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Re: [PSUBS-MAILIST] bionic propeller

I learned the term "yuloh" from encountering it in a photo caption in a book on ferrocement and concrete boat construction. I've never seen one in use, but it must be something to see. I remember being very impressed with the yachtsmen and yacht tenders in various ports, sculling their dinghies with a conventional oar. 

Best,
Maar

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On 11/20/2010 11:34 PM, JimToddPsub@aol.com wrote:

Thanks, Marc,
I knew "oar" wasn't the right term, but it was the best I could come up
with at the time. It's amazing to see those guys propel a sizable boat
and even back up using a /yuloh/. I had never heard the term.
In my design I'm trying to eliminate the possibility of snagging on
something as much as possible, and a Kort is part of that. Also, sharp
things spinning around scare me as they can be rough on divers,
manatees, etc. I plan to have a removable guard on the intake side so I
can operate with or without it depending on the situation.
Jim
In a message dated 11/20/2010 12:41:50 A.M. Central Standard Time,
piolenc@archivale.com writes:


    On 11/20/2010 1:29 PM, JimToddPsub@aol.com wrote:

     > As you mentioned, a larger diameter prop is somewhat more
    efficient than
     > a smaller one. The problem is that it bumps into things and otherwise
     > gets in the way.

    Which brings up another motive for using a shrouded propeller (Kort
    nozzle), namely that the effective diameter of the propeller can be
    larger than its physical diameter, thanks to the stream tube distortion
    caused by the shroud. In machinery operating in air, it can allow
    higher
    propeller rpm without worrying about compressibility effects at the
    tip.
    In submersibles it's just...convenient.

     > You may have seen boats used in the orient that are propelled by
    a long,
     > hinged oar that is wagged back and forth at the rear of the boat much
     > like a fish tail. Sorry I don't know what it's called. The oarsman is
     > standing and the boat rocks back and forth with each stroke. I've
    only
     > seen them in National Geographic type films. Maybe someone has
    eyes-on
     > experience.

    I think that special oar (or scull, rather) is called a yuloh.

    Marc de Piolenc

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