Gary, I will venture a guess without doing the proper research work. It might be that the north flowing Gulf Stream is further from the shore in that area. Sailing south in it would slow the ship down. You got the time to check it out let me know if I am right.
Excellent answer and probably correct. Think fuel usage fighting a 3 knot current. My suggestion would be to ask one of the crew members while you were on the ship. If they don't know they could easily find out. You could also call the company who would be only too happy to answer your question.