Bazaki wrote:About the outboardmotor, the Torqeedo 4.0 can deliver 4.0KW continuous, has that something to do with the gearing reduction inside so the motor has a lower resistance winding ?
Yes. it's current that heats motors up, and current is directly proportional to torque. Power is proportional to torque x rpm, so if you keep the torque (and hence current) constant and increase rpm you increase power. If you take a motor that is OK for 30 A continuous without overheating and double the voltage, you will roughly get double the power and a similar amount of heat. This is a bit of a crude approximation, because if you increase rpm enough then other losses start to make the motor get hot, but it's good enough to try and explain the principle.
The torqeedo uses a small outrunner running at high rpm and a planetary gearbox to get the prop speed down. This allows the motor to spin fast and produce a lot of power without cooking. There's more on this topic in the later posts in this thread: viewtopic.php?f=39&t=38897
