Sloop

A sloop can refer to two separate classes of sail-powered vessel.

(1) Historically, from the late 17th century the Royal Navy used a small two master, rigged either like a ketch or brigantine and formally known as a “sloop of war". It carried up to 12 small cannon, and was rated below the 6th raters. Later, in the middle of the 18th century, 3 masted sloops appeared with 16 guns. In the age-old tradition of naval lack of logic, it soon became a matter of the rank of the commander as to whether the vessel would be considered a “sloop” or brig (or exactly what sort of sloop or what sort of brig.)

(2) A sloop is a single masted sailing boat – your standard, common, popular cruising or racing yacht. Sloop rig refers to fore and aft sails, consisting of a triangular foresail, attached to the mast and either the bow of the boat, or an extended spar (bowsprit); and a larger mainsail, either gaff- or Bermudian-rigged (see Note below).

Historically, the rig has varied a bit over the centuries, according to the use of the craft - coastal trade, pleasure, racing, war, fishing - but has been essentially similar to its current form.

* Note:

A gaff is a spar attached, by means of a fixture that allows it to swivel and be raised and lowered, to a mast. To it can be “hung” a square sail with its bottom corners usually attached to a boom. This is “gaff-rigged” and is one of the two common forms of rigging for the mainsail on yachts and other fore and aft rigged boats and ships.
“Bermudian” (now usually referred to as "bermuda") refers to a triangular mainsail (rear sail) used on yachts and other craft since the early 20th century. It is more efficient, especially up-wind, than the gaff-sail, but requires a longer mast.