You can go to Iraklia by boat from the port of Piraeus through line Kithnos - Iraklia - Schinoussa - Koufonisia - Amorgos - Thira - Ios - Folegandros - Milos, and through the line Paros - Naxos - Iraklia - Schinloussa - Koufonisia - Katapola.
For more information:
PORT AUTHORITIES OF PIRAEUS 2104226000
PORT AUTHORITIES OF NAXOS 22850 22300