Towards a more efficient Yuloh ...

Discussion in 'Boat Design' started by SAE140, Apr 16, 2010.

  1. SAE140
    Joined: Apr 2010
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    SAE140 Junior Member

    I've just been looking at US patent 7223140, which is dated 2007, and in which the inventor comments that the yuloh is now pretty-much a perfected design, and he is just adding a small improvement to it - a small fin. But I notice that the sweep blade remains essentially rigid.

    I say 'essentially' because in the text he does mention that some flexibility is desirable - but by this he appears to be referring to the ability of grp, wood, or light metal to accommodate the bending force generated by the added fin.

    Now there is another form of propulsion which uses the same principle as the side-to-side action of the Yuloh, only in an up-and-down direction - the Scuba or snorkelling flipper. And, unlike the Yuloh, serious scientific research has been conducted on flippers to establish the trade-off between flexibility, drag, swimmer-effort and so forth ...

    So - question - why are boating Yuloh's not made with seriously flexible blades to mimic swimming flippers ?
     
  2. tom28571
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    tom28571 Senior Member

    Yulohs operate from side to side in a slicing motion and develop thrust from the angle of the blade motion similar to a propeller. Swim fins develop thrust from motion perpendicular to the fin surface.

    A yuloh should benefit from a flexible blade though. Perhaps a flexible joint between the shaft and blade of the yuloh would be helpful. Both might help equalize the thrust over the sweep of the blade. I've wanted to experiment with such a flexible system on a yuloh but never got around to it. The flex should allow the thrust vector to be more horizontal than the usual yuloh blade or sculling oar which has a large and useless vertical component..
     
  3. messabout
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    messabout Senior Member

    The yuloh is a fascinating device. Tom made the correct observation that the verticle component of force is useless and wasteful. Seems like the blade should be more nearly vertical such that more of the force is imparted in the horizontal plane. Still, it must be configured such that it will reverse its pitch at the begining of the opposite stroke. The whole thing is an intrigueng study in geometry.

    Genius that I would be, I built a sweetheart laminated and curved shaft, on which to attach a top, symetricately, cambered blade, camber facing forward. The whole of it is a candidate for the campfire. So much for genius. The Chinese used a very long shaft, some of them as much as 9 or 10 meters in length. Obviously the thing was used on sizeable boats. To be effective the user needs to be able to stand so that he can put his weight against the shaft, then walk around the end to push in the opposite direction. All this makes me think that a yuloh is good enough on a big boat but impractical on a small skiff or dinghy. Dinghy folks just need to learn good sculling technique, with a plain oar, like the Bahamians do.
     
  4. tom28571
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    tom28571 Senior Member

    I've seen plenty of small sampans being sculled about with a yuloh in the far east. Properly sized, I see no lower limit to the size of boat that can be propelled with a yuloh. Some in the far east have the camber on top and some have the camber on the bottom of the blade. My conclusion is that the camber should be on the leading surface which is the bottom of the blade. This matches the design of propellers which operate in a similar fashion.

    Larger boats often use several crew on a single yuloh and/or more than one yuloh.
     
  5. SAE140
    Joined: Apr 2010
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    SAE140 Junior Member

    I've got my appetite for understanding yuloh's well and truly whetted now (or should that be 'wetted' ?).
    By any chance does anyone on BoatDesign have copies of the enlarged graphics from:
    http://www.simplicityboats.com/ScullYulohaboat.htm
    The existing link refers onwards to a GeoCities webpage, which has been defunct for ages. And Internet Archive hasn't stored 'em.
    Cheers ....
     
  6. tom28571
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    tom28571 Senior Member

    Jack Dillon has done some research into yulohs.
     

  7. messabout
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    messabout Senior Member

    Matter of fact, I recall an article in Wooden Boat mag about the yuloh. Among the pictures and text there was a Japanese engineer/physicist type person who was using a yuloh in what appeared to be a tender. Little boat, big sculler thing. The Japanese person was doing R & D on variations of that theme. Some of his experiments were quite sophisticated.

    In contemplating the yuloh, or simple sculling oar for that matter, I was thinking of the horizontal force component of the strokes. That would make the tail of the boat wag, it would seem. Apparently not, as I have seen Bahama scullers, in Abaco dinghys, just haul *** without noticable yawing. OK so a yuloh can work on a little boat too.
     
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