Drowned Wednesday by Garth Nix

On the third day, there were pirates. Wednesday has rolled around, and Arthur Penhaligon has an invitation to return to the House that he can't refuse. Drowned Wednesday has sent a ship to pick him up from the hospital...even though his hometown is miles away from any ocean. From hospital room to the high seas, Arthur finds himself on an adventure that will pit him against pirates, storms, explosions of Nothing-laced gunpowder, and a vast beast that eats everything it encounters. Through it all, he is drawn deeper into the central mystery of the House. Arthur must find the third part of the Will and claim the Third Key - not just for himself, but for the millions (if not trillions) who will suffer if he doesn't. The first step? Surviving life aboard a ship on the Border Sea...