It's not actually that difficult to keep within sight of land sailing more or less straight across the Aegean. Modern-day Greece has over a thousand islands, as many as five or six thousand by some estimates (depends what an island is). The modern Greek Tourism Bureau lists 227 inhabited islands, most of them in the Aegean. Add in the large number of islands considered part of Turkey and you've got a lot of islands--if we were big enough we could probably run through the Aegean on the islands like stepping stones through a creek. The Aegean also isn't really all that big. Stanford's Orbis tool suggests a journey from Athens to Ephesus in summer should only take 3.5 days, with average winds and travelling only by day. The route they plot stops at Delos and Ceos along the way, as well as a brief stop at Sumium before setting out on the sea proper to supply and prepare. Potentially, if one wanted to travel at a more leisurely pace, one could stop at any of the thousands of smaller islands in the Aegean. Now, larger voyages across truly open sea occurred sometimes. The Athenian fleet on its way to Syracuse had to round the Peloponnese before hopping across the Adriatic and skirting the Italian coast. The journey would not have been totally on sea the whole time of course, since Athenian fleets regularly beached in Peloponnesian territory to raid and rest more or less with impunity, but the journey from Corcyra, where the Athenians and their allies gathered before setting off, to the heel of Italy takes a good couple days, without any possibility of stopping on the way. The Athenian fleet, Thucydides says, made the journey to Corcyra as rapidly as possible, stopping at Aegina before racing to Corcyra. We must suppose that the Athenians stopped at night along the Peloponnesian coast. From there Thucydides describes the fleet as sailing across the Ionian Sea from Corcyra to Tarentum, stopping briefly at the promontory at the Italian heel. That's at least a couple days of open sailing. The cities in south Italy shut their gates to the Athenians and did not allow them to come to market, so the Athenians lived on water and presumably the grain brought by allied grain ships. The grain was carried, we must assume, to land--the idea of trying to resupply while floating at sea on a delicate trireme is horrifying. Rhegium closed her gates to the fleet, but allowed them to pitch camp outside the city and provided them with a market. After that the fleet crossed into Sicily. The point of all that is to show that there were options, even if a fleet could not enter a city and could only rest. This of course is in a fleet, which would really need to stop regularly at large harbors--a single ship or a small squadron would have fewer problems beaching on some deserted islet somewhere for the night. When there was no other option but to hoof it across open ocean for several days, as in the crossing of the Ionian Sea, fleets of warships would do so, with some apprehension (luckily it was midsummer when the Athenians set out, so sailing conditions would have been excellent), but if any other course of action presented itself it was usually preferable