Thanks…
…for those links, they’re much appreciated. Carl
Excellent
Excellent demonstration video, and a good idea for retrofitting the scuppers. Epic should be buying this design from you (really). This is such a simple fix and obviously works well. You could probably manufacture the bullets with adhesive in the right place as an after market item.
I agree that there should be no concavity in the hull behind the drain — maybe they use a cylinder when laying up the hull to preserve the drain hole, and when it’s removed it leaves the concavity. Good for manufacturing, bad for fluid mechanics.
Other viscosity
If you compare kinematic viscosity (dynamic viscosity divided by density), then air is 15 times more viscous than water. Kinematic viscosity (essentially viscosity per unit mass) is used in dynamic situations, which is what we’re talking about. Also, as far as flow in air vs. water, both are fluids and testing in either is valid, as long as the Reynolds number of the test is equal to the actual flow Reynolds number.
Perhaps it is a patent or other
issue, who knows. I did not come-up with the idea of the bullet (Red or whatever the ski maker is) did some time back (at least for this application) and they sell “kits” to retrofit skis with bulleted drains. But mine works well enough and indeed is simple to make. The tric is that the size, shape, and position matter a lot and being able to quickly see the effect real time (by repositioning the bullet or changing to a slightly different shape) was interesting and allowed me to pick a shape, size, and a position that worked better than others. Still, I have no idea how closely that corresponds to in-water conditions and perhaps there something else might work better. There was an article at surfski.info with a pressure model of a scupper with and without a bullet, so one can visualize what is going on and why suction goes up and resistance - down.
Nomenclature
In the nomenclature of a wing paddle, lift is the force perpendicular to the path of the wing paddle through the water. It has a component in the forward direction of travel, so does propel the boat. This is confusing if you think of lift in terms of airplanes, in which case it is generally a vertical force. For a wing paddle, it should properly be called a thrust force, or something like that, but it’s called ‘lift’ in spite of being somewhat illogical.
Yes, I have, thank you,
Many a times, years ago, however, the material is pretty much dated and based on the premise that the the paddle moves laterally in the water. About the time that paper came out, paddlers were switching from narrow tip wings to broad tips. Why? Because broad tips were more effective in the water due to their ability to exploit more efficiently drag, the dominant force that propels us. I would say that drag contributes 95% to my wing paddle stroke and only 5% comes from “dynamic lift” at the catch, when the blades enter the water. The only time my wing blades move in the water are when they enter and exit it.
The truth about wing paddles.
– Last Updated: Apr-13-12 8:45 PM EST –
They have nothing to do with wings.
People see a shape that resembles a wing, and assume that it must operate in the same way as a airplane wing, embellishing this theory with diagrams and formulae. As they describe it, the operation of the "wing" occurs as you move the paddle sideways.
But to say that it resembles the cross section of a wing and must therefore operate the same by "generating lift," has no more validity in and of itself than to say that the curve of the blade resembles a banana, and operates similarly by allowing water to smoothly "peel" off the paddle.
You should immediately question this theory, as you have, for several reasons --
First, it doesn't really resemble a wing because there's no bottom edge enclosing the shape. But even if it had a bottom edge, it would be a stretch to believe that moving it a few inches per second through water was equivalent to moving at hundreds of times that speed through air.
And in operation, you don't propel the wing paddle sideways as you would a wing. Rather, it drifts to the side on its own as you pull rearward.
Lastly, if you were to stand in knee-deep water and slide the paddle sideways through the water, under the accepted theory you would feel the purported "lift" that the paddle is supposed to generate on the back side of the blade – only you don't.
In truth, the wing paddle works in a simple way that anyone can understand –
Basically, it's cupped and thus tends to stick in the water instead of wasting energy by moving water. If it were cupped on both sides, it would stick even more, but that would create problems for two reasons –it would go against ergonomics whereby your muscles want to operate through a range of motion. Second, if both edges were cupped, it would not exit smoothly from the water.
So, by cupping only the outer edge, only that edge sticks and prevent water from easily flowing around it, while water more easily flows off the flatter inner edge. As water flows off the inner edge when you pull, the paddle will naturally move in the opposite direction, or outward. And because it moves outward, it solves the ergonomics problem by providing a suitable range a motion for your arms, even without significant rearward movement of the paddle. Lastly, with a smooth inner edge, the paddle exits cleanly from the water in an outwards direction.
It's stunningly simple, and therefore likely to be disputed.
i like this
Ryan L.
A matter of interpretation?
While the “slicing through the water” is certainly there, there is a component of “lift” generated too. Whether that lift plays any role is a different matter alltogether and you got a good point about it…
From one of the referenced articles:
“Based on that data, and measuring a wing paddle, the Reynolds number is about 320,000 and about 2.5 to 3.0 lift coefficient. These are reasonable numbers as long as the stroke rate keeps the blade above the crtical Strouhal number (critical Strouhal is about 0.21, it is the rate below which the vortex flow breaks down and allows stalling and separation of the flow across the paddle blade). This critical stroke rate is about 70-80/min for most wing paddles. 1-D simulation shows these assumptions are reasonable and fall into the expected performance envelope of sprint kayakers”
The PDF article (can’t copy/paste as it is an image from a scanned page) also shows the forces profile.
The speed of the paddle through the water is not insignificant if one is paddling short distances at top effort. I would think there is a significant lift component at play there.
Your argument about speed through the water diminishing for leisurely or rather long distance paddling is certainly valid though. Might as well not be much lift component there to make a difference.
Look at Figure 5
In this paper: http://www.mech.eng.unimelb.edu.au/people/staffresearch/AFMS%20site/11/Jackson.pdf
The wing’s “lift” component is almost 2x bigger than the drag component. While the drag component of the wing is smaller than that of the “drag” paddle, the overall “power” is bigger. Add the lift and the drag for the wing and you see that the combined propulsive force is larger than that of a purely drag paddle…
For what it’s worth, the chart is titled “measurements” (as opposed to “speculations”, which is what we do here, he-he), so I’m inclined to trust it -
Wings
– Last Updated: Apr-14-12 11:01 AM EST –
Wing paddles do develop lift and there are measurements that demonstrate it. You could read the papers linked above if you want to see the evidence and explanation of the physics. The forces involved in paddling are all fairly small - after all, the total drag on a boat is generally around five to ten pounds, and the lift component of a wing blade might be only half of that, so it won't be a dramatic thing.
Re: standing in water and using the wing, it is important to realize that it's the relative velocity of the paddle to the water that is important, so the forward motion of the boat is part of the equation. And one does propel the paddle sideways in a correct wing stroke, to get the proper angle of attack between the blade profile and that relative velocity.
It may be true that in many cases, wing blades are used as drag paddles (e.g. due to low speed or poor technique), but that doesn't mean that when used properly they are not lifting bodies - they are.
Let’s think about this.
Putting aside all the learned treatises of those much smarter than us, if you believe that the wing paddle generates “lift” on the back side of the blade as you pull it rearward and/or sideways, then you must believe one of these statements:
A. If you sit in the boat, then put the paddle in the water and slide it sideways, you just hold on for the ride as the paddle propels itself, you, and the boat forwards.
B. If you pull the paddle rearward instead of sideways, it pulls back in the opposite direction, propelling itself, you, and the boat forwards.
C. Some combination of the above if you pull the paddle backwards and sideways together.
I don’t believe any of those. I believe that you stick the paddle in the water and pull yourself and the boat forwards. I also believe that the wing paddle sticks in the water better than a flatter blade because it’s cupped, in the same way that a bucket would resist being pulled through the water compared to a dinner plate of the same diameter which would shed water more easily off the sides.
Get your own Data
– Last Updated: Apr-14-12 2:05 PM EST –
Data acquisition paddle
http://www.merlingear.com/dataproducts.htm
Video
http://www.youtube.com/watch?v=OgtvEkNNzNE
Article starts on Page 26
Title "New smart paddles"
http://issuu.com/ckrmagazine/docs/mar-apr_2010
The Excalibur paddle manufactured by Talon Technology
in Sydney, Australia is fitted with a strain gauge
placed inside the shaft at both ends to measure
shaft bend in response to pressure placed
on the paddle blade.
Accelerometers are located in the 3 planes of the paddle.
http://www.abc.net.au/tv/newinventors/txt/s2203885.htm
missing the point
The focus on the interaction of wing blade and water misses the point of the wing, which is to enable the peculiar wing stroke. It is the efficiency of the body while stroking correctly that provides the added 5% or so. The wing’s lift encourages the blade to move outward, encouraging more torso power, encouraging higher cadence and shorter stroke.
That’s over-stating things
– Last Updated: Apr-14-12 3:24 PM EST –
Okay, I'm neither a kayaker nor a wing paddler, but your brand of logic here looks like an over-the-top attempt to justify too much arm-chair reasoning. I myself often try to "reason things out" without having a chance to scientifically test an idea, but standing in the water and dragging the paddle alongside you for the full length of a stroke is not the same as putting the blade through the same motion while paddling a boat. You should be able to see that for yourself if you've operated the paddle in both situations - the difference in how the blade interacts with the water when most of the motion is your boat through the water rather than the paddle through the water is like night and day even with normal paddle blades (I've noticed that the same goes for oars). What Carldelo says in his post above sounds perfectly reasonable to me, and I can accept it without going to the extreme of believing the exaggerated, or even magical, cause-and-effect which you describe. The article linked by Kocho looks believable to me also, and again, I see nothing magical there. I'm hopeful that someone will post a link to a video which has been talked about on this site before. The video supposedly shows a stationary-camera view of the water right where the paddle blade gets planted as a kayak goes by. If descriptions of the video have been accurate, the blade of a wing paddle actually creeps forward a small amount during the stroke rather than slipping backwards as a normal blade does. Heck, even if the wing blade were to remain motionless relative to the water as the boat goes by, that would demonstrate lift as well, since no increase in "bite" or "grip" of blade to water will completely eliminate back-slippage when paddling normally.
You are awfully quick to poo-poo the findings of people "much smarter than us", but if you've been around this site long, you must have figured out that Carldelo's career and area of expertise is fluid dynamics. In that context, your post reminds me of the old joke where someone makes a snide remark that "it's not rocket science" when actually, it is.
Straight Back Is Correct Wing Stroke
And not sideways. There has always been a lag between paddlers and swimmers when it comes to propelling oneself through the water. Back in the '60’s and '70’s when swimmers were all switching over to the new “S” stroke to take advantage of “lift,” us paddlers didn’t. We switched in the '90’s, after Barton won the Gold using a wing in '88. By then, swimmers were abondoning the “lift stroke” and have gone back to the old fashion straight back stroke, but utilizing an “Early Vertical Forearm” or “EVA” technique. Unfortunately, us paddlers haven’t followed, and insist on paddling laterally out to the side instead of parallel or straight back. Yes, there is “lift,” but of the “Newtonian (Dynamic)” type and not the “Bernoulli” kind. And that’s why, that paddler using the narrow “GP” paddle blows by you as you paddle incorrectly carving out sideways with your wing paddle.
i like this too.
Ryan L.
Combination
The wing paddle appears to function as a lifting body and drag-based propulsion device simultaneously, so choice C, I guess. I come to this conclusion based on personal experience of a wing paddle, use of a GP with a wing stroke (which produces a strong lift component, by the way) and close review of the scientific literature. You are free to ignore all of this and believe whatever makes sense to you. What you believe, however, does not alter the facts of the quantitative research that has been undertaken.
"Straight Back Is Correct Wing Stroke"
I’ve never heard anyone say this anywhere. Why would you make an airfoil shape and then drag it straight backwards? That’s like dropping an airplane straight down and hoping it will do something useful.
Because The Blade Doesn’t Move
It remains fixed in location to be effective. The brain miss interprets what the eyes see. The kayak yawls left and right while the blade stays put. However, when used “correctly,” the blade actually moves forward or ahead, just like a “GP” paddle or a canoe/SUP paddle (no camber needed). Moving the wing sideways is a waste of energy and slows the kayak down. The kayak pivots past the blade and not the other way around where the blade pivots past the kayak. The design of the modern wing blade is just more effective or better in capturing and transferring the reaction force, generated by the action force, to the kayak (beautiful example of forces working in pairs).