General descriptions of a colonial ship type named a "brigantine", and often used as a privateer.

Brigantine. The brigantine was the second most popular type of ship built in the American colonies before 1775.  (The most popular ship type was a "sloop.") A brigantine is a vessel swifter and more easily maneuvered than a sloop or schooner, and hence employed for purposes of piracy, espionage, and reconnoitering,  and as an outlying attendant upon larger ships for protecting the larger ship, or for supply or landing purposes in a fleet of ships.

The brigantine was generally larger than a sloop or schooner.  However, the brigantine was a vessel that could be of various sizes, usually in the range of 30 to 150 tons burden. 

 Generally, in the 1700's  a  brigantine was a two masted sailing ship,  having on the main mast both (1) a fore-and-aft main sail ( a triangular type of sail) and also (2) a square main topsail.  The fore-and-aft main sail  has an advantage over a square sail of being able to be better maneuvered and to allow better sailing of the ship.)    But after 1720 the main [square] topsail was omitted in most brigantines in favor of a large main sail.

The 1780 Universal Dictionary of the Marine by William Falconer further defined a brigantine as:

Brigantine . . . Among English seamen, this vessel is distinguished by having her [fore-and-aft] main-sail set nearly in the plane of her keel; whereas the main-sails of larger ships are hung athwart, or at right angles with the ship’s length, and fastened to a yard which hangs parallel to the deck: but in a brig, the foremost edge of the main-sail is fastened in different places to hoops which encircle the main-mast, and slide up and down it as the sail is hoisted or lowered: it is extended by a gaff above, and by a boom below.
 

It did not take much to convert a brigantine from use as a merchant ship to use as a privateer, or vice versa.  Privateers avoid navy battles, since the better prize was merchant ship loaded with goods that could be sold.  To attack merchant ships a privateer merely needed small cannon, such as swivel guns.

A swivel gun was mounted in an iron fork that was shaped somewhat like an oarlock.   The iron fork was bolted to the outside of the hull.   One very popular type of swivel gun was about three feet long and had a bore of about an inch and a half, and had a wooden handle, about the shape of baseball bat, attached to its breech.  This handle was used from the deck to aim the cannon.

Other popular types of swivel guns were the blunderbuss, which fired loose shot, like a shotgun; and the howitzer, a shortened cannon with a larger bore. These swivel guns were primarily used as anti-personnel weapons, rather than ship-sinking weapons.  And, of course, swivel guns did not have sufficient range to be useful in combat with the main English (or other sea power's) ships of the line. The main ships of the Navy's of the day had cannon with much longer ranges that swivel guns.