Here’s a video of me shedding ventilation on a silk 850. Can’t share a video without linking an upload
My rudimentary understanding is that the tubercles play more a role in lowering stall speed than shedding ventilation. In theory they are channeling flow over the wing into strips. This accelerates the average speed of water over the wing, increasing the pressure differential and thereby lowering stall speed.
that’s cool, shows the feeling I was describing below, where until you shed the bubble you sort of understeer
on what they do, I had a go at my theory here in this thread.
I agree that they are channelling water into strips, but I don’t really understand how they could accelerate the average speed of water over the wing. (a case of 2+2 or 3+1 both equal 4), speeding up in one area of the top surface means slower in another area. Maybe over simplifying.
In any case the AFS foils all like to go faster more than they like to go slow, so if your theory was true then it’s not working
I believe most of that, but not the last one. I would love to see any proof of tubercles improving efficiency, because I think it is the opposite: the improved stall properties come at the cost of efficiency. And top speed will be lower too, it’s the same thing.
When designing foils and sections, the way you improve efficiency (ignoring AR) is getting the maximum percentage of the foil in laminar flow. Drag of area that has turbulent flow is several times higher, so the whole objective of creating efficient foils is trying to minimize turbulent flow. The foil designer can play with the speed and angle where the laminar percentage is highest, and the efficiency is best.
Flow separation happens later with turbulent flow, so it is completely expected that foils with tubercles that create turbulence (“vortices“) have higher stall angle. There are other ways to create turbulence, such as using a nonlaminar section, that will also result in larger stall angle. Tubercles is an interesting way to introduce turbulence more locally and at higher angles. But until I see a foil with tubercles win races I believe they’ll always be less efficient.
they probably mean that they improve efficiency in real world conditions where you factor that there are turns, sudden changes of AOA, various turbulences in the fluid, all of which are significant deviations from the perfect model of laminar flow over ideal AOA.
Arguably, if that makes them easier to ride, more forgiving, more confidence inspiring to push them harder, then for everyone but the most extreme seasoned racer, that would lead to a gain in overall performance, and perceived efficiency.
At the end of the day, it all depends how you define performance. In our sports, be it kiting or foiling, if we’d only focused on L/D ratios to define performance, we’d probably miss out on a lot of fun!
You described exactly how they feel in real world conditions! They indeed are not the fastest, perhaps sometimes might be even a little draggy, but feel so clean thru water and stable thru turbulent waters that I do feel the difference of the effect of tubercles in various situations.
You’re not wrong, but efficiency has a defined meaning: getting the most distance or time from your energy. I understand it’s more efficient when you do not fall, but that way you are redefining efficiency to mean something entirely different. That’s marketing, which the original quote claimed it was not.
you’re right, of course, but at the same time, the energy available in the wind, in the swell, is also quite hard to properly quantify once you’re in real world conditions. That’s why I prudently called that perceived efficiency, which is what essentially matters for us riders.
Surely the mentioned CFD simulations would be able to provide a clear answer about that efficiency claim. Does that appear in the simulation, or in the real world testing, or in both? Sure, it is very legit to challenge that, for science.
@Velocicraptor on second thought, it could be that the tubercles are complementing by unlokcing a more aggressive foil section that would be unridable without. So I think possibly some variant of what you are describing makes more sense.
Couple this with
yeah, that’s where my head is on this - we get to extend the low end of a very efficient foil section that would otherwise be very hard to get up out of the water at slow speeds and dig out of a hole pumping.
yeah it must be.
Side note - The Silk seems to have some reverse aft camber (an indent on the top near the back trailing edge for the layperson).
Fwiw if you google image search reverse camber foil you get 3 x of my drawings from this forum! LOL!
That might be because people who know how this reverse camber is actually named use the word reflex when they reference it 
Yes, and if you search “reflex camber foil” you get even more of my (somewhat ridiculous in some cases) drawings from this thread:
Well, i’m not affiliated with AFS and have only ridden Axis, Jshapes and AFS but i think AFS is a total game changer for all but perhaps the top racers. The silks are so stable but at the same time so easy and fun to turn. They make nasty chop feel like a bluebird powder day. As others have said i’m sure theres way more to it than the tubercles but they sure do look cool imo because they remind me of whale flukes. FYI i’m primarily kitefoiling with some FD mixed in when the wind sucks. I can only foot change occasionally kitefoiling and have never tried a wing-a-ding.
Fun fact though for you foil surfers, Mr Adam Bennett’s used to ride AFS before he was with FliteLab and the designer of the Silk (Professor Laurent Borgna) worked extensively to develop the Silks with the late Chipri Courde. If your interested in how it was developed this is a fascinating translation from a french video on it Silk Launch Interview
Interesting conversation about tubercles.
Personally, I am skeptical of this design. It seems more about aesthetics than actual benefits. Why? Because in the natural world, only whales have these bumps. No other animals or birds possess them, which suggests they might not be very effective.
Greater efficiency can be achieved through the wing outline and profile. For example, as seen in ASF Enduro tips, they are quite sharp and swept back. Additionally, the wing outline at the center is curved backward to improve flow. These features help prevent ventilation much more effectively.
As someone else said, I don’t think it’s about efficiency in the conventional sense if speed vs power or speed vs area or something. Its about efficiency for you cause they keep you stable so you spend less time in the water and more time foiling 
A few interesting facts on them -
Whale tubercles—the large, knobby bumps found primarily on the leading edges of humpback whale flippers—function as sophisticated biological “vortex generators.”1 When a whale swims, these bumps change how water flows over its fins, providing several key hydrodynamic advantages that allow a 30-ton animal to move with the agility of a much smaller creature.2
In fluid dynamics, this is known as the “Tubercle Effect.” As water hits the leading edge of the flipper, the bumps channel the flow into the valleys between them.3
Vortex Generation: The water rushing between the tubercles is accelerated into swirling, tube-like currents called streamwise vortices. 4
Boundary Layer Energy: These vortices pull high-energy water down toward the surface of the fin. This “energizes” the layer of water touching the fin (the boundary layer), helping it stay attached to the surface for a longer distance. 5
Stall Prevention: On a smooth fin, if the whale tilts it at a sharp angle (angle of attack), the water flow “breaks away” or separates, causing a stall (a sudden loss of lift).6 The tubercles keep the water “glued” to the fin even at steep angles.
Because of these bumps, humpback whales can perform maneuvers that would be impossible for other large whales:
Tight Turning Radii: Humpbacks are famous for “bubble-net feeding,” where they swim in tight, upward spirals while blowing bubbles to trap fish.7 The tubercles allow them to tilt their flippers at extreme angles to make these sharp turns without losing lift.
Increased Lift and Reduced Drag: Research shows that flippers with tubercles have roughly 32% less drag and 8% more lift than smooth flippers. This makes swimming more energy-efficient .8
Acrobatic Maneuverability: They are the only baleen whales considered “acrobatic,” capable of breaching and rapid banking turns, largely due to the extra control provided by this passive flow-control system.
Scientists and engineers have used the “Tubercle Effect” to improve human technology. You can now see whale-inspired bumps on:
Wind Turbine Blades: To help them spin at lower wind speeds and reduce nois e.9
Industrial Fans: To move more air with less electricit y.10
Surfboards and Kayak Paddles: To provide better grip and control in the water.
Link: https://gemini.google.com/share/839957ec1a1f
I was skeptical too and now my quiver is literally 3 Silks and 4 Enduros 
hey man, we don’t really need you to post your AI “research”. we all know how to get that if we want it.
Idk, seemed relevant given the title of this discussion and was just responding to comment above 
agree, it’s tempting, but not additive. Rather share the link to your chat. We don’t know what you asked, what model you used, or how leading your question was.
Alright, let’s explore what CFD research reveals about tubercles.
grok summary
Tubercle-equipped wings show increased lift at high angles of attack.
They delay stall onset.
The best-performing configuration (maximum amplitude and minimum wavelength) achieves up to a 17% increase in maximum lift coefficient and delays stall to 20° angle of attack (versus earlier stall in the baseline).
The benefit is only noticeable at large angles above 10 degrees, while other factors indicate reduced lift, lower efficiency, and increased drag.
