This is accomplished using the sniper rifle (Jaeger-7) (Paris Mastery Level 5 Unlock). Place it in the stash in the ICA Safe house (and preferably start from there). Sneak near the Shore and shoot the Bells on the Ship (in the order shown) to unlock the Achievement. [click image to enlarge]
(1) halfway up the Mizzen mast (left most sail).
(2) very front of the boat (end of forstay for jib sail).
(3) top of the Main (middle) sail.
(4) the forward side of the cabin.
See solution video here:
TrueAchievements credit - King fiShiZ