Gosh, that is complicated!
I guess what I'm getting at, is, say for simplicity a ship has a three-watch rotation, 8 hours each. One from 00:00 - 08:00, another from 08:00 - 16:00, the other from 16:00 - 00:00, and the ship has a crew of say, 1,800.
Would there be 600 personnel on each shift...