Outboard prop modifications

Discussion in 'Props' started by Slowboating, Oct 22, 2021.

  1. Slowboating
    Joined: May 2021
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    Location: Cortes Bay

    Slowboating Junior Member

    @MrEfficiency that’s a silly idea.

    If three blades equal 150” squared, and a fourth blade would bring the total to 171” squared, (total blade area) Would it not be the same as adding 7” squared to each of the three blades, to get a total of 171” squared?
    Arbitrary numbers, not literal
     
  2. comfisherman
    Joined: Apr 2009
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    Location: Alaska

    comfisherman Senior Member

    Finding a 5 Blade 14inch Yamaha prop that isn't pitched for mega powrr.... might be easier to find Costco packs of unicorn steak.


    Harsh reality is using disparate tech in heavy crossover applications will lead to some compromise.
     
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  3. Slowboating
    Joined: May 2021
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    Slowboating Junior Member

    @comfisherman

    exactly! The highthrust aspect is what throws a lot of people off. You can get more blades, but the highthrust props always seem to have more total blade area with 3 blades. But these props only seem to be efficient under a certain speed.
     
  4. comfisherman
    Joined: Apr 2009
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    comfisherman Senior Member

    The high thrust outboards are really geared towards utility open skifs all around the globe. See a ton of them on the 18 to 22 foot aluminum open skiffs up here. But they will be much lighter than a 2670 and operate at a much higher rate of speed in the optimum rpm range.

    Operate with a heavier boat without being able to increase diameter and take out pitch, truthfully your in for few fun days killed welding and some settling for compromise.
     
  5. Mr Efficiency
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    Mr Efficiency Senior Member

    That prop isn't the high thrust prop for that engine, is it ? Why not just use their specified high-thrust props ?
     
  6. Slowboating
    Joined: May 2021
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    Slowboating Junior Member

    That is the ONE of the specific highthrust props for that engine. When compared to the other props that will fit on that leg, it is very obvious to see why.

    The make another highthrust pontoon prop, but best I can tell, it doesn’t have any extra blade area, just a different shape
     
  7. Mr Efficiency
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    Mr Efficiency Senior Member

  8. Slowboating
    Joined: May 2021
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    Slowboating Junior Member

    I am aware of that prop. My prop already has more surface area and a larger diameter. Though it’s splitting hairs as it’s only an 1/8 difference
     
  9. gonzo
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    gonzo Senior Member

    Unless the propeller is cavitating due to excess blade loading, adding blade surface are will only reduce efficiency.
     
  10. Slowboating
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    Slowboating Junior Member

    Where will it reduce it?
     
  11. gonzo
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    gonzo Senior Member

    You will increase losses through more friction. The blades on a propeller should have the least possible area to increase efficiency.
     
  12. Slowboating
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    Slowboating Junior Member

    I agree with you, if it was a speed boat. This boat is not, and thus can have more blade area for the given speed then most boats.
     
  13. gonzo
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    gonzo Senior Member

    It is irrelevant what kind of boat it is . The blade area is only related to loading.
     
  14. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    I'd be amazed if this made any worthwhile difference, in this particular application
     
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  15. Slowboating
    Joined: May 2021
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    Slowboating Junior Member

    Greater surface area, less blade loading but more drag. I know how it works. I have to props the same, might as well modify the one and compare the two. In my books, I’m not looking for speed, just looking to see if it’s possible to reduce prop slip in this application. The numbers and math will prove it in the end, if it will work enough.
     
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