Koufonisia, the tiny, flat island of the Small Cyclades famous for its turquoise coves, and Santorini, the caldera island with the international airport, make an obvious pair at the end of a trip. Plenty of travellers finish a week of swimming and cycling on Koufonisia with a few nights on Santorini, or simply need to reach Santorini to catch a flight home.
The difficulty is that the direct sea link is poorly documented. Our older route data lists Blue Star Ferries and Seajets sailing from Koufonisia to Santorini, with a crossing of around 2 hours, but we have no recent Ferryhopper route page, fare table or sampled timetable for this direction to back that up. In the opposite direction, our 12 August 2026 sample did show a Seajets high-speed boat from Santorini to Koufonisia, so a summer return on the same line is possible. Treat it as something to search for rather than something to rely on.
The good news is that the two-leg route through Naxos is easy and runs all year. Boats leave Koufonisia for Naxos every day, and Naxos has daily sailings to Santorini, including fast boats in summer. With a sensible connection time, you can do the whole journey in a day.
Whichever way you go, book early for July and August, keep your first night on Santorini flexible, and do not plan to arrive on the same afternoon as a flight: a missed connection in Naxos or a windy day can push you back by hours.