This achievement requires you to thoroughly scour the ship for reading material and audiographs every time you show up. There are a lot the first time you end up on the ship, but there will be a few new ones (with the old ones disappearing) each time you end up back on the ship, so explore every time you end up on it. Before the final mission (when you assault Dunwall Tower), you also have to pickpocket Meagan's key and use it to unlock her cabin in order to read the last journal.