DIY Human Powered Wooden Hydrofoil - the "Hydrothopter"





Introduction: DIY Human Powered Wooden Hydrofoil - the "Hydrothopter"

About: Tim Anderson is the author of the "Heirloom Technology" column in Make Magazine. He is co-founder of, manufacturers of "3D Printer" output devices. His detailed drawings of traditional Pacific...


The human powered hydrofoil you can build yourself.
It's made from mother nature's favorite material, WOOD!
As seen in Fly a Human Powered Hydrofoil, this amazing thing will be bigger than the Segway and the Internet put together!

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Click on this picture to see a movie of the hydrothopter's maiden voyage.

Step 1: Anatomy of the Hydrothopter

There's a big purple MAIN WING in back that does most of the work.
Two UPRIGHTS connect it to the CROSSBEAM.
Four FRAME STICKS connect that to the FORK with two HINGE LASHINGS at the EYEBOLT and HANDLEBAR.
At the very front of the machine is the SURFACE FEELER, a wooden disk that skips a long the surface of the water. It's bolted to the FRONT STRUT and sets the angle of attack of the FRONT WING, also called the CANARD WING.

Step 2: Parts

I painted these wooden parts with epoxy then put them out here in the sun to heat up and cure.
In the lower left are the two UPRIGHTS.
To the right is the HANDLEBAR.
In back is the CROSSBEAM, with the nails still sticking out of it from gluing it together.
Resting on the nails are the STRUT, FRONT WING, and SURFACE FEELER.

Step 3: Crossbeam

The crossbeam is 41.5" long, not counting the tenons. A regular 2x4 would have been stiff enough.

I'd planned to have two small ash crossbeams, but they turned out to be too wiggly.
So I boxed them together with thin birch plywood and epoxy.
I thickened the epoxy with beltsander dust from the dustcatcher. I used a few copper nails to hold the ash parts together. When I epoxied the plywood on I used lots of little nails that I pulled out after the glue set.
I'd planned to dowel them together with bamboo skewers.
The bamboo split when I pounded them, so I switched to nails.

Step 4: Main Wing

This MAIN WING is 87.25" long, 5.5" wide, 0.717" thick, which is approx 13% of chord.
The bolt holes to attach it to the UPRIGHTS are 48" apart.
The foil section is a very crude approximation of the NACA 63013 section. I left the trailing edge square, truncating the section, just to make the trailing edge stronger. The bottom of this foil is mostly flat, also due to laziness. There are lots of foil sections that would work. Try them all.
Scroll down to see the data for Trampofoil and Aquaskipper wings.

I made this wing from a fir board. It was a shelf I had on hand.
It was about the right size, straight grained and knotless.
I drew foil shapes on the ends of the board and shaped it with full-length passes with an electric planer. I made some mistakes so the shape wasn't quite what I had in mind, but because of the full-length passes the section is pretty uniform from end to end. Having made tapered foils such as rudders and centerboards before I was amazed how fast it is to make an un-tapered foil. Joy.

After the planer I smoothed it with a disk sander then hand sanded it.
Then I sprayed it with quick-drying auto-body primer, let it dry, wet-sanded, and repeated a couple of times til it seemed smooth enough and sufficiently sealed. Then I sprayed it with purple spraypaint, also from an autoparts store.
The primer is a lot more important than the paint that goes over it. The topcoat paint dries a lot slower than the primer. Don't use any primer that doesn't say "fast drying".
Having made various wood, epoxy, and fiberglass boat parts, I was thrilled with not having to wait for epoxy to cure. That fast-drying autobody stuff is a revelation for boatwork. Definitely good. Finishing the wing took less than an hour, including waiting. Joy.

After having subjected the wing to much exposure to water and mechanical trauma, I'm pleased that the surface is still good. Although the paint has worn off at the edges and is scratched a fair bit, The grain hasn't risen any and there are no visible cracks appearing. I'll definitely use autobody methods to finish wings in the future.

Malin Dixon writes:
"The Trampofoil wing is about 12 cm chord, and about 1.5 cm thickness. The section is
asymmetrical, and it is slightly concave on the underside, from about halfway to near the
trailing edge. The span is about 280 cm. It is extruded, with little end bits that only add
about 3cm to the span each. The wing is hollow, but there isn't much hole in the middle as
the wall thickness of the extrusion is about 0.5cm. The front wing is a solid extrusion."

The Aquaskipper rear wing has 91" span plus some little plastic winglet caps
that add 4" or so at each end. the caps fall off and it doesn't seem to make any difference.
Chord is 4.75" and the section is 12.8 % of chord thick(.608"). The section is similar
to a 63010 scaled up to that thickness, but it has a bit of hollow in the tail.
I haven't found that section in the foil library yet. The wing is a hollow aluminum extrusion with a web down the middle. The front factory wing is solid aluminum. It is 2' span, 2.42" chord, 12% thick.

Here's a flatbed scan of end views of the Aquaskipper Main and Canard wings.
Following that are some airfoil plots of other sections my designer pals like to use.

Step 5: Uprights

The UPRIGHTS are ash wood, same as a hockey stick.
They are .95" thick and 5" chord. The foil is thus 19% thick.
How long are they?
It is 22.5" from the underside of the CROSSBEAM to the top surface of the MAIN WING.
The bottom end is left thick and is shaped to match the curved top surface of the wing. The top is ornamentally long like an antique saw or a Kenyan outrigger canoe.

Cut two mortises to mate with your crossbeam. At the bottom drill a vertical hole for the bolt through the wing. Drill a horizontal hole into that for the nut the bolt screws into. Just like an Ikea futon couch.

Don't worry about foil section. Make them blunt in front and taper to a thin square edge in back.
If you can't help yourself, here's a NACA 0018 section to look at.

Step 6: Front Fork and Handlebars

The front FORK is ash wood, 0.9" thick. It is 3.95" wide at the top where it tenons into the handlebars.
It is 66" long and tapers down to 2.25" wide at the bottom, where there is a slot and a bolt hole for the STRUT. 19" below the top of the handlebars is a hole for the EYEBOLT.

The FORK is springy about like a giant slalom ski, if that means anything to you.
Any downhill ski would work fine. I'll use one of those next time.

Step 7: Canard Assembly

The CANARD WING is maple, 25" long, 2.4" chord, .28" thick. See step 4 for foil section. Any 12% or 13% thick section that's strong enough would be fine.

It's bolted up into the STRUT with the same bolt-to-nut-in-cross-hole method as the main wing uses.

The STRUT is .72" thick plywood, 27.5" in the longest dimension. The vertical part has 3.9" chord and is shaped into a foil similar to the UPRIGHTS. It is 11" tall and is shaped to mate with the top of the CANARD WING.

The SURFACE FEELER is a 6" disk of plywood. When the canard wing is flat on the ground, it is 3" off the ground, inclined upward at a 5 degree angle.

Step 8: FRAME STICKS and Setup.

Using a plumb bob and level I set up my frame so the handle bars are 22.5" horizontally from the back edge of the CROSSBEAM and 32" vertically. I would prefer to have them a few inches higher. Next time maybe 35". I attached the FRAME STICKS to the CROSSBEAM with epoxy mixed with wood dust and some small bits of fiberglass cloth over that.

I attached them at the front to the EYEBOLT with a HINGE LASHING.
I did mine with some string covered with bicycle innertube.


Then I lashed on two more sticks with bicycle innertubes to complete the fame. I thought it was temporary but after some tests and more lashing it was good enough. Here it is after the rides you saw in the video.

As you can see, the lashing at the top is a bit strange. It sort of slipped into that configuration and works really well. There's cord around the thin part of the HANDLEBAR, and a big ball of innertube lashing around that between it and the top FRAME STICKS. This lets you steer and also move the HANDLEBARS up and down relative to the top FRAME STICKS.

Don't think too much about how you make this lashing, just do it. It'll naturally get itself into this condition.

Enjoy! Let me know how things go with your Hydrothopter project!

Step 10: Gabriel's Hydrothopter

Gabriel Benito Sobrino built one in Spain. It looks great! Soon he'll be soaring like an angel!!



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Please be positive and constructive.




like to see a video


Is there anyplace where I can find the bolt or screw measurements for this?

So did you basically just sand down the board to closely match the airfoil? I was thinking about building a hydrofoil boat powered by a 55lb thust trolling motor, do you think that would work at all?

2 replies

yes it would work! Just make sure your wings are big enough to get to liftoff at a speed your motor can achieve

What is the best distance you have been able to achieve in this?
Also, is it possible to ride continuously if you have the energy or does it get slower by itself?

I've been working on my own for the past couple weeks, using 1/2 inch galvinized steel pipe for a lot of the framework. It has come out quite nice (if I might say so myself), but I am having some issues. How important is it for the fork to flex? Does it have to flex, or is being able to pivot a couple degrees ok?

Also, how important is it for the wings to be exact? Ie, my front wing definitely has a teardrop shape, its just a little bit flat.

I'll post some pics of it soon.

When I look at the Canard, I don't see the dimension between the pivot
point and the leading edge of the canard wing. Or should it be the ratio to the Feeler arm and the Canard foil? It looks like its about 3"

Allways enjoyed the science behind these but never would want one. Looks like to much work and a bit silly but still fun. Im much happier in my kayak. Think my camp would enjoy one tho.


i really believed that is possible/ (to not to pay $800 for aquaskipper)

I am curious about the efficiency of this baby compared to the Aquaskipper.
I noticed that Sahlin(original inventor) went through a lot of iterations before
getting long distances out of these. Is it that hard to get efficiency?
Did you ever use it again after the video?

Of course the "holy grail" of this type of device would be one that could be restarted from deep water without massive floats.

A rough calculation shows that loading on the main foil is about 1/2 lb per square
inch. this puts about 60-70 lbs on the approx 2 feet that extend past the upright.
Most any board should be just fine until you stomp on a rock stopping in shallow
I was going to cobble one together until I saw all my boards had dried with a twist.
Has anyone duplicated this baby?

Try japanese interlocking techniques and gorilla glue. no nails are used and it wont slip like lashings.

The thing that really amazes me about this is craft is that it could have been built centuries ago. No space-age materials or techniques are required - just a set of drawings and traditional boat-building techniques. Straight out of Da Vinci's notebooks into the water!

8 replies

The thing that really amazes me about this is craft is that it could have been built centuries ago. No space-age materials or techniques are required - just a set of drawings and traditional boat-building techniques.

No. They a) didn't have the design skills, or b) simply didn't see the need for such an outlandish sport.

Though Da Vinci would have been a good designer for this.


Suggesting that people centuries ago didn't have the design skills is trite and uniformed. Simply because they didn't do something is not proof that they were unable to do something. All good designers recognize the power of serendipity. Beyond that, the point of my comment was that you could hand the drawings of this craft to a boat-builder of 1000 years ago, and he would have success replicating it. To your second point, the driving force behind this is to better understand aerodynamics and the possibilities of human powered flight. This is something that people have obviously been thinking about for ages. Perhaps your comment wasn't intended to sound so negative, but try to imagine new and exciting possibilities rather than arbitrarily shutting them off.

Actually, the bit about the design skills is fairly accurate, as the physics behind aerodynamic (or hydrodynamic) foils wasn't accurately understood until the early 20th century. While it's not totally unthinkable that someone before then could have built something like this, it's unlikely.

You've missed the point, too. Talking about how people didn't make this craft thousands of years ago because they didn't understand aerodynamics is uninteresting and obvious. We're not digging these things up all along the coast. What is interesting is that Tim used only materials and techniques available thousands of years ago to make a pretty advanced craft. I think that is really interesting. What other objects do you use that with only a drawing could have been built thousands of years ago?

Well, yeah... Crystal radios, floating arm trebuchets, copper-zinc batteries, heck, even an internal combustion engine that uses alcohol as fuel could have been made with the right combination of craftsmanship, inspiration and (say) iron or bronze age materials. But to leave the available prior art out of the overall view of development is a bit shortsighted. A person thousands of years ago wouldn't know WHY the hydrofoil had to be shaped the way it is, and the leap from birds flying to personal watercraft isn't exactly very intuitive. In short, while the material science and construction technology involved in a given project such as this one is minimal, the other disciplines (and inspiration) needed to invent something like it aren't similarly trivial.

Let's not forget that people have been making boats (ocean going ones, at that) for thousands of years. The hulls, and rudders certainly had to be fairly hydrodynamic, not to mention mastery of aerodynamics for sails. The Chinese junk rig is said to still be one of the most efficient there is. But I digress. I helped build the front end of the wooden hydrofoil. Tim and I used power tools (you should see what he can do with just a grinder!), but short of some threaded fasteners, it could have easily been built with the hand tools of yore.

Marcos, the junk rig certainly has some very desirable characteristics, but efficiency (at least in the matter of driving force) is not one of them.

I don't know what to think anymore.