'''Slupp''' er et lite seilskip, ofte med én, to-delt mast, gaffelseil og tre forseil. Den har permanent baugspryd eller klyverbom. Sluppen ble i store trekk bygd og rigget som en kutter, men var mindre enn denne.

I distriktet Sunnhordland / Hardanger var også ordet slupp brukt om fartøy som og ble rigget med to master. Folk fra Sunnhordlandsdistriktet har fått stipend for å reise til Holland å studere hvordan  hollenderne bygde disse seilsskipene. De tidlige sluppene hadde bare en mast, men etter hvert som de ble bruk i Nordsjøfiske ble alle bygd eller rigget med 2 master. Noen få var rigget med "stengerigg", en todelt mast som kunne taes ned, og klyverbom som kunne taes inn. De eldre sluppene kunne ha optill 4 råseil men i senere tid var det vanlig med en breifokk og noen få hadde rå toppsegl. Senere ble nesten alle rigget med "pålemast". Når motoren ble innført endret betegnelsen seg til kutter, motorkutter.

Forskjellen på kutter og slupp gikk ofte på skroget, hvor smekkert det var, riggen var stort sett lik.

Slupp brukes også i sjømilitær terminologi og betegner da en mindre skipsbåt (evnt. med motor) for personbefordring. En slupp er mindre og lettere enn en barkasse.

:''For the military definition of sloop see: Sloop-of-war.''
thumb|200px|right|The [[sail plan of a typical sloop, with a gaff rig on the mainsail]]

:''For the open learning project see: SLOOP Project.''

A '''sloop''' (from Dutch ''sloep'') is a mast farther forward than the mast of a cutter.  A sloop's fore-triangle is smaller than a cutter's, and a sloop usually bends only one headsail, though this distinction is not definitive.  Unlike cutters, sloops usually have only one headsail, though some sloops such as the Friendship Sloop have more than one.  Ultimately the position of the mast is the most important factor.

On a cutter is the run of the forestay. On the sloop, it runs to the outboard end of the bowsprit, which means that spar must always stay in position and cannot be retracted. On the cutter, the forestay runs to the stem head of the hull. This allows the bowsprit to be run back inboard and stowed. This can be helpful in crowded harbours or when stowing the jib in strong wind conditions.

==Rationale behind the sloop rig==
210px|thumb|right|Typical [[Bermuda rigged sloop]]

No design is perfect for all conditions; sloops are designed to optimize upwind sailing. However, sloops also offer an excellent overall compromise acceptable, if not optimal, to all points of sail. It is clear that the most difficult direction to sail is to the windward (known as sailing ''close-hauled''); this requires some specific design features. The sail should be as vertical as possible to optimize the energy of the wind. 

Two forces act on a vessel to push it from vertical (also known as heeling over): (1) the weight of the rig itself will tend to heel the boat, and (2) the sideways force of the wind on the sails. The sloop is a light rig with fewer lines and spars, and the sails on a sloop tend to be flat which minimizes sideways force when well trimmed. The heeling forces are also counterbalanced by the keel, which uses weight and hydrodynamics to offset the forces from the rigging and sails.

When sailing upwind, it is also important to minimize the drag of the wind on the sail and rig. A major cause of drag of the sail is a turbulent air generated by the top of the mast and sail. Secondary causes are non-optimal aerodynamic shapes of masts, stays and control lines. The sloop minimizes the drag of the tip-vortex with a high and narrow sail design (high aspect), maximizing the amount of sail for a given tip-vortex compared to a square-rigged or gaff-rigged ship. Also, the simplicity of the rig reduces the drag induced by control lines, masts and spars.

==Sails carried==
thumb|300px|right|A sloop-rigged J-24 sailboat

To maximize the amount of sail carried, the classical sloop may use a genoa jib, which overlaps the mast by as much as 55 to 100 percent for racing rules and sometimes more. The mainsail and Genoa form an efficient double wing.

===The Bermuda Sloop===

The modern yachting sloop is known as the ''Bermuda sloop'', due to its Bermuda rig (also known as the ''Marconi rig'', due to its resemblance to the wireless towers of Guglielmo Marconi), which is the optimal rig for upwind sailing; consequently sloops are popular with sport sailors and yachtsmen, and for racing. The rig is simple in its basic form, yet when tuned properly it is maneuverable and fast. The main disadvantage is the relatively large size of the sails, especially on larger vessels. It is also less successful sailing downwind; the addition of a spinnaker is necessary for reasonable downwind speed in all but the strongest winds, and the spinnaker is an intrinsically unstable sail requiring continual trimming.

The ''Bermuda sloop'' is a type of fore-and-aft rigged sailing vessel developed on the island of Bermuda in the 17th century. In this sense, the term applied to small ships, rather than boats. In its purest form, it is single-masted, although ships with such rigging were built with as many as three masts. Its original form had gaff rig, but evolved to use what is now known as Bermuda rig, making it the basis of nearly all modern sailing yachts. Although the Bermuda sloop is often described as a development of the narrower-beamed Jamaica sloop, which dates from the 1670s, the high, raked masts, and triangular sails of its Bermuda rig are rooted in a tradition of Bermudian boat design dating from the early 17th century. Part of that tradition included long, horizontal bowsprits, and large jibs. Three jibs were commonly used on Bermudian ships. Triangular sails appeared on Bermudian boats early in the 17th century, a development of the Dutch ''bezaan'', or ''leg-of-mutton''  rig, itself derived from the Lateen rig. This became the Bermuda rig, and was appearing on Bermudian ships by the early 19th century. A large spinnaker was carried on a spinnaker boom when running down-wind.