What is the propulsive efficiency of oars?

Discussion in 'Hydrodynamics and Aerodynamics' started by daiquiri, Jun 27, 2013.

  1. Leo Lazauskas
    Joined: Jan 2002
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    Location: Adelaide, South Australia

    Leo Lazauskas Senior Member

    As you appreciate, it is not an easy problem, Slavi. Even the diagrams you
    have seen or will see don't tell the whole story.
    People here are already ignoring effects like partial submergence at catch and
    blade exit, splash, wave drag, wave-breaking, surface tension and boundary
    layer elasticity, and other effects. :)
     
  2. El_Guero

    El_Guero Previous Member

    I would like to point out, rowing, or paddling, is more like a paddle wheel than it is a propeller.

    I think.

    However, as I mentioned above, the ability for the paddle to 'stick' to the fluid it is moving through is related to the ability of the paddle to reduce vortices. And that normally requires a slight angle to the blade as it is moved through the water.

    From what I remember, paddle wheels are not as effective as paddles. Which was why screws, propellers, won in the steam age. But, I cannot remember all the details. One detail would be what the difference is between a paddle and a paddle wheel.
     
  3. El_Guero

    El_Guero Previous Member

  4. jehardiman
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    Location: Port Orchard, Washington, USA

    jehardiman Senior Member

    No, you want the wheel to operate in the slower (relative) flow of the wake. This gives the paddle float a larger del V relative to the inflow, giving more thrust for the same rotational speed (so higher efficiency).
     
  5. El_Guero

    El_Guero Previous Member

    Sweet!

    I was falling asleep when I wrote the above, and then a sandwich woke me up. I do not know if I can get back on SA time, and Odessa time is bad enough.

    But, back to paddle wheels, it looked like that little boat got up and moved. Other than the fact that paddle wheels have been out of favor, are there any other reasons to prefer a prop over a paddle?

    Paddle is above shoals. You could even back up to beach with one.

    The .pdf seemed to imply a much better overall efficiency, and green is good when it goes in my wallet.

    The only downside I saw was the 'plume.' But, I am not gonna be behind.

    :)
     
  6. jehardiman
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    jehardiman Senior Member

    As in the HMS RATTLER trials, the reason a propeller is fitted rather than paddle wheels is the ability of the propeller to provide constant thrust when the vessel is heaving, rolling, and pitching in a seaway. Too many seagoing paddle ships were damaged/lost so that by the mid-1880s they were regulated to thin and flat water applications. Not that they didn't have a niche in the low-pressure steam engine market along with sparred steamers, but the 1889 Samoa typhoon sealed the fate of sparred ships.
     
  7. El_Guero

    El_Guero Previous Member

    Interesting. And that mostly makes sense. But, what is a spar steamer?
     
  8. jehardiman
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    Location: Port Orchard, Washington, USA

    jehardiman Senior Member

    A sparred steamer is a steamship that was also completed with a full set of masts and sails...they also passed out of history about the same time. Engine reliability and efficency was increasing fast and the masts became an unneccessary cost and hinderance.
     

  9. El_Guero

    El_Guero Previous Member

    Thank you.
     
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