Emma Mærsk: The Largest Cargo Ship in the World. Emma Mærsk is the largest container ship ever built, and the longest one in use today. The ship's five engines weigh 2,300 ton and are capable of generating 110,000 horsepower. It has a capacity of over 11,000 containers. Links: Wikipedia entry | Photo gallery - via reddit
But Emma Mærsk wasn't the largest ship ever built. That distinction belong to Knock Nevis, a retired supertanker. Links: Wikipedia entry | Photo gallery
http://www.boatoperatorcard.ca/resources/knock-nevis-super-tankers.aspx