"When pirates are put to death, it is because they have been out on the high seas violating Admiralty Law, whose jurisdiction extends only to the high-tide mark. The implacable logic of the Law dictates that pirate-gallows must, therefore, be erected in the intertidal zone, and that pirate-corpses must be washed three times by the tide before they are cut down. Of course mere death is too good for pirates, and so the sentence normally calls for their corpses to be gibbeted in locked iron cages so that they can never be cut down and given a Christian burial."

- from Quicksilver: the Baroque Cycle #1 by Neal Stephenson

How sophisticated!
It seems to be a way to open an opportunity to endure duress before a rescue scene is played.

I don't know if I like more the three washes or the iron cage. Each one has its own pleasures and possibilities.