This ring motor is used in underwater vehicles and boats. In ring motors, there is no connection between rotor and stator during operation. The magnetic ring (rotor) is simply held by a magnetic field (stator). This means that a bearing is only required during the start-up phase. Since the motors are permanently exposed to humidity and salt water, conventional metal bearings cannot be used because they will corrode. For this reason, the design engineers used iglidur® polymer bearings from igus®, which do not have any problems with mechanical load either, unlike the ceramic bearings that were also tested.