Historically speaking,
Pirate ships often had twice or even three times the crew needed for the type of ship they were on for a number of reasons. The first was a "many hands, light work" mentality where they could get things done way faster, or worked in shifts that kept the men generally well rested. The second was so that during an attack, the pirate crew could simply overwhelm the opposing ship. Also, so that even if a number of their men died in the battle, they'd still have enough to not only sail their own ship but sail their newly aqquired ship as well.