Once a week, after touring the Caribbean, the cruise ship Oasis of the Seas calls into its home port in Fort Lauderdale, Fla., for what is called “turnaround day.”

Just as an airplane makes money only when it is flying, keeping a cruise ship out at sea is essential for its profitability. But instead of turning over a few hundred airline passengers, this ship offloads 6,000 people, takes on new supplies and welcomes 6,000 more travelers — all in under 12 hours.

Logistics are essential on turnaround day, at once the first and last day of a cruise, and the busiest time for the ship’s 2,140 crew members. Oasis docks at about 6 a.m. and leaves by 4:30 p.m. In that time, more than 12,000 bags need to get off the ship, food must be stocked, beds made and bathrooms cleaned. Getting everything ready in time is part Nascar pit stop, part loading of Noah’s Ark.

“Embarkation day is frantic,” said Rodolfo Corrales, the ship’s provision master, whose job is to keep the vessel fully stocked for its journey. “It’s not just busy, it’s crazy busy.”