How many ships are in a fleet?

12 and a half

There is no specific set number of ships in a fleet. It may involve anywhere between four and several dozen, but it always takes a group operating under a single command.

Cabral had thirteen ships under his command, with over 1500 people working on them.

13

There are currently 21. Their website lists 22 but Independence of the Seas will not go into service until next year.