There is at least one Kasos to Karpathos ferry per day during the summer, and a couple of times a week, more than one ferry.
Dodecanese Islands
Where Is Kasos Island?
The Greek island of Kasos is the southernmost of the Dodecanese islands, located between Karpathos and Crete.
Piraeus To Kasos Ferry Guide
The Piraeus to Kasos ferry service typically sails overnight 3 times a week, and the ferry crossing is operated by Blue Star Ferries.
The Dodecanese Islands In Greece
The Dodecanese islands in Greece are a good place to go island hopping, with many ferry connections between the main islands.