The Stranded, by Sarah Daniels

The Arcadia was a luxury cruise vessel.  When the countries of Europe destroyed themselves in biological warfare, the ship (and many others like it) became an escape route for refugees.  But when the boats reach the Federated States on the other side of the Atlantic, anti-immigration forces refused to allow them to disembark.  Forty years later, the passengers and their descendants are still quarantined off the coast and the government has tired of maintaining them.  It initiates a plan to solve the issue for good by imprisoning in labor camps or massacring the inhabitants.  But the passengers won't go down quietly.  A rebellion has long been brewing to liberate the passengers and with the ships being cleared, a plan kicks into high gear.

Esther is a sixteen year-old studying to become a medic and, if she can pass her exam, win a coveted slot to study on the mainland.  She and her boyfriend Alex are loyal citizens, but they find themselves dragged into the conflict as the land forces ratchet up their suppression and start implementing their genocide. 

There is some elaborate world building but the book doesn't waste much time before diving into the thick of the action.  Told in alternating chapters by three narrators -- Esther, her older sister's boyfriend Nik (who works for the rebellion), and Hadley (the leader of the government forces charged with controlling the boat) -- it maintains a breathless pace through over 400 pages.  It's a fast read, but doesn't leave much time for sorting out the characters or for the reader to establish much attachment to them.  Rather, the story screams out "film option!" and seems designed for a visceral and visually immersive adventure.  It would probably make a great film, but as a dystopian novel it's fairly average.