I started the quest and completed all the objectives. All I am left with is boarding the ship and returning. And this is something I cannot do. Each time I try to talk to Adelaisa to go back, the game either freezes on the loading screen or crashes to the desktop. I cannot fast travel, loading up the previous save does not work either. How can I fix this?
If you have any mods running (excluding the DLC of Dawnguard, Dragonborn and Hearthfire), disable them and try again. If that doesn't work, your save is corrupted and you will need to return to a save from before you started the quest.