The problem with powering any form of vehicle with electricity is that it requires bulky batteries. This is a particular problem for boats because they experience resistance in the water. To get around this, Candela used a hydrofoil, where the legs extend down into the water and act like wings, pushing the boat into the air as it accelerates like an airplane during takeoff. “In port, the foil is fully retracted and therefore protected,” Hasselskog said. “But then you lower the foil and hit the throttle and close it. The control system takes care of the whole takeoff, just like an airplane.”
Hydrofoils aren’t new, but power and automated controls are. The carbon fiber Candela P-12 will feature a dual propulsion system powered by a 180 kWh battery, allowing it to run for three hours before needing a charge. The 8.5 metric ton vessel is 12 meters long and 4.5 meters wide and can carry 30 seated passengers.
A super-fast flying boat might sound like a surefire way to lose breakfast on your morning commute, but Candela’s sensors feed into an automatic control system that adjusts altitude and roll and pitch 100 times per second to ensure smooth sailing weather. “With the control system, we can stop any vertical movement of the boat,” Hasselskog said, which often leads to seasickness. “So far, no one has gotten seasick on our boat.”
All of this means that when the Candela P-12 is built, it should consume less energy per passenger than a hybrid electric bus, travel faster than a car, and reduce fuel and maintenance costs by 40 percent. As it glides over the water, it is less disruptive to the local environment above and below the water.
Candela can’t simply expand its existing boat to build the P-12 – regulations call for thicker hulls, batteries for fire safety systems, and, confusingly, separate toilets for passengers and individual crew members who will drive all the time.
Besides toilets, there is another regulatory challenge: Speed limits on inland waterways tend to be as low as six knots (7 mph), but hydrofoils are most efficient at top speed. Such speed limits are for safety and to reduce wake turbulence, which a boat like the P-12 does not create. “The solution is to work with port authorities and ferry operators to obtain exemptions,” said Charles Haskell, decarbonisation project manager at maritime consultancy Lloyd’s Register. Near Stockholm, the limit is 12 knots, although Candela has a temporary exemption during the trial.
Not all cities can use waterways as highways like this, but it could be an attractive idea for coastal urban agglomerations. Rival airship maker Artemis is testing its version in Belfast, while Hasselskog has held talks with authorities in Istanbul and across the Middle East. Representatives of the Water Emergency Transportation Authority (WETA), which operates ferry services in the San Francisco Bay Area, have visited Stockholm to find out how the Candela P-12 works.
For coastal cities like Stockholm, ferries could become the water equivalent of trams without laying infrastructure such as railways, albeit with a charging system. “If it’s like a sea light rail, providing convenience to hundreds of people who would otherwise travel by car, then that’s more of what we need,” said Paul Chatterton, professor of urban futurology at the University of Leeds. “Speed is a red herring… In a big city river setting, you need large, large crafts that can carry a lot of people over short distances.”
Hasselskog argues that larger fleets of smaller vessels offer more flexibility than larger ferries, and could mean they can be used on demand without timetables or fixed stops. The idea is also being touted by a hydrogen-powered hydrofoil water taxi made by SeaBubbles, which has been trialled in Lyon, France. The smaller vessels have another use: to transport maintenance crews and supplies to offshore wind farms, Haskell said, solving the problem of getting crews far out to sea without getting seasick.
Even without top speeds, water taxis and boat buses offer hope for cities with waterways, Chatteron noted, noting the popularity of motorboats in Venice. In addition to passenger traffic, slow electric canal barges can take cargo off the road. “You can move a lot of things with little or no energy, and a lot of European cities have canals,” Chatterton said. Whether it’s electric flying ferries or low-energy barges, Hasselskog said, better use of urban waterways is important for sustainable development. Development is meaningful. “You don’t need any special infrastructure, the water is there,” he said. “That’s probably why they’ve been used in the past – there you go.”