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  1. #1
    carbuff91's Avatar
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    Help me understand 13/19 vs 14/20 depitched to 13/19

    Ok,

    I see a lot of things on here about the stock solas 13/19 getting taken off in favor of a 14/20 depitched to 13/19 or some other type of pitch. Why is the 14/20 the pitch of choice for this and not just re-pitching the 13/19? Is the hub or something bigger on the 14/20?

    I don't mean to be smart or anything by asking...just trying to understand the mechanics behind prop pitch/size/angle...etc..

    Thanks everyone,
    Steve


  2. #2
    Hydrotoys's Avatar
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    I don't pretend to understand WHY.
    However, the root angle of the BLADES AT THE HUB on the 14/20 is the defining factor.

  3. #3
    Moderator RX951's Avatar
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    I gained more speed when I went from a base 13/19 to a depitched 14/20>13/19.

    If you put both impellers side by side on a flat surface, you can see the difference in the geometry of both impellers.
    I can't explain anything about it.

    I'm sure an impeller specialist such as Impros or Carl can explain it in detail for ya.

  4. #4
    carbuff91's Avatar
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    Hey Fernando....do you have any knowledge on this one?

  5. #5

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    Mark is completely right.
    During the hey-day of SD runabout racing, Skat Trak often sold and marketed same pitched props from different castings (ie. a 16/24 or 16/24 from a 17/25, or 16/24 from a 15/23 etc). I'm not sure if Skat still offers these custom pitch/hub combinations... but I know Impros does.
    In short, the steeper prop castings had steeper root pitches that loaded motors much harder at lower rpms, while netting close to the same smooth water rpm peak (as is often the need on big bore GPRs). Some of the smaller displacement 720 SDs had very poor low speed torque, and so reqired a base casting whose root angle was mild enough to allow decent low range acceleration.
    It bears noting that the incrament of loading between the Skat castings was not huge ... but the incrament of engine loading between the different Solas Concord castings is pretty big by comparision. A 14/20 Concord repitched to 13/19 would load the motor "alot" harder at low rpms than a conventional 13/19.
    Hope that helps,
    Respectfully, Harry Klemm

    Quote Originally Posted by hydrotoys
    I don't pretend to understand WHY.
    However, the root angle of the BLADES AT THE HUB on the 14/20 is the defining factor.

  6. #6
    carbuff91's Avatar
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    ahhh, I think I'm starting to see the lightbulb come on.

  7. #7
    Hydrotoys's Avatar
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    Mark is completely right.
    I make a nice parrot.

  8. #8

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    Quote Originally Posted by GroupK
    Mark is completely right.
    During the hey-day of SD runabout racing, Skat Trak often sold and marketed same pitched props from different castings (ie. a 16/24 or 16/24 from a 17/25, or 16/24 from a 15/23 etc). I'm not sure if Skat still offers these custom pitch/hub combinations... but I know Impros does.
    In short, the steeper prop castings had steeper root pitches that loaded motors much harder at lower rpms, while netting close to the same smooth water rpm peak (as is often the need on big bore GPRs). Some of the smaller displacement 720 SDs had very poor low speed torque, and so reqired a base casting whose root angle was mild enough to allow decent low range acceleration.
    It bears noting that the incrament of loading between the Skat castings was not huge ... but the incrament of engine loading between the different Solas Concord castings is pretty big by comparision. A 14/20 Concord repitched to 13/19 would load the motor "alot" harder at low rpms than a conventional 13/19.
    Hope that helps,
    Respectfully, Harry Klemm

    Quote Originally Posted by hydrotoys
    I don't pretend to understand WHY.
    However, the root angle of the BLADES AT THE HUB on the 14/20 is the defining factor.
    THAT is the BEST prop info I have ever read!!! It is spot on and makes SOOOOOO much sense it's not even funny!!!

    Hats off to you for the info!!!!!!!!!

  9. #9
    Moderator RX951's Avatar
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    Thats what helps make this a great forum.....lots of input from several people who have exparience to share in this hobby and industry

  10. #10
    good info here---
    also comparing the solas 13/19 to the 14/20 in addition to the "root angle" being different, the blade statrs about 3/8" higher on the hub and the blade length is also about 5/8" longer on the 14/20.

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