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Yuloh

Page history last edited by PBworks 17 years ago

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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