‘‘ THE Voice’’ will hit the ocean when John Farnham joins the swell of Australian artists signing up to perform on cruise ships. Farnham will headline Cruise’n’Groove next year. He and a string of acts will perform on a cruise ship that sails from Sydney to New Caledonia between October 9 and 17. The “music festival on water” genre has taken off in the past five years. The Farnham cruise also features John Paul Young, Pseudo Echo, Jon English and the Chantoozies.