If you are a sailing lover, Greece is an ideal place to fully enjoy it. Thousands of islands, unseen beaches, and seas you can choose to visit. But you must know some tips to choose the correct area for you.
From July end to August end, there is a strong local North direction wind called Meltemi. Starts at North Aegean Sea, and goes down to Cretan Sea. Over the Cyclades can be very strong during the day and reach up to 8 Beaufort scale very often. Sailing from W to E and the opposite can be very tricky to sailors without extensive experience. During the night the wind is calming and winds-up again with sunshine. The Ionian Sea is not affected by this phenomenon so it is better suited for relaxed trips by sea.
A very good site for wind/sea forecasting is Poseidon System: http://poseidon.hcmr.gr