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Anke and I are building our next boat, and writing about it at ABargeInTheMaking.blogspot.com. Access to the net comes and goes, so I'll be writing in fits and spurts.

Please feel free to browse the archives, leave comments where you will and write, and I'll respond as I can.

Fair winds!

Dave and Anke
triloboats swirl gmail daughter com

Sunday, April 6, 2014

Yuloh 2.0 and Beyond

For full recipe see Some Thoughts on the Yuloh by Slieve McGalliard

Yuloh 2.0 and Beyond

A while back, I wrote this post on our yuloh implementation. Since that time, we ran across Some Thoughts on the Yuloh by Slieve McGalliard, R&D Director of the JRA (Junk Rig Association). Very good thoughts, indeed, including a general recipe induced from drawings and photos of Chinese Junks and Sampans.

Turns out our approach was in the ballpark, but was significantly improved by following this recipe. We don't seem to move appreciably faster, but maintain speed with considerably less effort.

That's a good thing, in case you were wondering.


Yuloh 2.0

The diagram above shows a simplified version of the McGalliard recipe (check out his article for his full discussion and geometric construction method). 
Note that the decimal fractions used in the diagram have percent and fractional equivalents. For example, 0.66Y = 66% of Y = (2/3)Y.
The Yuloh's overall length - designated as Y - is 60% of Hull Length. Personally, I have a feeling that the height of transom is more likely to be a relevant figure. Eastern, yuloh powered vessels tend to be high sterned relative to modern western hulls. Check your results against common sense.

The '30% to WaterLine' distance determines the position of the Loom, relative to the water surface and angled at 45 degrees.

By moving the Loom fore or aft, the Fulcrum point along the Loom (2/3rds of its length from the Tip) determines the upper endpoint of the Fulcrum system. Adjust position until the Fulcrum height and angle agree with your situation.

Once the Fulcrum position and height are determined, operator height is adjusted, if possible, until the loom is slightly above their head. Height can be raised by standing on a platform or plank (more on this, below).

The Lanyard is fixed near the end of the Loom (or to the lower end of a right angle pin, offset from a straight Loom) and led to deck level and made fast. The original recipe calls for about 14 degrees, but we find a steeper angle (8 to 10 degrees) more comfortable.

Note that the aft, upper face of the blade is flat, while the lower, forward face is rounded (cambered). This develops low pressure on the forward side, developing hydrodynamic, forward thrust.

Details we favor are still those presented in the original post.


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The chief difference between our first try and this one is that we now scull using the Eastern system:
  • Facing the Loom nearly athwartships, we place our aft hand on the Loom, about shoulder height... it remains more or less relaxed, riding the Loom and acting mostly as a 'damper'.
  • Our forward hand grips the Lanyard at about chest height and does most of the work - alternately pushing and pulling as we rock our torso back and forth.
  • We can change the 'pitch' of the blade by moving our grip up or down the Lanyard. Low makes for a steep pitch (good for 'shovelling' the stern around in a turn, feathering the blade or lifting clear on the backstroke). High makes shallow pitch for short, rapid strokes (good for accelerating from standstill). Medium for cruise control.
This method increases our leverage, puts more joint-forgiving play in the system and allows for greater control with less involvement from wrists.


*****

I tend to think the numbers are more like guidelines, really.

The difference between perfection of efficiency and pretty good, as usual may demand a price. For example, to adjust one's self to the derived loom height by standing on a platform is inconvenient, to say the least. A shorter Loom and lower Fulcrum height might drop a fraction of a knot, but keep the cockpit clear of contrivances.

I'd personally sooner juggle solutions - fitting the proportions to our hull and layout - than to fit ourselves to the numbers. So far, it's not been an issue for our situations and the recipe as given, but (like Eastern vessels) we're high-sterned for our length.

I'm just sayin'...


And Beyond

Many of the 'improved' sculling systems I've seen over the years lack KISS, a prime ingredient in DIY and carefree cruising. So I really perk up when something comes along that is KISS, elegant and powerful!

Atsushi Doi is a Japanese inventor with due appreciation of traditional virtues. He's come up with several simple sculling inventions whose performance is impressive.They go by names such as ADScull, Ve-Scull, I-Scull, Ro-Scull and PowerFin. Several have been patented.

Not sure we'll ever get around to trying these out, but they bear thinking about!

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Here's an article (translated from his site) to get you started.

To get a feel for the potential, here's a sample video of the PowerFin in action, pushing a Layden LITTLE CRUISER to 2.8kts:



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