[derstosstrupp]

For what it’s worth, in reality, the lowest RPMs did not mean the most silent speed. Somebody should mod it if they haven’t done so already to make it so say 100 RPM or slightly higher is more quiet. That would be more in line with reality.

It comes down to 2 factors: resonance, and the motor fields. For the first, every component, even of a U-boat, has a resonance . Just like an old truck, sometimes the bumper rattled at slow speed, until you reach a certain speed where the rattling of the bumper ceased, only to start again at a little higher speed. Every boat went through listening tests as part of its workup. And almost without exception, from the data I have seen, the quietest RPM is typically at 100 or just above 100. The other factor that contributes to this is that in order to achieve a very low RPM like 50 or 55, the motor fields need to be at full excitation, and they get very hot. Per the E-motor manual, in order to run like that for any extended period of time required the motors’ blowers to be on to cool them, and that made noise. So these are all factors as to why slow RPM does not mean the most silent operation. Hopefully somebody can take that into consideration if they are trying to create a new mod or modify an existing one.