One car ferry from the port of Gaženica and two catamarans from the old-town waterfront.
Zadar has two departure points for island boats, and they are not close together. The car ferry to Rava and Bršanj sails from Gaženica, the ferry port south-east of the centre, and is the only way to take a vehicle to Iž. Passenger catamarans leave from the quay on the old-town peninsula: one runs to Mali Iž and Veli Iž and on to Rava, the other calls at Rivanj, Sestrunj and Zverinac on the way to Božava on northern Dugi otok.
If you are going to Iž on foot, the catamaran from town is the simpler choice; bring a car and you need the Gaženica ferry. Both pages say exactly where to board and until when the off-season timetable is valid.