Bark (or Barque) were light and fast ships with a shallow draft. Because of its small size and a schooner was the most famous ship in Caribbean and definitely one of pirate's favorite.
They were very fast with a narrow hull. Small sized with average tonnage around 100 tons, schooners were easy to maneuver.
A schooner could reach up to 11 knots in the right conditions, carried up to 75 crewmen and had 8-12 guns. All those features enabled the pirates to navigate easily in shallow waters and shoals, allowing them quick escape or to attack suddenly. There were usually two-masted, but also there were versions which had three or four masts. All masts were fore-and-aft rigged. A disadvantage was that schooners had limited cruising range.