You will talk with Dock Boss last, this time he'll give you information about the ship with drugs. This ship will set sail soon. Use helicopter and fly. When you see the ship, it will be the time for several flights around to kill how many guards as you can.
After the landing you must unload three bombs. First is before you, go downstairs. Second in the loading section, third on the end of the ship. This is the hardest part of the mission, because the method is identical as extortion. During this task, use often the first aid kit and destroy the boats (to do this use cannons).
After that go upstairs and kill captain.
Come back to Miami. The rest of Nacho's gang will be waiting for you... You must go to the place, which is determined on the map by cross, so fire to everyone and go ahead.