Hi Georgina,
I can't answer your question, but maybe you can answer mine. I'd like to to travel from Dubrovnik to Hvar Town to Split in late August / early September, but I can't seem to find very clear info on ferry schedules (especially the hydrofoils). Can you post a link? Also, if you figured out your speed question, that info would be great b/c speed is a factor for me as well.
Thanks,
John