at sea

at sea (1)  {adv.} or  {adj. phr.}
1. On an ocean voyage; on a journey by ship.
They had first met at sea.
2. Out on the ocean; away from land.
By the second day the ship was well out at sea.
Charles had visited a ship in dock, but he had never been on a ship at sea.
Categories: {adj. phr.} {adv.}