 or 4-blade prop.


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