Keelhauling meant being dragged under a barnacle-encrusted ship — so calling a harsh reprimand "keelhauling" is one of English's most dramatic understatements.
To punish by dragging under the keel of a ship; to rebuke or reprimand severely.
From Dutch kielhalen, from kiel (keel of a ship) + halen (to haul, to drag), from Proto-Germanic *halōną (to fetch, to haul). The punishment involved dragging a person under the ship from one side to the other, scraping them against the barnacle-encrusted hull. Key roots: *keluz (Proto-Germanic: "keel (ship's backbone)"), *halōną (Proto-Germanic: "to fetch, to haul, to drag").
Keelhauling was as horrific as it sounds. The victim was tied to a rope looped under the ship, then dragged from one side to the other — or from bow to stern — scraping against the hull, which was encrusted with razor-sharp barnacles. Survivors were often severely lacerated and sometimes drowned. The Dutch Navy formally