I wonder how many stacks of containers are no longer viable (and how many more journeys will be needed) on vessels fitted with those two enormous sails.
It could also be feasible with tankers, gas or liquid.
I think the answer to that is to build it into a hightop container and make it the last on top of a large stack. Plug ship power into it and control from the main deck.
I don't think the physics checks out on that one.
The concept rendering made me ask the same question. I have cargo ships parked out my windows, and that's a lot of space.
You could probably mount these on top of some sort of mast so the actual sail clears the containers. You'd lose the space the columns take but that's still a lot less containers lost than the picture suggests.
The problem with using it for container ships isn't necessarily the height (although that could be a problem, as retraction for bridge clearance requirements makes mast engineering a lot harder). The problem is heeling due to the wind. We already have a fairly large problem with containers falling off of ships and being lost at sea, and this could only make it worse.
I would imagine that they thought of that!
For one, this could be used on tankers.