Airborn

2005 EOS mass market paperback, kenneth oppel (The Boundless). Matt Cruse is a cabin boy on the Aurora, a huge airship that sails hundreds of feet above the ocean, ferrying wealthy passengers from city to city. It is the life Matt's always wanted; convinced he's lighter than air, he imagines himself as buoyant as the hydrium gas that powers his ship. One night he meets a dying balloonist who speaks of beautiful creatures drifting through the skies. It is only after Matt meets the balloonist's granddaughter that he realizes that the man's ravings may, in fact, have been true, and that the creatures are completely real and utterly mysterious.