The Scar — China Mieville

Aboard a vast seafaring vessel, a band of prisoners and slaves, their bodies remade into grotesque biological oddities, is being transported to a fledgling colony of New Crobuzon. They are joined by a handful of travelers, each with a reason for fleeing the city. When the ship is besieged by pirates on the Swollen Ocean, the senior officers are executed. The surviving passengers are brought to Armada, a city constructed from the hulls of stolen ships -- a floating, landless mass whose bizarre leaders harbor a sinister agenda.