First there is fuel cost to run 2 additional diesel motors on separate ship and then there are port fees , docking fees licensing fees harbor fees. I bet they do save a lot. It is like the US trucking right now trying to push for heavier weight ratings trucks already max cap at 80,00lb w/o special permits. Imagine being even heavier and trying to control an articulated frame vehicle on the downhill. The people operating the equipment on a day to day basis will tell you it is foolish but the corporate leaders only see the $$$ and know if they say so some idiot will do it.