I don’t know if Salva Nos, by the Mediaeval Baebes, is an authentic medieval hymn. But I do know that even the oldest hymn was new, once. Anyway, what could be more timeless than “Save us, O Star of the Sea and Queen of Heaven”?
Nor do we forget Who it was who stood up when the waves tossed and the boat began to fill with water, and bid the wind be still, and the water be at peace: and so it was (Mark 4). When Jesus Christ bids the sea be still, it is still.