Officer ratio (and high ranks) IS really off there. For something that small, you really wouldn't have anything higher than Lt Cmdr at most running that, I'd expect. Unless it was a dead-end job for a bad Captain.
On a Navy sub, for example, you've got around 10% officers, maybe? Something like a dozen or so out of around 150.
As for shifts, you'd be unlikely to run 12 on/12 off, as well. People have to eat, bathroom breaks, move around to not get sluggish, etc. More likely you'd have 2 teams of 7, and they'd run on 6 hour rotations. At least, suspect that's how the Navy would handle that.
And then for emergencies or heavy lifting, it's all hands on deck...