I have never had men get tired in repair work - even when my U-boat was going down to the bottom of a 100 meter deep sea floor stern first because of flooding. But I have had repair men almost die from exhaustion JUST WAITING FOR REPAIR WORK.
This scheme does not provide a REAL TIME exhaustion effect. Instead it attempts to simulate a tiring effect over a week to several weeks, and merely forces a captain to take storms, battle stress, into account and makes medals have some value.
The standard fatigue engine of SH3 was simply too simple and shallow. You find that as you try to dink with it. I don't think parts of it function correctly if at all. There are times, when certain crew sections sould exhaust men to near death, and yet, they will often fail to reduce crew strength for 24 to 30 hours. Then there are other sections where men should remain strong and yet, they waste away (like in the radio room playing records) and nearly die.
SO my fix is merely a bandage to insure that while men tire (generally) over 10 days of constant action, the critical operations of the boat can be used to return home. Because I have never read any account of a sub or u-boat that was dead in the water cause men lost sleep.