I find the ferry schedules in Croatia very confusing. I would like to go from Split to Korcula and then from Korcula to Dubrovnik. Can anyone recommend a site that lists the schedules for car ferries? Any help would be appreciated. thanks

Though there are a few other companies that run catamarans (high speed, car free), this is the only company you need for car ferries:
http://www.jadrolinija.hr/
Though with a car, I would drive from Korcula to Dubrovnik. It is about a 4 hour drive, and the short ferry hop over to Orebic has frequent departures.

Note that the Korcula town ferry port is Domince (for getting to the mainland at Orebic). Ferries from Split arrive at Vela Luka, which is about a 30 minute drive to Korcula town.

...and there may be no car ferry at all between Korcula Island and Dubrovnik this year.
Last year, it left Korcula town Tuesday and Saturday at 2pm

Are you fully committed to using a car for this part of your trip? It could be more of a liability than an asset....

Consider whether you really need the car between Split and Dubrovnik. You could take the catamaran from Split to Korcula, then a bus from Korcula to Dubrovnik, though I think that bus leaves at the crack of dawn. Korcula Town is small and no car required unless you want to explore more of the island.