Route of Water Transport ASDP Kupang-Sabu/Raijua-Waingapu on the map of Kupang

Sabu-Raijua: Saturday, morning; occasionally, and sometimes the ferry goes back to Sabu before going to Waingapu
Sabu/Raijua-Waingapu: Saturday, ~8am
Waingapu-Sabu: Sunday, ~2am
Sabu-Kupang: Sunday

The ferry schedules from Kupang (Bolok port) and other NTT ports tend to be very flexible (status 2021) with often delays and sometimes cancellations (weather, emergencies). Awkward as only the people in the port seem to know if a boat will go or not that day (Kupang, +62 812 3791 1732, indonesian only!). Official timetables can be found on https://www.asdp.id or https://www.indonesiaferry.co.id, but they are not always correct anymore and have been amended with the recent local newspaper departure times.

On the long distance (night) ferries there is always the choice between VIP (AC, few people) and ekonomi (fan, lots of people) - the price above is for ekonomi, VIP will be more expensive.

Payment was still cash in 2021, but there is a transition ongoing to cashless payment. The cashless payment is complicated: you need to pay online via transfer (indonesian bank only) or via (indonesian) flashcard (BNI, BRI, Mandiri, ...) The latter you can buy and top up in any Indomaret/Alfamart. An alternative option is to go buy the ticket in the nearest Indomaret/Alfamart and you can pay cash there (at a premium of course). With the payment slip you can enter the port where this paper will be changed to a ticket, with which you can board the ferry.