I think there is an error when going from ship to port. as you can see in the image, it sometimes takes 14 move points instead of 4. I have seen this going from a ship to a dock and also from a port to a dock.
http://twitpic.com/1xyp77/full
I know it is cut off in the image but i have a minotaur in the boat. the other time i saw this i had a wizard going from a dock to a ship