Define what a Surface-Piercing propeller is

Discussion in 'Propulsion' started by tom kane, Jul 12, 2009.

  1. tom kane
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    tom kane Senior Member

    I fully agree with you.So an efficient s/p propeller works by lifting the water into the lower pressure of the atmosphere and flinging it rearwards.
     
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  2. powerabout
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    powerabout Senior Member

    Well no, lifting the water up is wasted energy as it pushing the prop down.
    Hard to prevent though
    You want all the rearward drive exactly opposite the direction the boat is going.
     
  3. tom kane
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    tom kane Senior Member

    Fast boats have extreme pitch angles as in the image which makes it almost impossible for them to just move the water back without lifting most of it to the surface like a scoop and not a foil directing the flow rearwards and if the prop is only half in the water and the boat is prop-riding it is only the bottom half of the prop doing the work.
     

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  4. tom kane
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    tom kane Senior Member

    Orlo 111 Hickman`s sea-sled had a plate across the transom to stop the rooster tail rising.
     

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  5. daiquiri
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    daiquiri Engineering and Design

    So what is this discussion about?
     
  6. linda.vrdoljak
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    linda.vrdoljak Junior Member

  7. tom kane
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    tom kane Senior Member

    Good movie..some people say you can not run S/P props submerged and the movie seems to show at start the props are deeper in the water then raised to true S/P mode. How do others see this.
    S/P props usually have to run deep at start if there is not mechanism to raise them until dynamic pressures lifts the hull.
    With a retractable shaft drive raising and lowering the shaft angle at the helm is easy, and that is how I used my pivotal drive. A choice of subsurface or S/P mode.
     
  8. blisspacket
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    blisspacket Junior Member

    Instructive video, Linda V. Thank you. A picture tells a thousand words. A video....I'm still digesting!
     
  9. tom kane
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    tom kane Senior Member

    Define what a Surface-Piercing propeller is.

    You could read the thread to find out, that would be the easy way.
     
  10. powerabout
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    powerabout Senior Member

    Surface drive duo prop is what we need.
    Merc made an prototype outboard with this.
    Mercruiser also made the black hawk but the boat builders struggled to make the changes to suit the drive.
    Big learning curve for the props designers and they never really got there, just more time i guess.
     
  11. tom kane
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    tom kane Senior Member

    Retractable shaft drive with duo props is better!. Stern drives are to troublesome and heavy.
    Even a duo prop long-tail-drive would be better.
    Why do boat builders put all that weight on the back of a boat,spoils center of gravity and wastes the most used space?.
     
  12. ChrisN67
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    ChrisN67 Senior Member

    What is a "Retractable shaft drive with duo props" is this something that exists or is it theoretical?
     
  13. Rik
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    Rik Senior Member

    Reality was with the Blackhawk is that it had twice the stern lift as a single propeller driven surface drive. Well that and it didn't reverse well, it didn't get on plane well, they tended to bow steer excessively to the point boats would hook and roll, were really fragile etc....
     
  14. powerabout
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    powerabout Senior Member

    as I said they needed new hull designs as they had quite a performance advantages and I'm sure we will see that format again one day
     

  15. tom kane
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    tom kane Senior Member

    Perhaps we can take a lesson from hydroplanes that have sponsons to keep the bow from burying and so design a recreational boat with those features using prop riding features as well. You could build quite a glamor boat that works well too, even for rough waters. I would be into that, especially not so much rolling turning. But you would still need an adjustable depth control.
    Duo props must have twice the drag just in the props.
     
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