What is the Black Boat in Pokemon Black?

Question

At night when I go to Castelia City ther's always a Black Boat there. Does It have do anything special?

Answer 1

The black boat leads to the United Tower (Check on YouTube or Serebii for further details).

This place can be accessed AFTER E4, and can only be accessed by trading with other nations on GTS. I have already accessed the United Tower by trading with people (Not on negotiations) from England, the US and Japan.

Answer 2

If its a small boat than its team plasmas boat and it doesn't matter at all in the whole game. You can never interact with it before and after the game.