Wiktionary
ac45
n. (context lang=en sports) a catamaran sailing racing yacht, with a wingsail mainsol, developed for the http://en.wikipedia.org/wiki/en:2013%20America's%20Cup world tour, the 2013 America's Cup pre-regatta tune-up league, called the http://en.wikipedia.org/wiki/en:America's%20Cup%20World%20Series.