Machine Design Magazine had this. But they have not yet considered a catamaran. This unit they show would need ballast water even more than present cargo ships. Ship ballast is one of the leading causes of invasive species.
And see from a few years ago a catamaran proposal. http://multihullblog.com/2012/02/catamaran-container-ship/
On the cat, displacement would be 864,000 lbs per hull. Draft 7′ and power to go hull speed 1050 hp per hull. That speed 23 knots.