ISSUE 011 Autumn 2021 Candela C-7 hydrofoil speedboat dossier l In conversation: Robert Hoevers l Battery recycling focus l Vehicle dynamics insight l ZeroAvia hydrogen-electric aircraft digest l Motor materials

Hydrofoiling gives this serial production boat high speed and long endurance. Rory Jackson examines the engineering decisions behind its design Wing commander W hen it comes to designing new kinds of boat hulls that will get as much power and endurance as possible out of battery- electric powertrains, one of the smartest things a maritime architect can do is simply to lift the boat out of the water so that it doesn’t have to deal with all the drag and impacts that come from propelling boats through waves. We last featured such a solution in EME 6 (Spring 2020); as featured in that issue’s cover story, Green City Ferries and Echandia Marine have collaborated to create their BB Green all-electric boat. This Swedish commuter ferry uses a 60 kW fan to generate a surface-effect air bubble beneath the centre of the hull, effectively raising about 80% of the boat’s ‘wet area’ out of the water. That cuts down the hefty energy bill induced by hydrodynamic drag, giving the companies’ vessel a considerable boost in energy efficiency, not to mention side-benefits for commuting applications, such as a much-reduced wake wash and a significant increase in speed. It seems, however, that Swedish engineering is never quite ‘finished’ when it comes to pioneering new zero-emissions vehicles and maritime technologies. Rather than be content with pushing only 80% of the boat above the waterline, Stockholm County-based Candela Speed Boat has successfully engineered a hydrofoiling boat that works by using a wing beneath the keel to lift the entire hull out of the water. Candela’s flagship product is its C-7 speedboat. In July, this two-seater, battery-electric craft competed (and came first) in the YCM International Speed Record race – the world’s biggest competition for electric and new energy boats – during the Monaco Energy Challenge. Among the competitors it beat were boats packing e-motors with 10 times the C-7’s horsepower. Its electric motor produces up to 55 kW (73.7 bhp), which enables the 1300 kg, 7.7 m-long boat to move at a top speed of 30 knots. It cruises The C-7 is capable of a top speed of 30 knots thanks to its hydrofoiling technology (Images courtesy of Candela Speed Boat) 20 Autumn 2021 | E-Mobility Engineering