A yuloh is a sweep oar to propel a boat.
Wooden boat article
Yuloh page
Thanks guys,
I appreciate your responses regarding my Yuloh questions. I felt the
more curved side of the blade should be underneath,(forward) so as to
achieve lift like an aeroplane wing, but I was confused by poor photos
which gave the impression the more curved side was uppermost.
Cheers,
Bill.
Hi Bill, I use an old Chinese style yuloh, from the handle to the
blade tip it has about 150mm curve (like a bow) - it is the same
length as the one drawn on the plans. The blade is 150mm wide and is
flat on the underside (forward) and curved on the top edge. It does
not need a rope to the handle and works well. I got the design from
the Mariners Catalog, volume 3. Hope this is not too confusing.
regards Hugh
Well, thanks for that. It seems to me that yulohs with more curve
longitudinally are easier to work. Al is of the opinion that the
cross-section of the blade is not significantly important. You may
be interested in Simon Fishwick's comments on my smallsailboats yahoo
group which I've pasted below:
Bill
Worcester's classic drawing of a yuloh in use can be found at
http://www.ayrs.org/yuloh.gif.
The important features are:
1. The plane of the blade is "parallel" to the transom, not
perpendicular to it.
2. When in use, the blade pushes downwards and forwards, so the
lower/forward face is convex, the upper/after face is flat or concave.
The force of the blade is resisted by the fulcrum, and the rope.
3. The attachment point of the rope to the handle needs to be below
the
projected axis of the blade (looking side view). This can be achieved
either by a curved (as Worcester) or an L-shaped handle.
4. The yuloh is commonly driven by pulling and pushing on the rope.
Because the attachment point is offset, this twists the blade so it
drives the boat through the water. The amount of offset affects the
"gearing" of the yuloh - low offset = low gear = a low angle of attack
of the blade, means you can use a large(r) blade area to produce
large(r) drive force for the same effort; large offset = high gear.
50mm offset doesn't sound like much to me, unless you're using an
L-shaped handle (in which case the curve is simply to give the whole
lot
some stability). There probably though are subtleties (like where you
hold the rope) that I am ignorant of.
Hope this helps
Simon
I am interested to note the s shaped curve in Worcester's drawing. As
the thrust from the blade is always perpendicular to the blade I
would have thought that the more vertical it is in the water the more
efficient it would be. Possibly this is a better shape for very
shallow water where little of a vertical blade would be in the water.
Paradox is light enough that the rope is not needed.
I too have seen pictures apparently showing the curved side
uppermost/rearward. This is why I suspect that what lift you get from
the blade shape is probably small, otherwise this hydrodynamic error
would soon have been corrected.
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