Is It a Bird? Is It a Plane? No, It’s a Flying Ferry

The problem with powering any form of transport with electricity is it requires heavy batteries. That’s a particular problem for boats, as they suffer drag in the water. To address this Candela uses hydrofoils, legs that extend down into the water and act like wings, propelling the boat up into the air as it picks up speed like an aircraft during takeoff. “In harbor the foils are fully retracted, so they’re protected,” Hasselskog says. “But then you lower the foils and hit the throttle and off it goes. The control system takes care of the entire takeoff sequence, it’s like an airplane.”

Hydrofoil boats aren’t new, but electric power and automated controls are. The carbon-fiber Candela P-12 will have twin propulsion systems powered by 180-kWh batteries, letting it run three hours before requiring charging. At 12 meters in length and 4.5 meters across, the 8.5 metric ton boat will carry 30 seated passengers.

A superfast flying boat sounds like a surefire way to lose your breakfast on the morning commute, but the Candela has sensors that feed into an automated control system to adjust the height and roll and pitch up to 100 times a second to ensure a smooth ride regardless of the weather. “Through the control system we can cut out any vertical movements of the boat,” Hasselskog says, which is what tends to cause seasickness. “So far nobody has gotten seasick on our boats.”

All of that means the Candela P-12, when built, should use less energy per passenger than a hybrid electric bus, go faster than a car, and bring down fuel and maintenance costs by 40 percent. And as it glides above the water it’s less disruptive to the local environment both above and beneath the water.

Candela couldn’t simply upsize its existing boat to build the P-12—regulations require a thicker hull, fire safety systems for the batteries, and, confusingly, separate toilets for passengers and the single member of crew, who will be driving all the time.

Toilets aside there’s another regulatory challenge: Speed limits on inland waterways tend to be as low as six knots (7 mph), but hydrofoil boats are most efficient at top speed. Such speed limits are for safety and to reduce wake, which boats like the P-12 don’t cause. “The solution is working with port authorities and ferry operators to get dispensation,” says Charles Haskell, decarbonization program manager at maritime consultancy Lloyd’s Register. Around Stockholm that limit is 12 knots, though Candela has a temporary exemption during the trial.

Not all cities can use waterways as highways like this, but it could be an appealing idea for coastal conurbations. Rival flying boat maker Artemis is testing its version in Belfast, while Hasselskog has held talks with authorities in Istanbul and across the Middle East. Reps from the Water Emergency Transportation Authority (WETA), which operates ferry services in the San Francisco Bay Area, have visited Stockholm to see how the Candela P-12 works.

For coastal cities like Stockholm, ferries could become the watery equivalent of trams without having to lay infrastructure like rail, though charging systems will be needed. “If it’s acting like a sea-based light rail facilitating hundreds of people who would have gone by car, then that’s what we need more of,” says Paul Chatterton, professor of urban futures at the University of Leeds. “The speed is a red herring … in a big urban river environment you need big large crafts that can take a lot of people short distances.”

Hasselskog argues that a large fleet of smaller boats offers more flexibility than larger ferries and could mean they’re used on demand, ditching the need for timetables or fixed stops. The idea is also being touted by hydrogen-powered hydrofoil water taxis made by SeaBubbles, which have been trialed in Lyon, France. Smaller boats have another use: ferrying maintenance staff and supplies out to offshore wind farms, says Haskell, solving a problem of getting staff to locations many miles offshore without them arriving seasick.

Even without top speeds, water taxis and boat buses offer promise to cities with waterways, Chatteron says, pointing to the popularity of Venice’s vaporettos. And beyond passenger transport, slow, electric canal barges could take freight off of roads. “You can move a lot of things with little or no energy,” Chatterton says, “and a lot of European cities have canals.” Whether its electric-powered flying ferries or low-energy barges, making better use of urban waterways makes sense for sustainability, says Hasselskog. “You don’t need any special infrastructure, the water is just there,” he says. “That’s probably why they were used back in the day—you just go.”