The term keelhauling, popularly associated with pirates
along with such fun activities
as walking the plank
and being whipped with the Cat o' nine tails
, is actually from the Dutch
which means "to drag along the keel".
In order to keelhaul someone a rope was tied to one end of the boat and then drawn underneath the boat, from bow to stern (or the reverse), along the keel. The offending sailor was tied to the other end of the rope and then pushed off to be dragged along the keel to the other end of the boat. The keel, being the very bottom of the boat, collected wonderful little nasties such as razor-sharp barnacles and other marine growths which could cut up the sailor quite badly. If the sailor managed not to drown during his punishment, he could die from the wounds.
If, by chance, the sailor wasn't properly keelhauled - for example, the rope broke and the sailor was able to swim away (not that he'd get very far) - the Captain would order the punishment to be administered again. This punishment, administered for minor infractions, often resulted in death.
The practice of keelhauling as an official form of punishment for sailors was only used by the Dutch Navy until 1853. It was also, unofficially, used in the British Navy and Merchant Marine and probably other Navies as well.