Superfast Ferries and Anek lines jointly operate that route.

Times and bookings can be made at Superfast site.

https://www.superfast.com/en-gb

A large discount is available on seats for passholders, add your pass as discount.

Besides these there are dozens of others-the shorter the boat ride, mostly the lower the fare=price. Brindisi was far better known as port, Ancona can also do-more north, the furthest out, and without a treNIt (but with an actual now child of TrIT: FSE) Otranto. It may well be these work out cheaper, most give out general junior discount for all young people. But all also have extra to pay for fuel, hi-season, port tax etc.

Hallo LenaAimee, in der App kommt es darauf an, die richtigen Stationsbezeichnungen zu wählen. 

Du musst von Bari M.Ma nach Patras Ferry Terminal eingeben, dann findest du die Fähren auch in der App.

Eine Übersicht über die Verbindungen mit Interrail-Rabatt findest du hier: https://www.interrail.eu/de/plan-your-trip/tips-and-tricks/trains-europe/ferries - von den jeweiligen Unterseiten kommst du auch zur Buchung. 

Herzliche Grüße, Hektor. 

This is very useful thanks, I am searching online but if there are any specific alternative ferry companies from  you know, that would be great thanks. Or are they more local booking only, rather than online? We are trying to book Patras or near Athens to Bari / Brindisi (in order to get to Amalfi coats) on April 5th? Thanks in advance

Update to above, I can find Grimaldi Lines do a ferry from Patras to brindisi but it appears their booking system currently only goes to April 2nd so hopefully this will change soon to include later dates..

Hi, regarding departures after April 2:

this was the ferry we were planning to take so I checked with grimaldi:

     “ Dear Madam/Sir, 

we are traveling through Europe in April/May 2023 and 1 of our plans was to take a ferry from Patras to Brindisi. 

When I was looking at the website I could only find a schedule until April 2.

Does this mean there is no ferry in May between Patras and Brindisi? Or it is just not possible to book yet and are the tickets yet to be released?

Thanks for your reply. 

Kind regards,”

The ANSWER I got was:

Good morning,

i confirm that we don’t have departures to Patrasso in May, the last departure will be 02/04

So I googled again and found the Patras- Bari ferry - with Anek/superfast. 

(but perhaps plans will change anyway - since the severe train accident between Thess. and Athens, I’’m not sure if we will do Greece. I do not know how quick connection has been restored and/or the Greek railway company will provide alternative bus connection on a part of this route) 

Thank you very much for the update,  great to know, safe travels