A crow's nest is a structure in the upper part of the main mast of a ship or structure that is used as a lookout point. This position ensured the best view of the approaching hazards, other ships or land. It was the best device for this purpose until the invention of radar.
In the early 19th century it was simply a barrel or a basket lashed to the tallest mast. Later it became a specially designed platform with protective railing.
The first recorded appearance of the term was in 1807, used to describe William Scoresby's barrel crows nest platform. According to a popular naval legend, the term derives from the practice of Viking sailors, who carried crows or ravens in a cage secured to the top of the mast. In cases of poor visibility, a crow was released and the navigator plotted a course corresponding to the bird's flight path because the crow invariably headed towards the nearest land. However other naval scholars have found no evidence of the masthead crow cage and suggest the name was coined because Scoresby's lookout platform resembled a crow’s nest in a tree.
Since the crow's nest is a point far away from the ship's centre of mass, any small movement of the ship is amplified and could lead to severe seasickness, even in accustomed sailors. Therefore, being sent to the crow's nest was also considered a punishment.