Around the world without exhaust fumes

An electric motor with a permanent magnet can easily be switched into an efficient dynamo. Technically, this type is the same as the old-fashioned bicycle dynamo. The revolutions of the current electric motor (and therefore dynamo) do not have to be very high. So you don’t need a reduction box. And a slow rotating propellor is more efficient, in generation and in propulsion. But on slow rotations, the propellor must be bigger and should be designed differently to create such good efficiency.

With one button, each of the two 6.5 kW E-Tech engines can be switched into dynamos. These engines/dynamos have been chosen for several reasons. These motors are permanent magnet motors and perfectly suited as a dynamo. Five things were decisive for choosing E-Tech

• They are brushless. Just like most marine electric motors, they no longer have brushes that “drag” along the rotor. These should be replaced frequently. This applies in particular to the Sustainable Yacht, because they will run in almost all sailing hours: as a dynamo (60-70% of the time) and as a motor (10-15% of the time).
• Full liquid cooling. Not only the engine, but also the controller containing the transistors and the like is liquid cooled. Good cooling means that no power is lost to heat. This is both a gain in generation and in propulsion.
• Double thrust bearing. A thrust bearing is put in between engine and propeller and absorbs the pressure the propeller emits. This prevents the propeller from exerting its force on the motor itself. A permanent pressure on the engine would causes wear, so this is prevented. Most electric motors only have a thrust bearing on the “drive side”. But on the Sustainable Yacht the engine is usually generated and the power is usually in the other direction. The propellor does not “push”, but “pulls”. The E-Tech engine is therefore equipped with a second thrust bearing.
• Synchronous motor. A synchronous motor is ideally suited as a motor and as a dynamo. He can, as it were, “flow” into it.
• Low maximum rotation. The maximum rotations per minute can be adjusted by the factory. On the Ya the max RPM is only 1040 RPM, with a pretty high torque (Nm). Slower rotations of the prop have three advantages: more efficiency, less noise, less wear out.

However, such a motor is more expensive to purchase, so people buy the cheaper one and then use a reduction gearbox. However, due to the gear transmissions, such a reduction means resistance, so less energy to (propulsion) and from (generation) the propellor. Another advantage of the lower revolutions is that all moving parts don’t wear out. A more durable life and a higher reliability.