This service is run by Adriatica which is now a division of Tirrenia. The English-language pages on Tirrenia's website have not yet been updated to show Adriatica's services, but the information is in Italian on <a href="http://www.tirrenia.it/LineeOrariTariffe/Istria.asp. The vessel is the Marconi, a fast craft carrying passengers only, and leaves Trieste at 8am every day except Mondays for Rovinj ('Rovigno' in Italian).
Geoff Hamer