Reefing

Reefing is the means of reducing the area of a sail, usually by folding or rolling one edge of the canvas in on itself. Reefing improves the performance of sailing vessels in strong winds, and is the primary safety precaution in rough weather. Reefing sails improves vessel stability and minimizes the risk of damage to the sail or other gear. Proper skills in and equipment for reefing are crucial to averting the dangers of capsizing or broaching in heavy weather.

Conventional reefing

Sails may have built-in alternative attachment points that allow their area to be reduced. In a mainsail, one to four horizontal rows of cringles or lines, called reef points, may be placed above the foot of the sail. Rolling up the foot of the sail and tying these reef points to the foot of the sail forms a new tack and clew, reducing the sail's area. More than one row of reef points increases options for possible sail area.

To reef the sail of a Bermuda rigged sloop:

Sail

A sail is a catchment device designed to receive and redirect a force upon a generous surface area. Traditionally, the surface was engineered of woven fabric and supported by a mast, whose purpose is to propel a sailing vessel. Sails may be configured in many ways to include traditionally understood maritime purposes, as well as land vehicles and solar collection purposes. The rich encyclopedic history of maritime sails suggests alternative uses of the technology well documented.

History of sails

Archaeological studies of the Cucuteni-Trypillian culture ceramics show use of sailing boats from the sixth millennium onwards. Excavations of the Ubaid period (c. 6000 -4300 BC) in Mesopotamia provides direct evidence of sailing boats. Sails from ancient Egypt are depicted around 3200 BCE, where reed boats sailed upstream against the River Nile's current. Ancient Sumerians used square rigged sailing boats at about the same time, and it is believed they established sea trading routes as far away as the Indus valley. The proto-Austronesian words for sail, lay(r), and other rigging parts date to about 3000 BCE when this group began their Pacific expansion.Greeks and Phoenicians began trading by ship by around 1,200 BCE.

Sail (Lake District)

Sail is a hill in the English Lake District, lying between Derwentwater and Crummock Water.

Topography

The North Western Fells occupy the area between the rivers Derwent and Cocker, a broadly oval swathe of hilly country, elongated on a north-south axis. Two roads cross from east to west, dividing the fells into three convenient groups. The central sector, rising between Whinlatter Pass and Newlands Pass, includes Sail. The highest ground in the North Western Fells is an east-west ridge in this central sector, beginning with Grasmoor above Crummock Water and then gradually descending eastwards over Crag Hill, Sail, Scar Crags and Causey Pike.

Sail is in every sense a satellite of Crag Fell, although having sufficient prominence to be listed as a Hewitt. From the summit of Crag Hill the eastward ridge narrows between opposing walls of crag. This rocky crest is The Scar, the depression being at around 2,425 ft. The roughness decreases as the rounded top of Sail is reached, and the ridge then turns east north east. A further depression at 2,015 ft leads to the summit of Scar Crags. This col is unnamed on maps of the Ordnance Survey, but Alfred Wainwright termed it Sail Pass in his influential Pictorial Guide to the Lakeland Fells

Sail (anatomy)

A sail is a large, flattish protrusion from the back of an animal colinear with the spine. Many extinct species of amphibians and reptiles have very extended neural spines growing from their back vertebrae. These are thought to have supported a sail. Paleontologists have proposed many ways in which the sail could have functioned in life.

Function

Many suggestions have been made for the function of the sail. The consensus amongst modern scholars is that, at least for the pelycosaurs, the sail was used for thermoregulation.

Thermoregulation

The structure may have been used for thermoregulation. The base of the spines have a channel which it is proposed contained a blood vessel supplying abundant blood to the sail. The animal could have used the sail's large surface area to absorb heat from the sun in the morning. As ectotherms they required heat from an external source before their muscles would start to function properly. A predator would thus have an advantage over its slower moving prey. The sail could be used in reverse if the animal was overheating. By standing in the shade, the sail would radiate heat outwards.

Reef

A reef is a bar of rock, sand, coral or similar material, lying beneath the surface of water. Reefs may be up to 261 feet (80 m) below the surface.

Many reefs result from abiotic processes—deposition of sand, wave erosion planing down rock outcrops, and other natural processes—but the best-known reefs are the coral reefs of tropical waters developed through biotic processes dominated by corals and calcareous algae. Artificial reefs such as shipwrecks are sometimes created to enhance physical complexity on generally featureless sand bottoms in order to attract a diverse assemblage of organisms, especially fish.

Biotic reef

There is a variety of biotic reef types, including oyster reefs, but the most massive and widely distributed are tropical coral reefs. Although corals are major contributors to the framework and bulk material comprising a coral reef, the organisms most responsible for reef growth against the constant assault from ocean waves are calcareous algae, especially, although not entirely, species of coralline algae.

Vein (geology)

In geology, a vein is a distinct sheetlike body of crystallized minerals within a rock. Veins form when mineral constituents carried by an aqueous solution within the rock mass are deposited through precipitation. The hydraulic flow involved is usually due to hydrothermal circulation.

Veins are classically thought of as being the result of growth of crystals on the walls of planar fractures in rocks, with the crystal growth occurring normal to the walls of the cavity, and the crystal protruding into open space. This certainly is the method for the formation of some veins. However, it is rare in geology for significant open space to remain open in large volumes of rock, especially several kilometers below the surface. Thus, there are two main mechanisms considered likely for the formation of veins: open-space filling and crack-seal growth.

Open space filling

Open space filling is the hallmark of epithermal vein systems, such as a stockwork, in greisens or in certain skarn environments. For open space filling to take effect, the confining pressure is generally considered to be below 0.5 GPa, or less than 3-5 kilometers. Veins formed in this way may exhibit a colloform, agate-like habit, of sequential selvages of minerals which radiate out from nucleation points on the vein walls and appear to fill up the available open space. Often evidence of fluid boiling is present. Vugs, cavities and geodes are all examples of open-space filling phenomena in hydrothermal systems.

Reef knot

The reef knot, or square knot, is an ancient and simple binding knot used to secure a rope or line around an object. It is sometimes also referred to as a Hercules knot. The knot is formed by tying a left-handed overhand knot and then a right-handed overhand knot, or vice versa. A common mnemonic for this procedure is "right over left; left over right", which is often appended with the rhyming suffix "... makes a knot both tidy and tight". Two consecutive overhands of the same handedness will make a granny knot. The working ends of the reef knot must emerge both at the top or both at the bottom, otherwise a thief knot results.

Although the reef knot is often seen used for tying two ropes together, it is not recommended for this purpose because of the potential instability of the knot, and over-use has resulted in many deaths (see #Misuse as a bend).

Naming

The reef knot is at least between 4,000 and 9,000 years old. The name "reef knot" dates from at least 1794 and originates from its common use to reef sails, that is to tie part of the sail down to decrease its effective surface area in strong winds. To release the knot a sailor could collapse it with a pull of one hand; the sail's weight would make the collapsed knot come apart. It is specifically this behavior which makes the knot unsafe for connecting two ropes together.