Syros and Andros are neighbours in the northern Cyclades, about 35 nautical miles apart, yet the direct ferry between them is one of the least frequent in the group. Most boats from Syros head for Piraeus, Tinos, Mykonos or Paros, while Andros looks towards Rafina and Tinos. The weekly direct sailing is what ties the two together.
It is worth the planning. Ermoupoli, the capital of Syros and of the whole Cyclades, is a handsome neoclassical port town with a real year-round life. Andros is unlike most of the Cyclades: green, full of springs and streams, crossed by long marked hiking paths, and scattered with the mansions of old shipowning families. Its main town, Chora, has a strong contemporary art museum, and the lively resort of Batsi sits close to the ferry port.
The catch is frequency. In Ferryhopper's figures, based on last year's data, Blue Star Ferries sails from Syros to Andros once a week in almost every month, twice a week in one. So this crossing works best when you fix the day first and fit the rest of your trip around it.
If the weekly boat does not fit, the usual workaround is to go through Tinos, which has frequent boats to both islands, or to return to the mainland and take the Rafina ferry to Andros. Either way, check the whole chain for your date before you book rooms.