Once it is completed, the $190-million Maersk Triple E will be the world’s largest and most efficient class of container ships. Its 1,312-foot-long, U-shaped hull will hold 18,000 containers—about 2,000 more than the next biggest ship. Whereas most container ships are propelled by a single diesel engine, the Triple E has two. But even traveling at 19 knots, it will require only half as much fuel to deliver its cargo, in part because of recovery of engine waste heat. South Korea based Daewoo Shipbuilding and Marine Engineering will complete the first 10 for Maersk by 2015.