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In 2018 High Power Media launched E-Mobility Engineering as a quarterly magazine focusing on the electric and hybrid vehicle industry, providing concise coverage of the array of engineering challenges presented in this fast-growing market. Reporting independently on the engineering at the heart of electric vehicles providing unbiased commentary on full vehicles, hardware components, software programming, and other innovations and via interviews with leading EV/HEV engineers.

Article : Candela C-7 speedboat

The C-7 is capable of a top speed of 30 knots thanks to its hydrofoiling technology


History of the C-7

Candela was founded in 2014 by now-CEO Gustav Hasselskog after a holiday in the Stockholm Archipelago. While various factors motivated him to spearhead the development of a clean and energy-efficient speedboat, initially it was the high fuel costs incurred by repeated trips to and from the mainland during the holiday.

“Many people in northern Europe live either in island towns, island suburbs or similar, where regular commutes or other short trips are most conveniently made by boat,” explains Candela’s communications manager Mikael Mahlberg. “Gustav had looked into electric boats but found existing hulls consumed too much energy to get decent range at high speeds.

A fully submerged hydrofoil enables the speedboat to ‘fly’ above the waterline. It is made from a carbon composite that can be twisted for performing banked turns

“For reference, a conventional 25 ft speedboat consumes about 15 times the energy per kilometre of a standard family car. And lithium-ion batteries contain just one fifteenth of the energy of gasoline.”  

Anyone hoping to make an electric boat with a conventional hull hits something of an engineering wall. If they want high speeds, they get very short ranges, even with the highest-quality lithium-ion batteries currently available.

The optimum with present technology is around 120 kWh of energy for roughly 20-25 nautical miles of range, since integrating any additional battery packs will increase the vessel’s weight and drag to offset any potential gains in range, until eventually the boat simply sinks.

Faced with this hurdle, Hasselskog opted to create an electric hydrofoiling system that would lift a boat’s hull above the water and remove the problem of hydro drag altogether. He therefore began gathering a development team in 2014 that soon became Candela Speed Boat. Building the first prototype began in 2016, the final prototype followed in 2018, and serial production started in 2019.

With the boat and its unique technology now highly optimised and matured, Candela has now started manufacturing and selling the C-7, making it the first electric hydrofoiling vessel to enter serial production, with about 30 boats produced and sold each year. That is currently the maximum capacity of the 50-person company’s production capacity, but the company plans to scale up production, its next target being 400 units a year by 2024.

There is one last technology in the C-7 worth noting. Green City Ferries’ latest version of its fast commuter electric ferry design now does without the surface-effect air bubble technology in favour of a hydrofoil-assisted catamaran architecture, making the hydrofoil a de facto blueprint for the future of maritime e-mobility.


Hull materials and hydrodynamics

In the earliest design stages for the C-7’s hull, very little was defined – only that it had to fly, and would therefore need to be as light as possible. The first prototype was built in an aerospace carbon fibre factory, made entirely from the best composite material Candela could find.

Philippot says, “The only downside with a carbon fibre hull is in fact the expense of building it, to make the boat affordable for serial production. Carbon composite is around half the weight of fibreglass composite while being stronger and stiffer. Every gram added would mean we’d need a more powerful, heavy and expensive powertrain, which would risk reducing our range.”

Judicious mechanical and software engineering enables the C-7’s to make banked turns

Although carbon composite is pricier than fibreglass, Candela has striven to use thin carbon parts to reduce the overall bill of materials in the structure. Philippot points out that the labour cost of carbon fibre is a bigger concern than the material cost.

To optimise the value for money in the factory processes, vacuum infusion is used to embed the resins into the carbon fibres for the larger hull sections. The advantages of this process were also espoused by Green City Ferries: by enclosing the fibre and resin within airtight soft plastic bagging, and forcing the latter through the former at -1 bar, it ensures a uniform spread and density of resin.

This is used for the large hull and deck sections, while the struts and rudders (each being around 2 cm thick) were made using a different carbon composite and an undisclosed manufacturing process to ensure they could handle the loads and stresses coming from the waves, from turning, and from carrying the 1.3 t boat, as was the foil to ensure it could twist and deform as needed for turning the boat.

“We searched for a long time for suppliers who could produce the parts with the strengths we needed at a reasonable price, and we did a lot of testing to make sure those thin, lightweight parts could safely handle and transmit huge loads while maintaining the stability of the boat, to be certain we were choosing the right manufacturers,” Philippot notes.

The deck is also topped with teak for aesthetic reasons, and is manufactured with hatches for maintenance workers to access the battery pack, flight controller, and other parts. Beneath the deck is a network of aerospace-style ribs and spars, to maximise the structural strength of the boat while minimising weight.

“If you look inside an Airbus or Boeing aircraft structure, you have a rib, spar or string every 10 cm or so, and the outer skin is just 2 mm thick,” Philippot explains. “Their engineers know from impact tests that this arrangement works, and we know that having a similar system in our boat is key for minimising weight while maintaining safety.

“Most speedboats opt for a sandwich-type outer skin instead, but not only is that too heavy for the C-7, it also isn’t strong enough to help with distributing the loads that concentrate around the three ‘legs’ of the boat.”

To simulate the load distributions, CAD and FEA were used extensively to closely predict the behaviour of the carbon composite, although as mentioned, a lot of real-world tests were needed to get the foil to twist without breaking or being too pliable.

Future plans

The C-7 is now the best-selling premium electric boat in Europe, thanks in no small part to its foiling-based powertrain that offers its owners 95-97% lower operating costs compared with a traditional diesel- or gasoline-powered speedboat.

The P-30 is the largest of Candela’s planned vessels; its design will be scalable for carrying up to 300 passengers at a top speed of 30 knots while foiling

From a commercial perspective, such low operating costs and the greater profitability they could bring, naturally appeal to maritime fleet operators. To that end, in addition to expanding its productive output of C-7s, Candela is growing its portfolio to develop and produce larger boats for use as water taxis and commuter ferries  – an immense market across not only northern Europe, but also the Gulf States, East Asia and realistically any coastal city with large waterways.

At the time of writing, the Candela P-12 water taxi had been officially launched, and will be delivered to its first customers soon. This 8.5 m-long vessel carries up to 12 passengers (hence its name) and consumes 1 kWh/nautical mile, which the company estimates as a twelfth of the energy consumption of standard IC-engined water taxis.

The Candela P-30 is still in development. Its dimensions are less clear – a 30-passenger initial version is the target – but the concept is scalable up to 300 passengers. In addition to a top speed of 30 knots and a cruise of 20-plus knots, with minimal wake disturbances for other ships and 95% less g-force disturbance for customers, Candela sees this boat being a game-changer for waterborne commuting and urban transport in general.

“Waterways these days are mostly seen as obstacles that have to be overcome: you build a bridge over them, or a tunnel under them,” Mahlberg says. “What if we could use them for low-cost, high-speed electric transport instead? In many cities, waterways offer excellent cross-traffic connections but are mostly unused.”

Data gathered on these new vessels and the new electric components they use can be expected to inform the engineering on future versions of the C-7 and other vessels that Candela is likely to build.

Auhor : https://www.emobility-engineering.com/candela-c7-speedboat/ Posted on 08 October 2021, 02:58:53
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No. 1 By Mr. Imtiaz Ahmed , 25 February 2022 ,17 : 09 : 16
nice one
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