Pirate ships could be almost any floating thing for pirates in
the 17th and 18th centuries, but the most desirable pirate ships
were swift, well-armed, and nimble enough to evade
counterattack.
With the exception of certain ports in New England, there was no
place to see a "pirate ship" already built and waiting for your
custom Jolly Roger flag. Although some were previously paid for or
later paid off, the best pirate ships were the ones most easily
available.
This usually meant stealing a ship or boat and customizing it:
removing forecastles, upper structures, and cabins for extra speed,
stripping interior bulk heads for more crew space and guns, Space
was hard to come by on a pirate ship, because so many more men were
needed both to fight with superior forces and to sail any vessel
taken in battle.
A ship could start off in great condition, but regular
maintenance was vital to keep it shape. In some remote cove or
river inlet, the vessel would be run aground in a way that would
leave the hull exposed at low tide, prepared for careening. After
pulling the ship over for optimum exposure to the cleaning routine,
it was scraped clean of all barnacles, weeds, mold, and any other
extras which increased drag. Any planks were replaced which were
too damaged from teredo worms, rot, battle wounds, or age, and the
renewed hull was then coated with a layer of sulfur, tar, and
tallow to help slow down any sea beasties which would destroy the
ship.
Authorites would often wait to strike until the pirates were
more vulnerable during the ship's careening, when their ship was
out of water and their pants were around their knees.
Common Pirate Ships

Sloops- The favorite little wonder boat of Caribbean and Atlantic
pirates in the late 1600's was first produced in large numbers by
master builders in Jamaica, and her single-mast configuration was
later changed by Bermudans in the 1700's. Although usually rigged
for a larger fore-and-aft mainsail, it could easily be altered for
various sail combinations. The huge bowsprit also added more canvas
area for more maneuverability.
Thirty to sixty feet long with a top speed of over 10 knots, a crew
of 20 to 70 men could easily work this father of the modern sailing
yacht for lightning-swift attacks, avoiding broadsides, and
outrunning pursuit. In spite of weighing as much as 100 tons and
having perhaps 15 cannons, its draft was amazingly shallow at eight
feet. This allowed it to find safety in shallower waters far beyond
any warship's range. A shallow draft was also was the reason that
those entrusted to pursue pirate ships often favored the sloop to
get access to their hiding spots. (more info)
Schooners- The two-masted schooner was another favorite of the
Caribbean and Atlantic pirates. With many of the same features of
the sloop such as terrific speed, maneuverability, and gun
capacity, this swift American variant was first built in the 1700's
with a narrower hull and a shallower draft of only 5 feet. This
meant it could easily take a large haul and 75-man crew further
inland to hide or to divide the booty, but a smaller hold stored
fewer spoils.

Brigantines- This shallow-draft, two-mast brigand's ship gave
terrific maneuverability and speed from its various square and
fore/aft-rigged sail variations. It was prized in the
Mediterranean, where its earlier versions sometimes included oars
that were better for diminished winds. Heavier, longer, and roomier
than the smaller sloops and schooners, it was usually first choice
for prolonged battles instead of quick hits. Adequate firepower and
a larger hold meant the versatile pirate ship also saw widespread
use as a trade ship. 70-80 foot length, 125-150 tons, 100+ men, 12
guns.
Permission for cache placement was given by Martin Morse, Park
Service Specialist.