There are big catamarans from most of the port cities that go out on routes dropping people off on different islands. Most are daily in the summer, but only once or twice a week in the off season. Last week I flew a morning flight into Rijeka with time to catch the 5pm catamaran to Susak, then left by taking an 8:30am to Zadar, leaving me time to get to the airport for an afternoon flight to Munich. I also took a short catamaran ride over to Mali Losinj for a morning of seeing different island one day. There are 2 main companies that operate them. I think the common port cities are Pula, Rijeka, Zadar, Split, and Dubrovnik - depending on which island you are trying to get to. They have a new one from Rijeka this year and it doesn't have a bar! https://www.jadrolinija.hr/hr/schedule/ScheduleSearchResults/Index/2331783/2331799/16072023 https://www.krilo.hr/plovidbeni-red/pula-unije-susak-mali_losinj-ilovik-silba-zadar/#