What are the ships in Settlers of Catan Cities and Knights?

In "Settlers of Catan: Cities and Knights," ships are used to facilitate trade and exploration on the maritime expansion of the game. Players can build ships to connect their settlements across water, allowing for the establishment of new trade routes and access to resources from islands. Ships also play a role in the game's development by enabling players to gain resources or points through maritime trade. Additionally, the introduction of ships adds a strategic layer to the game, as players must manage their maritime routes alongside their land-based settlements.