The south coast of western Crete is very rugged and
doesn't have a coastal road. Whilst this has probably helped to keep
tourist developments low key, it makes moving from village to village
rather difficult and this is why there is a ferry service between
the vilages of Paleochora, Sougia, Agia Roumeli, Loutro and Hora
Sfakion as well as to the island of Gavdos.
In the winter months the service is kept to a minimum and may stop for a week or more if the weather is bad and the sea stormy. In the months of April to October it aims at being regular, sea conditions permitting.
You can find the ferry time-table at www.anendyk.gr/pages/en/timetable.php
There is a new (2018) also running some ferries along the South Cost. See their website and time-table here
Note that the time-table can change quite suddenly and frequently (I once received two time-table updates in a single day from the ferry company!).
You can view the prices at the page www.anendyk.gr/pages/en/prices.php