It's a longstanding naval tradition for new ships to be sponsored by a civilian -- typically a woman. With this honorific title, the cruise ship godmother is selected to bring good luck and protection to the vessel. The duties are simple; godmothers attend their ship's ceremonial ship launch and naming ceremony, where they bless and officially name the ship. In past years, they would crack a bottle of Champagne on the hull of a new ship for good luck. Today, due to sheer size and logistics, that usually means the godmother pushes a button or pulls a lever that triggers a bottle of bubbly to swing down and crash on the bow.
Naming a cruise ship godmother is also a great way to get publicity and build excitement for a new-build. Hence the tradition of celebrities; Kristin Chenoweth is godmother of Royal Caribbean's Quantum of the Seas, and Princess Cruises was honored to have Catherine, Duchess of Cambridge, agree to be godmother for the aptly named Royal Princess. And it's not just a sole woman who acts as godmother these days; Pitbull (a man) christened Norwegian Cruise Line's Norwegian Escape, while The Rockettes troupe shared the ceremonial title for Norwegian Breakaway.