Believed to have been invented by the Dutch, keel hauling was a particularly nasty punishment practiced during the 15th and 16th centuries. Rope was rigged from yardarm to yardarm under the ship and secured to the poor wretch who was to be punished. Sometimes iron or lead weights would also be attached to his legs. The crew would then hoist him to one yardarm and drop him in the water then haul him under the boat to the opposite yardarm. This would be repeated once the unfortunate had recovered his breath.
To add insult to injury, during the process they would fire a ‘great gun’ to both shock the offender and give a warning to other’s amongst the fleet to be wary and behave.