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Candela Seven Candela Seven © Kerstin Zillmer
Boat test Candela Seven

The remarkable story of electric Candela

Longer range, higher speed and a silk smooth ride. This is how the Swedish foiling Candela Seven is changing electric boating.

Kerstin Zillmer
9 Minuten

Candela makes other boats look old: The Candela Seven is the first day cruiser that can fly. The development of the first electric foiling motorboat Candela was far from hassle free. But now it flies farther, smoother and faster than traditional e-boats. In November 2019, it won the Best of Boats Award for the most innovative boat in the category Best for Future.

Gustav Hasselskog made it: After studying mechanical engineering in Stockholm and Munich, the swedish engineer managed a chemical company. But Hasselskog is a wandering spirit, waiting for a “real“ challenge. Another hefty bill after refuelling the boat on the way to the summer cottage brought enlightenment: He wanted to make boating more energy-efficient. Hasselskog wanted to develop something technologically new, something that would also advance the world.

Candela Seven
The visionary Gustav Hasselskog © Candela

From hull to propulsion: an energy-saving boat must be light and have low frictional resistance. Since the 1960s, hulls made of glassfiber have become the standard. Although they are usually lighter than wooden hulls, they still require powerful combustion engines. In order to build an energy-efficient boat, you have to use other, lighter materials. Carbon, for example.

Water resistance absorbs energy

There is still the water resistance to beat. To drive a boat which is seven or eight meters long, you need about 15 times as much gasoline as a car. The reason for this is the water resistance. The power needed for propulsion can only be reduced if the hull comes out of the water.

Candela Seven
The hull has no more water resistance when foiling © Candela

Hydrofoil boats implement this principle: At a certain speed, the hull lifts out of the water, then the boat only moves on hydro-foils. Of course foils have a dramatically lower water resistance and this leads to significantly lower energy consumption.

If this is combined with an electric drive, the energy saving effect is even higher. Electric motors pass on almost 90 percent of the energy used, while a combustion engine converts only about 25 percent of the thermal energy into mechanical energy.

Candela Seven
Usually invisible: the 55 kW electric motor from Torqeedo © Kerstin Zillmer

Hasselskog gave himself a year’s time

By 2014, Gustav Hasselskog had progressed so far with his development that he made a decision: he resigned, sold his summer house and gave himself a year’s time. Time to search for the right people: some with knowledge, for example on hydrofoiling, and some with money to finance his idea.

The Swedish online magazine Hamnen was a stroke of luck for him: when the journalists published an article about the engineer’s plans, a private investor contacted him. The man was so enthusiastic about Hasselskog’s concept of the Candela Speed boat that the financing of the project was now secured. Gustav Hasselskog started the first project phase in 2015.

New knowledge needed

The inventor found support all over Europe: He talked to hundreds of experts. In the meantime, know-how from twelve countries has flowed into his project. The Candela team includes experts from the fields of composite materials, engineering, control electronics in combat jets, America’s Cup hydrodynamics, truck transmissions and hydraulics, dynamic modelling and drone control software.

The accumulated knowledge went into the development of the first prototype that Hasselskog’s team launched in August 2016. Seven months later, in the experimental phase, they were ready for the pre Candela boat to take off.

Candela Seven
The foils work like aircraft wings © Kerstin Zillmer

The hydrofoil technology in the water works similar to an airplane flying: The system of the Candela Speed Boat consists of large “inverted π foils” close to the center of gravity, which stays under water during the ride, and a smaller T foil at the stern, directly at the propulsion in front of the propeller. In interaction, they lift the boat out of the water. Both foils are controlled electronically.

Motorboats must be stable while turning

The V foils, which are known from  quadrofoilers of the fast Imocas and Sea Bubbles, work differently. the SeaAir-System, tested by float, also uses V foils. With this system, cornering stability is a problem, and the autostabilized foils cannot compensate for high waves. That’s why the Candela team chose T Foils and the electronic solution. Because a fast motorboat has to be particularly stable on turns and waves.

Candela Seven
In the cross-section the Candela foil looks like an aircraft wing © Kerstin Zillmer

The wing, which is the supporting foil, is mounted on two spars. The angle of the foil is permanently electronically adjusted so that the boat is horizontally stable, moves smoothly in wakes and leans natural while banking. At the wing, which is formed like an airplane wing in cross section, an overpressure develops at the underside, at the upper side a negative pressure.

The thrust of the propeller gives the candela 13 to 14 times more lift than resistance. 100 kg of propeller power will easily make the 1.3 tonne fuselage of the Candela float. With a glider it is only 3-4 kg lift per kilogram of drag, i.e. 300-400 kg.

100 times per second

The big challenge is to calculate the position of the foils (and thus of the hull) accurately and in a flash, so that they keep the boat stable outside the water and the hull does not buckle in turns or waves.

The solution is a state-of-the-art sensor system that calculates all water movements and provides this information to the control of the foils.

Candela Seven
Six pairs of sensors permanently calculate the position of the foil © Kerstin Zillmer

Two ultrasonic sensors measure the height of the wave at the bow, accelerometric sensors the acceleration, gyro sensors measure the heel, a GPS the speed, hygrometer the height differences. All data is evaluated with a self-developed software. Mathematically it is determined where the boat is located in space, at what angle it does this, with what acceleration and what speed at how much wave.

Service management via the cloud

This flood of data is recalculated 100 times per second. In this way, the software can permanently predict how the boat will behave in the next moment under the given conditions, as known from space technology.

The position of the wings is also calculated 100 times per second. Of course there was no ready-made software for this technique, it had to be written first. The printed circuit boards are also manufactured in-house at Candela. For service management, the boat is connected to a cloud, data download is also possible.

Candela Seven
Heckfoil mit Getriebe © Kerstin Zillmer
Candela Seven
Candela PCBs © Kerstin Zillmer

The mechanics make the difference

But there is more innovative technology in the candela: It is essential how the data is forwarded to the respective foil and how the foil is then directed. Together with his experts, Hasselskog has developed a mechanical wing connection that works as a coupling between the spars and the wing. This was very complicated to construct because the joints had to be able to move permanently in all directions.

The next big challenge was the drive unit. For the optimal hydrodynamic design, the correct weight had to be calculated in proportion to the drive and the wing. The transmission had to be very small to make the whole drive lighter and more efficient. The team managed to develop a gearbox with an extremely small diameter of only 83 mm to keep the drag as low as possible.

Candela Seven
The extended shaft with the self-developed motor housing © Candela

Since the shaft to which the rear foil is attached must be longer than a conventional electric outboard, Hasselskog and his crew also had to develop the engine casing and the shaft itself. The shaft with the mounted T- wing must be as flexible as the front wing. The right angle of inclination is essential to lift the boat out of the water.

Candela for everybody

Hasselskog’s goal is to achieve very high wave stability. The engineer believes it is possible and not too complicated to ride through four to five metre high waves on foils. His mathematics expert from India is already working on learning systems to predict wave movements. Future technologies will quickly bring better solutions.

The most important thing for Gustav Hasselskog is to be able to build a cheap candela in the future. All the technologies used are still very expensive and the materials are also quite expensive. In order to really save energy over a wide area, the boat must become cheaper, otherwise it will only be a toy for rich people, says the inventor. It’s like Tesla’s electric car, the „early adopters“ made it possible for many people to buy it today. The Swede would also like this for the Candela, whose name derives from the physical unit for luminous intensity.

Candela Seven
Many people should be able to afford a candela in the future © Kerstin Zillmer

Float above the water

But how does the first foil-end motorboat drive? We drive from the shipyard on Lidingö before Stockholm to the nearby harbour, where the Candela is located at the jetty. It is a late autumn day, grey are the water and the sky, only on the shore the trees shine.

In the water, the bowrider looks like a normal small motorboat. Gustav Hasselskog and Alexander, his marketing man, step over with me. It is striking how stable the 7.70 m long boat lies in the water and does not bend when the three of us are standing on one side. The foils, which are at a depth of 1.30 meters across the hull, stabilize the boat.

Before setting sail Alexander and I pull the plug, start the electrical system of Torqeedo and set sail quietly. On the large display all essential data are clearly readable: consumption, speed, range and the inclination angle of the boat. Under our feet lies the large BMWi-3 battery in the center of gravity, the boat is built around it, so to speak. The Bowrider has two benches in the bow, four chairs in the cockpit and a bench in the stern.

  • Candela SevenMuch space is available on the six-person Bowrider © Kerstin Zillmer
  • Candela SevenLarge display and clear steering position © Kerstin Zillmer
  • Candela SevenThe light seats are comfortable and weight-saving © Kerstin Zillmer
  • Candela SevenThe place for the BMWi3 Bstterie © Kerstin Zillmer
  • Candela SevenThe Deep Blue System of Torqeedo © Kerstin Zillmer
  • Candela SevenEasy to trail with raised foils © Kerstin Zillmer

Driving experience: light and quiet

The outboard motor, a Torqeedo Deep Blue with 55 kW, is located in a special chassis with very special characteristics. The shaft of the propeller is at the same time the stern foil, a fin that runs across the propeller and lifts the boat aft.

Alexander and I take off, Gustav takes the second candela for the photo shoot. Already during the manoeuvring in the harbour a high stability in the driving behaviour shows up. It feels firmer, but also a bit slower in the rudder. We accelerate slowly outside the harbour, the water is smooth, we have hardly any wind in the bay. I take over the rudder. Slowly I accelerate: Five knots, ten knots, at thirteen knots – about 24 km/h – I feel a slight jerk and the boat gently lifts itself out of the water: We film.

Below us lies about half a meter of air between the keel and the surface of the water. The sailing feeling is light and quiet. I need a bit to get used to the completely new feeling of floating. I accelerate to 20, 25 knots and find the best cruising speed at 23 to 25 knots. The boat is so stable that I can let go of the wheel and go straight ahead like an autopilot. I accelerate further to 30 knots – top speed. The stable driving feeling remains the same, only the driving noise gets louder because water splashes under the hull.

Candela Seven
The electronic system also controls cornering © Kerstin Zillmer

Up to 80 km range

I take a turn, the boat reacts a little slower than a glider hull. I draw the circle tighter. At an angle of 12 degrees, which I read from the display, the electronic system slows me down. That’s what I wanted. If the angle became steeper, the foil would come out of the water, air would interrupt the negative pressure and tilt the boat to the side. Turning is different with a foil boat. With the exercise the safety comes with the fun. It feels great to float.

A little more courageously I take the wave of a passing boat and feel hardly movement in the Candela. That is extraordinary. I test the reliability of the foil by removing the throttle. The boat gently sinks back into the water and I immediately notice the resistance, accelerate again or better thrust. The candela lifts again out of the water. This of course costs energy.

If we drive consistently energy-saving, the boat will manage 50 nautical miles, i.e. 80 kilometres with one battery charge. As a conventional boat, the Candela would only be able to cover about a quarter of the distance, and by no means as comfortably. But with the foils you float wonderfully quietly and energy-efficiently – to the summer house or much further away.

Technical data Candela Seven

Hull material: Carbon
weight: 1.300 kg
length: 7,70 m
width: 2,40 m
Draft: 0.50 m in shallow water mode, 0.40 m in foil mode, 1.20 m without foil
Passengers: 6 persons
Speed: 22 knots (cruise), maximum 30 knots
Range: 50 nautical miles at 22 knots, 8 nautical miles at 5 knots
Engine: Torqeedo Deep Blue 50 with 55 kW
Battery: Deep Blue BMW i3, 40 kWh
Charge: full charge in 12 hours at 230V/16A
Price: 245.000 Euro net

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