The Pros And Cons Of Hydrofoils

Hydrofoils have fascinated naval architects and marine designers for years. Fitted with underwater wings, these designs traverse the waters at great speed with a minimum of drag. As with many innovative technologies, though, the use of hydrofoils is riddled with challenges that often offset the vast benefits they offer.

While hydrofoils promise a better marine transportation experience, their adoption hasn’t been smooth sailing. In this article, we’ll dive deep into the potential and pitfalls of hydrofoil designs, and look at the unique niches this technology serves today.

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the active foil flying across the water

Hydrofoils Love This One Simple Trick

Earlier in the year, [rctestflight] created an active hydrofoil RC craft but found the actual performance very lacking. Luckily for him and for us, he continued to tweak it and one tweak suddenly turned it from a nightmare to a dream.

That tweak was adding ArduPilot’s airplane model. The design had three servos, which each actuated the angle of a foil underneath one of the three pontoons. The ship propelled itself via some propellers mounted near the top. If you know much about ArduPilot, you notice that active hydrofoil boat doesn’t show up on the list of supported platforms, and you’re right. [rctestflight] points out that the three servos actually function as a plane underwater. The front two are ailerons and the back one is an elevator, all things that ArduPilot knows how to handle with a tightly controlled loop except for one thing; there’s no altitude data.

So he stole a trick he developed earlier for his ground effect plane and used a distance sensor to let ArduPilot know how to adjust things. He used a sonar sensor instead of lidar as it works better with water and he was pleasantly surprised when he took it out on the lake and it just worked wonderfully. The original goal with the active stabilization was to have the efoil immune to choppy waters, and we’re sad to say that it didn’t quite reach that lofty target. The single sonar sensor follows the wave in front of it beautifully but can’t handle the complex waves being thrown at it. Perhaps some sort of sensor fusion algorithm could provide the necessary data to be truly resilient. But we love watching the foil glide across the water and it is hard to remember that it’s actively flying rather than just floating that way.

Others have tried and failed to 3D print a hydrofoil while others have succeeded. We love that [rctestflight] came back to finish the fight and came away a champion. Video after the break.

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Trying And (Mostly) Failing To 3D Print A Hydrofoil

[Sam Barker] had a boring dingy that he wanted to spice up a bit, so he resolved to 3D print a hydrofoil wing for it so that it could fly across the water. (Video, embedded below.)

With a large wing designed and sliced into several pieces, and a total print time of 200 hours, [Sam] was ready to glue the foil wing together when he realized his scale was way off and the wings were far too large for his boat. With some hacking, [Sam] was able to use a single wing across the bottom of the ship. [Tom Stanton] came over to help with fiberglassing, and they were ready for a test.

As you might have guessed from the title, the test wasn’t particularly successful. Swapping the engine on the boat for a more potent motor gave the lift he needed in the front, but without a back foil, it was a wheelie rather than what [Sam] hoped for. Back at home, they printed a second wing and went back for a second test. The boat would start to lift out the water, but the shaft of the engine lifted out of the water, sending him back down. Unfortunately, a downpour cut the test short.

Not to be defeated entirely, [Sam] connected it to a much larger boat once the weather cleared and pulled his dingy along behind. To [Sam’s] credit, they did get some solid foiling, and the ship did lift out of the water until the wings sheared off from the stress. All in all, an entertaining story of engineering while racing against the weather.

We admire [Sam’s] ambition, and if you’re thinking about building a whole hydrofoil, we suggest starting with a smaller RC model and scaling up from there.

Shoot Above The Waves On This E-Foil Made From A Rifle Case

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.

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Fly Across The Water On A 3D-Printed Electric Hydrofoil

Paddleboards, which are surfboard-like watercraft designed to by stood upon and paddled around calm waters, are a common sight these days. So imagine the surprise on the faces of beachgoers when what looks like a paddleboard suddenly but silently lurches forward and rises up off the surface, lifting the rider on a flight over the water.

That may or may not be [pacificmeister]’s goal with his DIY 3D-printed electric hydrofoil, but it’s likely the result. Currently at part 12 of his YouTube playlist in which he completes the first successful lift-off, [pacificmeister] has been on this project for quite a while and has a lot of design iterations that are pretty instructive — we especially liked the virtual reality walkthrough of his CAD design and the ability to take sections and manipulate them. All the bits of the propulsion pod are 3D-printed, which came in handy when the first test failed to achieve liftoff. A quick redesign of the prop and duct gave him enough thrust to finally fly.

There are commercially available e-foils with a hefty price tag, of course; the header image shows [pacificmeister] testing one, in fact. But why buy it when you can build it? We’ve seen a few hydrofoil builds before, from electric-powered scale models to bicycle powered full-size craft. [pacificmeister]’s build really rises above, though.

[pacificmeister], if you’re out there, this might be a good entry in the Hackaday Prize Wheels, Wings, and Walkers round. Just sayin’.

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3D Printed Hydrofoil Boat RC Flies

hydrofoil boat

[Wersy] has been trying out different designs for 3D printed RC boats — his latest is a hydrofoil!

He’s using a high power RC plane out-runner motor, which he found is simply… too powerful. It would cause his first boat to flip and sink if he opened the throttle up too much! To counter this — and make full use of his motor — he’s made new two boats; a hydrofoil, and a dual-hulled  air(?) boat.

He based the hydrofoil’s profile off of NACA 63-412, a typical profile for sailboat hydro foils like the Moth. What he found was it’s still extremely difficult to get the right balance between the pitch of the wings, and the throttle output to hit a steady condition for driving smoothly. It works, but it will still needs a few more iterations!

His other solution, a quasi-jet engine-dual-hulled-boat is pretty fun too — he’s 3D printed a large impeller for his motor, and strapped it in between two of his boats! It’s quite a bit more stable to drive, and looks pretty unique!

Stick around after the break to see both of them in action.

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Human Powered Hydrofoil, The Wingbike!

[Steven] has been working for the past year on a very cool pedal powered hydrofoil, which he calls the Wingbike.

We’ve seen plenty of trampofoils before, which are hydrofoils that can convert a human bouncing up and down… to horizontal movement. There have even been some pedal powered versions before, but its a rather tricky mechanism to get just right.

[Steven] has built his Wingbike almost entirely out of carbon fiber, and it only weighs 10kg.The biggest problem is balance, as you’re about 1.5M above the foils. If you lean too much, you fall. If you slow down too much, you sink. The current model he is working on has fairly large foils, which does help a bit with the balance, but that also increases the amount of energy required to propel it. He plans on creating new designs with much smaller and faster foils in the future.

Unfortunately, the water is getting quite cold in the Netherlands, so he’s going to spend the rest of the winter months optimizing the bike from a design perspective. Stick around after the break to see his latest successful test video!

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