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"Safety first!" "Am I going to need this?" "Yes, you're going to need this." What's about to happen certainly wasn't on my bingo card for this year. "Let's do this!" We're at a lake in Stockholm, Sweden. "You'll have to be like… in the surfer mode. Standing up like this." And this guy, Ola Lustig, is showing me how to ride an efoil, an electric surfboard that lets you fly above the water. Well… theoretically. This is what it looks like when you know what you're doing. "He makes it look so easy but it's just a lot harder than it looks."
I'm trying this because there's a company, here in Stockholm, that does the same thing - but with actual boats. "Woah!" How does this work? And why would you want to do it? "Hey, welcome!" "Hey, Malte, hey!" "Nice to meet you, Mikael." "Nice to meet you. Well, we picked a great day for a boat ride." "Yeah, I mean, sun is shining, right?" This is Mikael Mahlberg. His job is to explain to journalists like me what Candela, the company behind those boats, does.
It calls them a "revolution in water travel". So let's see if they can live up to that. This is the ferry Candela uses for testing new features. That's why it looks a little rough around the edges. "We don't have that many seats on this prototype. But on the customer boats we have 30 seats. So think of it like a city bus, really." "And where's the real magic?" "The real magic lies underneath your feet, the hydrofoils." These are the underwater wings that lift the ferry out of the water.
They're essentially a bigger version of what's under the e-foil. "This is like an airplane wing. When you hit the speed with this, it's going to fly out of the water." And an electric motor makes sure you hit that speed. Under a surfboard that's a lot of fun. But under a boat, at least according to Candela, it's the key to solving the biggest challenge that's still holding back electric vessels. It takes quite a lot of energy to move a vessel - electric or not - through water. Today this typically comes from fossil fuels burning in engines. But it's also possible to do this without spitting toxic fumes into the air… by using batteries
that drive an electric motor. But there's a big catch. Batteries store a lot less energy per kilogram than fossil fuels. For big ships going long distances, you'd need a lot of them. Which would make the ship really heavy and take away space for cargo or passengers. Impractical. For smaller ships going shorter distances fewer batteries can work. Norway, for example, already has dozens of electric ferries in operation. But there's a trade-off. They can either go fast but not very far, like this one that can only travel around 40km at its typical speed. Or they have to go pretty slow to save energy,
like the world's first electric car ferry, that typically only goes under 20km/h. But Candela says it has found a way to make battery-powered boats go further and faster. And that's by making them fly. "Our captain here is going full throttle forward." "Woah!" "Power on. The speed is increasing. We're doing 12 knots and at 18 knots we're going to start to lift out of the water. You can almost feel it." "Yeah, wow, now it's lifting out." "Yeah." "Are we flying now?" "Now we're flying."
"That is so smooth and seamless. But you feel that little lift." "Yeah!" "So how does this work?" "So well, when we're taking off, there's a lot of water flowing around the hydrofoils, and these creates an upward pressure. Just like an airplane wing. And that means that at a certain speed, you will have enough pressure to actually lift the whole vessel above the water." The shape of the foils makes water flow faster around the top than the bottom. This creates a difference in pressure between the two sides. At the same time, the foil redirects water downward.
All this creates a force called lift that eventually pushes the boat out of the water. "And why would you want to do that?" "So a conventional vessel that is fast and flows through the water creates a lot of drag." Drag is the resistance a vessel experiences as it moves through water. This is the main reason moving a boat takes so much energy. "You can't really, really go far on battery power in a conventional boat. So we want to kind of reduce that drag and that we do by flying above it and doing so, we reduce the energy consumption
by around 75 to 80% over a conventional vessel of the same size." We're going pretty fast now, roughly 45km/h. But the boat creates barely any waves behind it. "It's flat. And this, this lack of waves is also a testament to the efficiency of the vessel, because now we're not pushing any water to the side, so we're not creating a big wave." Just for comparison: This is what it looks like on a "normal" boat. By avoiding water drag, Candela says its ferry can go up to 75 km on a single charge - without having to slow down to save energy.
Actually, all these advantages only apply when the boat is going fast on its foils. Once it "lands", it's just a normal boat. "It's almost like a plane landing. It feels like the last few seconds before a plane hits the ground." "Yeah, it's the same thing, right? And the flight control is designed, so the landing is as smooth as possible. You're not really supposed to feel the transition between foiling and non-foiling. You're just on a very efficient vessel.
It's public transport, safe. And almost to the point of being a little bit boring." "Well, I certainly didn't find it boring." "Ah, that's great." "Whoppa." "Can you please pass me the charger?" "Just this one here?" "Yeah, that's the one." "I mean this… looks just like an electric car charger?"
"Exactly, it's an electric car charger. So same infrastructure as for a car." "And how long does it take to charge the boat?" "We do it in a little bit less than an hour. So pretty quick." Gustav Hasselskog founded Candela in 2014. He faced a real first world problem: his sport boat guzzled too much fuel. So he looked for ways to make it more efficient.
"I saw that something needs to be done that is sort of out of the ordinary. And then this old technology of hydrofoils was there. I started to read about it. It's a technology which is more than 100 years old." As far back as the early 1900s, people have built and experimented with hydrofoils. In 1919, this one, the HD-4, broke the record for being the fastest boat in the world. They were tried and tested in the military… "In the age of speed, we need ships that go fast." And on civil passenger ships.
Back then, they were still powered by fossil fuels, of course. But one big problem they had was rooted in their design. A lot of these older boats' foils are sticking out the front, often fixed to the sides of the hull. This setup is called "surface-piercing". "The surface-piercing approach means that you have no or very limited dampening in the system. So if you go in big waves, you're going to start move the boat up and down and you get into very dramatic swings. So the usability of such boats is limited." That's why the handful of companies that are working on modern hydrofoils today are using a different approach - including Candela.
They attach their foils to struts under the vessel, with the actual wings staying underwater the whole time. This setup is called "fully-submerged". The key here is that, to keep the boat stable, the foils need to move. On Candela's ferries, sensors tell a "flight computer" where the boat is - and this computer makes lots of tiny adjustments to the foils' position. This happens up to 100 times per second. And it's only possible because computer chips and sensors have become incredibly powerful and cheap.
Candela serially produces ferries in this dedicated factory. Which gives it a real edge over its competitors. "Wow, that's a lot of boats…" "A lot of boats." "So how many boats are you building here?" "Uh, we're building ten here. We have ten in the production line currently, so we're building one every month approximately. That's the pace now." They come with different designs for different purposes - like hotel shuttles or the public transport one that we looked at.
"And how much is one of them?" "Well, so it depends on what market. But the price is roughly in the ballpark of what a fossil fuel vessel of the same size would cost you. But then the cost for operating is much lower because you don't have any fuel expenses, no service expenses, and it's very efficient." Candela says it has received orders for 65 ferries so far. Eleven of them go to a private company in Mumbai. The plan is to use them to cut travel times, using the megacity's waterways. In the future, they're, for example, supposed to run between the center of the city and the newly-built Navi airport.
A trip that can take up to 90 minutes by car - but only around 30 by boat. This is part of a first, tentative step in a plan by the city to build out what they call a "Water Metro" system. In Stockholm, Candela ran a real-world trial for six months. They took people on the 15 km route from the suburb of Ekerö to the city center. The final report the company wrote with the Transport Administration found: With a speed limit exemption, travel times compared to diesel ferries dropped from up to 55 minutes to 30, the hydrofoil ferries saved 94% of emissions - and 95% of passengers said they had a positive or very positive experience. But still the city hasn't ordered any ferries.
"Well, overall in public transport, the procurement cycles are fairly long and slow. And I think for Stockholm it has been seen as: okay, this boat is now in sort of pilot operation and not sort of considered to be something that they can start to use. So that means we are a few years down until we're going to see them operate widely in Stockholm." What makes new hydrofoils a lot better than those of the past are three technological leaps. The first one, electronics, we already touched upon. "So this box contains the brain of the boat, the flight control computer, which actuates the hydrofoils to keep the boat level.
The box also contains a sensor called the IMU, an Inertial Measurement Unit." The same type of sensors also get used in smartphones and drones. Candela uses more advanced ones in its boats, but it says it profits from dropping prices across the board. The second technology is: As the car industry has been pumping them out to make electric cars, they've become a lot better - and a lot cheaper. Since the 90s, prices have dropped by 97%. "I mean, making a vessel like this 20 years ago would have been impossible." And the third one is the material the boat is made from: It comes in sheets like this that then get molded
into different parts for the boat. Those then get soaked in epoxy resin, kinda like a glue that binds it all together. Candela makes pretty much the whole boat from this. From big parts like this hull - to smaller parts like this foil. "Without this material, it would be hard to build a flying electric boat. And I mean, the thing with carbon fiber is that it's kind of, I mean, it's both strong and it's light, right?" At first, this material was used to make planes, later race cars and then also stuff like tennis rackets. The downside is that it takes lots of energy and emissions to produce - even more than steel. But it doesn't corrode in salt water - so it's an obvious choice for boats.
Now if all this fits together so well… why don't we just chuck a hydrofoil under every ship and boat and make all of them electric? "For applications where foiling technology works, it is a perfect technology to reduce consumption." This is Mikael Johansson, who helps shipping companies make sure their new technologies are safe and sound. "But at least how we see it now, no, we will not see the biggest container ships with foiling technology in the near future. Or at least I would be quite surprised to see that."
Theoretically, it would be possible. But because the foils would have to be enormous, they're pretty much impossible to engineer. So foils probably won't help much in making big container ships, cruise ships or car ferries go electric. Which is a real shame when we look at hydrofoiling's potential to reduce emissions. "Where does the bulk of the emissions from shipping come from: the bigger the ship, the more emissions you have. But we also need to consider that every drop counts and that sort of paving the way for this sort of technology now can also lead to advancements in the future." Today, hydrofoils already make sense in relatively light vessels when speed matters - like in passenger ferries. In places that are built around waterways
and suffer from bad traffic, electric hydrofoil ferries could replace existing diesel ferries. Or even go as far as helping take cars and buses off the road. All this is possible thanks to decades of innovation in different fields. Candela's focus now is to build and sell as many ferries as possible. It's already planning to open a second factory. The company is convinced the time of the hydrofoil has come. The challenge ahead is to convince others that's true.
"What do you think? Would you like to take a ride on a flying ferry like this in your city? Let us know in the comments, hit subscribe and go to dw.com for more info."
