Yuloh and Sculling Oar auxiliary power for sailboats

The dinghy is too light to provide a firm reaction point to the sculling oar when towing a heavy boat. A part of the power input will be lost by moving the dinghy's stern back and forth. Sculling would be much more effective from the main vessel with an appropriate oar in a proper oarlock.

Good Luck !
Angel

 

I'm thinking the main force component is angled forward and down, perpendicular to the yuloh blade. IMHO This would contribute to excessive pitching the dinghy due to it's diminutive size. I think that you are right that there will be some lateral movement, but I think that the lateral forces are much less than compared to an oar used with the blade perpendicular to the surface(not that you are suggesting this). I have on occasion, used my rudder for propulsion in my sailboat when the wind died. Very inefficient and a fair amount of yawing along with it, but forward progress was made.

Along other lines, reading the paper you presented, it looks/sounds like there is not a lot of empirical data that was used to determine the most efficient foil shape. Having to be bi-directional really throws a twist into all data compiled for uni-directional airfoils. Perhaps there is a fair amount of research that has gone into the "Frisbee-foil" and it is actually a valid and developed shape.

Another point that I'm curious about is the fact that the tip operates at a higher angle of attack than the surface foil. If my recall of aerodynamics serves my correctly, wouldn't a higher angle of attack call for more camber(I believe this is in the paper), a thicker section(not in the paper) and maybe a longer chord(also in the paper). Operations at a lower angle of attack could utilize a thinner shorter section with less camber, but that may not make sense as the goal is to produce as much lift as possible for the least amount of energy expenditure. Camber and thickness would best be optimized since angle of attack is fixed, or at least limited by the angle of attack at the tip. I'm thinking the parameter that drives the shape of the blade is set by the actual/maximum angle of attack that the tip will be expected to operate at. To digress though, a thicker section has a higher drag penalty and the fact that the tip is operating at higher velocities goes a long ways towards explaining the need for a thin section at the tip.

A quick search on the web reveal some information regarding bi-directional foils. Some had lift vectors that reversed with direction and others relied on advanced technology to change foil shape as direction changed. Neither of which would apply here, but I did find a link to an interesting paper by our very own TSPEER. It will take some time to digest, but I think it provides an insight into designing efficient foils section that could be applied to the yuloh.

The first link directs to where these foils sections were applied.

http://proafile.com/archive/article/302

And, this goes to the paper itself.

http://www.basiliscus.com/ProaSections/ProaIndex.html

 

The post to which I responded spoke of sculling, so I assumed a sculling oar* was used and not a yuloh, hence I think lateral movement of the dinghy's rear end and loss of efficiency occurred when towing the 30 tons heavy boat.

* blade perpendicular to the water surface during work strokes​

As for the rest of your post, I also would like to learn what the perfect yuloh shape and angle is, hope this thread will provide some clarity here

Thanks for the links and sharing your considerations

Cheers,
Angel

 

I was using a yuloh as the main propulsion, and seriously take it in deep weather and bad weather, is very reliable. But for a sailing boat a sculling oar is better, more simple and your sculling style be more verstaile under different circumstances.