Hi all, I just did a little test.
I put one machinist in the diesels and filled the rest of the slots with sailors, I than put three sailors in the electrics. That means that three sailors will stay put in both compartments while the rest moves back and forth. I then ordered standard ahead and put Tc to 256. Under the next eight hours, game time, I ordered Pd and surface, up and down until the whole crew threatened to kill me
The result was this: the three sailors in the electric engines had not tired at all, the three in the diesels had tired a little and the rest, those that had moved back and forth had tired notably.
Going at surface or at Pd in really heavy seas will tire your engine crew as they keep switching enginerooms even at high tc.