Fast, silent and smooth - electric revolution hits the water
Image credit: Candela
Electric boats, like electric cars, are not a new idea, but worries about climate change have spurred innovative design in the boating community and new models are out on the water near you. E&T learned more from electric pioneer Candela and others at the Düsseldorf International Boat Show.
Outside the rarefied and highly specialised world of top-of-the-range racing yachts, the world of leisure boating has, until recently, been slow to innovate. After a three-year Covid-induced hiatus, Boot Düsseldorf (Düsseldorf International Boat Show) opened to the public in late January 2023. One of the largest exhibitions of its kind in the world, over 1,700 exhibitors showcase their latest designs to the trade and well-heeled clients. From super-yachts to sailboats, many new vessels were on show. Most exhibitors were displaying incremental improvements, but Swedish company Candela went back to basics and presented a completely redesigned powerboat and won out at the Oscars of the boat world in the powerboat class.
Unlike many other designers at the show, who were displaying prototypes, these boats are in production and on the water around the world from California to Sweden. Candela’s story starts back in 2014, when founder and CEO Gustav Hasselskog calculated that his 28ft power boat (8.5m, but boats are usually measured in feet) used 15 times more fuel than a car for an equivalent distance travelled. Much of that fuel is used to push the hull through a medium that is 700 times more resistive than air – water. Huge energy-efficiency gains can be made by lifting the hull out of the water on hydrofoils, freeing the boat from drag. That is exactly what Hasselskog and his team of engineers set out to do. These flying boats consume a remarkable 80 per cent less energy than conventional boats and are up to 90 per cent less expensive to run. A 100km journey that would cost €250 in fuel in a conventional internal combustion engine-powered 28ft boat, becomes almost free, costing around €20to charge the battery. As Hasselskog says: “We felt that conventional electric boat designs were always going to be extremely range-limited by the use of standard hulls and electric motors, which is why we went for a hydrofoiling catamaran design initially. This reduces the water friction by 80 per cent: 80 per cent less energy, and 80 per cent less resistance... 80 per cent is a crazy number.”
The first production day-cruiser model was released in 2019, with the latest, the C-8, launched in January 2023. Essentially, Candela has come up with an entirely new class of boat. Not content with a complete hull redesign, the hydrofoils are also novel, being controlled by a group of sensors (again designed in-house). Six height sensors around the hull point downwards from the bow and out in front of the boat to create a constantly updated 3D image of the waves and sea surface. Data from these key proprietary height sensors are combined with signals from the boat’s IMU (an inertial measurement unit with a gyro and accelerometer) and a GPS signal, and are fed to the boat’s flight controller, the onboard computer that calculates the optimal angle of attack and twist of the hydrofoil surfaces in order to perfectly balance the boat as it moves through the water.
Twisting the hydrofoil is how Candela controls the roll of the boat. This is similar to the way that the flaps and ailerons on an aircraft wing work, except that the whole hydrofoil wing can be twisted. All of this happens 100 times a second and is what the designer calls active stabilisation. Five years in development, assisted by calculating the computer fluid dynamics in a University of Barcelona supercomputer simulator, the software can rotate and even twist the leading surface of the hydrofoil. One of the hardest things to achieve in the software development phase was compensation for data spikes in the different sensors, especially in steep banking turns.
Being raised on the hydrofoils, the hull is not slamming into the waves and is actively stabilised. The propulsion pod is completely submerged, and no powerful outboard motors are revving and belching gasoline fumes, so the ride is silent. There is an additional bonus for reluctant boaters – the Candela appears to offer a seasickness-free experience.
The boat hulls at Candela are designed in carbon fibre by an ex-aircraft and military helicopter design engineer for maximum aerodynamic efficiency. The hydrofoils can be retracted up into the hull resulting in a draught of less than 2ft (61cm), making the boat practical in the shallows, when mooring, or when transferring to trailers. The eight-seater C-8 is a monohull, has a cabin that sleeps four, reaches a top speed of 30 knots (56km/h) and can cruise at 20 knots for two hours with a range of over 50 nautical miles on a single charge.
Candela has partnered with Swedish luxury electric car designer Polestar to supply the batteries and charging systems for the sleek flying boats. High-capacity automotive batteries are far more cost-effective than sourcing from niche suppliers of marine batteries, one element that has prevented electric boats in general from becoming competitive with their diesel and petrol-fuelled counterparts. Fast charging technology means that recharging the battery takes two hours.
Not content with redesigning the hull and the hydrofoil, the team of engineers at Candela set to work on developing a new electric-powered propulsion mechanism. Down to the nuts and bolts, all components of the C-POD have been designed from the ground up for maximum efficiency and low drag. The direct-drive electric pod motor has no gears, no need for oil changes and no energy losses, resulting in a 99.5 per cent transmission efficiency powering the contra-rotating propellers, which produce enough power to make a 28ft, 1,750kg boat plus a load of eight passengers fly along at 30 knots. Candela claims that this is the most efficient boat motor ever built. The pod itself is implausibly tiny. The diameter of the C-POD is a mere 10.5cm and consumes 75kW on take-off, settling down to a steady 50kW when the boat hull is up and flying on its hydrofoil. A similar-sized combustion boat uses around 600kW to achieve the same speed.
There is also a big win in terms of the servicing needs and costs. Where a standard commercial outboard requires servicing every year at a cost of a €1,000 or so, regardless of the number of hours in use, the pod-driven E-boat system has a drivetrain that can go for 3,000 hours of operation without intervention. Because it is a direct-drive system, there is no gear box or transmission, no oil changes, no filters, and no cooling system, as all of the heat generated is conducted away from the shell into the water. The only checks needed are on exposed wiring, which can be protected with regular cleaning after use.
As if that’s not enough, these flying boats also produce almost no wake, about 5cm, which is very important in environmentally sensitive areas, where banks, foundations or canal sides are prone to erosion, and where sensitive seagrass meadows and other habitats, as well as their fish populations, can be disturbed. Initial sea trials of a 30-passenger P-12 shuttle will start this summer in Sweden – with the Region of Stockholm beginning a nine-month trial in April 2024 – and will halve the commuter time between the suburb of Ekero and the city centre. At a cost per passenger-mile less than 10 per cent that of a comparable diesel ferry, the P-12 shuttle is already attracting a lot of interest from harbour and river cities around the world keen to reduce emissions, and get city commuters out of their cars. A design for an eight-passenger taxi vessel is in the works and it is unlikely to be too long before vessels like these are deployed in sensitive areas such as the canals of Venice, a city whose very foundations are threatened by the plague of boat wakes.
Hasselskog says: “It’s a far superior experience to old-school hulls with combustion engines. Boaters no longer must contend with vomit-inducing pitching and slamming, or the deafening roar from revving outboard engines. Once you’ve experienced flying above the surface in absolute silence, it’s hard to go back.”
Could methanol be a practical alternative fuel?
Container shipping giant Maersk has a target of decarbonisation of its shipping business by 2040 and has placed major bets on methanol as a fuel in dual-fuel engines, capable of running on very low sulphur fuel oil or methanol. Maersk has 19 green methanol container vessels on order and has secured contracts to supply the vessels with methanol. This is a pragmatic choice, as Maersk says: “Green methanol is the only market-ready and scalable solution available to shipping today.”
It is inevitable that as the infrastructure to support methanol extends in the commercial ports, that this will, in time, trickle down to the leisure boating community.
Naval architect Chartwell Marine in Southampton has been awarded a £320,000 smart grant from Innovate UK to develop and test the feasibility of a market first, a methanol-fuelled vessel design that would fit applications in the offshore wind and commercial workboat arenas, as well as the leisure sector. Biomass-produced methanol would have a near zero-carbon production footprint, and offers a practical alternative for long-distance offshore use. It is 50 per cent less energy-dense than diesel, but can be used as feedstock into a reformer which splits the methanol into CO2 and hydrogen, before feeding the hydrogen into a fuel cell to produce the propulsive energy.
The use of methanol and a reformer means that there is no need to store hydrogen under pressure to supply a fuel cell. Methanol reformers are available commercially but are largely untested in the marine environment, and have not been tested in the leisure marine industry at all.
The company is in discussions for the funding of a prototype and hopes to have vessels in commercial operation by 2025.
At the show
Many boat builders had hybrid craft on display, mostly twin-hulled catamarans to maximise the area available to mount panels on the outer roof and roof deck space. These hybrids use solar power to drive an electric motor and store excess energy in batteries, but all have a diesel-fuelled backup generator.
The best example was from Silent Yachts of Europe, based in Mallorca, Spain. E&T spoke to Dr Stephan Kress, its chief innovation officer. Silent Yachts was launching its Silent 120, which, at almost 40m, was one of the largest hybrids on show, complete with helipad, and can be yours for around €25m. Kress said: “Energy is primarily generated from the solar array, supplemented by the backup generator. Energy is stored in the battery pack, which runs the electric motor and the ‘hotel’ loads: air conditioners, desalination plant, fridges and so on.”
The Silent 120 can generate 40kWp of solar power, has a battery capacity of 640kWh, powering 2 x 720kW electric engines. In the sunny Mediterranean, the solar panels will produce enough energy for a 38 nautical mile cruise at a leisurely 6 knots.
The company has embraced the circular economy, with every element on the boat upgradeable and recyclable. The exception is the core hull design, which cannot be changed or retrofitted. The first Silent 120 is being built in Turkey. Six of the smaller Silent 60 are already in the water, and a test drive is available to would-be buyers.
The electric boating revolution has not left the world of sailing yachts behind. One of the interesting benefits of electric propulsion is the ability to motor-sail in very light winds, when very little power may be needed to add a couple of knots of boat speed. Just a little extra forward propulsion helps build apparent wind, so if the wind direction is suitable, a small amount of electric power will silently boost boat speed from three to five knots.
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