I am trying to find out if the ferries will provide travel from athens to mykonos or santorini? The ferries have no bookable travel on their websites, and many message boards are saying they do not follow their normal travel times. Other than air flight, does anyone know if their is another way to get to these islands?
There will be at least one daily ferry from Piraeus to Santorini (Blue Star Ferries, ANEK, Zante Ferries), and two or three to Mykonos from Piraeus and/or Rafina (Blue Star, Cyclades Fast Ferries, Golden Star Ferries). You can see past schedules on http://www.openseas.gr/openseas/en/ by backtracking to December 2016. If you're planning to visit both, Santorini and Mykonos, then be warned that direct ferries between these islands operate only from April to October. It's a seasonal route, in winter you will need to go via third island (Syros, Paros, Naxos), go back to Piraeus or fly via Athens.
You do not need to book in advance in winter. Just go to the port and buy before departure.