I have been seeing some people asking about tubercles and whether or not they are just a marketing gimmick. Thought I’d post here as i’ve done some research on what they actually do and find it pretty intresting.
I sell AFS, so take what you will, heres the write up from my website:
Tubercles: What Are They & Why Do They Matter?
Tubercles (those bumps on the leading edge) have one job—to delay flow separation.
What’s flow separation?
It’s when water stops following the foil before the trailing edge, causing instability, inconsistent lift, and loss of control. Every foil deals with this problem.
Tubercles fix this by creating tiny vortices that keep water attached to the foil for longer, making the Silk:
More stable at all speeds—no unexpected lift changes.
Incredibly smooth through turns—even at high bank angles.
More predictable in turbulent water—great for white water and choppy conditions.
You know when your foot pressure changes when a wave builds power or your speed changes?
The Silk eliminates that. It stays steady no matter what, so you can push harder with total confidence.
Are There Any Downsides?
Only one—a slight reduction in absolute top speed. That’s why AFS race foils don’t use tubercles.
But here’s the thing:
Unless you’re an expert racing at max velocity, this won’t matter.
The Silk’s stability actually lets you ride faster, because you can push harder without hesitation.
Thanks to its thin, ultra-efficient design, the Silk is still one of the fastest surf foils in the world.
Why Don’t All Foils Have Tubercles?
Simple—they’re harder to design and manufacture.
Outsourced production = lower quality control → Most brands can’t get tubercles right.
AFS owns their own factory → They have the precision needed to make them work perfectly.
This is why AFS is the only brand making high-performance tubercle foils at this level.
Tubercles Have Proven Benefits In Research
This isn’t just marketing—tubercles have been extensively studied in hydrodynamics & aerodynamics, with CFD simulations and real-world testing proving their ability to reduce flow separation, increase stability, and improve efficiency.
Interesting because i tried the enduro recently and it’s was exactly what i experienced, the feeling of having nothing under my feets it’s weird because it’s an absence of feeling , i turned too quick and got surprised to not have any return of the foil while on other brand you feel the foil pushing.
I installed these on a large sailboat rudder back in 2010. The boat had problems with rudder ventilation at high angles of heel when the root of the rudder would break the surface. Tubercles solved the problem by not allowing the ventilation to progress down the foil thus keeping laminar flow on the lower sections of the foil. The higher drag was easily offset by the increase in control and being able to push the boat harder at higher angles of heel particularly when reaching.
That said, I don’t think they help anything when ventilation isn’t present at the root of the foil. Their purpose is to disrupt ventilation and stop it from progressing. Foil “fences” (flat plates perpendicular to the foil surface) have been used for decades for this purpose, but add significant drag because they are rarely perfectly aligned with water flow.
I can see them being useful when the foil regularly breeches the water surface or in turbulent water. Straight line in undisturbed water I don’t see much benefit.
You’ve put too much emphasis on “why is the Silk great due to tubercles”
That’s why AFS race foils don’t use tubercles.
This is somewhat wrong, the Ultra has them and is a race foil. I think the reason is that the Pure is designed by their other designer, where the Ultra/Silk/Enduro designer is the big fan of tubercles, and came from Takuma where his foils also had them.
according to my understanding, the other benefit tubercles is make the flow stay attached at higher angles
See here, where the angle goes higher with the flow staying attached.
Tubercles are vortex generators that change the laminar flow from a giant sheet into several strips. Stalls and ventilation both start at the wingtips and normally work their way towards the center where low pressure is highest but the isolated strips of laminar flow prevent it from migrating across the rest of the wing.
Perhaps. But I question whether wind tunnel testing has that much relevance to hydrodynamic properties. Also, what are the highest angles of attack we experience with hydrofoils? If they are generally inside the range where tubercles help avoid stalling in the tests then they’re not doing much…
Anyway fascinating stuff! Certainly the advances made in hydrofoils in the past decade are incredible, whether tubercleized or not
The only way to find out if they make a difference is building the same foil without the bumps and test them against eachother as every CFD is also not 100% sure.
Personally I don,t care if it are the bumps or not. To me they feel freaking awesome on the water (but so does the bumpless Pure1100 in its own way and many other foils)
I wonder how to design them.. if you take the exact same foilsection and just scale it smaller you wouldnt you get ripples/ tubernacles on the top and bottom too? So do they have a different foil section in the valley of those tubernacles? Maybe some can enlighten me!
Yeah this is supposed to sell the foil, so probably not the best thing to share here, but the points are still legit.
I thought most people used the HA800 for racing. The ultra certainly feels fast to me winging, but comparing the Pure 700 to other foils is no competition (although probably more at play than just the lack of tubercles).
The mentions of bumps helping with ventilation is interesting, as to me the Silks don’t breach that well (the enduro is better and ultra even more so) but I’ve ridden other foils that are much better in that regard.
I have ridden and loved the Kujira 1210,980 and 1095.Huge fan of those foils.
Now i am on a Duotone Superglide 2.0 750 and 900 , they absolutely rip ,no tubercles.
You can design a great foil with or without them.
Lots of paper on what they do but the only way to know what they do for us foilers would be to build 2 identical foils with&without and ride them.back to back as Jeroensurf wrote above.
And even then you could probably optimize the designs for tubercles or no tubercles.
So it is a grey area IMHO, and the OP is kinda simplistic, like marketing blurb.
This not a useful test as, if the foil without tubercles is any good, then the foil design with tubercles was failing to properly utilize the design options tubercles permit. Namely, a much thinner, lower drag, stall prone foil section than would be rideable on a design without tubercles. Or in the case of the Silk, a low drag section that can still handle high angles of attack as in ripping hard carves.
The only way to find out is to design the best foil you can with tubercles and the best without and compare them back to back. And, surprise surprise, some people will prefer one and some will prefer the other.
This is the main benefit of tubercles. They are angle of attack dependent turbulence stimulators. That the vortices they generate can act as fences for ventilation can also be handy in certain situations as with the sailboat rudder, is definitely a huge plus but in most applications not the main thing.
I also have the same understanding regarding the two designers at AFS.
?
We already have dozens of “best foil you can design” , and we still do not know what tubercles really do or not.
Probably Takuma and then AFS know this but they ain’t gonna tell how much of it is eye candy and marketing.
My point was that adding tubercles changes the optimum design point of every other parameter of the foil, you cant just do with and without to understand what tubercles can bring to foil design.
I understand what you mean about optimization, but i still think that the only way to learn what a sinle design factor changes is to modify only that factor.
Just like tuning your gear, change one thing,go ride,see what it did.
Nope, point still hasnt landed. Lets try an example.
Take one of the good old super thick foils from 2018 or so and add camber, just to see what that single factor changes. The already very low stall speed would drop a tiny bit lower, the already low top end would be pulled way down, and the pitch moment would be way more speed sensitive. Even after working hard to address the last point with stab tuning, you would almost certainly conclude that camber sucks and sticking with thick foil sections is the way to fly. We all did for several years.
Conversely, take a thinner, high performance section that has too high a stall speed to be easy to use, add that same camber, and the result seems amazing - hello latest gen HA foils.
Every foil design parameter influences every other one. You cannot just add one to see what it does, the percieved impact varies depending on all the others. It takes many many prototypes, as per Laurent and the Kujira/Silk foils, or a large sweeps of the design space with simulation as per Kane and KT, to start teasing out what camber does to foil performance.
Ok…
So to learn what tubercles do (or camber, or whatever…) you design a totally new foil with all variables altered plus tubercles.
And you reach what conclusion?
What’s flow separation?
