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| The downward edge is the leading edge. Note upward bend at the inboard end. Source |
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| Atsushi Doi''s I-Scull from his US Patent The downward edge is the leading edge. Note upward bend at the inboard end. In recent versions, the handle pin has been moved to the upper side. |
In a fishtail gleam
She leans to kiss me as she goes...
-- From The King of Britain's Daughter(?) byGillian Clarke
A First Look at Vertical Sculling Oars
The Chinese Yuloh and similar Japanese Ryo are horizontal blade sculling systems. The blade follows a 'falling leaf' pattern, angling across the sweep and switching leading edges at the end of each stroke, and kicking up a little turbulent 'fuss' at each switch.
Atsushi Doi, Douglas Martin and others have been taking a good look at vertical blade sculling systems.
The blade is still swept to and fro, but the forward edge always leads, with less fuss at the switch (especially once moving forward). This otherwise wasted energy is, in theory, availlable to generate thrust.
A second refinement is that the relatively high aspect ratio blade (long for its height) is not only allowed, but encouraged to twist, much as might a propeller blade. This has positive, hydrodynamic effects (laminar effects discussed here). In part, water is turned and tossed aftward... increasing its equal and opposite thrust forward.
In Douglas Martin's oar, shown above, the slender tip is hooked aft of the blade's Center of Lateral Resistance (CLR). As the blade is pushed sideways (albeit at an angle) through the water, it resists and twists the flexible end of the blade, causing it to lag behind the plane of the main blade.
Atsushi Doi gets a similar effect via a small fin attached low on the blade. Not nearly as pretty, in my opinion, but is powerful, removable and allows easy experimentation.
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| Atsushi Doi's Ve-Scull Fin |
In a yuloh/ryo, the inboard end of the loom bends downward (or the mechanical equivalent). A lanyard led from this end to deck torques the loom outboard over the top, helping its horizontal blade to reverse.
In a Atsushi/Martin oar, the inboard end of the loom bends upward. A lanyard led from this end to deck torques the loom inboard over the top, helping the leading edge reverse.
If all goes according to theory, the same thrust should be developed with less effort than horizontal blades, or more thrust with the same effort.
As a bonus, the vertical blade system appears much easier to use than yuloh/ryos (which can be challenging for beginners). The video beow shows a monkey flinging down the gauntlet by using one of Atsuhi Doi's oars on the first go!
So I'm jazzed!
*****
There is considerable interest in these (including my own), and information is beginning to fill in. Most of it is for small craft, but there is now at least one video available for larger craft (relevant section comes after a bit).
Be aware that Atsushi Doi has patented several of his approaches to vertical blade sculling oars. While DIY is allowed, commercially interested persons should be aware of his intellectual rights.
Sources:
Atsushi Doi's Pages (translated and hosted in English)
Reprint from Small Boat Journal... note 'sculling aid' toward bottom.
YouTube, image and web searches using such phrases as "atsushi doi scull" and "vertical blade scull"
It seems to me that this would require less effort than a conventional yuloh since most it would go to thrust. Conversely with a yuloh, thrust is a vector force since some of the sculler's effort goes to forcing the stern down on each sweep. That would be wasted energy I would think. However, I don't KNOW. Your thoughts on that Dave? How's Wayward?
ReplyDeleteHi Alan,
DeleteIt may be similar... both make most of their lateral pass at about the same angle, as far as I can tell, so both will tend to depress the stern (inboard lanyard counters the dive, so we don't have to).
Hope to try one out, soon!
WAYWARD's poking along. We've nearly finished the OCBs (almost a leeboard), and are picking away at the electrical system. Should go faster now that some cramped mountings are in place.
Emptor Lux!
Dave Z
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DeleteThis comment has been removed by the author.
DeleteHello Alan and Dave,
DeleteI use an AD sculling oar, and have had the same thought about the direction of the force. Therefor I use the oar with a lot steeper angle in the water than most of the other users I can find on the net (judging from videos/pictures). The difference in speed seems to be less then I expected though. It could be that easier handling of a shallower angled oar makes up for the loss in efficiency ?
BTW the end of the stick from which the lanyard comes should be at the rotational axys of the oar/oarlock. (difficult to explain in English - hope it's clear).
Greetings, Hans
Hi Hans,
DeleteYou could be right that more force can be applied to a shallow angled oar, and that would reduce any advantage. Atsushi Doi's Power Fin achieves a fully vertical blade with a horizontal loom, but at the cost of a much less stowable setup.
Yulohs that angle high are worked primarily via the lanyard... did you try that?
I'm thinking that the oarlock should be halfway between the point of lanyard attachment and the center of lateral resistance of the blade... does that seem about right?
What size boat are using the oar on?
Great to have some actual experience weighing in... thanks for writing!
Dave Z
Hello Dave,
DeleteI use my oar on a small multihull, so unfortunately I have no experience of a setup on a big boat. I wrote an article with some drawings of my setup. You can find it here : http://smalltrimarans.com/blog/how-to-scull-a-multihull/
In my setup, the oarlock halfway the CE of the blade and the spot where you grab the oar sounds about right.
But you could experiment with "gearing" - change length of levers / area of the blade / frequency of the stroke.
For bigger boats I would think it is important to be able to use more muscles than only you arm i.e. legs/upper body. The human power available is not very big so you might need all the muscles that can help to move a heavy boat.
Good Luck, greetings from Amsterdam, Hans
Hi Hans,
DeleteBig muscle groups are great to bring online! Especially if oaring over the long haul. 8\
Dave Z
I distinctly asked that my sculling efforts on that video not be published!!!
ReplyDeleteYes, but did you ask in Japanese? -- DZ
DeleteI was looking into making an I-scull for my old boat last year. I never did it, but I did get into contact with Mr. Atsushi for some advice and I found him very helpful and just a fine man all around. One thing he stressed to me was that while the basic shape is expressed in the patent drawings, the proportions must be adjusted to transom height and that of the oarsman. What I needed for a 22 foot sailboat was huge!
ReplyDeleteHi David,
DeleteHuge in what ways? E.g., length of oar, length and/or depth of blade?
Definitely may be the fatal flaw for larger boats. Some of that may be fudgeable, but we'll see!
Dave Z
Yeah, huge like long. I dont remember now, but it would have had to break down in at least two if not three bits.
DeleteI can't help thinking this would require less exertion than an ordinary yuloh since most it would go to push. Alternately with a yuloh, push is a vector drive since a portion of the sculler's exertion goes to compelling the stern down on each scope. That would be squandered vitality I would think.Thanks for sharing this nice info expect some more in near future. educeviri of very nice information.
ReplyDeletesailing cruises in san blas islands
Hi MD,
DeleteFrom what I can tell, the downward vector may not be as different between the two as might be imagined.
In many cases, the loom/blade for the AD oar and yulohs are at the same profile angles... once settled into the cross sweep, the transverse angle for both is about 45deg.
However, my guess is that the AD will 'stand up' toward vertical easier than a yuloh... about the same as a ryo.
Dave Z
l always liked the many contributions Atsashi Doi has contributed to alternative boat design and simple drive units..
ReplyDeleteHere is another concept l find admirable, simple and portable..
https://www.youtube.com/watch?v=uW8MWFvT-Eg
Hi Tim,
DeleteHe sure has an OPUS! So many good ideas, so little time.
Those fish tail oars look very good to me, too. Once we're sailing again, I'd love to play with them.
Dave Z
Hi. I'm just beginning to research yulohs/sculling oars as a means of propulsion. Is there a reason the vertical oars pictured here kick up at the inboard end, as opposed to down? In both cases, the intent of the kick (as I understand it) is to set the angle of the blade through the water, and either set up will do that, but an upwards kick means either a much longer oar is needed, or that the oar by necessity will sit much more shallow in the water. No doubt Mr Atsushi has done his homework and come up with the most effective design, but I struggle to understand the mechanics behind it.
ReplyDeleteHi Charlie,
ReplyDeleteYes, it's important for the hook to be on the upper edge.
It's function is to twist the blade as you stroke side to side by dragging that upper edge behind the leading edge this orients the leading edge downward.
Oriented thus, the whole blade wants to dive and thrust is forward. This tensions and is prevented by the lanyard at the forward end. As long as the operator doesn't fight the effect, things stay taut and efficient.
If the hook were on the downside edge, the leading edge would twist UPward and thrust is backward, and the whole blade would want to skip to the surface. You'd need a strut (rather than a rope lanyard) to resist.
It may help to picture the blade as one of a variable pitch propeller... It functions like a screw, screwing its way through the water.
In theory, you could overpower the geometries of the oar (or yuloh) and scull backwards. I've tried it but without mastery. It's awkward and strenuous, but possible. Might even be worth practicing,
Have fun!
Dave Z
How has yours been working with the Wayward?
ReplyDeleteHi Peter,
DeleteWe used a straight loom / no handle version of the Martin MOCKINGJAY approach.
It has been working very well... a significant improvement over our yuloh.
Given our implementation (less blade area), we don't seem to reach quite the same top speed on a sprint(judging by wake). 16ft overall, it powers our T32x8 hull.
But we maintain very nearly top speed with noticeably less effort. We can scull continuously for much longer periods without pause to rest. I think our overall (average) speed is higher.
The hook definitely reduces the forearm effort for orienting the blade between strokes.
More soon in a full post.
Dave Z
Do you have some dimensions, photos or design sketches of your particular sculling oar?
ReplyDeleteHi,
DeleteI don't at the moment... once I'm back in the USA I intend to update this post as we now have a lot of experience with the Martin oar.
The blade we're using is 5ft long by about 10in deep in the belly. The total length with loom is (I think) 16ft. We set it up like a yuloh (deck lanyard and and a lanyard to position it outboard).
More to come!
Dave Z
I await with hot interest a lot more about the construction, dimensions and implementation of your big boat sculling oar.
ReplyDeleteHow much of the overall length of your sculling oar is blade? Is it the same proportion as the Mockingull diagram, above?
ReplyDeleteIt would seem that transom height measured from the waterline would play a lot into how long one needs to make the loom. What is the transom height on the Wayward for your 16' sculling oar?
ReplyDeleteHi,
DeleteWoo... seems as if I DIDN"T get back to this. I'm in correspondence with Douglas Martin on the topic, and I'm in a ways over my head!
Our blade is 5ft on 16ft overall. Stern height is about 4ft (a little less when overloaded).
Yes, transom height is important. We start long, then cut down if necessary. When stowed, the blade hangs outboard while the loom crosses the cockpit with enough to land securely on the main deck.
All these oars do better with a steeper Angle to rotate their thrust more aft than upward. The formulas are good starting points, but consider getting the feel of it, then trying variations that work with your body and boat.
The idea is to get good thrust at an easy, hours-long pace. Sprints are convenient, but we (at least) can't keep them up, so we don't try to optimize for them. Easy on the joints and muscles beats a fraction of a knot gain, IMHO.
Dave Z
PS, the loom is 12ft with a 1ft slot overlapping the blade and cross-fastened.
Delete