Was Marchaj having us on?

Discussion in 'Hydrodynamics and Aerodynamics' started by Sailor Al, Apr 12, 2021.


Did Marchaj know he was wrong when he claimed, on P199 in my post #63, that "A arrives ...before B".

  1. Yes, and therefore he was "having us on".

  2. No, he didn't understand that the air flows faster over the upper surface.

    0 vote(s)
  3. He was right, air flows travels over the respective surfaces at equal speed.

    0 vote(s)
  4. He confused A with B. (The pic shows B arriving at the TE before A!)

    0 vote(s)
Multiple votes are allowed.
  1. Sailor Al
    Joined: Feb 2021
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    Sailor Al Senior Member

    If we want to debate the applicability of Lift in a discussion about how sails work, have at it! but not on this thread please.
    I've encouraged you to once again to divert this thread away from a discussion about Marchaj.
  2. patzefran
    Joined: Feb 2011
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    Location: france

    patzefran patzefran

    About Mark Drela's comment :
    He says outside the boundary layer, rotation cannot be transmitted to the fluid.
    I did not read this Nasa web page and cannot support it, but I have been learned that boundary layer is a convention defined to separate the treatment of highly viscous effect region near the wall ( high velocity gradient) with region with low viscous effect (low velocity gradient) wich is very close to inviscous potential flow. IMHO, viscosity still acts outside the boundary layer and can transmit a torque to the outside fluid .
    However, I admit in the case of the rotating cylinder, the boundary layer is much thicker (and it is difficult to define his thickness , as for a Couette flow !) than on an aerofoil
  3. Howlandwoodworks
    Joined: Sep 2018
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    Howlandwoodworks Member

    Reply: I said nothing about a debate or a discussion. Are you putting words into my mouth?

    Reply: As you wish!
    I would say, in my humble opinion your past 30+ posts within the last 8 pages neither convinces nor satisfies me that Marchaj was having us on" and your question has nothing to do with a boat design.
    I have broken this rule before and hope to use this great forum as it is intended.

    May I suggest:
    You read the forum rules before starting a new thread or continuing to post in this thread.
    If you have any question about a boat design in the future you could first enter it in the search window in the upper righthand corner of the forum. Then if you don't find a existing thread that address your question there then start a new thread about your boat design question as described in the forum rules.

    Thanks to all for sharing their knowledge freely.
    Last edited: Apr 26, 2021
  4. Sailor Al
    Joined: Feb 2021
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    Location: Sydney

    Sailor Al Senior Member

    Can we get back to discussing Marchaj?
  5. Howlandwoodworks
    Joined: Sep 2018
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    Location: MO

    Howlandwoodworks Member

    Sailor AI,
    This is a Boat Design forum not a conspiracy theory forum. If you want to discuss conspiracy you should go to a conspiracy theory forum.

    Forum Rules
    Keep threads & posts on topic.
    1a.) New threads must be on topic based on the forum title. A thread in the Boat Design forum must be about boat design.
  6. Sailor Al
    Joined: Feb 2021
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    Location: Sydney

    Sailor Al Senior Member

    I see that there is a separate sub-forum called "Boat Design" which should probably concentrate on boat design.
    This sub-forum is titled "Hydrodynamics and Aerodynamics". Marchaj's book is titled: "Aero-hydrodynamics of Sailing". That seems like a pretty close match to me.
    I really am interested in what the sailing world currently thinks about his book.
    I'm not sure why you're so hung up on the meta data.
  7. messabout
    Joined: Jan 2006
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    messabout Senior Member

    Plus one for Howland
  8. wet feet
    Joined: Nov 2004
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    wet feet Senior Member

    Having opened this particular can of worms,wouldn't it be best to rigorously debate it to a logical conclusion?That would mean we won't have to re-visit it in the future.
  9. Doug Halsey
    Joined: Feb 2007
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    Location: California, USA

    Doug Halsey Senior Member

    While we're at it, we could also have a rigorous debate about whether the Earth is flat, or whether we live inside a hollow shell. There would be no logical conclusion, no convincing the true-believers. Feeding the trolls is never a good strategy.
    Remmlinger likes this.
  10. Earl Boebert
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    Earl Boebert Senior Member

  11. CT249
    Joined: May 2003
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    CT249 Senior Member

    Sailor Al may be a troll, because he ignores many posts and points that provide opposing views to his own.

    For example, in the thread where he attacked the use of the concepts of lift and drag, IIRC, he ignored the fact that some of us DO find it useful to break down the different forces. He also ignored the fact that in some sailing craft you CAN feel drag, and in some sailing craft you DO use vertical lift from the rig, and that in some sailing craft heeling forces are NOT always harmful.

    When someone infers that they are seeking a truth but refuses to deal with contrary evidence it appears that they may be just trolling.
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