Ac 2 v 47 - Thicker Than Water
0Unlocked After: Sequence 7 - Memory 1: Benvenuto
To get to your target you must first tail a gondolier, who is marked by a blue target on the map. Make your way to the gondolier and look east for an unoccupied gondola by the dock across the water. Swim out to it, hop in, grab hold of the oar and start following the gondolier
Follow the marked gondolier out to a boat. Your target is on this boat; use Eagle Vision to identify him. The water surrounding the boat and the boat itself is a restricted area during this memory, meaning the guards are on high-alert and will attack on sight. Row the gondola to the east side of the boat, just outside of the red circle on the Mini-Map, and dive into the water. Hold the A/X button to dive underwater to avoid being spotted and swim up to the side of the boat. Assassinate the patrolling guard while he's near the ledge, then climb on board and use the Hidden Blade to assassinate the target. - https://www.supercheats.com/guides/assassins-creed-ii/