A punishment aboard a ship or boat in which the offenders arms are tied to two seperate ropes. He is then thrown off of the ships bow and hauled under the ships keel (bottom) from bow to stern. Ships keels are covered with barnnicals which are sharp ans shred skin. Half the sailors do not survive this punishment due to drowning or loss of blood.
The Ships Bosan's Mate is going to be keel hauled by the Captain for stealin rum.