Flapping Dolphin Tail for Hydrofoils & AXIS rear wing / stabilizer review 

I'm always blown away by the incredible detail in your analysis and the excellent way you edit the video to show your results. Thanks so much for all the work that goes in to your research.

Love your videos and especially the dolphin tail experiment. So you know, aluminum only returns about 40% of spring energy, steel returns about 60%, titanium and carbon fiber both return 80% to 85% so would be preferred for the spring tail. This is one less understood reason for example that carbon fiber SUP paddles are so much better than aluminum ones, its partly the weight, though also alot is the better spring energy return from the carbon fiber. For your flexible member on the dolphin tail for sure titanium or carbon fiber would work better than steel or aluminum. PS - The aluminum fuselage doesn't hurt that much as its very stiff from its thicker cross section so this only really effects the things that flex alot.

I’m happy that my new $700 Zetti Coast 1800 has a compatible rear bolt pattern to Axis!

I thought up the dolphin tail this morning, searched to make sure nobody already thought of it and found this. You're 2 years ahead of me lol. Great job experimenting with it, was cool to see. I wonder if a far less aggressive form would be beneficial like relief cuts into the back of the fuse maybe even filled with silicone or something to keep the water flow, yet allow for a touch of give only near the tail. I was thinking not just the pump, but in a big carve - if the fuse could arc a touch, the tail would better follow the front wing and create less drag, then spring out of the turn. I never thought about the lack of stability you mentioned thought. Makes sense.

Great video. I think the next big leap in efoil innovation will come with a new propulsion system that mimics dolphin tail propulsion. The robotics crowd has already done this work with things like soft body pneumatic designs using pulsed compressed air, but no one has yet applied that knowledge to efoil designs. You are moving in that direction though. 😊

love this guy, I had to subscribe I'm one light year away from foils , that's why we need these guys ... testing without BS

Very interesting results,great job. I think not even manufacturers are putting as much effort in testing and comparing the gear they make as you are!.

I'm glad I stumbled across your videos. I recognized a chart from NASA's Bioastronautics Data Book immediately in one of your other videos. I've had similar thoughts on flapping foils, but more along the lines of a flexible trailing edge on the wings, not a flexible fuselage - maybe that would give you the flap AND the stability you seek. You should also trademark and sell T-shirts that say, "I'm pumping it like an animal!" That works on so many levels! I would've said pumping it like a fish, and if you look at a big fish like a tuna, the amplitude of their flap is small, but the frequency is fast - sort of like the stutter hop pumping motion you discovered. Maybe with a flexible wing, you can reduce the amplitude and increase the frequency get closer to how an animal really pumps! Keep up the great work.

Great video love the innovation

Cool project 👍 I can’t wait to see the next one !

This clip is soooooo cool!!!!! Thank you... I am a wing foiler and this clip helped me so much in choosing my additional rear wing. Thank you... Thank you... 😍😘

Thanks for your great learning video !

Great clip, love the innovation!

Just discovered your channel, subbed immediately. Just got into foiling a year ago with the wakefoil 2.0 from liquid force. Planning on stepping up to something from the Axis foil line this spring.

Great video!

Great video. I'm using the 400 and the 460. I really feel a difference in speed in the 460, and I can't wait to try the 420.

I would try some 1 or 2 mm carbon fiber flat sheets off eBay. You can stack different amounts to vary the stiffness in order to see what works best. They are not too expensive either. Keep up the good work and stay warm!

Maybe if you can make it so it can flex more down than up you can get more strust out of it because by pushing it down it creates trust but by pulling it up it does not give more resistance.

I've got a 390 and 370 (IIRC!) at the moment, and kitefoil 90% of the time with a 660 and short fuse. Also have an 820 as a backup, as that and a 720 were my previous wings on a regular fuse with 400 stab. I found with the 660 and the 370 I got some rough feeling while riding, which I suspected was turbulence from the gull of the wing impacting the stab's winglets... I got a 390, and lo and behold the "rumble" is gone. That's as much testing as I've done... shut up and ride! :D On the handling of the 390 stab -- I agree. It's more stable loaded up and in a carve. When you're a straight tack, it's a little roll-unstable, but it tips into a carve beautifully. My theory for stable-while-carving is that the anhedral is "cupping" the water, and the downturned tips are cutting in, rather than plowing like the bottom of a spoon as the up-turned tips on stabs do. I'm probably talking crap though :D

This is a great idea and when you mentioned that the rear wing is also for stabilization, one problem came to mind. A dolphin can use muscular effort to hold his fluke steady or to flex it and pump. On the foil, it is kind of always in a flex mode. I can't imagine how you could turn the flex on and off when you needed it. As an ice skater, you know what it is to be kind of 'one with your skate'. Your boot needs to be snug enough to completely connect you to your blade to make the blade go where you want on the ice. Boots that are too loose break the connection. Here it seems the connection is sort of broken or ends at some point- probably at your ankles. I'm just guessing and as the son of a lawyer, my legal disclaimer is that everything I say might be wrong!

Please keep us up to date of the "flexible stab" wing...I think you are deff into something revolutionary on the sport...specially and it pump category...great job....Just a question...it looks like you use aluminum for the "flex"...don you think carbon fiber will be better or it will be stiffer?

After watching your prototype, I briefly watched a video on how dolphins swim underwater. What I noticed is that not only does their rear fin kick, but the rear half of their body also moves significantly while they're swimming. I drew out something on a sticky note, but I don't event know how to describe it to you with writing you a 3 paragraph comment lol. The main idea would be to have a pivot point behind the front wing where it connects to the fuselage and another pivot point where the fuselage connects to the rear wing. There would also need to be a way for the fuselage to stay connected to the mast while it is pivoting during the "dolphin kick". Hope that makes sense :/ I guess I need to find a fabrication facility and build my own prototype lol

You should make "I'm pumping it like an animal" t-shirts

Interesting trial. What was the material you used for the flexible section? Looks like Al but I may be wrong... I think a material with more energy return like carbon fiber may perform better? I freedive and use the long carbon blade fins as they have more 'spring', energy return and are the most efficient compared to glass and polymer. Seems like a similar application here where you are trying to minimize the losses during pumping. Any significant findings if you changed the stiffness by stacking less or more flex plates?

it would be good to ditch the full height nuts on the dolphin attachment for subsequent tests, the drag from those 2 nuts is possibly equal to the entire front foil , depending on the speeds of course. With water at 800x more dense than air small things make a much bigger difference in water . Perhaps you could also try your fav stock foil setup but fill all the exterior voids with silicone and fair them in inc the screw head voids, a bit like caulking a bathroom and see what difference you got from that. maybe a couple percent, the silicone should peel off once done so long as you fill it After it was assembled.

Great to see your progress here. Your assembly make all rear-wing Aoa to change on flex so maybe that is why stabilization is less as AoA difference to front wing AoA will go from positive to negative. I think Hobie Miracle drive would be more fixed AoA aka stabilization then trailing edge allows the flapping. So I hope you did not ditch the Miracle drive flipper idea yet, and I really hope you could IRL touch&build that idea and have proper testing. I am still so far behind to be at your level at foil pumping..

Cool ! What if make the soft edge(end) tail wing, but not the connect bar?

I love the dolphin tail experiment. Try a hinged rear wing. If the rear wing can pitch up, the board will pitch down with less resistance because you aren’t forcing the rear wing to change its angle of attack relative to the water flowing across its surface. This should let the board build speed quicker on the press. then when the board is leveled out the rear wing will stop at the level position parallel to the front wing to increase glide. I imagine it would feel super weird at first because even slightly increased front foot pressure would drop the board like there’s no stabilizer, but if it works it would be long easy pumping cadence.

I figured that the flex would take away some energy from the pump, but if it changes the pumping motion to be more efficient then it would be negligible

Well, I think it's time TO GET PAID for making them videos!!

As a skateboarder who is used to pumping and slaloming to generate speed I wonder if a pair of "skyhooks" would allow you to pull up after pushing down, basically speeding up your pump and letting your legs oppose each other to generate more force

Anhedral wings might reduce the tip vortices that form on the wingtips during the downstroke, which would reduce drag. As for the dolphin tail, I wonder if adding a third smaller wing might be the way to go. I think a very high aspect ratio (maybe 12x1) carbon fiber strip held in about 3" behind the rear wing by a couple of pieces of flexible carbon fiber rod might do the trick. This would not compromise the fore aft stability while being in the best position to have the greatest vertical movement for generating thrust. It might be too draggy, but I think it is pretty low investment in time and materials.

I have slingshot everything.. in your experience are the axis parts interchangeable with the slingshot parts?

Perhaps mimic an actually fish tail, more of a triangular shape. Manatees have an interesting shape. Also thinking if it was tapered to make the edges more flexible.

So does the deck really matter? Wouldn't a skim board or a wake skate work ok? Would some kind of binding system be beneficial? Like tow in surfers use for really big swells. Thanks for the information and content man ur doing great!! Also i would maybe start looking into concave/convex designs and transition pitch thereof. I think of an airplane wing, naturally generating lift while air moves over it. Is there a particular layout that a convex design with a asymmetrical transition radius from front to back would improve efficiency and lower rider input/effort effectively deciphering an individuals wing choice based on stature, strength, skill level etc. Some people weigh more and have super strong and long legs, some do not. This has my attention and curiosity BIG time, i build drift/time attack cars for a living so this is just, right up my alley. With a few suspension adjustments and less downforce, a rear wheel drive grip car (with sufficient steering and Ackerman angle, limited bump steer, and ability to adjust for at least 12° of castor) can actually become a really fun and competitive pro-am drift car.

Put a fix stabiliser in normal position and the dolphin one behind on the "flapper"???

You can’t completely replace the tail stabilization with a flexible tail. you need to add a flexible tail in addition to the tail stabilization in order to add tail thrust to stabilization

It seems like a flexible rear wing would have some spring to it. As if it would build up some tensions, then release all the pent up energy.

Sounds like Jimmy Chang

How speed do you need when you trolling by boat?

Holy Flipper Batman! Check out that foil wake while you're pumping at 8:10! That's so cool. Yeah like Arno said, maybe a variable spring rate to increase stiffness on the down stroke while making it more flexible on the upstroke would increase forward thrust. Rad idea! :P

First of all I'd apply for changing your name to Wave Chief !!? I was just thinking about the effects of a flexible rear foil while you just did it. The better flexibility of carbon would be very usefull, as a better streamlining of the flexible device too. How about to increase the length of both foils to achieve an slower pumping frequence in order to reduce power that's needed to 'fly ' !? When you continue the possibilities one could even imagine that this principle could lead to success in human powered flight.

👀👍

Have you had a chance to try the 420?

Everyone in the comment section is so smart

Question. Can you foil (not pump!) without a rear wing?

New lingo invented. Wake thief 😆

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