Just did this day trip 2 weeks ago. If more than one traveller you save a few euros using the OBB Einfahrt Raus day ticket over the Combi ticket. Show the Einfahrt Raus ticket to get a 20% discount on the boat tickets. We got off the boat in Dürnstein, the bus to Krems runs hourly at 24 min past the hour, but the bus was a few minutes late and lost more time getting to Krems so we just missed the train to Vienna and had to wait an hour. There are 2 bus stops around Dürnstein at each end of the town. Franz Josef station is connected to at least 3 tram routes, including the D tram which takes you to the Ring, stopping by the Hilton Plaza, otherwise the 2 stations prior to Franz Josef are connected to the U Bahn.

Well worth the trip, very scenic, Monastery was very nice too and it has a good restaurant with reasonable prices.

Bus was 2.20 per person, the lady at the boat ticket office knew the bus schedule which was also posted at the bus stop.