I finally got this done and decided to bring a guide up for everybody who has problems with it. It's pretty easy if you first know hot it works. At first I'd say play trough the game and maybe you will find them all over the time. BUT if not, you have to search them. What i did was the following: I sailed once around the map until i found somtethin. If you can't find anything, quit out to the main menu and go into the MP. You just have to be in the Menu of the Mp. No need to play a game. And then start the Sp again. If you find something now, THEN STAY IN THIS SESSION, BECAUSE THERE YOU'LL FIND THEM ALL! So, now you just have to use this little map here and search for them. :) White Wales and Convois shouldn't be a problem. :) And a few things for the social Chest:
1. You have to go on the land to be safe that it is or is not there
2. Some of them are in Caves and others underwater
3. The Trophy only popped for me once i opened the chest. (I don't know if it's necessary.)
And here is the Map:
If you still have any questions, feel free to ask me. I know how much this Trophy sucks.
And if i forgot something, let me know!