No fooling... The problem with electric machines is much like thermal machines like steam plants and diesel engines... they have been designed for a certain loading or most efficient point of operation. But electric machines fool you because they are pretty much just lumps of iron and copper or magnetic material and turn on an off with the flip of a switch... so that is somewhat misleading. What is interesting to me is that in this forum often I hear about generator sets running at their best efficiency at full load... as far as fuel consumption per unit output. This is herein always explained as the engine part is most efficient at that point. No that is not the case. The generator is most efficient at that point as it was designed for that point. The diesel likely is not. But the diesel is actually most efficient near its torque peak which is usually at lower rpm than rated. In fact, diesels are typically best at part load at part rpm of full rated. Now this is heavily dependent on the particular diesel. But as a typical a diesel rated at 1800-2000 rpm... might be most efficient at 1400 rpm and about 2/3rds rack. Now an example... and maybe Nilo can help here... it seems to me Moonen typically tailors the cruise speed of their displacement yachts at a point of most efficient per unit output on the diesel main engines. The problem I have in explaining this is that engine manufacturers often have several ratings for the same engine.