Cruise operator Carnival has ordered three new cruise ships, which will be the biggest ever built for its Costa and Aida cruise lines.Italian shipbuilder Fincantieri will construct one 132,500-ton vessel for its Costa Cruises brand.The 3,700-passenger ship is scheduled for delivery in October 2014 and tips the scales at almost twice the weight of the QE2.A memorandum of agreement has been signed with Japan's Mitsubishi Heavy Industries to build two 3,250-passenger ships for its Aida line, which are scheduled for delivery in March 2015 and March 2016.These will weigh in at 125,000-tons a piece.Carnival said the new Costa ship was expected to replace capacity from the sale of older Costa ships, beginning with the sale of Costa Marina, which will leave the fleet in November 2011. The company said that it would record a loss of on that sale of approximately $0.02 per share. Carnival is the largest cruise vacation group in the world and its brands operate 101 ships totalling approximately 200,000 berths.