What Is Curling?
Curling is a sport in which players slide stones on a sheet of ice towards a target area which is segmented into four concentric circles. It is related to bowls, boules and shuffleboard. Two teams, each of four players, take turns sliding heavy, polished granite stones, also called rocks, across the ice curling sheet towards the house, a circular target marked on the ice. Each team has eight stones. The purpose is to accumulate the highest score for a game; points are scored for the stones resting closest to the centre of the house at the conclusion of each end, which is completed when both teams have thrown all of their stones. A game may consist of ten or eight ends.
The curler can induce a curved path by causing the stone to slowly turn as it slides, and the path of the rock may be further influenced by two sweepers with brooms who accompany it as it slides down the sheet, using the brooms to alter the state of the ice in front of the stone. A great deal of strategy and teamwork go into choosing the ideal path and placement of a stone for each situation, and the skills of the curlers determine how close to the desired result the stone will achieve. This gives curling its nickname of "chess on ice".
The playing surface or curling sheet is defined by the World Curling Federation Rules of Curling. It is a rectangular area of ice, carefully prepared to be as flat and level as possible, 146 to 150 feet (45 to 46 m) in length by 14.5 to 16.5 feet (4.4 to 5.0 m) in width. The shorter borders of the sheet are called the backboards. Because of the elongated shape, several sheets may be laid out side by side in the same arena, allowing multiple games to be played simultaneously.
A target, the house, is centred on the intersection of the centre line, drawn lengthwise down the centre of the sheet and the tee line, drawn 16 feet (4.9 m) from, and parallel to, the backboard. These lines divide the house into quarters. The house consists of a centre circle (the button) and three concentric rings, of diameters 4, 8 and 12 feet, formed by painting or laying coloured vinyl sheet under the ice and are usually distinguished by colour. A stone must at least touch the outer ring in order to score (see Scoring below), otherwise the rings are merely a visual aid for aiming and judging which stone is closer to the button. Two hog lines, are drawn 37 feet (11 m) from, and parallel to, the backboard.
The hacks are fixed 12 feet behind each button; a hack gives the thrower something to push against when making the throw. On indoor rinks, there are usually two fixed hacks, rubber-lined holes, one on each side of the centre line, with the inside edge no more than 3 inches (76 mm) from the centre line and the front edge on the hack line. A single moveable hack may also be used.
The ice may be natural but is usually frozen by a refrigeration plant pumping a brine solution through numerous pipes fixed lengthwise at the bottom of a shallow pan of water. Most curling clubs have an ice maker whose main job is to care for the ice. At the major curling championships, ice maintenance is extremely important. Large events, such as the Brier or other national/international championships, are typically held in an arena that presents a challenge to the ice maker, who must constantly monitor and adjust the ice and air temperatures as well as air humidity levels to ensure a consistent playing surface. It is common for each sheet of ice to have multiple sensors embedded in order to monitor surface temperature, as well as probes set up in the seating area (to monitor humidity) and in the compressor room (to monitor brine supply and return temperatures).The surface of the ice is maintained at a temperature of around 23 °F (−5 °C).
A key part of the preparation of the playing surface is the spraying of water droplets onto the ice, which form pebble on freezing. The pebbled ice surface resembles an orange peel, and the stone moves on top of the pebbled ice. As the stone moves over the pebble, any rotation of the stone causes it to curl to the inside or outside. The amount of curl (commonly referred to as the feet of curl) can change during a game as the pebble wears; the ice maker must monitor this and be prepared to scrape and re-pebble the surface prior to each game.
The curling stone (also sometimes called a rock in North America) is made of granite and is specified by the World Curling Federation, which requires a weight between 38 and 44 pounds (17 and 20 kg) a maximum circumference of 36 inches (910 mm) and a minimum height of 4.5 inches (110 mm). The only part of the stone in contact with the ice is the running surface, a narrow, flat annulus or ring, 0.25 to 0.50 inches (6.4 to 12.7 mm) wide and about 5 inches (130 mm) in diameter; the sides of the stone bulge convex down to the ring and the inside of the ring is hollowed concave to clear the ice. This concave bottom was first proposed by J. S. Russell of Toronto, Canada sometime after 1870, and was subsequently adopted by Scottish stone manufacturer Andrew Kay.
The granite for the stones comes from two sources: Ailsa Craig, an island off the Ayrshire coast of Scotland, and the Trefor Granite Quarry in Wales.
Ailsa Craig is the traditional source and produces two types of granite, Blue Hone and Ailsa Craig Common Green. Blue Hone has very low water absorption, which prevents the action of repeatedly freezing water from eroding the stone. Ailsa Craig Common Green is a lesser quality granite than Blue Hone. In the past, most curling stones were made from Blue Hone but the island is now a wildlife reserve and the quarry is restricted by environmental conditions that exclude blasting. Kays of Scotland has been making curling stones since 1851 and has the exclusive rights to the Ailsa Craig granite, granted by the Marquess of Ailsa, whose family has owned the island since 1560. The last harvest of Ailsa Craig granite by Kays took place in 2013, after a hiatus of 11 years; 2,000 tons were harvested, sufficient to fill anticipated orders through at least 2020. Kays has been the exclusive manufacturer of curling stones for the Olympics since the 2006 Winter Olympics.
Trefor granite comes from the Yr Eifl or Trefor Granite Quarry in the village of Trefor on the north coast of the Llŷn Peninsula in Gwynedd, Wales and has produced granite since 1850. Trefor granite comes in shades of pink, blue and grey. The quarry supplies curling stone granite exclusively to the Canadian, Canada Curling Stone Co., which has been producing stones since 1992 and supplied the stones for the 2002 Winter Olympics.
A handle is attached by a bolt running vertically through a hole in the centre of the stone. The handle allows the stone to be gripped and rotated upon release; on properly prepared ice the rotation will bend (curl) the path of the stone in the direction in which the front edge of the stone is turning, especially as the stone slows. Handles are coloured to identify each team; two popular colours in major tournaments being red and yellow. In competition, an electronic handle known as the eye on the hog may be fitted to detect hog line violations, the game's most frequent cause of controversy. This electronically detects whether the thrower's hand is in contact with the handle as it passes the hog line and indicates a violation by lights at the base of the handle. The eye on the hog eliminates human error and the need for hog line officials. It is mandatory in high-level national and international competition, but its cost, around US$650 each, currently puts it beyond the reach of most social curling.
The curling broom, or brush, is used to sweep the ice surface in the path of the stone, (see sweeping), and is also often used as a balancing aid during delivery of the stone.
Prior to the 1950s, most curling brooms were made of corn strands and were similar to household brooms of the day. In 1958, Fern Marchessault of Montreal inverted the corn straw in the centre of the broom. This style of corn broom was referred to as the Blackjack.
Artificial brooms made from man-made fabrics, rather than corn, such as the Rink Rat, also became common later during this time period. Prior to the late sixties, Scottish curling brushes were used primarily by some of the Scots, as well as by recreational and elderly curlers as a substitute for corn brooms, since the technique was easier to learn. In the late sixties, competitive curlers from Calgary, such as John Mayer, Bruce Stewart, and, later, the world junior championship teams skipped by Paul Gowsell, proved that the curling brush could be just as (or more) effective without all the blisters common to corn broom use. During that time period, there was much debate in competitive curling circles as to which sweeping device was more effective: brush or broom. Eventually, the brush won out with the majority of curlers making the switch to the less costly and more efficient brush. Today, brushes have replaced traditional corn brooms at every level of curling; it is rare now to see a curler using a corn broom on a regular basis.
Curling brushes may have fabric, hog hair, or horsehair heads. Modern curling brush handles are usually hollow tubes made of fibreglass or carbon fibre instead of a solid length of wooden dowel. These hollow tube handles are lighter and stronger than wooden handles, allowing faster sweeping and also enabling more downward force to be applied to the broom head with reduced shaft flex.
Curling shoes are similar to ordinary athletic shoes except that they have dissimilar soles; the slider shoe is designed for the off foot (or sliding foot) and the non-sliding shoe for the hack foot.
The slider shoe is designed to slide and typically has a Teflon sole. It is worn by the thrower during delivery from the hack and by sweepers or the skip to glide down the ice when sweeping or otherwise traveling down the sheet quickly. Stainless steel was once common for slider soles, and "red brick" sliders with lateral blocks of PVC on the sole are also available. Most shoes have a full-sole sliding surface, but some shoes have a sliding surface covering only the outline of the shoe and other enhancements with the full-sole slider. Some shoes have small disc sliders covering the front and heel portions or only the front portion of the foot, which allow more flexibility in the sliding foot for curlers playing with tuck deliveries. When a player is not throwing, the player's slider shoe can be temporarily rendered non-slippery by using a slip-on gripper. Ordinary athletic shoes may be converted to sliders by using a step-on or slip-on Teflon slider or by applying electrical or gaffer tape directly to the sole or over a piece of cardboard. This arrangement often suits casual or beginning players.
The non-sliding shoe, or hack foot shoe, is worn by the thrower on the hack foot during delivery and is designed to grip. It may have a normal athletic shoe sole or a special layer of rubbery material applied to the sole of a thickness to match the sliding shoe. The toe of the hack foot shoe may also have a rubberised coating on the top surface or a flap that hangs over the toe to reduce wear on the top of the shoe as it drags on the ice behind the thrower.
The purpose of the game is to score points by getting stones closer to the house center, or the "button", than the other team's stones. Players from either team alternate in taking shots from the far side of the sheet. An end is complete when all eight rocks from each team have been delivered, a total of sixteen stones. If the teams are tied at the end of the game, play continues for as many ends as may be required to break the tie. The winner is the team with the highest score after all ends have been completed (see Scoring below). A game may be conceded if considered unwinnable.
International competitive games are ten ends, so most of the national championships that send a representative to the World Championships or Olympics also play ten ends. However, there is a movement on the World Curling Tour to make the games only eight ends. Most tournaments on that tour are eight ends, as are the vast majority of recreational games.
In international competition, each side is given 73 minutes to complete all of its throws. Each team is also allowed two 60-second timeouts per 10-end game. If extra ends are required, each team is allowed 10 minutes of playing time to complete its throws and one added 60-second timeout for each extra end.
The process of sliding a stone down the sheet is known as the delivery.
The skip, or the captain of the team, will usually determine the required weight, turn, and line of the stone. These will be influenced by the tactics at this point in the game, which may involve taking-out, blocking or tapping another stone.
The weight of the stone is its velocity, which depends on the leg drive of the delivery rather than the arm. The turn, handle, or curl is the rotation of the stone, which gives it a curved trajectory. The line is the direction of the throw ignoring the effect of the turn. The skip may communicate the weight, turn, line, and other tactics by calling or tapping a broom on the ice. In the case of a takeout, guard, or a tap, the skip will indicate the stones involved.
Before delivery, the running surface of the stone is wiped clean and the path across the ice swept with the broom if necessary, because any dirt on the bottom of a stone or in its path can alter the trajectory and ruin the shot. Intrusion by a foreign object is called a pick up or pick.
Players must push out of the hack to deliver their stones. The thrower throws from the hack. Another player, usually the skip, is stationed behind the button to determine the tactics, weight, turn, and line, and the other two may sweep in front of the stone to influence the trajectory (see Sweeping, below). The players, with the exception of the skip, take turns throwing and sweeping; when one player (e.g., the lead) throws, the players not throwing (the second and third) sweep. When the skip throws, the third, or vice-skip, takes his role.
The thrower's gripper shoe (with the non-slippery sole) is positioned against one of the hacks; for a right-handed curler the right foot is placed against the left hack and vice-versa for a left-hander. The thrower, now in the hack, lines the body up with shoulders square to the skip's broom at the far end for line.
The stone is placed in front of the foot now in the hack. Rising slightly from the hack, the thrower pulls the stone back to the toe (some older curlers may actually raise the stone in this backward movement) then lunges smoothly out from the hack pushing the stone ahead while the slider foot is moved in front of the gripper foot, which trails behind. The thrust from this lunge determines the weight and hence the distance the stone will travel. While not compulsory, most curlers deliver the stone while sliding out from the hack. Balance may be assisted by a broom held in the free hand with the back of the broom down so that it slides.
The stone is released as the thrower's momentum wanes, or the hog line is approached, at which point the turn is imparted by a slight clockwise or anti-clockwise twist of the handle from around the two or ten o'clock position to the twelve o'clock on release. A typical rate of turn is about 2½ rotations before coming to a rest.
The stone must be released before its front edge crosses the near hog line, and it must clear the far hog line or else be removed from play (hogged); an exception is made if a stone fails to come to rest beyond the far hog line after rebounding from a stone in play just past the hog line. The release rule is rarely enforced in club play unless abuse is suspected. However, in major tournaments it is strictly enforced; the "eye on the hog" sensor in the stone will indicate whether the stone has been legally thrown or not. The lights on the stone handle will either light up green, indicating that the stone has been legally thrown, or red, in which case the illegally thrown stone will be immediately pulled from play instead of waiting for the stone to come to rest.
After the stone is delivered, its trajectory is still influenced by the two sweepers under instruction from the skip. Sweeping is done for two reasons: to reduce friction underneath the stone, and to decrease the amount of curl. The stones curl more as they slow down, so sweeping early in travel tends to increase distance as well as straighten the path, and sweeping after sideways motion is established can increase the sideways distance. When sweeping, pressure and speed of the brush head are key in slightly increasing the layer of moisture that builds up under the stone.
One of the basic strategy aspects of curling is knowing when to sweep. When the ice in front of the stone is swept, a stone will usually travel both farther and straighter. In some situations, one of the two alterations in path is not desirable. For example, a stone may have too much weight, but require sweeping to prevent curling into a guard. The team must decide which is better: getting by the guard but traveling too far, or hitting the guard.
Much of the yelling that goes on during a curling game is the skip calling the line of the shot and the sweepers calling the weight. The skip evaluates the path of the stone and calls to the sweepers to sweep as necessary to maintain the intended track. The sweepers themselves are responsible for judging the weight of the stone, ensuring the length of travel is correct and communicating the weight of the stone back to the skip. Some teams use stopwatch timing, from back line to the nearest hog line as a sweeping aid. Many teams use the Number System to communicate in which of 10 playable zones it is estimated the stone will stop.
Usually, the two sweepers will be on opposite sides of the stone's path, although depending on which side the sweepers' strengths lie this may not always be the case. Speed and pressure are vital to sweeping. In gripping the broom, one hand should be one third of the way from the top (non-brush end) of the handle while the other hand should be one third of the way from the head of the broom. The angle of the broom to the ice should be so that the most force possible can be exerted on the ice. The precise amount of pressure may vary from relatively light brushing ("just cleaning" - to ensure debris will not alter the stone's path) to maximum-pressure scrubbing.
Sweeping is allowed anywhere on the ice up to the tee line, as long as it is only for one's own team stones. Once the leading edge of a team stone crosses the tee line only one player may sweep it. Additionally, when a stone crosses the tee line, one player from the other team is allowed to sweep it. This is the only case that a stone may be swept by an opposing team member. In international rules, this player must be the skip; or if the skip is throwing, then the sweeping player must be the third.
The winner is the team having the highest number of accumulated points at the completion of ten ends. Points are scored at the conclusion of each of these ends as follows: when each team has thrown its eight stones, the team with the stone closest to the button wins that end; the winning team is then awarded one point for each of its own stones lying closer to the button than the opponent's closest stone.
Only stones that are in the house are considered in the scoring. A stone is in the house if it lies within the 12-foot (3.7 m) zone or any portion of its edge lies over the edge of the ring. Since the bottom of the stone is rounded, a stone just barely in the house will not have any actual contact with the ring, which will pass under the rounded edge of the stone, but it still counts. This type of stone is known as a biter.
It may not be obvious to the eye which of two rocks is closer to the button (center) or if a rock is actually biting or not. There are specialized devices to make these determinations, but these cannot be brought out until after an end is completed. Therefore, a team may make strategic decisions during an end based on assumptions of rock position that turn out to be incorrect.
The score is marked on a scoreboard, of which there are two types; the baseball type and the club scoreboard.
The baseball-type scoreboard was created for televised games for audiences not familiar with the club scoreboard. The ends are marked by columns 1 through 10 (or 11 for the possibility of an extra end to break ties) plus an additional column for the total. Below this are two rows, one for each team, containing the team's score for that end and their total score in the right hand column.
The club scoreboard is traditional and used in most curling clubs. Scoring on this board only requires the use of (up to) 11 digit cards, whereas with baseball-type scoring an unknown number of multiples of the digits (especially low digits like 1) may be needed. The numbered centre row represents all possible accumulated scores, and the numbers placed in the team rows represent the end in which that team achieved that cumulative score. If the red team scores three points in the first end (called a three-ender), then a 1 (indicating the first end) is placed beside the number 3 in the red row. If they score two more in the second end, then a 2 will be placed beside the 5 in the red row, indicating that the red team has five points in total (3+2). This scoreboard works because only one team can get points in an end. However, some confusion may arise if neither team scores points in an end, this is called a blank end. The blank end numbers are usually listed in the farthest column on the right in the row of the team that has the hammer (last rock advantage), or on a special spot for blank ends.
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