ponytug
Super Member
There are definitely tie downs. Lots and lots of them.How do those containers stay on the ship, especially in rough seas? They seem to be stacked pretty high, and at least from any pictures I've seen there don't seem to be any sort of tie-downs.
https://theloadstar.com/wp-content/uploads/lashing.jpg

Time for IMO to tie down the rules on how to secure containers on ever-larger ships - The Loadstar
With the debate on container weight verification concluded, attention has now turned to container lashing for the next steps in safety

Containers lost overboard are a significant hazard to other vessels, and a great deal of effort goes into preventing it, starting with the manufacture of the containers themselves. Oftentimes, the cause is poor seamanship in not checking the tie downs, but sometimes the cargo itself weakens the container (acids, fire, etc.).
If you are interested, Maersk did a nice series on life on a containerized cargo ship that gives a sense of the pace and challenges. (YouTube).
All the best,
Peter