[Rupert]

I can't find anything either, but considering that a small ship without an engine room has no maintenance staff and has -1 to base HT, I'd say running a ship with less maintenance crew than required would result in -1 HT to start with. I'd rule that if the shortfall was minor, the captain (or chief engineer, or even the crew as a whole) could choose between having the ship slowly get worse, or have the crew work extra time, and slowly run down. If the shortfall in crew is major, say under 50% of the expected levels (working 16 hour days), or maybe under 70% (working 12 hours days), both things would start happening.

How to represent this? HT rolls for the ship, probably with an increasing penalties as time goes on, (a failed roll means an under-maintained system is disabled) and increasing levels of FP loss for the crew (that won't go away without days off, doing nothing). How often the rolls should be made and/or FP lost depends on how robust you think a ship in this condition should be. Losing 7FP means the crew will be, overall, moving and working half as fast. Losing 10FP and they aren't working at all.