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Thread: Educate me - Impeller size

  1. #1
    OK, I am putting together a new combo for the boat - but I don't know if I should treat the impellor like a gear ratio / stall combo in a car, or is it something different? If I get the projected curve, how can I tell what impellor would best suit the berkely 12-JC?
    2K 155 408
    3K 239 436
    4K 372 488
    5K 472 495
    5.5K 495 472
    6K 501 439

  2. #2
    Sleeper CP
    Someone will post the stock Berkley Chart for you.
    You may run a search on it.
    Sleeper CP

  3. #3

  4. #4
    you may want to post your boat specs and what you want to do with the boat.

  5. #5
    Squirtin Thunder
    I think you would be very happy with a MPD A impeller

  6. #6
    It's a 21 foot Daycruiser'ishV hull - Use skiing, cruising and occasionally going fast.
    If I read these right, if you make more torque you want a bigger impeller, A2/3/4 (or is that AB??) which acts like a low numerically gear and will give you a greater top speed (and vice versa), correct? I'm still unsure of how to get from that chart to where I need to be. I'm looking for someone to explain it to me.
    It would almost seem I would want the C impellor for max top speed, but the A would be better all around? See I'm not understanding fully how it affects things...

  7. #7
    Am I correct if I said the C would give me quicker acceleration but the A would theoretically give me more speed per RPM?

  8. #8
    Squirtin Thunder
    The bigger the impeller the more forward thrust that is created at a given RPM.
    The C impeller would have to turn about 600 - 800 rpm more than the A to equal the same thrust.

  9. #9
    big boat that pulls skiers = big impeller.

  10. #10
    If your engine makes it's power at a higher RPM, you will need a smaller impeller like a "C" some cases being able to get to this power range will give you more top speed. Say for example that your engine makes 500 hp at 6000 RPM. With an A impeller you wont be able to reach 6000, so you wont be using all the available power, and your speed will be dependent on getting more RPM, which = pumping more water=more thrust...
    Hope that helps

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