Princess Cruises will add a third ship to its Royal Princess fleet, a 3,560-passenger vessel that will cost about $800 million, the Santa Clarita company announced on Wednesday. The 143,000-ton ship will be constructed by Fincanteri, an Italian shipbuilder based in Trieste, and is expected to set sail in 2017. The vessel will be similar in design to a pair of sister ships: Regal Princess which entered service in May and Royal Princess, introduced last year. The ship will offer multiple dining, entertainment and retail venues, including an outdoor movie theater. About 80 percent of staterooms will have balconies. “We are incredibly excited to add this fabulous new ship to our already formidable fleet,” said Jan Swartz, president of Princess Cruises, in a statement. After completing construction, scheduled to begin immediately, the vessel will add to Princess’ existing fleet of 18 ships. The Royal Princess fleet serves destinations in Europe and the Americas. Princess Cruises is a subsidiary of the world’s largest cruise ship company, Carnival Corp. & plc, based in Miami and Southhampton, U.K. Swartz said the Princess ship is the only new ship currently on order among Carnival’s cruise lines, which include Carnival, Holland America and Seabourn.