A pirate's ship had to be fast, and not have too many leaks! Medieval ships included the cog and carvel. The cog had its timbers put up against each other, called "clinker built." When they were first used they had an open top, later covered with the deck to protect the cargo. "Castles" were built at the front and back of the ship. When ship builders started to overlap the timbers, the cog became the caravel. In the sixteenth century, galleons came into use, along with galleys in the Mediterranean. Irish pirate, Grace O'Malley, may have used some from of galley. No matter what kind of ship a pirate was on, the living quarters were cramped, dirty, and wet.
Next time- fighting!
(From my SCA class, So you want to be a Pyrate.)