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Old    surfdad            05-06-2009, 1:14 PM Reply   
It's lunch time! I've been following a thread on Sways as a few folks test foils on boogey boards and surfboards. I've got a wild hair now to try it on a wakesurfer. :-)

So a few pictures. Most of us are familiar with the airchair - those are so cool to watch, but the foil and the strut weigh 87.3 bazillion pounds and you have to be strapped into the chair to prevent that huge mass from whacking you on the head - or other important body parts. :-)

Old    surfdad            05-06-2009, 1:20 PM Reply   
So...I think I can fabricate a foil and struts out of carbon and coremat without the risk of creating a guillotine. I can salvage an old board to attach the foil to, as it will mostly be out of the water, it just needs to float and that's all.

Attaching the foil needs to spread the load a bit so that it doesn't just rip off the board. The only thing that bugs is that you can't really start it like a wakeboard, it would have to be submerged and then brought up.
Old    surfdad            05-06-2009, 1:29 PM Reply   
So the foil, itself, would look something like this, rather than the front and back foils as on an airchair.

Old    surfdad            05-06-2009, 1:33 PM Reply   
The theory, as I understand it and THAT is limiting factor in and of itself. :-) the curved leading edge will allow the foil to turn - up and down the wave face - the swallow tail, such that it is, will allow the board to pitch a bit.

If I can get it to work, I think it would be cool to ride a foot or so about the water. :-)
Old     (leaks)      Join Date: Oct 2005       05-06-2009, 2:18 PM Reply   
I wish I had even a fraction of your spare time Jeff. Lol. You are the KING !!!
Old    surfdad            05-06-2009, 2:56 PM Reply   
Indeed! It's just effective time management - virtually everyone struggles with it. This web page is one of the best "free" resources. The single most important concept I think the author espouses is the 80/20 rule. That on your to-do list of 10 items, if you accomplish the 2 most important, you'll be 80% effective.

I did a little looking at the FOILSIM by NASA and as noted in the sway's thread:

using a foil 6 inches by 18 inches and at 7 degrees angle of attack

at 5 mph gives 38 lbs of lift
at 10 mph gives 154 lbs of lift
at 15 mph gives 360 lbs of lift

So at 11 mph it's producing close to 200 pounds of lift. That's why those airchairs can have such heavy foils, it's generating hundreds of pounds of lift at speed.
Old     (bltcollins)      Join Date: Feb 2007       05-06-2009, 3:07 PM Reply   
Laird Hamilton rides a tow in surf board in "step into liquid" something like that, with a hydrofoil. Very cool. Probably a different concept on a 70 foot wave compared to a 2 or 3 foot wave but still a very cool idea. Here's a clip I found on you tube. 8FF58&index=6
Old    surfdad            05-06-2009, 3:13 PM Reply   
Yeah - I've seen that video clip. Like you point out Bryce, a 70 foot wave creates a huge increase in speed. Speed increases seem to generate some crazy exponential increase in lift.

It'll be a fun experiment at least. :-)
Old     (bltcollins)      Join Date: Feb 2007       05-06-2009, 3:42 PM Reply   
Agreed, looking forward to seeing what you come up with.
Old     (deben)      Join Date: Aug 2008       05-06-2009, 5:04 PM Reply   
This is my first post, but I've been reading this forum and swaylocks for a while now and actually was reading the thread you did and had the same idea. Now, I'm not familiar with hydrofoils, but I'm curious about how easy it will be to turn.

From reading the thread over on sways, it sounds like turning is going to be a little tougher, especially with a relatively small wave (wider turning radius and less room to turn).

I'm thinking that by having hard edges on the hydrofoil will improve turning. The photo looks like the edge might be more 50/50 (i could be wrong). Although I wouldn't be surprised if it didn't make a difference seeing that the foil isn't that thick. Other than that I think the design seems like it will work well.

Keep us posted and if I am able to work on one I'll let you guys know. I'm in the middle of working on my second surfboard and after that I'm trying my hand at my first wakesurfer, so it wouldn't be for a little while.
Old    surfdad            05-06-2009, 5:22 PM Reply   
Hey Jonathan,

I'm glad you decided to join the discussion. I know NOTHING of hydrofoils, but from what I can tell the longer two blade foils - like on the air chair and sky ski offer more stability, more surface area, but like a longer board will increase the turning radius. So like on Sways, I think a single blade will be needed.

Now, from what I can tell, a surface area of around 150 sq in, should provide enough lift at 11 mph - I believe around 200 pounds. An 18 x 12 blade with a curved leading edge would render the 150 sq in and THAT is smaller than the foot print a wakesurfer uses...maybe we can duplicate the feel...2 feet in the air. :-)

I found a hydrofoil kiteboard that uses a carbon blade - so it's not necessary to use the heavy aluminum like on the air chair and sky ski.


Shape it out of EPS, laminate it heavy with Carbon and I think I agree with you that it can be done.

Please, if you pursue it, post up any research or progress you make. Thanks again for joining in.
Old    surfdad            05-06-2009, 5:24 PM Reply   
Another angle of that blade

Old     (nwrider)      Join Date: Oct 2002       05-07-2009, 10:49 AM Reply   
we've tried to get the stand up into the pocket on a sup foil, pretty hard, but behind the boat at 16mph sic fun, the carbon fiber would be the way to go other than cost!

Old    surfdad            05-07-2009, 11:14 AM Reply   
Cool picture...I think the key is going to be getting the right size and shape of the foil based upon the speed we are using. My guess is that the foils used in airchairs and foilboards don't really develop the lift needed until 15+ mph. A larger foil, "I think", should resolve that issue.

The CF isn't too expensive if you're doing the work yourself...manufacturer's command a huge price tag for products built with CF.
Old     (notsobueno)      Join Date: Dec 2004       05-07-2009, 5:33 PM Reply   
Dad, if you ever need another income source, here is my suggestion:

Surfdad Camp. People pay to come spend a week with you. Check in, wakesurf, shape, wakesurf more, post on the internet, shape & build, wakesurf more, post on the internet again, and at the end of camp, the camper gets to ride the board he or she made. One Week per camp. Along with a couple days on the water with Dennis, I'm sure This could be very successful.

I will be your first camper by the way.
Old     (bigshow)      Join Date: Feb 2005       05-07-2009, 9:41 PM Reply   
Jeff, you have a job right? Where do you find the time!

Jeff's new quest, develop the most expensive wakesurf board!
Old     (cwkoch)      Join Date: Aug 2006       05-15-2009, 3:32 PM Reply   
Carafino is the main builder of those stand up hydrofoil surf boards. Their foil is Carbon. Sky Ski also builds some stand-ups meant for towing. They are aluminum. The carbon will hold up for surfing, but they build the sit-downs and stand-ups for towing out of aluminum because of the huge stresses we put on them. Guys have tried building them out of carbon in the past and have shattered them I believe.

When you're riding a hydrofoil, you control the angle of attack on the wings just by leaning the board forward or back. I can fly my Sky Ski at under 10mph.... I've never tried surfing with it though!
Old    surfdad            05-15-2009, 4:08 PM Reply   
Nice invert in your profile. So if you can fly at 10 mph, that gives us a useable surface area to work with.

I don't think that Aluminum is necessary for the stresses. A laminate stack with CF then Kevlar would take care of any impact issues and with sufficient layers, CF is substantially stronger than aluminum. The Boeing 787 uses CF for the wing skins and spars - far more load than would ever befall a hydrofoil behind the boat:

No doubt the experiments didn't have sufficient layers or there may have been defects in the layup - even a pinhole will weaken CF substantially. I'd think it will require about 2 to 3 mm thick build up of CF and probably each layer laid up individually. THAT's incredibly time consuming. At retail, I think an $1,800 foil in Aluminum, probably becomes a $4,000 foil in CF :-)

Thanks so much for the input on your ability to fly the foil at low speeds, that's the validation we were looking for.
Old     (cwkoch)      Join Date: Aug 2006       05-15-2009, 4:24 PM Reply   
Something else to think about.... it looks like you're trying to use just 1 wing? The rear wing is what gives the foil the vertical (up and down) stability. Without that rear wing to stabilize things, it would be extremely touchy up and down, and you probably wouldn't be able to control the flight. On the higher end sit down foils, the rear wings is on a slider and you can slide it about an inch front to back to adjust just how responsive it is. The rear wing is approximately 10" from the front wing. This one inch of adjustibilty in that wings makes a big difference in responsiveness. I would think about adding a rear wing, otherwise that board will be going from stuck on the water when you're leaning forward, to shooting out of the water as soon as you lean back just enough. Without the rear wing it will be very unpredictable, and probably uncontrollable.

As far as lift goes, you probably don't need to worry about programming much into the wings for the slow speeds. Just leaning the board forward and backward is what will control the flight. On the sit-downs, we deal with shims in 1/4 degree increments for fine tuning lift, but we're riding at 22-26 MPH. That's just how touchy the foils are!!

This surf board project seems pretty cool.... Let me know if you want me to take any measurements on my ski....
Old     (cwkoch)      Join Date: Aug 2006       05-15-2009, 4:27 PM Reply   
You might also want to check out the hydrofoil forums at for more info and ideas. There are some very bright guys over there building aftermarket wings and struts running run CFD analysis on everything!
Old    surfdad            05-15-2009, 4:38 PM Reply   
I was afraid of the rear wing being necessary, although I like the idea of putting James out on the board that is uncontrollable. :-) "try it again" would be the watch word. :-)

Thanks so much for the link, I'll bookmark that.

If it's not too much trouble, I'd like to take you up on your most generous offer. I'll need to build that pedestal first, so that would be my starting point. It looks like it has a foil shape to it for the water flow? Also, it looks as if the rear wing is on the same plane as the front wing or possible above the front wing?

If I could get some dimensions of the distance between the wings, the general dimensions of the wings and then the height of the pedestal. Without putting you out too much - just general dimensions would be fine.

Old     (dennish)      Join Date: May 2005       05-15-2009, 5:30 PM Reply   
I thought I was the only one who liked to have James do things behind the boat that are uncontrollable.
Old     (cwkoch)      Join Date: Aug 2006       05-18-2009, 10:42 AM Reply   
Jeff- I'll try to get some detailed pictures and measurements for you. I could probably even trace my wings and t-bar and send you the traces so you know the exact shape of them. I'll probably be taking my ski apart to polish sometime real soon here and could do it then.
Old     (surffoils)      Join Date: Jun 2009       06-14-2009, 5:38 PM Reply   
Hi all, Im the guy that JeffWalker (surfdad) mentioned from Sways whos making foils for standard surf/body boards. I got the idea from the Airchair and the whole 'tow behind a boat' principles.
Im amazed by the physics and control that hydrofoils exhibit and its a similar style of riding that Id like to transfer to wave riding however the hydrodynamics are different with an ocean wave but certainly similar to riding the vertical part of a wake I believe.
Any tips or tricks you can share would be most grateful and I'll see if I can post some pics of my progress for you guys to scratch your heads over.
Thanks, Brett.





(Message edited by surffoils on June 14, 2009)
Old     (saceone)      Join Date: Jan 2009       06-15-2009, 11:51 AM Reply   
I can't imagine falling on that thing!!! life threatening for sure!
Old     (surffoils)      Join Date: Jun 2009       06-15-2009, 5:04 PM Reply   
Pete, I always thought Id wipeout and get a massive slicing from a fin during my surfing years,but I never did.
I think most water sports are inherently dangerous but its just a risk each person takes but I dont think that carbon foils or struts are any more dangerous that a standard surfboard with 3 fins.
We have been testing these boards behind boats before we tried them in the surf and no injuries yet.(touch wood)
Heres a few earlier prototypes...
Old     (surffoils)      Join Date: Jun 2009       06-15-2009, 7:57 PM Reply   
The struts on the earlier foils above were only 4 inches high as I was testing stability and control, now they are 12 inches so the board rides about 8 inches above the surface.
The foil shape has also change from the accepted rectangle across the board (as seen in the above pics) to a rounded shape that is more consistent in its lift.
The profile of the foil (eg NACA) made little difference at all so I advocate a flat plate with rounded edges. Surfdad, let us know if you go thru with making a foilboard.

Old    surfdad            06-15-2009, 9:17 PM Reply   
Hey Brett,

Glad to see you on Yeah, I'm going to build one, but I had planned to shape it in low denisty eps and then laminate it with carbon. Brett, I'm not sure I am following your last post. The NACA foil had no effect? So you're just running a flat foil, just a rounded leading edge?
Old     (surffoils)      Join Date: Jun 2009       06-16-2009, 5:13 PM Reply   
Hi Jeff, I found Wakeworld recently after I spoke with another boat owner and I was amazed to see your post about foils.
I make surfboards and other watercraft so I too had thought about making the foils in EPS, epoxy resin and carbon but for the sake of expense, I used ply.
I never thought it would work so I used standard ply, quickly rounded the edges and just painted the first one. Since then Ive made about 20 or 22 foils, lost a few in the surf and all of them were just flat boards.
Im aware of how foiling a shape (like a planes wing) increases its lift,speed and control and so I made a highly foiled foil and I couldnt tell the difference.
The reason why, I believe , is that in this instance, the foil is not getting its majority of lift from the high/low pressure difference due to its shape as Bernoulli suggested.

However upon riding the foils it appears very obvious to me that it is getting its majority of lift from the Newtonian concept of interrupting the upward flow of water of the wake or wave face and redirecting it. All I do is round all the top edges with a bit more attention to the trailing edge.

Something with an area of about 200 sq in (a large dinner plate) is enough to lift me at about 10 kph but 250 sq in is a good beginners size.
The above shape is a partially foiled 'foil' and despite its futuristic look it performed poorly compared to this simple oval with slight foiling.Both have the same area.


I think the EPS/carbon would make it a lot lighter but I will work on getting the shape refined before I spend up big on the construction.
Im happy to pass on the results I get as I try more shapes.

Regards, Brett.
Old     (surffoils)      Join Date: Jun 2009       08-12-2009, 1:49 AM Reply   
This is the latest foil on a bodyboard, ply and carbon fibre. Its just safer to test foils lying down.
Im still trying to design the best 'board' shape to attach the foil to for stand up.Upload
Old     (bac)      Join Date: Feb 2008       08-12-2009, 5:24 PM Reply   
Oh man, I can't wait to see the next project out of SurfDad's Lab!

I've been fascinated with surfing on a foil board after I saw a video with Laird doing it back in '99 or '00. Looks like a blast, but I would have never imagined in a suf wave behind the boat. Always pushing the envelope
Old    mobster            08-12-2009, 6:21 PM Reply   
When we built concept Board #1 we got foil type effect that could be worked into a foil type of ride but wave length would be the limiting factor on the ride IMHOUpload board #1Upload Board #2UploadBoard #3
UploadBoard #3 Air
Old    surfdad            08-12-2009, 7:08 PM Reply   
Hey Brett,

Thanks so much for the pictures! It looks like your foil is relatively thin and if that simple oval shape works, that would be perfect for behind the boat. One question that would be helpful for me is the location of the foil fore and aft. Have you found a "best" location in terms of distance from the tail, or a ratio based upon length or....some other way to locate it?

Thanks so much.

A Txsurf....I have a donor board ready, now I just need to get a reasonably shaped foil.
Old     (hawaj)      Join Date: Aug 2005       08-13-2009, 2:46 PM Reply   
wow Board #3 is interesting. Thx for nice big pictures!
Old     (ericlassiter)      Join Date: May 2007       08-13-2009, 6:48 PM Reply   
j.l. are you towed in or what? did you paddle in those waves?
Old     (jdjjamesz)      Join Date: Mar 2008       08-13-2009, 10:51 PM Reply   
Im pretty sure josh paddled into those waves.
Old     (rallyart)      Join Date: Nov 2006       08-14-2009, 8:58 PM Reply   
As Charlie was saying you increase senstivity by shortening the distance between the front and rear foils. That also increases the turning speed. Just like shortening the wheelbase of a car. It would also apply to a single foil design. I agree that a second foil, or a slot, working in opposition to the main foil would improve the control.
The biggest problem I could foresee is the difficulty in controlling lift in a small wave. The foil angles, in relation to water direction, would be radically different at the bottom of the wave than they would be four feet away at the top of the wave. Perhaps using a significant curve in the blade would compensate for some of that.
Old     (surffoils)      Join Date: Jun 2009       08-25-2009, 3:22 PM Reply   
Sorry to Jeff Walker for not answering,(dang computer lost the reminder)
The fore/aft position works out to be where your COG is, no need to complicate it with math but because the board is lifted from the water the board shape become irrelevent.
If you put the foil forward you'll have to shuffle forward to balance over it so I just put it under where I guessed my COG is and it works well. About 40% of the boards length from the tail approx.
I am finding that even a 250 sq in foil gives a massive amount of lift in the tube so Im working on putting vents/ slots in the foil.
Would you be interested in pics and theory ?
Old    surfdad            10-26-2009, 8:58 AM Reply   
Brett I'm sorry I missed your question! Yes, please if you get a minute, I'd enjoy the pics and theory. Also, can you give me the general dimensions of the oval shaped foil, please.

I'm a little concerned about the struts. I don't have access to metal fabrication facilities and I believe I've read where the struts are subject to failure most frequently. I'm going to need to make mine out of foam and then laminate them. Any words of wisdom in this area?
Old     (surffoils)      Join Date: Jun 2009       10-26-2009, 4:49 PM Reply   
Hi Jeff, I just got your email, Ive been working on the foils and then a guy asked me about bodyboard design and now Im about to put a line of my own designed bodyboards out on the market !
Heres the link to blog and a few pics of the prototypes.

These are styrofoam and epoxy proto boards but the finished ones will have a styrofoam core and an ABS 1.8mm shell vac formed over it. ABS is the plastic used for car bumper bars.

Please have a look because the plan is to add a foil onto these boards as another way to ride them on wake and wave.

But back to the foils, the best one I used was an oval 23in X 9.5in, area of 180 sq in, but if I do a new one I would make it 27 X 10 and change the outline. But obvoiusly a smaller area for faster wake speeds.

In the above pic, the front entry shape controls how the foil attacks a turn or vertical lifts with a straight edge being very sensitive and a rounded front being smoother.
A rounded front feels good to me when riding but a symmetrically shaped tail makes the release or exit of the turn a bit loose or soft so I would square it up a bit to make it feel a bit snappier.
Its all personal, but thats my take on the shape and my foils are just flat 5 mm ply with a layer of 6 ox fibreglass and epoxy resin,and unfoiled.
Struts I use 4 mm aluminium that havent bent at all and you could get them made up at a metal fabricator.
You can see more of them at...

(Message edited by surffoils on October 26, 2009)

(Message edited by surffoils on October 26, 2009)

(Message edited by surffoils on October 26, 2009)

(Message edited by surffoils on October 26, 2009)
Old    surfdad            10-26-2009, 5:00 PM Reply   
Thanks for the details Brett. I appreciate the picture and measurements. I'll have to see if I can find someone close that can cut and weld the aluminum.

Congratulations on bringing your bodyboards to market! That's great news! May I ask what you're gluing the abs to the styro with?
Old     (surffoils)      Join Date: Jun 2009       10-26-2009, 5:24 PM Reply   
Jeff, its just an off the shelf epoxy glue from FGI (fibreglass int.) but the trial boards have survived without fail.
Old     (DIYeFoil)      Join Date: Aug 2017       09-01-2017, 10:56 AM Reply   
I just posted some info on another setup allowing the eFoil drive to quick connect onto any surfboard or SUP, and why I prefer under-mount VS jet impeller for an electric surfboard
Old     (brewkettle)      Join Date: Jan 2009       09-03-2017, 2:36 PM Reply   
some customs a customer wanted for wake, and river use all in one
Attached Images
Old     (getssum)      Join Date: Jul 2005       09-15-2017, 2:32 PM Reply   
That's some awesome looking work right there. Really want to try this foil board stuff!
Old     (DIYeFoil)      Join Date: Aug 2017       09-17-2017, 4:56 AM Reply   
There is new electric hydrofoil being developed on Kickstarter that will bolt onto almost any hydrofoil using different mount types and the project ends in 24 hours.


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