Swedish electric marine propulsion specialist Candela says its latest product, the C-Pod, is the most efficient electric outboard produced to date. “What would be the best boat propulsion one could imagine? Here are some ideas: electric, completely silent, without oil changes and with an almost unlimited lifetime. Add to that almost no losses – converting most of the energy to thrust,” remarked Gustav Hasselskog, Candela’s founder and CEO.
To achieve noiseless and efficient operation, Candela’s engineers have placed a pair of motors in a torpedo-shaped housing, directly linked to a pair of propellers. Careful thought had to be given to the motor design, with Candela opting to increase motor rpm rather than size, which boosted power – albeit at the expense of torque. The use of twin propellers allows for smaller units, which in turn can be spun faster without running into issues with cavitation. Furthermore, as the motors are mounted underwater, they are well cooled, allowing them to run at a higher power output without fear of overheating.
“The first obstacle toward a very small, high-power motor is heat. You can take any motor and give it three times more electricity than it is rated for. It will work. But only for a few seconds. Then it melts. With Candela C-Pod, we have almost unlimited cooling power – we just need to get heat from the coils to the surrounding water flow,” said Hasselskog.
Further benefits of the design include very low noise, due to all moving parts being below the waterline and the lack of gears in the drive system. “The Candela C-Pod has no gears and is therefore totally quiet. No rattling, no squeaking, absolutely no noise, even at 30kts,” claimed Hasselskog. Additionally, the minimal number of moving parts means maintenance requirements are far lower than on a traditional outboard, or even electric versions with geared drives, with the company specifying a 3,000-hour service interval.
Developing 50kW for take-off, the company says a single C-Pod has enough thrust to propel one of its 28ft, 12-person water taxis at a speed of 30kts. For the company’s bigger 30-person shuttle ferry, the Candela P-30, two Candela C-Pods will provide the same speed.