Superior propulsive power and overall efficiency don’t just fall out of the sky.
They come from focused development, the use of the latest technology and from the uncompromising and systematic optimisation of all drive components.
And they are the result of carefully matching all components with each other.
Torqeedo has always concentrated on brushless, electronically commutated motors from its earliest beginnings in 2005. With conventional electric motors, the rotor is placed on the inside and the stator on the outside of the motor. The magnets are located in the interior of the motor while the coils that create the alternating field are located on the exterior. The magnetic field where the torsional moment is generated is typically situated far within. This tends to give motors constructed like this a lack of torque.
At Torqeedo we use external rotors, with the stator and the coils located on the inside, allowing the magnets to rotate – on a kind of bell – around the stator. This method of construction produces greater torque since the field in which the torque is produced is further out – up to twice as great as in conventional motor designs. Since there is more space on the outside than the inside, twice as many magnets can be used in this type of motor design, again doubling the torsional moment. And by using rare-earth magnets, which have about 5 to 6 times the strength of regular hexaferrites, we obtain even greater torque. All in all, Torqeedo outboards deliver torque that is up to 20 times higher than conventional electric motors – an advantage from which the propeller in particular benefits.
Incidentally, the types of motor used by Torqeedo are commonly called "torque motors" owing to their high torque. We took our company name from the terms "torque motors" and "speed" as we were the first people to use this technology in the boat industry back in 2005.
The alternating field required for electric motors to operate is traditionally switched using sliding contacts or brushes. Since 2005 Torqeedo motors have created the alternating current they need to run via contactless electronic digital switching. Integrated into the drive system, it switches the current flow through the coils 35,000 times a second. The advantage of this method is that the offset angle of the alternating field adapts exactly to match load and speed and is thus more efficient. And because there are no brushes, there is no friction loss. And of course no maintenance that brushes constantly require.
A number of other manufacturers of electric drive systems for boats now also offer brushless motors. They typically use standard power electronics that can be used for a large number of motors to power different machinery. The power electronics for Torqeedo motors are always tailor-made for our drive systems, providing maximum performance and efficiency and optimum fit in the space available for the drive.
Besides benefits in terms of efficiency and space, tailor-made electronics also allow special intelligent solutions for marine drive systems. For example at low power, our power electronics are speed-controlled, enabling slow, inch-perfect manoeuvring. In other cases, the electronics are controlled by power consumption, giving very light boats higher final speeds. Moreover, the intelligent control logic allows the control of the motor to be independently adapted to the use of alternative propellers in order to optimise speed or thrust, depending on the application.
Since propellers are run most efficiently if they turn with high torque at low rotational speed, Torqeedo motors always use gears for transmission.
Planetary gears from the tooling industry are typically used. They feature prime quality, like our motors they come from German precision manufacturing and they feature service lives up to 50,000 hours.
According to conventional wisdom, there are three main characteristics of efficient propellers:
In other words, motors with high torque can work efficient propellers, motors with low torque can't. This is where our high-torque motors can make the most of their advantages and drive efficient propellers very effectively.
But it is not just maximum torque that enables a motor to drive efficient propellers. There should be as few differences as possible between the highest and lowest points on a motor's torque curve in order to be able to operate efficient propellers. The greater the differences are on the torque curve, the closer the design of the propeller must follow the weakest point – with the consequence that an inefficient propeller must also be driven in the high-torque range. Since electric drives have an advantage over combustion motors in this respect, they can work with more efficient propeller concepts. This is particularly true for Torqeedo drives optimised for overall efficiency.
But conventional propeller optimisation is not everything. Many propellers for petrol outboards, especially in the low-power categories, share a very similar form. Torqeedo propellers look very different because they are calculated using the same methods (and, incidentally, by the same experts) that equip advanced commercial ships and submarines with optimised propeller technology. All propeller parameters – diameter, chord length, pitch, skew, rake, camber and thickness – are calculated using multidimensional propeller optimisation calculation methods. Many thousands of iterations are needed for each propeller segment.