Candela C-POD Is the Most Efficient Boat Motor Ever Built

The Stockholm-based tech firm Candela revolutionized the nautical market and introduces the most efficient and long-lasting boat motor ever made. C-Pod consists of two electric motors. Each module drives a propeller that rotates in the opposite direction, providing a total power of 50 kilowatts (67 horsepower) for each module.

Although this drive unit is an ultra-compact torpedo-shaped design, it weighs only 50 kilograms (110 pounds) and still has very high power.

In addition, the C-Pod is designed for "almost unlimited service life" thanks to its 3000-hour maintenance interval, and no need for oil changes or other major maintenance. For a typical recreational boat user, this means years of maintenance-free use. Or, as Candela CEO Gustav Hasselskog said:

"For the leisure boat user, what is the best boat motor device that people can think of? C-Pod is electrical, almost silent without changing fossil fusel which means no maintenance need to be consider of in winter. C-Pod will live longer than you and your children, and there is almost no loss other than that------it converts most of the energy into thrust."

The C-Pod Candela only designed to improve gasoline and diesel outboard motor, but also better than the traditional design of the electric outboard motor.

The engines of fossil fuel-powered boats are very noisy, outboard engines are one of the noisiest machines. As they reached full throttle, the decibel levels rose to 90 degrees, the individual noise reaches 100 decibels, enough to damage people's ears.

But even electric outboard motors make a buzzing sound, which is caused by the connection that transmits power to the underwater propeller. Candela's C-Pod is basically silent because it has no gears or other connecting devices, and the entire device is underwater.

Several challenges must be solved for Candela’s engineers in order to create new design
The first question is how to generate enough energy from a slender torpedo-shaped "capsule". The motor power is not directly related to its diameter instead of torque function. Since, Hp = torque x rotation speed, to maintain a high horsepower engine, designers use a narrower reduced torque but with a higher speed is compensated.

It leads to another problem: cavitation. When the propeller spins too fast, it will form bubbles in the water by drawing a vacuum, which makes partial of the water boil. Over the time, it reduces efficiency and damages the propellers. To avoid this situation, they used two smaller counter-rotating propellers which improves efficiency and allows higher speeds to be used.

Apart from that, to avoid additional complexity connecting rod from a motor to drive two propellers, two motors with direct drive shaft. This also helps to reduce maintenance, increase the life of the entire module, and significantly improve the efficiency of the unit.

Another advantage of using twin propellers is that the propeller losses are much lower. The loss of the traditional single helix structure exceeds 30%. About 20% to 30% is burned by rotating water. After the propeller, the water not only flows backwards, but also circulates, which is a useless movement.

Put one propeller behind the another and let it rotate in the opposite direction to make the water flow behind the second propeller completely straight. As a result, the main propeller will lose about 30%, and the rear propeller will lose only 10%. The overall efficiency has increased from 70% to 80%, which means a 14% increase in range.

Finally, the team must solve the heat dissipation problem. If the current is increased, any motor can generate additional electrical energy. But if there is no effective cooling, the engine with too much power will burn out very quickly. The slender, streamlined shape of the "capsule" and its submerged design allows the engine cooled by a large amount of water. Due to the reason, when C-Pod's engine run at a higher power level than an electric outboard engine that does not have the advantage of continuous water cooling.

Source：Boatsfamily