When the group is tying to make there way up through the ship they run into hallways that is either flooded waist deep on them or is ankle deep flooded. Problem is that they are upper decks so any deck below should have water in it. For instance the ballroom should have already been flooded when the Janitor had drowned. No matter if the ship had the watertight doors closed or not, the water would have escaped when the group went through regardless.