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Thread: Has anyone. Tried this?

  1. #1

    Default Has anyone. Tried this?

    Reducing the total pitch by reducing the diameter? It seems to it me it would be a viable solution for running hot. One could simply just chuck it in a lathe and cut it to a smaller diameter? Has this worked for anyone? Thanks,-Ken-

  2. #2

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    It should make a difference if done right. But if you can get a smaller prop that might be the better option because a the smaller prop is not only smaller in diameter but length also.

  3. #3

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    Changing the prop diameter does nothing to the pitch, it remains the same. A smaller diameter will reduce the load on the motor if that is the goal.

    BTW, reducing a prop’s diameter is one of the most common prop mods.


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  4. #4

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    Thanks again, you've both confirmed my thoughts exactly. Diameter is simply the size of the water column it is pushing. Pitch is how far the boat would move forward per revolution(assuming 0% slippage). So what they refer to as "total pitch" (Diameter x Pitch) can be referred to as "overall load". I am looking at a CNC prop which measures at 38mm x 1.4 for a a total of 2.1 inch ("Overall Load"). This prop fits a 4mm shaft & won't require a 3/16 adapter, I should think this would have a smaller hub O/D than a 3/16 prop? - Ken -

  5. #5

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    Quote Originally Posted by Fluid View Post
    Changing the prop diameter does nothing to the pitch, it remains the same. A smaller diameter will reduce the load on the motor if that is the goal.
    Exactly. One of the other reasons props are cut down is that the total pitch does change in relation to an unmodified prop of the same diameter. For example, cutting an Octura 447 down to 45mm would result in a prop with more total pitch than a standard 445 prop would have.
    Vac-U-Tug Jr (13mph)

  6. #6

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    It is the pitch ratio that goes up,, but pitch does not change as Jay has said,, I'v been reducing diameter it for 30 years

  7. #7

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    I might add, the rpm will go up some, not much.

  8. #8

    Cool

    ....So what they refer to as "total pitch" (Diameter x Pitch) can be referred to as "overall load". I am looking at a CNC prop which measures at 38mm x 1.4 for a a total of 2.1 inch ("Overall Load")....
    I’ve never heard this definition and I don’t know who “they” are. Pitch has nothing to do with diameter. And “overall load” cannot be diameter x pitch, it must include the area swept by the blades, which is based on the square of the prop radius. It is not directly proportional to the diameter. Reducing a 47mm prop to 45 mm is a 4% reduction in diameter, but is an 8% reduction in the volume of water moved.

    But the load a prop imposes on the motor must also include the blade shape and its type of pitch. Is the pitch progressive? How much cupping on the trailing edge? How big is the tongue? What is the blade area? It’s not as simple as A x B = C.

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  9. #9

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    I understand some of this. De-tonging will reduce load,as well as reducing diameter will, but it will also reduce the boats ability to get on plane. Cupping increases pitch at the trailing edge of the blade. Am I correct? If I'm wrong please tell me so. Thanks again. -Ken-

  10. #10

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    Quote Originally Posted by dasboata View Post
    It is the pitch ratio that goes up,, but pitch does not change as Jay has said,
    Got it.
    Vac-U-Tug Jr (13mph)

  11. #11

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    I think I understand what you are saying fluid; What would you suggest, a prop in the ABC 1745 series? They have not been available until recently (I never got the notice). Will they still be available when I'm off of furlough? I would like to buy several of these & send them off to Dasboata! But ca$h is scarce right now. Government shutdown is vicious. I'm not going to get political but it literally @#$%%^&*!!! And it hurts everyone! Thanks again,- Ken-

  12. #12

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    I just recieved a CNC 38MM prop, 1.4 inch. Pitch for 4 mm shaft. It is beautiful! I can see why they don't require balancing, it only weighs .087 ounces as compared to the .079 ounces that the brass nut that holds it on weighs! It looks good! Now I can continue with the rest of my build. I'll test & report later. Thanks again, -Ken-

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