The Captain. Whitman is mourning the death of Lincoln whom he (Whitman) considered the most moral of men. Whitman genuinely appreciated who Lincoln was and what he was forced to do as president. Lincoln is the Captain.
The Ship. The ship is what is left of the United States after the Civil War. It was a bloody confrontation and America is left momentarily poorer after the war was over.
The Prize was the "peaceful" reunification of the United States.
The Port was the end of the ship's journey. It is made up of people glad to see the ship returning
