Girl at Sea by Maureen Johnson

Sometimes you have to get lost . . .
The Girl: Clio Ford, seventeen, wants to spend the summer smooching her art-store crush, not stuck on a boat in the Mediterranean. At least she'll get a killer tan.
The Mission: Survive her father's crazy antics. Oh, and also find some missing underwater treasure that could unlock the secrets of civilization.
The Crew: Dad's wacky best friend Martin, his bizarre research partner Julia, her voluptuous daughter Elsa . . . and then there's Aidan, Julia's incredibly attractive, incredibly arrogant assistant.
What's going on behind Aidan's intellectual, intensely green eyes, anyway?
As Clio sails into uncharted territory she unveils secrets that have the power to change history. But her most surprising discovery is that there's something deeper and more cryptic than the sea-her own heart.
. . . to find what you're looking for