HELP have the same problem. I see black point, i click its external part around, hundred times, and my convoy go into city. I can only sell/buy. If i click left button on black circle i have an info about pirate cave. Black point appears there where Edinburgh town in my game. Could it be, cause i play with 40 cities moded map ?
The only way was to become a pirate, attack the city, and then, after capturing the city, I got information about the defeated pirate.