First of all sorry for being late in my answer but I am still on holidays till August 24.
Regarding your question about low season ferry schedule for 2010 I must say it’s too early to give you the precise answer. The low season ends on June 1.2010. Comparing the timetable of 2009, the differences will be minimum or the same as this year. During low season the coastal ferry from Rijeka to Dubrovnik, via Split, Stari Grad (Hvar island) and Korcula , runs only three times a week. If you are planning to start from Split to Hvar, you shouldn’t be worried too much because you have local ferries from Split port to Hvar (town) and to Stari Grad (Hvar island). The second one is very frequent (from three to five times a day). Once you get to Hvar or Stari Grad you can easily plan your trip by coastal ferry from Hvar to Korcula. After a few days to Korcula you have another one from Korcula to Dubrovnik. For your sake I suggest you to contact Jadrolinija website
(the only Croatian ferry company). They will update 2010 ferry timetable by the end of 2009, but you can contact me any time you need help. I will be happy to provide you with right information.
Best regards and once again, sorry for lata answer.