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33-742: The Kaʻū Desert is a leeward desert in the district of Kaʻū , the southernmost district on the Big Island of Hawaii , and is made up mostly of dried lava remnants, volcanic ash , sand and gravel. The desert covers an area of the Kīlauea Volcano along the Southwest rift zone. The area lacks any vegetation, mainly due to acid rainfall . Kaʻū desert is not a true desert in that rainfall exceeds 1,000 millimeters (39 in) per year. However, rain combines with sulfur dioxide , released by volcanic vents, and forms acid rain . The pH level of

66-420: A beam reach is called a close reach . At 135° off the wind, a craft is on a broad reach . At 180° off the wind (sailing in the same direction as the wind), a craft is running downwind . A given point of sail (beating, close reach, beam reach, broad reach, and running downwind) is defined in reference to the true wind —the wind felt by a stationary observer. The motive power , and thus appropriate position of

99-412: A circle, starting with 0° directly into the wind. For many sailing craft 45° on either side of the wind is a no-go zone, where a sail is unable to mobilize power from the wind. Sailing on a course as close to the wind as possible—approximately 45°—is termed beating , a point of sail when the sails are close-hauled . At 90° off the wind, a craft is on a beam reach . The point of sail between beating and

132-417: A few degrees to one side of its course, necessitating sailing with the sail sheeted in for most points of sail. On conventional sail boats, the sails are set to create lift for those points of sail where it's possible to align the leading edge of the sail with the apparent wind. For a sailboat, point of sail significantly affects the lateral force to which the boat is subjected. The higher the boat points into

165-414: A reach. A variety of high-performance sailing craft sail fastest on a broad reach with the sails close-hauled at speeds several times the true windspeed. Depending on the angle of the true wind with respect to the course sailed, a reach may be close , beam , or broad , as follows: Sailing with the wind or running before the wind , the sails generate power primarily through drag (like a parachute) with

198-454: A stop—it will be "in irons". The recognized points of sail are judged relative to the true wind direction. They include: The range of directions into the wind, where a sailing craft cannot sail is called the no-go zone . A sailing craft cannot sail directly into the wind, nor on a course that is too close to the direction from which the wind is blowing, because the sails cannot generate lift in this no-go zone. A craft passing through

231-409: A vessel sails alternately in the directions 45° from the downwind direction, it will sail √ 2 (≈1.4) times farther than it would if it sailed dead downwind. However, as long as it can sail faster than 1.4 times its dead downwind speed, the indirect route will allow it to arrive at a chosen point sooner. Craft running downwind increase power from the sails by increasing total area presented to

264-402: A wing , relying on lift to propel the craft forward on a course as close to the wind as the sail can provide lift. This point of sail lets the sailing craft travel upwind, diagonally to the wind direction. The smaller the angle between the direction of the true wind and the course of the sailing craft, the higher the craft is said to point . A craft that can point higher or sail faster upwind

297-419: Is a zone of approximately 45° on either side of the true wind, where a sail cannot generate lift, called the "no-go zone". The angle encompassed by the no-go zone depends on the airfoil efficiency of the craft's sails and the craft's lateral resistance on the surface (from hydrofoils , outriggers , or a keel in the water, runners on ice , or wheels on land ). A craft remaining in its no-go zone will slow to

330-427: Is said to be more weatherly . Pinching occurs as a craft's point of sail approaches the no-go zone and its speed falls off sharply. In order to sail upwind, sailing craft must zig-zag across the direction of the oncoming wind, called beating to windward . The higher a vessel that can point into the wind, the shorter its "course made good" to an upwind destination. Beating upwind, a vessel alternates between having

363-531: Is subject to the prevailing wind , and is thus the wetter (see orographic precipitation ). The leeward side is the side distant from or physically in the lee of the prevailing wind, and typically the drier. In an archipelago windward islands are upwind and leeward islands are downwind of the prevailing winds, such as the trade winds of the Atlantic and Pacific oceans. Points of sail The principal points of sail roughly correspond to 45° segments of

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396-644: The points of sail they create) are important factors to consider in such wind-powered or wind-impacted activities as sailing , wind-surfing , gliding , hang-gliding , and parachuting . Other terms with broadly the same meaning are widely used, particularly upwind and downwind . Among sailing craft, the windward vessel is normally the more maneuverable. For this reason, rule 12 of the International Regulations for Preventing Collisions at Sea , applying to sailing vessels, stipulates that where two are sailing in similar directions in relation to

429-568: The tradewinds from Halemaʻumaʻu . One of the most devastating explosions in Hawaiian history occurred in 1790. The eruption released volcanic ash , which formed spheres of tephra known as accretionary lapilli due to the effect of electrostatic forces and moisture. Chief Keōua Kuahuʻula was traveling then around Kīlauea to Kaʻū, after battling the dominant chief Kamehameha I . At least 80 Hawaiian warriors suffocated when volcanic ash entered their lungs . The footprints preserved in

462-411: The yardarms , to create a larger sail area for points of sail, ranging from downwind to a close reach. Sails for a fore-and-aft rig and a square rig in use downwind True wind ( V T ) combines with the sailing craft's velocity ( V B ) to be the apparent wind velocity ( V A ); the air velocity experienced by instrumentation or crew on a moving sailing craft. Apparent wind velocity provides

495-414: The apparent wind perpendicular to its surface, acts substantially like a parachute with the drag on the sail as the dominant force. As a sailing craft transitions from close-hauled to running downwind, the lifting force decreases and the drag force increases. At the same time, the resistance to sidewards motion needed to keep the craft on course also decreases, along with the sideways tipping force. There

528-400: The ash were supposedly of these warriors. However, recent research indicates a variety of people used this area for hundreds of years. Windward and leeward In geography and seamanship , windward ( / ˈ w ɪ n d w ər d , ˈ w ɪ n ər d / ) and leeward ( / ˈ l iː w ər d , ˈ lj uː ər d / ) are directions relative to the wind . Windward is upwind from

561-551: The desert, one can cross the Great Crack and the Southwest Rift Zone, a major fault zone that looks like a giant groove in the earth, before reaching Kīlauea Volcano . From the city of Hilo , take Highway 11 about 30 miles (48 km) west. The area is part of Hawaii Volcanoes National Park , but often is closed during periods of high volcanic activity, due to the potential for poisonous gas blown southwest by

594-416: The efficiency of a sailing craft's sails and its resistance to sideways motion in the water (using a keel or foils) on ice or on land, typically at an angle between 30 and 50 degrees from the wind. A craft stopped in the no-go zone is said to be in irons. A square-rigged vessel in irons by accident is taken aback with the sails blown against the mast or laid aback if deliberate. In either case,

627-420: The following wind, sometimes by putting out sails that adapt well to the purpose, such as a spinnaker on a fore-and-aft rigged vessel. Another technique is to place the jib to windward (opposite to the main sail)—called "wing on wing" or one of several other terms—for a fore-and-aft vessel going dead downwind. In light winds, certain square-rigged vessels may set studding sails , sails that extend outwards from

660-537: The late 13th century. Additionally, "wind" has been used figuratively in phrases like "which way the wind blows" to indicate the current state of affairs. The suffix "-ward," meaning "toward," is an adverbial suffix in Old English derived from Proto-Germanic *werda-, which itself comes from the PIE root *wer- meaning "to turn, bend." The original notion of "-ward" is "turned toward." Windward and leeward directions (and

693-490: The motive power for the sails on any given point of sail. The apparent wind is equal to the true wind velocity for a stopped craft; it may be faster than the true wind speed on some points of sail, or it may be slower e.g. when a sailing craft sails dead downwind. Sailing craft A is close-hauled. Sailing craft B is on a beam reach. Sailing craft C is on a broad reach. Boat velocity (in black) generates an equal and opposite apparent wind component (not shown), which adds to

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726-400: The no-go zone to change tacks from one side to the other, must maintain momentum until its sails can draw power on the other side. If it remains in the no-go zone, it will slow to a stop and be in irons . This is called missing stays . To recover, that craft typically must return to its original tack and pick up sufficient speed to complete the maneuver. The span of the no-go zone depends on

759-453: The point of reference, i.e., towards the direction from which the wind is coming; leeward is downwind from the point of reference, i.e., along the direction towards which the wind is going. The side of a ship that is towards the leeward is its "lee side". If the vessel is heeling under the pressure of crosswind , the lee side will be the "lower side". During the Age of Sail , the term weather

792-517: The rain, as low as 3.4 during an eruption, inhibits plant growth. Furthermore, water evaporates quickly on the ground and the tephra soil is extremely permeable. The Kaʻū Desert is popular for walking and hiking tours during inactive periods. It can be reached by following Highway 11 counterclockwise from Kona to the volcano. The trailhead is on Crater Rim Drive, coordinates 19°24′31″N 155°17′48″W  /  19.40861°N 155.29667°W  / 19.40861; -155.29667 . By traversing

825-401: The sails, is determined by the apparent wind : the wind relative to an observer on the sailing craft. The apparent wind is the combined effect of the velocities of the true wind and of the sailing craft. A sail with the airflow parallel to its surface, while angled into the apparent wind, acts substantially like a wing with lift as a force acting perpendicular to its surface. A sail with

858-505: The stopped vessel will be blown backwards, which with proper positioning of the rudder allows the vessel to point outside the no-go zone and resume forward motion, once the sails can draw power. Iceboats are often parked in irons with a brake applied to the ice to prevent motion. To commence sailing, the craft is guided to one side and boarded, once the sail can draw power. A sailing craft is said to be sailing close-hauled when its sails are trimmed in tightly and are acting substantially like

891-420: The true wind directly from behind the sailing craft. A sailing craft running more downwind than a broad reach cannot attain a speed faster than the true wind. However, higher-performance sailing craft achieve a higher velocity made good downwind, by sailing on whatever broad reach is most efficient on that particular craft, and jibing as needed. The longer course is offset by the faster speed. For instance, if

924-413: The true wind to become apparent wind. The speed of sailboats through the water is limited by the resistance that results from hull drag in the water. Ice boats typically have the least resistance to forward motion of any sailing craft; consequently, a sailboat experiences a wider range of apparent wind angles than does an ice boat, whose speed is typically great enough to have the apparent wind coming from

957-482: The wind come on the port and starboard sides (the port and starboard tack). Changing from one tack to the other, by steering through the wind direction, is called tacking , or going about . A craft sailing with the true wind on its side (within limits) is reaching . Wind is flowing over the surface of the sail, creating lift (like a wing) to propel the craft. Because lift is more powerful than drag on this point of sail, sailing craft achieve their highest speeds on

990-423: The wind, the stronger the lateral force, which results in both increased leeway and heeling. Leeway, the effect of the boat moving sideways through the water, can be counteracted by a keel or other underwater foils, including daggerboard, centerboard, skeg and rudder. Lateral force also induces heeling in a sailboat, which is resisted by the shape and configuration of the hull (or hulls, in the case of catamarans) and

1023-404: The wind, the windward vessel gives way to the leeward vessel. In naval warfare during the Age of Sail , a vessel always sought to use the wind to its advantage, maneuvering if possible to attack from windward. This was particularly important for less maneuverable square-rigged warships, which had limited ability to sail upwind, and sought to "hold the weather gage " entering battle. This

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1056-406: Was particularly important once artillery was introduced to naval warfare. Ships heel away from the wind, so the leeward vessel would expose more of her topsides to shot, in extreme cases even part of her bottom. The terms windward and leeward are used in reference both to sides (and climates ) of individual islands and relative island locations in an archipelago . The windward side of an island

1089-842: Was used as a synonym for windward in some contexts, as in the weather gage . Since it captures rainfall , the windward side of a mountain tends to be wetter than the leeward side it blocks. The drier leeward area is said to be in a rain shadow . The term "windward" has roots in both Low German and Old English. The word "lee", which means a place without wind, comes from the Old Norse "hle" for "cover" and has been used in marine navigation in Germany since medieval times. The word "wind," meaning "air in motion," comes from Proto-Germanic *winda- and has evolved over time, with pronunciation changes influenced by similar words like "windy." The word "wind" has been associated with emptiness and vanity since

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