ἐὰν ἀεὶ κατὰ πρύμναν ἱστῆται τὸ πνεῦμα

From LSJ

πάντα χωρεῖ καὶ οὐδὲν μένει καὶ δὶς ἐς τὸν αὐτὸν ποταμὸν οὐκ ἂν ἐμβαίης → all things move and nothing remains still, and you cannot step twice into the same stream

Source

English > Greek (Woodhouse Quotes Reversed)

if the wind is always favourable