From Germany and Austria you should take the Tauern motorway through the tunnel of Karawanke to Ljubljana.
From Ljubljana take the motorway via Postojna/Koper und take the exit which has Rijeka signposted. After the exit follow for approximately 60km the signs to Rijeka.
In Rijeka go to the ferry port and take the ferry towards Stari Grad which is on the island of Hvar.

- Marko Polo
In Rijeka take the car ferry to Stari Grad. This ferry leaves in the evening and takes the route along the beautiful adriatic coast line through the night to Split and then to Stari Grad.
The ferry should be arranged early enough in your local travel agency. It is recommendable to make a booking for your car and a cabin.
Ferry planner Rijeka-Stari Grad
http://www.jadrolinija.hr