Can cargo ships with empty containers actually sail back? In the past we shipped tons of alfalfa to China, partially because meat (and thus cow feed) is worth more in China, but I was under the impression that the main purpose was ballast for the ships because they can't sail without enough weight in them and alfalfa was the cheapest bulk weight they could source.
Completely empty with no cargo? The ship itself is designed to be stable under nominal conditions. Also, remember that fuel is heavy and part of the load & balance equation. Carrying empty containers or with minimal cargo, or depending on cargo distribution, ballast tanks can be filled to get the center of gravity in the right place.
