Hydrofoil Pumping Explained (how to pump a foil & what makes it work?)

This tutorial explains foil pumping in detail, including:
0:00 Introduction
0:23 A walkthrough of the technique
3:07 An explanation of how it works
8:50 Tips for practising the technique
9:35 Further tips for wing foilers

[@robertchliakhtine8872]

Absolutely wonderful video… love your series of videos enhancing skills learning by so many. The break down of the phases/steps is amazing. Thanks so much for making these videos available. Keep up your fantastic work 🤙

[@asquared01]

I'm an intermediate winger and coming up to the start of my third season. Thanks to this video, I understand pumping a foil for the first time. I made that classic mistake of only pumping my front leg and then the board would slow down after a couple of pumps. Yesterday I tried this technique and it was a revelation. Suddenly my foil felt alive as I pumped. I could also use the technique to pump slightly as I came out of jibes and even to catch waves. Thank you so much. Your video has unlocked the dark art of foil pumping!

[@devayonlett3321]

Is the motion like a repeated Ollie?

[@danillo7732]

Yes! Exactly like it.

[@wonderbymytroth]

Great video explaining the detailed physics of pumping! I haven't seen anyone do this.

[@kitesurfcollege]

Thankyou

[@DS-zs4ge]

Great video with good explanation. For clarification: Hydrodynamic lift does not depend on the water pressure (water depth), just on the density of the fluid (and speed and wing shape). The depth of the foil traveling through the water does not affect its lift. But in the sea there is more lift than in a lake due to higher density of salt water.

[@dcmackintosh]

Correct, the foil being deeper in the water effects the pressure both top and bottom, so does not increase lift. Depth has very little effect on the density of water (unlike air, which gets much less dense with increasing elevation). Salt water is more dense, so the buoyancy force increases, as well as the lift force at the same velocity. Colder water is also more dense, which would increase lift.

[@leapnlarry]

This is a good explanation to help pump onto the foil . Larry

[@dr.andrewbarnett8298]

Brilliant demo and explanation. I’d like to see a comparable one done showing pumping while still taxiing on the water to show as clearly how to pump up onto foil.

[@kitesurfcollege]

Thankyou Andrew. I do already have a video that explains how to take off using hand-wing pumping & basic foil pumping. It mainly focuses on training drills to help people synchronise their handwing pump movement with their body's extension & contraction movements - since I noticed most people got this out of sync at first. Here's the video: kzbin.info/www/bejne/rHmUiHRqgMx8qac

[@dr.andrewbarnett8298]

Watched it and you are right! I didn’t realize that I had watched it before but the two together are a perfect combo. I’m a big fan of all your videos - thanks and keep them coming please!

[@kshred3043]

9:37 Bingo ! In fact, I think that practicing pumping while already on the foil is a great way for a beginner to learn the fine art of how to pump up onto the foil in light winds. The technique/sensation/muscle memory all seem about the same to me (despite the fact that the foil can't move as much vertically in the latter case). You can also learn how to synchronise wing pump (scoop) with foil pump. There is of course a bit of a Catch-22: By this method, you already need to be on foil to learn how to pump onto foil. But the suggestion is, for those who are just beginning, on the first rides when you have succeeded in getting on foil using just wind power, make sure to take advantage of the opportunity to practice your wing/foil pumping. This will pay great dividends on the lighter wind days. No more flailing and failing. At least, that was my experience. This is by far the best treatment of this topic that I have seen. Thank you !!

[@kitesurfcollege]

Hi K Shred, thanks for sharing your insights on this.

[@skreebop]

"...or hit a sand bank." That gave me a chuckle. Great topic and wonderful video, as usual. I recently added front V footstraps and I have to say it makes everything easier (for me). Kind of like bike clip-ins, having the "cheat" of front lift force is allowing me to (start) to get the hang of pumping. I'm definitely not an expert, but I'm more willing to try the technique. I feel like I'm always using my hand wing to stay powered up so better pumping seems to be a necessity for other techniques that involve depowering the wing (like wave riding, as you stated).

[@kitesurfcollege]

Thanks for sharing skreebop. Yes I do find having at least the front foot in the strap helps you confidently control the board during pumping. You can put in a bit more energy without your feet moving. In this example I'm using a 1000cm2 aero free front wing (basically a surfing and freestyle front wing), so this does require a more energetic pump than my other foils and then the footstraps really help. In fact I picked that wing as the movement was much more obvious. With some of my more "glidey" front wings (like the 1305 glide) my body movement is less than half that shown in the video so then there's not much chance of my feet coming off the board and there's less need for footstraps.

[@jamesbuccarelli6055]

Excellant Demo and explanation. Thanks mucho

[@kitesurfcollege]

Cheers James

[@seandenga1479]

I love the video ❤

[@petrihirvonen]

It's often said that one should pump with the foil relatively close to the surface because that's apparently more efficient. I wonder if it's due to an "inverse ground effect" where the surface limits the size of the front wing's wingtip vortices, or if there's another more important mechanism at play there. Anyways, a great, clear explainer once again.

[@kitesurfcollege]

Hello Petri. I've heard that reverse ground effect explanation but the reasoning behind it doesn't seem to make sense, in fact it's pretty much backwards. It's not the vortices that affect drag, they are merely a sign of it, so limiting them once produced does nothing. The most sensible explanation would be that if you're riding a large, efficient, extreme-high-aspect, pumping foil (like the type designed for dockstarting) then you are easily getting more lift than you need from it. They are designed for high lift, and sacrifice structural strength, stability and roll rate to achieve that. With such extreme HA foils, you don't need an energetic pump (not much up and down movement of the foil) and you have plenty of lift so then it makes sense to keep the front wing close to the surface and the reason for that is reduced drag. The deeper the foil the more drag (from extra water pressure and from more mast in the water). So I'd say that tip (keeping the foil at the surface and using a small up and down movement) is more a reflection on the type of high aspect ratio foil used specifically for pumping and someone's erroneously linked it with ground effect as the feeling is similar. In this tutorial I'm using a 1000cm2 AERO free (which is surf & freestyle foil basically) as it requires a more energetic pump and a larger up and down movement, making the movement far more visible in the video. Ideally the top of the pump cycle should bring the foil close to the surface, I would add (but mainly so you have plenty of room to drop and accelerate). That's what makes sense to me from a physics perspective. Would love to test it in a lab one day.

[@frasershaw3071]

Drag increases in the last few cm close to the surface. You should ride waves close to the surface but pump a bit deeper to avoid the turbulent zone.

[@aschwa5]

​@@kitesurfcollege this makes sense, but I think the biggest issue is increased mast drag as the foil lowers. since drag is reducing speed and therefore fighting lift, keeping the foil close to surface makes it easier to keep speed and lift. lots of complex trade offs clearly, and yes I think you're right about your low aspect foil; looks like you're working very hard on this kit. 🙏🙏

[@giuvude80]

best video ever

[@dcmackintosh]

You're mistaken about the extra water pressure, because the top and bottom surfaces of the foil move up and down together. In an incompressible fluid, like water, one foot is the same as one hundred. This is not the same as an airplane traveling through air.

[@andybarber7563]

Do you think adding front straps will help.?

[@skobichevskii]

many many issues with basic physics here: 1) im pretty sure that lift is proportional to speed in water (it is its square in air). 2) water pressure has nothing to do with lift/drag in water (that is not compressible). 3) compressing your legs on the uptake does not help you much, because you need to lift your body's center of gravity too in order to return to the initial position. but qualitatively, your point about accelerating the foil at the bottom, may be the right explanation.

[@dcmackintosh]

They should've quit while they were ahead.

[@luksterp6049]

Back foot placement/location can also be important with certain foils..just as the rider in this video has his right above the leading edge of the mast 🦵👌

[@marekkaniewski8789]

great vid thank you...where is this location please?

[@kitesurfcollege]

Thankyou very much Marek. This was filmed at the Breede river mouth in South Africa.

[@flyerelite5153]

Just put a flipper at the tail in substitute of the rear wing and be done with it. You'll gain 40% more efficiency. Trust me.

[@jacobstr]

None of this shit makes sense to me until you explain it. Then I can usually do it.

[@wingcoachdavid]

This technique looks a lot more energy consuming than what Oskar teaches (see youtube.com/@OskarJohansson1 ). His ability to pump and surf long sessions is close to the best we have seen on YT. He says to minimize the hobby horsing (my term, I'm paraphrasing) and stand with a fairly narrow stance with 60% of the work being done by the front leg. I have been working to adopt his techniques for Wing foiling for some time now, with good results. Standing further back to load up the front leg has been key to a significant increase in speed when not pumping. Then it's easy to transition to pumping during the next lull. He also emphasizes using your legs to push the board forward with each pump. The increased speed naturally increases lift. Keeping the foil board flat pitch-wise via a fairly rapid "front-then-back" leg motion, with minimal time delta between pressing down with each leg, drives the foil board forward. He also emphasizes flying high on the mast to minimize drag. Your technique takes a larger up and down flight path, increasing drag at the bottom and spending undue energy on moving your weight up and down. All this to say, while you do a good job of explaining how your technique works, I wonder if you could explain why we would want to use it in the first place? I've been practicing to hone my high efficiency techniques for some time now, and will soon make a video on the same. I think a lot of your videos are very helpful, as we both appreciate the value of including the "why it works" technical aspects in our videos! Thanks for that!

[@kitesurfcollege]

Hi David. The technique explained here is absolutely the way it should be done. What you're referring to are variations of this technique specifically for large wing span, very-high-aspect ratio front wings (the type made for pump foiling, or dock starting on a lake for example). In the video I am using a general purpose mid-aspect-ratio foil (about 6.5 AR, something that would be typically used for wing foiling). These foils require a lot more energy input to pump, so you have to use the complete movement shown in the video. A very high AR foil requires less energy so less movement is required. More importantly, very high aspect ratio foils work best with a low angle of attack and stalls sooner when your pitch changes - which is really why you want less up and down movement while pumping. They are also huge and have an enormous amount of lift so it helps to be near the surface for a slight drop in drag. The narrow stance is for the same reason (less pitch change required and less leg burn while doing so). I could have used a pump foil for the video (I have a few) but decided against it. Firstly, the foil used in the video will be more similar to what most people are using, plus the larger movement required for it is visually easier to see and learn from, plus once you learn the full movement it is very simple to reduce that movement if you move onto pump foils. All our filming angles and equipment are carefully planned.

[@wingcoachdavid]

@@kitesurfcollege Thanks for the quick reply. I use high aspect foils so it makes sense his tips are working well for me.

[@joehopfield]

Some smarties at Cambridge published a paper about the physics of "gunwale bobbing", similar movements on a SUP or canoe on flat water surf one's own wake. Much slower, but fascinating parallel physics. Video by the paper's authors: kzbin.info/www/bejne/iHOXq5V7fdyifLs

[@robgrant7225]

Probably more like a Swing

[@trexinvert]

very similar to side to side wheelie pump for skateboards. Dont forget applying a "net" forward lean. main physics dynamic is potential energy of the gravity drop. fk the rest of the hydrodynamics mumbo jumbo. Peace.

[@markleng67]

BORING!