on board of prizes, because over and above their proper share, they are allowed a shift of clothes."
It's a clause of Pirate Code, and I'm having difficulty in understanding the meaning. Thanks for your advice!
Every pirate will be called in turn.
The list of prizes that have been captured by the pirates is to be found on board the ship.
Apart from receiving their share of the prizes, pirates are also allowed a suit of clothes.
My reading is that there was a crew list on Bart's ship and that each man in turn would be allowed to go on board a prize to take a change (shift) of clothes from those on board - ie the clothes left behind by the captured/slaughtered crew and passengers - but if they took anything else of value they would be punished severely.