Also, what is the maintenance like on these? When I was in the Navy we had huge crews to conduct routine maintenance but on cargo ships, there tend to be small numbers.
Love this - what a cool idea!
Container vessels are designed to sail at a very specific draught. The bulbous bows on most container vessels are fine tuned hydrodynamic shapes that impact ths wave patterns that ships generate. Sailing at a different draught because you're adding ballast will greatly decrease fuel efficiency. Additionally any added draught also increases the amount of water you have to displace, so again decreasing fuel efficiency.
Further more, I highly doubt regulations would permiss this. I'd have to dive in IMO statues to verify, but imagine because of any event the rolling moment from the sails decreases in a short amount of time. Now the vessel has the same instability that you initially tried to offset, just caused by your own ballast.
I'd be interested to hear what your thoughts are on these issues. Non the less, very interesting ideas