Yuloh design

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Chris Partridge Chris Partridge
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Yuloh design

Chris Waite Chris Waite
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Re: Yuloh design

It has taken me a little puzzling out

But this seems to be a hand-cranked, half of a Mirage drive.  That is, it works with a fin in a fore-and-aft direction with rotation produced by an offset handle - in this case formed by an ordinary stag-horn cleat.  It is not flexible, so does not produce the variation in pitch achieved by the Hobie Mirage.

To induce an angle of attack in the appropriate direction, the cleat necessarily has to be on the back of the shaft.  A cranked, bent, or curved handle in the same direction would work as well.

This is only effective if you can reach behind it to move it back and forth, so requires a multihull configuration, or a well/case forward of the operator's position.  I get the impression that blades working in this configuration are actually more effective at speed than a yuloh or sculling over the stern.  Either that, or hang it over the stern and apply some sort of stringy pedally gubbins.

Well goodness; nature has got there first again!

I can't think of any self-respecting fish

That sculls rather than flaps

Can you?

CW

(And don't come arguing with me over Cetacea; they flap like all the others, but do it horizontally)
simplesimon simplesimon
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Re: Yuloh design

As far as I can tell, a lot of the time he's using a straight yuloh where the  leading edge of the blade is always the same (compare European sculling where the blade reverses flow when the direction of push reverses). The little strut is to compensate for the need for a kinked line of shaft.

Beats me though why he's holding the top of the shaft instead of the bottom of the strut like any self-respecting tradional Chinese yuloh'er (or Japanese ro'er) would.

(or have I got that all the wrong way round?)

Simon
Chris Waite Chris Waite
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Re: Yuloh design

You're right there Simon

I suppose the question then becomes - "When is a yuloh not a yuloh?"

All the evidence from the Orient seems to support the yuloh being used across the direction of travel in a falling leaf motion where alternate edges of the blade lead - the same as sculling in Europe.

As mentioned elsewhere, the true advantages of the yuloh as opposed to the scull, are that it self-cocks and the tether on the handle prevents the blade trying to dive under the transom....

Devilishly cunning, as it allows the operator to use all their effort in propulsion.

So what is the correct term for this latest gubbins where, like the Hobie Mirage Drive, the blade has one leading edge and it follows can actually sport a true foil section -

Fishy-style as nature intended

CW

Chris Waite Chris Waite
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Re: Yuloh design

In reply to this post by simplesimon
I've looked at the pictures in more detail Simon

I'm not sure which strut and shaft you are referring to, but if you watch the traditional yulohers -

https://www.youtube.com/watch?v=UjyE7dyR2X4&feature=player_embedded#at=49

You will see that they also use both hands - I think this is to steady themselves, provide more power and control the rotation, therefore the cocking-angle of the yuloh itself.  My pedal yuloh has an inbuilt mechanical limitation to rotation of about forty-five degrees each side of neutral, which seems to work very reasonably.

The bend in the shaft is simply to offset the handle from the axis of the blade of course, so that the yuloh is always trying to set the blade to an angle of attack.  It doesn't have to be a bend, a crank, or simply a secondary offset handle (like the cleat the Dutch guy uses) will do just as well.  If a bend is chosen, the other question then becomes - "Should it be inboard, or outboard of the pivot point, or throughout the shaft.

They all work, but I keep it inboard as that reduces the non-driving movement of the blade itself which other wise swings through an arc at each end of the stroke, but produces no useful drive.

A case of wasted oomph

I thought you had seen the Pedyuloh in action, but perhaps not?  I'm doing my usual prevarication, (for the usual reasons), about the HBBR Barton trip, but in the hope that I do make it, I'll put the whole set-up in the van

And you can have a go yourself?

CW
alopenboat alopenboat
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Re: Yuloh design

In reply to this post by Chris Waite
On 14 Feb 2017 at 2:07, Chris Waite [via UK HBBR Forum] wrote:

> So what is the correct term for this latest gubbins where, like the
> Hobie Mirage Drive, the blade has one leading edge and it follows can
> actually sport a true foil section -
>

That would be a slalom stroke.

--
Sail when you can, row when you must, motor only
when you have to be at work in the morning.

Alastair Law
Yeovil, England.
<http://www.little.jim.freeuk.com>


simplesimon simplesimon
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Re: Yuloh design

In reply to this post by Chris Waite
By "shaft" I mean the long straight bit that goes from blade to the operators end, the "strut" is the little cross-piece at the top that compensates for the lack of bend in the shaft and to the end of which the rope is attached.

I hadn't seen the video you've found, I was thinking more of this sketch - https://en.wikipedia.org/wiki/File:Sampan-01.png - where the operator has his right hand on the rope and the left on the shaft for balance, and the oar is on the port side of the boat. I'm not sure in your video, where the oar is on the starboard side, which arm is doing the work.

I find it very difficult, sitting in front of a computer, to work out whether when I use an oar over the stern the flow is reversing (sculling) or the blade is reversing (fishtailing) and where I have to put my hands to achieve which (as I use both). I usually have to walk down to the staithe and get an oar out!

A yuloh I think is sculling, and reckoned to be good for heavy boats. Fishtailing I suspect is better for fast ones, and where a positive steering force is needed.

Yes, I've seen the pedyuloh in action, but only from the bank. I don't know whether it sculls or fishtails.
Cheers
Simon
inwe inwe
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Re: Yuloh design

Do you know what the length ratios are? How much of the 'oar' should be in the water, at what angle as against the length of handle out of the water and above the pivot point?

Richard
Chris Waite Chris Waite
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Re: Yuloh design

This is real "How long is a piece of string?" stuff, Richard

Depending on which of your fleet you have in mind, I'd suggest you start off with perhaps nine or ten feet total length and expect maybe a third inboard of the pivot/rowlock.

The real things are how you're going to stow it when not in use, how high above the water the pivot is and where you can position yourself to get at the handle.  Nothing to do with the actual mechanics at all in fact.

Have you tried simply sculling; the yuloh is just a scull with advantages.  The first thing is to decide where your pivot can be mounted so that you are in the region of three or four feet in front of it and perhaps conveniently off to one side.  I use a single nine foot oar to scull my little, one and a quarter ton gaffer around tight, peaceful spaces.  I had to make one mock up and two yulohs to get a satisfactory version for the Pedyuloh and I note the Dutch guy had six or seven stages to get what he wanted.

The Oriental yulohing action is the same as sculling, Simon....    that is a figure-of-eight, falling-leaf motion, with alternate edges leading and the blade sideways on to the direction of travel.  And again, I reckon you are right that the motion is better for heavier slow-moving vessels; the fishtailing being reserved for light, fast hulls

CW
inwe inwe
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Re: Yuloh design

Thanks Chris, I had the idea for Inwe but am going to have to throw the pivot point quite a way out from the stern post. I think it will work quite well if I get it right. As for stowing the oar I think there is enough room, provided it does not exceed about 16feet long.

Richard
inwe inwe
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Re: Yuloh design

Chris what length of your yuloh is actually in the water. I've calculated at about 30" to 33". doeas that seem about right ?

Richard
Chris Waite Chris Waite
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Re: Yuloh design

OK Richard

The blade has well tapered shoulders - like a Coke bottle really; most of it is over by about 36".  The whole Yuloh is just over seven foot long and the pivot is at about 21" from the handle's end....

But remember - it started off about eight foot long and the handle was cut down because it is designed to be used with the extra power of my little sailor's bow-legs.  For hand use, I suggest going back to eight foot or so for Inwe.  Really, pretty much the same as you would use for sculling over the stern.

Things to bear in mind -

1.  If you put a tether on the handle it causes the blade to rise toward the end of each stroke, so the length of blade in the water varies continuously in a sort of sine curve, but your guestimate is about right for maximum immersion.  The tether just means you don't have to manually prevent the yuloh diving at each stroke.

2.  You (?I) would have thought that the deeper, therefore more vertical the blade, the more effective it would become, but having tried that, it just ain't so and I can't for the life of me work out why.  Keep it between perhaps closer to 33 than 45 degrees from horizontal.

3.  Don't offset the handle more than a very minimum; it is only there to oblige the blade to rotate to the next angle of attack.  For me it also makes sense to keep all the offset inboard of the pivot, otherwise you are waggling the blade, as well as rotating it and that seems like a waste of good biceps.

Here are the experts again -

https://www.youtube.com/watch?v=UjyE7dyR2X4&feature=player_embedded#at=49
 
Maybe Al Law could cut in here and tell you his measurements

And the length of his blade

Of course

CW
alopenboat alopenboat
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Re: Yuloh design

On 5 Mar 2017 at 4:42, Chris Waite [via UK HBBR Forum] wrote:

> Maybe Al Law could cut in here and tell you his measurements
>
> And the length of his blade
>

My yuloh is 3m long. The blade morphs into the handle, starting 90mm
wide by 8mm thick at the tip and becoming 76mm wide by 32mm thick at
1.2m and ending up as 32mm by 36mm at 3.0m. The pivot is at 1.8m from
the tip.

The curve is 30mm, that is if you support each end on a 30mm block
the middle would just touch the ground.

Keep the blade thin with sharp(ish) edges to reduce drag.

--
Sail when you can, row when you must, motor only
when you have to be at work in the morning.

Alastair Law
Yeovil, England.
<http://www.little.jim.freeuk.com>