Santorini has two ports. Athinios port that is for ferry and commercial boats and the Old port that is only for cruise ship travelers. Athinios port is located in the area of Pyrgos where there is a car access and the Old port in Fira where the only way up and down to the town are the donkeys, the cable car or by walking.
All those people who take a ferry boat individually from the other islands or Piraeus, it is certain that they will dock in Athinios port and there are connections from Piraeus port (Athens), Ios, Naxos, Paros, Crete, Mykonos, Tinos and Syros islands.
The ferry from Pireaus needs 9 hours to reach Athinios port in Santorini