According to the route plan recently announced by Hellenic Seaways it will connect Santorini with Piraeus, Rafina and Heraklion.
More specifically, starting Spring 2018, Santorini routes are as follows:
PIRAEUS-SIFNOS-IOS-SANTORINI with the Hellenic HighSpeed
From 30/3 to 30/9
– From Monday to Sunday depart from Piraeus at 07:05 and arrive in Santorini at 12:35
– Return daily by departing from Santorini at 13:15 and arriving in Piraeus at 18:45
RAFINA-MYKONOS-NAXOS-IOS-SANTORINI with the Flyingcat 4
From 30/3 to 17/4 and from 25/5 to 30/9
– From Monday to Sunday depart from Rafina 07:15 and arrive in Santorini 12:00
– Return daily by departing from Santorini at 12:15 and arriving in Rafina at 16:55
HERAKLION-SANTORINI-IOS-PAROS-MYKONOS with Highspeed 7
From 5/4 to 15/10
– Monday to Sunday with departure from Heraklion at 09:00 and arrival at Santorini at 10:45
– Return daily with departure from Santorini at 17:25 and arrival at Heraklion at 18:50