So I finally decided to finish AC4 and, having an unhealthy appetite for completing nearly every AC game with 100%, did a lot(!) of exploration before finishing the main story. I only need to find two more buried chests and defeat three more legendary ships to get to 100%, I think. But why stop there? There are only five of the Abstergo challenges left for me to do, and four of them seem pretty easy, but one of them is really annoying. I still need to find one(!) social chest to get the "Share the location of three social chests" challenge, and I haven't stumbled across one for days. Is there any reliable way to find those? I already did some research, but everybody seems to be of a different opinion about what you can do to find them, so I thought: "Why not go to the best community you know and ask there?" (ass-kissing, me? where?). Thanks in advance for (hopefully) helping me out.

I remember looking this up because I had the same problem and I found a map, on IGN I believe, and it showed the places that they will spawn on. There are also some boards with locations. Gamefaqs. Trophies (This probably won't help, but it has some similarities I think.) Image

I happened to play this on PS4 when the social stuff was broken and only recently got two of the three things I need. Still need the chest though. Good luck and I hope this helps. The locations aren't always the same though.