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

Picture of DIY Human Powered Wooden Hydrofoil  - the "Hydrothopter"


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

Picture of 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

Picture of 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

Picture of 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

Picture of 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

Picture of 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

Picture of 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

Picture of 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.

Picture of 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.


Picture of Top HINGE LASHING

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!!


sav83 made it! (author)2015-10-14

here is my hydrothopter...didnt manage to get it to work but it did rise to the surface with a tow from a rib...may adapt it to fit on my windsurfer

Dr.Webb (author)2014-03-17

like to see a video

MZ98 (author)2014-01-10

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

zmatt (author)2007-06-04

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?

TimAnderson (author)zmatt2009-09-02

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?

vanpaun (author)2012-05-21

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.

TruthHunter (author)2012-02-08

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"

zigzagchris (author)2011-07-01

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.

useraaaaa (author)2011-07-01


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

TruthHunter (author)2011-01-06

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?

macgyverfan (author)2010-07-25

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

ewilhelm (author)2007-05-24

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!

Hugo.B (author)ewilhelm2007-05-26

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.


ewilhelm (author)Hugo.B2007-05-27

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.

cylver (author)ewilhelm2007-05-29

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.

ewilhelm (author)cylver2007-05-30

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?

cylver (author)ewilhelm2007-05-30

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.

Marcos (author)cylver2007-07-31

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.

devonfletch (author)Marcos2010-05-29

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.

Dr.Bill (author)Marcos2010-01-14

I don't know what to think anymore.

cylver (author)Marcos2007-07-31

As to the threaded fasteners, it's possible to do some pretty amazing things with interlocking wooden pegs.

_soapy_ (author)cylver2007-06-25

Internal combustion was demonstarted with gunpowder long before liquid fuels were a success, and the steam engine was made well over 1000 years ago, in the form of a sphere that spun when heated by a fire. You couldn't build a crystal radio without copper (or other) wire and a knowledge of the fundamental properties of the cat's whisker material. Plus, without modern high-powered transmissions, you would hear nothing, not even static, as the radio band was pretty dead back then! The FAT is completely un-workable as a military device, scale it up big and you have real issues with any way to reset the system in a timely manor. Copper-zinc batteries were known long before anyone understood how they worked, and there is a perpetual motion machine that runs to this day. The trick is, it uses a sealed jar and a small pendulum as the charge carrier, between two poles of a copper-zinc cell! This could have been built. It might have been. However, it is useless as anything more than a toy of the rich and idle (by which I mean, you don't spend all day trying to make enough bread to eat, or are trapped as slave or fuedal labour) since it has no military use! One man can go how far? 50 yards unladen? Since a crossbow (which uses the same sort of spring ideas seen here) goes further than that, I'd say forget it for crossing moats. However, I love the project, and Tim, you are my kind of loon!

surfreak (author)_soapy_2008-03-01

How is the FAT unworkable as a military device? Please elaborate.

_soapy_ (author)surfreak2008-03-02

Well, for one thing, we now have gunpowder. Back then, however, I really doubt that they could have reset a 10 ton (or more) mass used for a FAT. The way that the trebs were reset was by pulling the arms over with a few ropes, so getting huge leverage on the mass. But the FAT mass isn't directly connected to the arm (hence the name) so you would need some other, huge and expensive system to re-raise the mass, and then you would have to reset the arm as well. And the reset lifting system couldn't go above the mass, as it would be in the way of the arm. So not really, to my mind, practical as a war machine. And you didn't need them inside the castle to fire back, since you had your own machines raised above your enemies machines up on your walls, so you had greater range already.

surfreak (author)_soapy_2008-03-02

Floating Arm Trebuchet refers to the fact that the throwing arm is attached to a set of wheels. The counterweight is still attached to the opposite end of the throwing arm relative to the projectile. You can still return the machine to the loading position by pulling (or pushing, in the case of the few small ones I've built) down on the end of the throwing arm opposite the CW.

_soapy_ (author)surfreak2008-03-02

That one you have linked to (made?) is absolutely beautiful! It's not the design for a FAT I'd seen before. Most of them were, I thought, that the arm was on a pivot, with the mass dropping vertically on a guide, and not directly pinned to the arm. Either way, that axle on wheels and a steel pivot for the mass is going to be a real issue with a military size mass on the other end, in the middle ages The best they could have done was probably a cart wheel or two and a stubby forge iron axle. This means that it wouldn't have been practical as anything large. Don't get me wrong, 100 yards is pretty hot for only 470lbs, but if you wanted to get up to 300 yards with a larger projectile, you would probably start to have issues with bending those steel pivot points too.

Dr.Bill (author)ewilhelm2010-01-14

Yeah !

oooh proved wrong by the founder of ibles

Hugo.B (author)Zaphod Beeblebrox2009-10-05

Indeed. Who would have thought that a falliable human could get something so wrong? Personally, I keep wondering why there are timestamps on posts - doesn't really make much sense, does it?

Zaphod Beeblebrox (author)Hugo.B2009-10-05


Hugo.B (author)ewilhelm2007-05-28

I certainly agree with your point about a boat builder being to reproduce it a century ago, I think I was forgetting that they were very advanced in the boat building department then. So I'm wrong about (a).

the driving force behind this is to better understand aerodynamics and the possibilities of human powered flight.

I missed that when I read the instructable, but in that case it would be more of a research platform than an "outlandish sport".

arbitrarily shutting them off.
Far be the thought!


ewilhelm (author)Hugo.B2007-05-28

I missed that when I read the instructable, but in that case it would be more of a research platform than an "outlandish sport".

Tim isn't always so clear with his intentions, so I can see how that might be easy to miss.

Dr.Bill (author)Hugo.B2010-01-14

Yeah !

Dr.Bill (author)ewilhelm2010-01-14

Yeah !

stevennhl (author)2010-01-13

does it matter what kind of wood you use?

Zaphod Beeblebrox (author)2009-10-04

hammacher schlemmer sells these

kaiwilliams (author)2009-08-28

What made you chose one profile over another?

TimAnderson (author)kaiwilliams2009-09-02

A section with no hollows in it is a lot easier to shape. If the trailing edge doesn't get too thin, it's less likely to break or cut you. There are other concerns like lift/drag ratio, stall speed, etc. which you can estimate with xfoil or other utilities. I didn't get too concerned with that. I just wanted something strong and easy to shape that was similar to foils on the commercial unit. It turned out to be good enough.

bluenik (author)2009-06-09

Could you tell me how wide is the crossbeam (where you stand on)?

bluenik (author)2009-06-05

You are a legend.

Brumzzz (author)2009-04-14

I am not very big or something, but could this thing get to a high speed without breaking? I like the instructable, and it's very well explained. Good job

cathyoz (author)2007-06-20

someone did a similar projets in australia , i saw it in tv recently , but can not remember the name

MAD-1 (author)cathyoz2009-01-15

the product was shown on "shack tv" and is called Water Skipper the WS is made out of Aircraft Aluminum and Fiberglass

the link to the Manufacturer is

finton (author)2009-01-03

A great instr'ble! Nice to see people having fun while inventing. I feel special kudos should go to Andrea, though, for a stable and well thought-out video. Good combination of wide shots and closeups.

yoshhash (author)2008-03-29

Hey, did any of you take a crack at this? I am definitely going to try, but would like to understand it better. i also wondered about a slightly different fin design: i was thinking that if there was an arc shape, curving downwards, like a frowny face, it would harness more of an uplift. am i mistaken in thinking that? i also need a better explanation of how it works...does anyone here feel they really understand it? if i drew up some diagrams, with my interpretation of how it works, would someone be willing to tell me if i am on the right track?

surfreak (author)2008-03-01

Hmmm.... I wonder the force a wooden hydrofoil could take? They've got those ridiculously expensive foils for kiteboards now, and I've been wondering if there's a diy solution... Maybe my old (carbon fiber) hockey stick would be strong enough as the upright... I'll look into it (unless you or Eric beat me to it).

spylock (author)2008-02-22

Thats one of the coolest things Ive ever seen.

Huray4Insanity (author)2007-09-15

dude thats freakin awsome!!

adamvan2000 (author)2007-06-02

I may not be a history expert, but I believe this probably wouldn't have been feasible for a medieval craftsman/shipwright to build. Please let me know if there ARE other methods/materials that they would have had access to with which they could have done this. I believe that the rubber compounds of that period would not have had the same properties as current inner tubes, therefore making the stretchy, bouncy part that joins the stem to the body very tricky to accomplish. Granted, there may be another way to do it. I'm thinking rope would be too stiff and not flexible enough, , sinews would tighten upon drying, steel springs weren't possible as steel wasn't yet invented, and any other joining substance, such as glues, would be more for fixed joins. BTW, this is a very cool instructable! I'd like to try it out myself, maybe using steel springs? If you built a larger, laminated wood or aluminum model, it would probably require a large foil and a greater distance between the front wing and the rear foil, but might require a bit less effort with more gliding action due to the increased size and the decreased weight (if you use aluminum or laminated wood). You could then use steel springs to give the front fork more of a snap when it comes back, again, for less effort. I would definitely make a lighter foil, possibly fiberglass? Then again, if you made the whole thing out of fiberglass, it might be that much better. I don't know that for sure, though. The increased size might also make attaching pontoons for a floating takeoff possible, considering the added distance it would rise once underway. Please take all of the above with a grain of salt and do not demean me, as I am not an engineer, or fluid dynamics expert, or even an amateur scientist. That's just how it would seem to work in my head. Happy Instructable-ing! adamvan2000

About This Instructable




Bio: Tim Anderson is the author of the "Heirloom Technology" column in Make Magazine. He is co-founder of, manufacturers of "3D Printer" output ... More »
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