C-Pod electric drive
Candela’s revolutionary new high-power electric boat motors have an “almost unlimited service life”
Swedish electric boat manufacturer Candela has just introduced a revolutionary new electric propulsion unit known as the C-Pod for its electric boats, and it is a masterpiece of engineering.
Candela claims that these are the most efficient and longest-lasting boat engines of all time.
The C-Pod consists of two electric motors. Each drives a propeller that rotates in the opposite direction to provide a combined power of 50 kW (67 hp) per module.
That high power comes despite the drive unit being an ultra-compact torpedo-shaped design and weighing just 50 kg (110 lb).
In addition, the C-Pod was designed to have “almost unlimited life”, thanks to the design’s long maintenance interval of 3,000 hours and the lack of oil changes or other major maintenance. For a typical recreational user, that translates to years of maintenance-free use. Or as Candela CEO Gustav Hasselskog put it:
For the average recreational boat user, this means that you can use the engine and forget about the usual hassles with servicing and winterizing. The C-Pod will outlast you and probably your kids too.
Candela not only designed the C-Pod to be an improvement over gasoline and diesel outboards, but he also designed it to outperform traditional electric outboards.
The engines of fossil fuel powered boats are notoriously noisy, but even electric outboards have an audible hum that comes from the link that transfers power to a submerged propeller. Candela’s C-Pod is essentially silent because it lacks gears or other linkages and the entire unit is submerged under water.
To create the new design, Candela’s engineers first had to solve several design challenges.
The first big problem was creating enough power from a thin, torpedo-shaped capsule. The power of the electric motor is not directly related to the diameter of a motor. Instead, that’s largely a function of torque. Horsepower = torque x RPM, so to maintain high horsepower the designers reduced torque with a narrower engine, but compensated for it with higher RPM.
That led to another problem: cavitation. When a propeller spins too fast, it actually creates pockets of air in the water formed by drawing a vacuum and, in effect, boiling the water locally. This kills efficiency and damages the propeller over time, so the team avoided it by using two smaller counter-rotating propellers. The smaller diameter propeller pair greatly improved efficiency and allowed higher RPMs to be used.
But to avoid creating an additional complicated link to drive two propellers from one motor, two motors with direct drive shafts were used. This also helped reduce maintenance to increase the life of the entire module and significantly increased the efficiency of the unit.
A great additional benefit with two propellers is the much lower propeller losses. A conventional single helix configuration has losses of more than 30%. About 20 to 30% is burned by rotating the water. After the propeller, the water not only flows backwards, it also circulates, a useless movement.
By putting one propeller behind another propeller and letting it run in opposite directions of rotation, the flow after the second propeller can be made completely straight. Then you end up with about 30% losses at the main propeller and only 10% at the rear, increasing overall efficiency from 70 to 80%, which translates to a 14% increase in range.
Finally, the team had to solve the problem of heat. Any electric motor can generate additional power simply by increasing the current supply. But an engine with too much power will burn out quickly without effective cooling. The elongated, streamlined shape of the capsule and its submerged design mean that the engine is cooled by a large volume of water that spends a lot of time in contact with the sides of the engine. That allows the C-Pod’s motors to run at higher power levels than electric outboard motors that don’t have the advantage of constant water cooling.
The 50 kW engines are very efficient, but are made even more so on Candela ships due to their hydrofoil design. Candela’s 12-person, 28-foot (8.5-meter) P-12 hydrofoil water taxi can use a single C-Pod to reach 30 knots (34.5 mph or 56 km / h). The largest shuttle ferry in Candela for 30 people, the P-30, would require two C-Pods to reach that speed.
When flying over water, they use 80% less energy than a typical boat hovering on the surface of the water.
This is not only a big step up from fossil fuel engines, thanks to the lack of exhaust and much longer maintenance cycles, it is also a big step up from current electric motor technology for boats.
Literally silent operation means you can be traveling fast to
high speed without hearing anything but the sound of water hitting the hull. And in the case of Candela’s flying hydrofoils, you would hear almost nothing at all.