And how many rotations they are in use is dependent on how the duty hours set are they not? So up to 3 people could use the same berth technically. I’ve seen up to 3 racks of berths stacked up when we toured ships turned into museums. Even Chiefs ‘share’ quarters in duty rotation. Per Ret. SCPO hubby. Course lots of changes since he retired. And his major duties were Flight Opps.
Each division is assigned a berthing compartment. In the compartments racks are stacked three high and IIRC 12 to a cubicle roughly and on larger ships as many as 200 racks in a compartment. We did not time share racks with shipmates just the compartment and cubicle.
Whether anyone was sleeping {this happened at night so obviously many were} depends upon the divisions mission. In Engineering for example it would be rare for someone to be sleeping during the day unless on a no duty order or permission granted by a work center supervisor because the person had worked all night for special unscheduled repair etc.
In Engineering a typical day at sea could be muster on station at 0700 and working until 1800. Then at some point that evening or night the person would stand a 4 hour watch. Two 4 hour watches a day at sea was common one in the daytime one at night. On a good night a person got to stand the 1600-2000 watch and got to sleep until about 0630 next morning to start over. Watches got staggered so every few days you could do that. Some divisions operated on a 6 & 6 schedule especially snipes down in The Hole. That did not mean you'd get 6 hours sleep.
Officers berths were different they had staterooms. Junior Officers may be 6 to a room and senior officers 2 per stateroom.