Although sea biscuit was quite common at sea, it's far more likely that Captain Blood's crew of buccaneers kept cornmeal, rusk (light bread toasted for storage), or even cassava bread in the "bread locker" astern. Even so, many naval and merchant ships relied on ship's biscuit, and here's a recipe, thanks to the good people at the Erie Maritime Museum and the Flagship Niagara. This stuff keeps forever!
Treasure Light Press 