I don't remember having a problem with finding the key. And gosh I'm trying to recall which ship I had to sink, but there's been so many things are starting to blur lol If you had to capture, it would say flagship. But I think you only have to capture/board when looking for people. I dont remember having to board when I've been looking for items.
Also, you might want to join this group for hints to help you through the game
http://www.piratesonlineforums.com/f...ead.php?t=1444