Keelhauling (Dutch kielhalen; "to drag along the keel"; German Kielholen; Swedish kölhalning; Danish kølhaling; Norwegian kjølhaling) is a form of punishment once meted out to sailors at sea. The sailor was tied to a line that looped beneath the vessel, thrown overboard on one side of the ship, and dragged under the ship's keel, either from one side of the ship to the other, or the length of the ship (from bow to stern). As the hull was usually covered in barnacles and other marine growth, if the offender was pulled quickly, keelhauling would typically result in serious cuts, loss of limbs and even decapitation. If the victim was dragged slowly, his weight might lower him sufficiently to miss the barnacles, but this method would frequently result in his drowning.
Keelhauling was legally permitted as a punishment in the Dutch Navy by a Dutch ordinance of 1560, and the practice was not formally abolished until 1853. Keelhauling has become strongly associated with pirate lore. The earliest known mention of keelhauling is from the Greeks in the Rhodian Maritime Code (Lex Rhodia), of circa 800 BC, which outlines punishment for piracy. It is also pictured on a Greek vase from the same era. 
The term still survives today, although usually in the sense of being over-punished or receiving extreme discipline for lightly violating the rules.
- Etymological origins
- H. A. Ormerod, Piracy in the Ancient World (New York: Dorset Press, 1987), 54-56.
- kielholen entry in: Johann Hinrich Röding: Allgemeines Wörterbuch der Marine in allen Europäischen Seesprachen nebst vollständigen Erklärungen. Nemnich, Hamburg & J.J. Gebauer, Halle, 1793–1798.