So you say you want to fly above the waves on an electric hydrofoil, but you don’t have the means to buy a commercial board. Or, you don’t have the time and skills needed to carve a board and outfit it with the motor and wing that let it glide above the water. Are you out of luck? Not if you follow this hackworthy e-foil build that uses a waterproof rifle case as the… hull? Board? Whatever, the floaty bit.
If you haven’t run across an e-foil before, prepare to suddenly need something you never knew existed. An e-foil is basically a surfboard with a powerful brushless motor mounted on a keel of sorts, fairly far below the waterline. Along with the motor is a hydrofoil to provide lift, enough to raise the board well out of the water as the board gains speed. They look like a lot of fun.
Most e-foils are built around what amounts to a surfboard, with compartments to house the battery, motor controller, and other electronics. [Frank] and [Julian] worked around the difficult surfboard build by just buying a waterproof rifle case. It may not be very hydrodynamic, but it’s about the right form factor, it already floats, and it has plenty of space for electronics. The link above has a lot of details on the build, which started with reinforcing the case with an aluminum endoskeleton, but at the end of the day, they only spent about 2,000€ on mostly off-the-shelf parts. The video below shows the rifle case’s maiden voyage; we were astonished to see how far and how quickly the power used by the motor drops when the rifle case leaves the water.
Compared to some e-foil builds we’ve seen, this one looks like a snap. Hats off to [Frank] and [Julian] for finding a way to make this yet another hobby we could afford but never find time for.
Thanks to [Chris] for the tip.
How on earth does balancing on such a board even work? Does it self-balance from left to right like a skate-board or bicycle? And how about the front to back rocking motion? Wouldn’t you simply fall? Judging by the first 10 seconds of the video it doesn’t even need active stabilisation by a human being! Is there some smart gyro stabilized motor control going on?
I’ve ridden a hydrofoil while being towed by a boat before. Lemme tell you that looks are deciving, you need a LOT of active stabilization by the rider to be stable. It’s kind of like log-rolling? Except in three dimentions instead of two.
The wings do most of the work for balance if I’m not mistaken. Also, it acts a little like the keel of a boat.
Keep watching. The keel and foil are pretty stable. Turning is tricky.
And if the deck rolls, you have a nice sharp keep and turning prop coming at you.
Would definitely shroud that prop.
Even shrouded is not enough, have a look here (WARNING BLOOD & BONES): https://stabmag.com/news/french-professional-surfer-nearly-loses-fingers-in-hydrofoil-propellor-incident/
Wow! Thanks for the warning!!!!
I wonder if there would be a way to incorporate active stabilization using reaction wheels or something similar to the anti-earthquake mass shifters on sky scrapers.
that would add a capton of weight…a much better solution would be control surfaces on the foil
A good analog to look at would be a remote control plane as operating on same lift principles. the tail fin is providing most of the passive stabilization although you can see there is some torque steer going on when it is moving sans rider. the case is mounted on top of the lifting surface so rider movements would be very similar moment forces to those applied by a planes ailerons so the rider can control pitch and roll by shifting weight and a slight control of the yaw with throttle. But like a plane very susceptible to stalling or going into a dive.
Is that actually watts on the overlay? 5KW?
Seems reasonable to me, big heavy human and large board in water is going to need a great deal of power to get going. I admit not being an expert I wouldn’t have guessed right, I figured it would need a fair bit more than the electric skateboards which are often it seems are in the 1Kw range but I wasn’t thinking peaks of 5Kw…
Not like cooling the motor is major issue either its surrounded by water… The battery and controller have a pretty large volume of air to heat inside that case, and the case is always moving through the air/water. If they stayed at full power up on the plane maybe it would get hot enough to matter, but I doubt it. And I’d be very impressed if they could stay on at that speed for long.
Jup thats actually Watts. Last week I used an optimised prop and another front wing, beat 46km/h @ nearly 8 kW with the rifle case (I’m one of the guys in the video)
Hi nice work. I had two engineer friends trying to create such an item. I own a lift efoil. Have that experience. I kite foil and now I wing foil board. Doesn’t take much energy source once you get up on foil. And the foil you ride on can make a huge difference.
I have lots of winger friends and a couple of water foils they are saying are best in class and you should bolt to ur gun case would be a 21 takuma kajuri. Or 21 Lift foil.
Anyway you did great: is there a list you can email of the actual parts. Motor, prop, controller battery hand held controller and actual case and mods?
How long is battery lasting as is? I get 45 to 60 min of ride out of my Lift battery. Putting a larger front water foil wing increases ride time and stability and a better choice for inexperienced riders .
Their beginner boards come with bigger foil wings to make it easier to learn
Winging is kind of same way; as a beginner a bigger water foil gives you more lift and stability and as you get the skills you can ride half as much cm sq foil as your skills improve. So keep that in mind as well. I’m sure you both are kite foil boarders.
Anyway thanks for sharing what you can. I registered. Lloyd in USA
I like the aluminum baseball bat for shark protection!
Duh, such a simple solution – here I was cutting holes in a fiberglass board and trying to fit everything in and creating positive pressure in the various housings.
I’m going to revamp my whole project. Thank you Frank and Julien!
january, it’s a perfect time to do some swimming, not many people are around :) and you even not need to worry about sunburns :) yes, the water must be a bit cold, but you can wear that monkey suit :)
Nice work, Frank and Julian!
I wouldn’t be surprised to see this in a Bond film if it hasn’t been done already. The movie version would go about 150km/h, all the parts would break down to fit inside the case… and it’d have “all the usual refinements” ;)