CurlTech Curling School Curling School





The term "Field of Play" refers to two essential parts of the game, the ice and the rocks.In this section, the field of play is discussed in depth.

Topics included in this section are:

  • The Ice
  • Ice Performance Standards
  • Ice Control Factors
  • Ice Maintenance
  • The Rocks
  • Rock Performance Standards and Rock Maintenance
  • Assessing the Field of Play
  • Arena Curling
  • Measuring Devices and Procedures




A discussion of modern day curling and the success of your club, events, team, programs, etc.would not be complete without talking about the ice.Today's curlers expect the ice conditions to be fast and true.However, the ice is constantly changing and will change from club to club, event to event and even during the game.Local ice technicians study the control factors, listen to playability feedback and make adjustments to always improve the ice conditions.

In addition to your good delivery, sweeping mechanics and strategy, the ability to assess and monitor the ice (and rocks), will determine you team's success.

Ice playability has evolved rapidly in the last twenty years to thirty years.The invention of the curling ice scraper and the use purified water has changed the game.The ice of the past; slow, straight and dirty, is no longer acceptable.



Modern Ice Performance Standards

What do we expect when it comes to the ice?In some countries rigid field of play standards have been developed for championship play.To date, the World Curling Federation has not developed a set of printed standards.In the United States, for example, club and championship field of play conditions must meet the following standards:
  Standard Acceptable Deviation
Curl 4.5 feet both ways 1/2 foot either way
Speed 24.5 - 25 seconds hog to tee .5 seconds either way
13.5 - 14.5 seconds hog to hog .5 seconds either way
3.75 - 4.00 seconds back to hog .25 seconds either way
Durability Pebble conformation ends 1-11 None

The above standards were developed through a partnership between athletes and US governing body.They represent a good balance between ice that plays well for the athletes and ice that is suitable for an aggressive game, where lots of rocks are in play.Television audiences prefer the action of a house cluttered with rocks.



Timing Rocks

See the section dedicated to Timing Rocks for a full explanation of how and why we time rocks.



Ice Maintenance

To achieve the above standard, the ice must be maintained using some basic maintenance techniques.Ice should be scraped daily to remove the pebble from earlier games.A proper scrape completely removes the old pebble so new pebble can be applied.In many clubs, the ice is either not scraped daily or under-scraped.It may also be over-pebbled.This means the pebble will build up over time, creating a course surface which be slower and straighter and keep dirt from being scraped away.The ice will also slowly increase in thickness as the pebble builds-up.

In championships conditions, the ice is leveled during the pre-event preparation and is scraped after each game.This completely removes the old pebble before the new pebble can be applied.

The information below is a guideline for ice making.Every facility is different and ice standards may be different.Work with your facility to make the best ice possible.

Club Ice Maintenance Recommendation

  • Maintain your ice surface temperature in the 23-24 degree range.
  • Keep your air temperature 40-43 degrees at chest level.
  • Dew Point - 2-5 degrees above surface temperature.
  • Scrape daily with a freshly honed blade.
  • Minimum of three scraping sets adjusting the blade angle after each set.
  • Scrape as close to the draw time as possible (4-6 for a 6:15 draw)
  • Social League Play - Single, fine pebble, 120-degree water, 40 seconds, 80 swings.
  • Competitive League - Use a double pebble, 35 seconds, 80-100 swings.
  • Nip (preferred) before the game.

To re-pebble the ice during back-to-back games, adjust you're your time and coverage.A 30 second, 80 swing pebble could work.Be sure to nip again.



Ice Performance

Several factors come into play when trying to achieve the ice playability standard.We break them down into three categories:

  1. Facility related.
  2. Ice tech related.
  3. Athlete related.

Facility Related 


Ice sub floor
Sand based vs. concrete base and the amount of insulation under the base.Concrete is preferred due its durability, levelness and even distribution of cooling.Sand bases can cause pipe runs due the uneven cooling of the feed and return cooling pipes.

Overhead lighting
Light creates heat.Certain lighting systems create more radiant heat than others.Fluorescent and LED lights create almost no radiant heat.

Ice paint
In some cases, dark painted ice can absorb heat more than lighter colors.

Radiant energy from the sun
Radiant heat from the sun can penetrate the roof and ceiling.A barrier (Low E curtain) can be created to reduce the radiant heat.

Compressor Cycling
The capacity of the compressor(s) will dictate how fast the heat can be "pulled" from the ice bed.Surface temperature sensors and control set points will determine the temperature range of the surface.Large capacity compressors combined with tight set points (a tenth of a degree) will allow the ice technician to maintain a constant surface temperature.During a championship, the compressors may cycle more often with a tighter temperature range.For example, the system could be set to maintain a surface temperature between 23.0 and 24.0 degrees.This is not necessary for league play as you can use a larger range (maybe 22.0 - 24.5 degrees).

Heat and Humidity control
Heat will make your members comfortable and at the same time suspend moisture.Dehumidification will remove moisture.A combination of the two is preferred.Heat will also create a load that the compressor will have to pull out.The humidity in the rink should be controlled to provide a proper amount of humidity.High humidity will result in frost.A low humidity environment may result in "sublimation" which means the ice is changing from solid to vapor without passing through the liquid stage.

Finding the right heat and moisture combination depends on your needs, budget and equipment capabilities.Remember, the more heat you add to your ice shed, the more heat needs to be pulled out with the compressor.Burning fossil fuels to heat a large ice shed will be extremely inefficient without a heat recovery system. A "closed system" is always preferred but not always practical.In a closed system, fossil fuels are burned to heat the shed.The warmer air in the shed reaches the ice and causes the compressor to pull it out.Then the heat and is dissipated through the condenser and back into the atmosphere.The closed part of the system is a heat recovery process that takes the heat from the condenser and uses it again, back into the ice shed.It's not 100% efficient but a lot better than losing the heat to the atmosphere.

Ice Technician Based 


Amount of pebble
The ice tech can control the amount of pebble applied.He or she will consider the type of play and length of game.Generally, after a clean scrape (scraping the ice back to flat with no pebble build-up) the ice tech will apply a double pebble with either a medium or small pebble head.Club play at eight ends and no practice will require only a single pebble.

Size and shape of the pebble
The size and shape of pebble will depend on the temperature of the ice surface (freezing base) and the temperature of the pebble water.Warmer water is desirable because it melts into the surface and freezes in a rounder form.Cold pebble freezes on the surface with a tall shape.Experiment with different pebble heads and listen to your curlers.

Pebble water quality
Pebble water should always be a good quality de-ionized or RO water.Pebble water will adhere best if there is no gas or impurities in the water.The ice tech can de-gas the pebble water by letting it stand open for several minutes after heating.

Pebble water temperature
As mentioned above, warmer water (120 f) is best for pebble.

Ice Surface temperature
The ice temperature is critical to achieving your performance standards.Surface temps must be kept between 22.5 and 24.5 degrees.This allows the proper frictional melting needed for speed and curl.All clubs are different, but there is a "crash" point with your surface.In the 24-degree range, the ice has good frictional contact with the rock.As the surface warms, the ice gets faster.At some point (maybe 27-28 degrees) the ice loses its playability and gets too soft.It is also difficult for players to grip a surface that is too warm.

The ice tech can control the amount of heat in the rink area.Heat suspends moisture and will not allow it to condense on the ice.Players also like warmer conditions.Air temp should be kept in the 40-42 degree range.

Humidity and Dew Point
Humidity can also be controlled.The perfect humidity or dew point in your shed won't allow frost to condense OR the ice to sublimate.Try to keep the dew point in the shed just above the ice surface temp.

Rock running surface
All rocks (running surface) polish with time.The friction of the ice will slowly polish the running surface creating a straighter curl profile.Adjusting ice conditions may help keep your desired curl.However, it is necessary from time to time to "scratch" or texture the running surface to make a more aggressive curl profile.It is recommended the club rocks be scratched on a controlled schedule.See the section on scratching rocks.

Athlete Based 


Weight of the athletes
Heavier athletes create more friction on the pebble with their shoes.A men's draw will break down pebble faster than a women's draw (for the most part).

Types of shoes
Hi-grip shoes will also cause more friction.Players wearing a slider when sweeping will create less friction.

WCF Tournament Compliant Broom Heads
The new compliant broom heads create less friction to prevent "scratching" the ice.A side benefit to the use of these heads is longer lasting pebble, particularly down the heavy-use center path.



Ice Technician Control Points

A good ice technician will assess the facility and the rocks to develop a plan of action.There are four main areas that an ice tech must control:

  1. Ice levelness
  2. Ice surface temperature
  3. Ice surface moisture
  4. Pebble durability

Moisture is an ice technician's biggest problem.It causes condensation on the surface which leads to frost.Moisture lubricates the running surface, causing straighter ice.



The Rocks

As stated in earlier sections, curling rocks are made of solid granite quarried in only two places in Europe.Rocks come in different types, mainly distinguished by the types or types of granite used.

Types of Granite 


Blue Hone
Blue Hone (from Ailsa Craig, Scotland) granite is light gray in color and has a smooth, tight grain.These rocks have superior running surfaces and are usually well matched.Blue hone rocks chip easily and are usually chipped at the striking band due to their poor striking characteristics.

Trefor (pronounced Trevor)
Trefors are quarried in Wales and come in different colors, red, brown, gray and blue.The striking bands are usually in good condition due to the great striking characteristics. However, depending on the age and care of the rocks, the running surfaces are probably in poor condition due to pitting.These rocks must be checked carefully for a proper match.

Common Green
These rocks have a distinctive, green, speckled color.They are particularly good rocks but should be checked carefully like the Trefors.

Types of Rocks 


With the three main granite types, rock types are either solid trefor, blue hone or common green or a combination of the granite types.

Inserted Rocks
A common practice today is to insert Trefors and Common Greens with blue hone insert to act as the running surface.This is done by coring-out the running surface of a rock and gluing in a blue hone insert.As far as matching these rocks, they will behave like a solid blue hone with better striking characteristics.These have the best of the best as far as overall playing characteristics.

Figure 1.This is Trefor granite with a Blue Hone insert.The lighting reveals the running surface which is approximately 5 inch in diameter.You can see the slightly raised running edge just inside the gold band.

Why Rocks Curl 


Let's understand what is happening underneath the rock as it travels down the ice.Curling rocks are approximately 12 inches in diameter; however, there is a smaller, ringed portion that the rock rides on.This narrow ring is about 5 inches in diameter and is called the running surface.

Rocks are intentionally rotated either clockwise or counterclockwise when thrown.Intentional rotation provides the necessary degree of predictability as the rock travels down the ice.Most rocks, if thrown without a rotation, will assume a rotation at some unpredictable point.As the rock is rotating, one side of the running surface will always be moving faster than the other as it travels over the ice surface.

Example: If a rock traveling down the ice has a clockwise rotation, the left side of the rock is traveling faster over the ice than the right side.

For most of curling history, no one was clear about why rocks curl.A breakthrough 1990's study by a University of Northern British Columbia physics professor, Mark Shegelski identified the physics under the rock (described below).In 2015, a Swedish study by Harald Nyborg of Uppsala University in Sweden provided a different insight into the physics.This brings up the two main theories of why rocks curl.

  • Theory #1: Differential frictional melting (Canadian study)
  • Theory #2: Ice grooving/scratching (Swedish study)

Why Rocks Curl Theory #1: Differential Frictional Melting
Differences in pressure between the right and left sides of the running surface create frictional melting that cause a rock to pivot (or drag) over the slower side.This right/left asymmetry is influenced by ice temperature, running surface thickness, pebble, etc.

How Sweeping Affects Differential Friction
First of all, let's discuss what is happening under the rock as it travels over the ice.The rock travels over the pebble.The pebble provides a low friction interface with the running surface (the rock rides up on the pebble).The limited contact area created by the pebble allows a low friction environment to exist.Simply put, the heavy rock creates friction and causes frictional melting on the faster moving side.The melted ice is more slippery.This naturally occurring frictional melting helps explain why rocks seem to "glide" down the ice.

Now add sweeping.The sweeping motion briefly polishes the ice (pebble) just before the rock travels over it.The sweeping action melts a molecular layer of ice for a very brief moment, resulting in a molecular layer of moisture.This creates an even lower friction environment that helps the naturally occurring frictional melting.This combination allows the rock to decelerate slower.This results in the rock traveling farther.The overall reduction in friction has another effect:Since the rock is dragging less on both sides, the rock will travel straighter.

Sweeping cannot make a rock move faster, only farther!

Why Rocks Curl Theory #2 - Grooving/Scratching
Swedish researchers argue that the running surface, which is much rougher than the rest of the polished granite, creates scratches in the ice that the rock tracks through.The leading, front edge of the rock is scratching in the direction of rotation.The rock would then track along the scratch lines, which are about 20 degrees to the right of an in-turn (depending on speed and rotation).

Which is Correct?
Both theories have unanswered questions.Consider the following:

  • Why do rocks curl "more" with less rotation?
  • Does the amount of rotation affect scratch angles?
  • What are the angles of scratch based on speed and rotation?
  • What are the best sweep scratch angles compared to actual?
  • Are rock speed deceleration and rotation deceleration different?

See the Section on Sweeping for more.



Rock Performance Standards

  Standard Acceptable Deviation
Rock Type Blue hone inserts Well-matched rocks
Rock Pairings Closely matched by pair None

Rock Performance & Maintenance
Even though the rocks are solid granite, they do wear down in certain areas.The width of the running surface starts at about 5mm from the factory.Over time, the running surface wears and gets wider.As they wear, they begin to lose their "aggressiveness" or sharpness and start to straighten-out and sometimes get faster.Running surfaces in the 7-8 mm range need to be reconditioned to regain their sharpness.The striking bands also wear over time.Factory striking bands may be in the 2 cm range and wear to the 4 cm range.As they wear, they lose their "activeness" meaning they don't bounce as well.This is due to the increased contact area.

Treat your rocks with care.Limit their use by NOT using them to drag the ice before games.Rotate the rocks by sheet occasionally since most practice rocks are thrown on center sheets.

Cleaning the Rocks 


The rock's running surfaces get dirty by picking up small dirt on the ice.Small pieces of rubber from deteriorating grippers can attach themselves to the running edges. Solvent clean rocks running surface once per week.

Scratching the Rocks* 


There is a method to gain aggressiveness in your rocks.Scratching or texturing the rocks will roughen the running surface and gain aggressiveness.This method is very popular in the competitive world as the world class curlers demand more and more rock performance. It is not uncommon to scratch the rock mid-way through a world or provincial championship.This method does not actually sharpen the running surface.It roughens it.

Rock manufacturers will agree that texturing the rocks should be the last step in the overall ice/rock performance plan.There are several ice maintenance tricks that will give you more curl without touching the rock's running surface.

Every time a rock is played, practiced with, and/or used for dragging it is slightly polished by the ice friction.The more the rock is used, the more polished it gets.This gradually changes the rock ice interface.

If you decide to texture your rocks, use a texturing jig to roughen the running surface.The jig allows you to consistently sandpaper the running surface.Several methods can be used based on how aggressive you need them.

Adjust your texturing schedule after considering the following:

  • Is your ice normally frosty?
    More friction
  • Cold surface?
    More friction
  • Do you run rocks before games?
    More friction

On the other hand, warmer, freshly scraped ice has less friction.Nipping instead of running rocks will lengthen the interval.

*Note: Contact rock manufacturer for more information and any possible warranty issues.

Determine how many rocks throws occur at your club.

Scratch Frequency 


Use the following as a guide to rock texturing frequency.

Determine if your rocks are high, medium or low use by counting the number of times each rock is thrown per week.Count your regularly scheduled draws, practice sessions and the number of times the rocks are used to drag.Multiply that number by the number of weeks in your season.

High Use Club 3000 annual or more throws each
Medium 1500 - 3000 annual throws
Low Below 1500 annual throws

If you keep your ice warm (23-25 degrees) which is recommended texture your rocks every 2000 throws.

If your ice is cold and/or frosty (20-22 degrees) texture every 1500 - 1800 throws.

Type of Scratch 


Using the texture jig and aluminum oxide paper.One piece per rock.

Type Grit Process
Full 80 Push, pull, 90 degrees turn, push, pull again
Maintain 100 Push, pull, 90 degrees turn, push, pull again
Light 150 Push, pull, 90 degrees turn, push, pull again
Using a flat surface (2X4) wrapped with sandpaper
Cleaning 150 Light circular motion



Field of Play Summary

Championship rock performance and ice conditions go hand in hand.The performance of the rocks is generally related to the aggressiveness and consistency of the running surface.As stated earlier, differential pressure from a rotating rock creates uneven friction and frictional melting.It also creates deeper grooves in the ice.The term "aggressive" refers to the running surface that creates good overall friction.The rougher the running surface, the more friction is created.Rock-makers create a balance between a rough surface that will curl and a surface that will still run at speeds within the standard.A more difficult task for the rock-maker is creating perfectly matched running surfaces.All rocks on a given sheet must perform the same.

Running surfaces (running edges) don't last forever.The manufacturer shapes the edge on the lathe with a cutting tool.When the rock is placed into service at the cub, it begins a slow polishing and deterioration process.The edge can either wear away or "pit".Pitting occurs slowly as the rocks expand and contract.A pitted edge is very inconsistent in how it plays.

Aggressive edges smooth-out as they age and must be retouched occasionally.Some ice techs believe rocks should be "worked" before every large event."Working" the rocks or "scratching" the rocks is achieved by sanding the running edges with sandpaper or emery. Different techniques exist but they all involve turning or dragging the rock on a piece of sandpaper.This roughens the edge and makes the rock more aggressive.It also helps gain consistency in the rock sets.



Assessing the Field of Play

Good teams have a plan to assess the field of play before each game.Below is a sample plan for assessing the conditions.

Assessing the Ice
Assessing the field of play conditions is not the same as reading the ice.Good teams understand ice and the variables that affect performance.There are four key ice variables a player should know.

  • Ice surface temperature
  • Pebble size and amount
  • Climate control (heat and humidity)

Scraping Methods 

˙Method˙Temperature˙Pebble˙Heat & Humidity˙Rocks˙Sheet˙

The type and frequency of the ice scraping will have huge impact on the ice speed and curl.Understand how often the ice is scraped and if the pebble is completely scraped off before it is pebbled and nipped again.

Surface Temperature 

˙Method˙Temperature˙Pebble˙Heat & Humidity˙Rocks˙Sheet˙

Teams should know the ice surface temperature at the beginning of the game.They should also know when the compressor "pulls".Surface temperatures in the 21-22 degree range will produce a slower, straighter condition.Temperatures in the 23-24 range will produce faster and swingier ice.Know the factors that affect the surface temperature during a game.There is no such thing as a constant surface temperature.At night, when the lights are off and the ice is not in use, the refrigeration system will maintain a surface temperature in the set range with very little margin of error.Large heat loads (lights, players. heaters, etc.) are difficult to remove quickly resulting in a spike of surface temperature.For example, a surface that will remain at or near 23 degrees when the ice is not in use may increase or spike to 25 or 26 degrees when the players start the game.The capacity of the plant and the set points dictate how high the spike will be.

A curling club maintains a 23-degree surface when not in use and the lights and heaters on.When all of the players enter the ice area and begin to play, an enormous heat load is added to the static condition.Each player represents a certain BTU (British Thermal Units) heat load.This heat will be transferred to the ice surface and the compressor will have to pull it out.There is a lag between the addition of the heat load and the compressor sensor.In some cases, the compressor is unable to pull the heat out fast enough and the surface temperature rises.When players leave the ice (removing a heat load) the surface will either remain constant or drop (if the compressor is pulling).

Begin your ice assessment by having a discussion with the ice technician.Prior to the competition, ask to see the refrigeration plant and ask what the compressor cycles on;

Sensing Area Short Result Long Result
Brine temp Long lag time Large temp range
Bed temp Medium lag time Med Temp range
Surface temp Short/No lag time Small temp range

Ask the ice tech what the ice surface temperature will be at the beginning, middle and end of the game.Ice with surface temperatures in the low 20's may be straighter and slower.As the temperatures rise, the rocks curl more and it becomes faster.This is the case until about 27 degrees.Temperatures higher than that create soft, unplayable ice and there's probably something wrong with refrigeration system.The pebble will last longer in lower temperatures and will break down faster in higher temperatures.

The key to managing the surface temperature is knowing when it changes.Everyone has experienced a change in speed and curl after the all the other sheets have left the ice.With four to six sheets of people on the ice, the refrigeration system is working to remove the heat load (BTU's).If the heat load leaves quickly, the compressor lags behind and continues to operate.The surface temperature can drop a full degree by the time the system shuts off on temperature.In addition, the heat source offered by the players is no longer available, resulting in the air losing its moisture-suspension qualities.

Pebble Size and Amount 

˙Method˙Temperature˙Pebble˙Heat & Humidity˙Rocks˙Sheet˙

Ask the ice technician what size pebble he or she plans to use.A medium pebble will last longer while a fine pebble will break down earlier.

Heat and Humidity Control 

˙Method˙Temperature˙Pebble˙Heat & Humidity˙Rocks˙Sheet˙

Ask the ice tech if the club or arena has heat and/or dehumidification.Dry air has less moisture than humid air.With no moisture in the air (dehumidification) there will be no condensation on the surface.This means no visible moisture (frost).Early condensation looks like a dull film across the ice.You will notice that the sweeper's shoes will displace the moisture and cause a smooth spot.The moisture taken up by the shoes may even leave a spot on the ice where the shoe stops.Dry ice conditions promote speed and curl.Moist conditions lubricate the running surface and prevent curl.

Assessing the Rocks 

˙Method˙Temperature˙Pebble˙Heat & Humidity˙Rocks˙Sheet˙

At the higher levels, your ability to assess rocks is critical.Games have been decided on a team's inability to spot a bad rock and deal with it.The following is a guide to rocks and how to assess them.

There are many different types of rocks in play across the world.Wear and tear on these rocks differ with the type of granite used and the amount of playing time they get.As mentioned earlier, some granite is susceptible to wear and pitting causing them to behave differently.Mismatched rocks are a growing concern.With the good ice conditions we have today, particularly the speed, mismatched rocks can play an important role in the outcome of the game.As rocks age, the running surfaces change shape.They either wear (get flatter) or they "pit" which means small pieces of granite break lose due to constant freezing and thawing (expansion and contraction).This aging process is important to advanced curlers because it rarely happens evenly across a given set of rocks, causing the speed and curl of some rocks in the same set to differ.Most players use the rock numbers to throw rocks in sequence but there is no guarantee that these rocks travel over the ice at the same speed or in the same manner.

Know the Granite
Your first step in rock assessment is knowing what granite you're playing with. Most rocks today are Trefor granite with blue hone inserts.This is the best rock type.The running surface is made of blue hone which is a durable running surface.Visually inspect the running surface and determine if the rock is aggressive or conservative.An aggressive running surface will feel rough to the touch.The aggressive running surface will curl more with less speed.

Matching Rocks
Mismatched rocks (one slower or faster than the other) can greatly affect your ability to calibrate draw weight.A rock that is ten feet slower than the other will cause you to over compensate on each throw.

The best way to determine if two rocks are running at the same speed is to throw many, many draw shots on a good quality ice surface.The larger the sample size, the more accurate the data.Record the results and use the information in the future.

Steps for assessing rocks during a competition:

  1. Ask the locals for rock information
  2. Visually inspect the running surfaces
  3. Throw the rocks in practice and look for patterns
  4. Run the rocks together
  5. Track game patterns
  6. Watch other teams throw them

Throw the Rocks
In practice throw the rocks that you will be throwing in a game.Start by playing the rocks straight up the numbers.If you suspect a mismatch move to step 2.

Run the Rocks
If you suspect a bad rock, run the two rocks one in front of another for about fifteen to twenty feet.If the rocks are matched, they will run together in both directions.If one is faster, it will pull away from the other.This is not an exact science.Use this process only to determine really bad rocks.

Look for Patterns
Since most players do not have the luxury of running rocks (particularly at other clubs), the next best thing is to watch each rock closely for signs of unusual behavior.Designate a player to watch the rocks and the tracks on the ice.Bad rocks usually create a pattern (always light but with a good split, for example).Always confirm split times with the team timer if you suspect a bad rock.

If time is not a concern (rocks at your own club) a good way to match rocks is to time them.If you have an opportunity to throw practice rocks, or you want to match rocks at your club, throw as many rocks to tee line as you can.Time them from hog to tee.This will give you the rock's speed in seconds.When complete, match the similar times.Teams using "split" or "interval" timing can match rock speed quickly by monitoring the splits.Consistent rocks will have consistent times in either case.

Understanding the Geometry of the Sheet 

˙Method˙Temperature˙Pebble˙Heat & Humidity˙Rocks˙Sheet˙

At first glance, the sheet of ice, excluding the houses, has many parallel lines and other lines that intersect at 90-degree angles.In particular, the center line and the four-foot lines, if in use, represent reference lines for throwers and sweepers.However, only a few shots in a game will run parallel to these lines.Since all shots are thrown from the hacks that are fixed a few inches away from the center line, most shots will initially travel at an angle to the center line.Compounding the issue is the draw back point of the individual player.Some will draw back on the center line while others will draw back to the hack toe.This represents four inches or so at the front end of the line of delivery (imaginary line between the skip's broom and the starting point).

The Outturn Issue
Outturn shots, particularly the ones farther outside, are visually complex since the LOD in most cases, crosses the centerline first, then the four-foot line.These shots will, for most of the path, be travelling away from these lines.Since they are actually moving away from the parallel lines, the rock "appears" to be "falling" to the outside.If the center line and four-foot lines were not there, there would be no apparent fall.In addition to the visual, sideways delivery and release energy may straighten the rocks' curl profile contributing to the wide and/or fall problem.See the Wide Trifecta.



Arena Ice Considerations

With the popularity of curling growing every year, new clubs are forming without dedicated curling facilities.By acquiring rocks and basic equipment, new clubs can form using ice at the local skating rink.This is a great way to enjoy curling at a low cost.Curling on arena ice does present some challenges.Most arenas share ice with hockey and figure skating.Preparing the ice temperature and surface for each group looks different.Hockey players want a cold, flat surface at about 20 degrees.Figure skaters want a warmer, flat surface at about 25 degrees.Both hockey and figure skating don't necessarily need a level surface.Curlers want a level, pebbled surface at about 23 - 25 degrees.

All preparations for daily use involve the Zamboni.The Zamboni is an efficient machine for prepping hockey and skating ice.For curling however, it can be a problem.The machine scrapes the surface and lays water down to fill holes and create a seemingly flat surface.It does not create a level surface.Even the curling scraper can't level the surface properly.

A surface that's not level may produce a "negative ice" situation.Negative ice happens when the surface is not level.The physics under the rock that make it curl no longer exist (see Why Rocks Curl).In this case gravity may make the rock curl, even against the turn.Our staff has arena experience and they report situations where rock curl twelve feet with the turn and back up eight feet against the turn.

Your game strategy and shot calling may have to be adjusted to make shots on the non-level surface.

Tips for Playing on Arena Ice
Throw shots down the middle of the sheet.Typically, the center of the sheet is the most level.Because of this, shots down the center can be more predictable and very effective.Playing the outside sheet is dangerous and is where the fall (negative ice) exist.

Throw more draws than takeouts.Even on a non-level surface, draw weights can be normal.A team that can fill the house with draw shots has an advantage since the takeout is less predictable.We've seen teams throws eight takeouts in a row and miss everyone.

Is the ice is running negative, gravity is making the ice curl and not differential frictional melting.If gravity is making the rock curl, sweeping makes it curl more.Of course this is the opposite result from normal curling.



Measuring Equipment and Procedures

Occasionally, two or more rocks are too close to measure by eye, whether it is to the tee or around the perimeter.Measurements come in two categories:

  1. Closest to the Tee - Rocks in the house
  2. Perimeter - Rocks in Play

Measuring the rocks by device will help.There are four types of measuring devices available at most clubs.

  1. Mechanical Measure
  2. Laser Measure
  3. The Six-Foot Measure
  4. T-Square

The Mechanical Measure 

˙Mechanical˙Laser˙6 Foot˙T-Square˙Procedures˙LSD˙

The first and most often used device is simply called the "measure".It is used to determine the counting rock or rocks in the house.There two types of mechanical measures, the spring gauge and the manual touch no touch device.Since the spring gauge is a mechanical device with moving parts (springs, levers, etc.), there may be some inaccuracy on very close measures.The TNT device eliminates the mechanism and the determination is made based on where the device touches or not.This is far more accurate.The spring gauge device can also be used as a TNT.

A note on both devices:
Any downward pressure on the device may cause a bad reading.In addition, many of these devices have significant "play" when trying to move the device from a point near the center.On very close measures, have a teammate moving the device from the end, near the twelve-foot.This will eliminate the play.

Laser Measure 

˙Mechanical˙Laser˙6 Foot˙T-Square˙Procedures˙LSD˙

The Laser is an electronic device that reads distance via laser and provides a reading in 100's.

The Six-Foot Measure 

˙Mechanical˙Laser˙6 Foot˙T-Square˙Procedures˙LSD˙

The six-foot is used to determine whether or not a rock is in the house.It is also used as a perimeter measure at the back of the house at the intersection of the center and backlines.Unlike the above device, it may be used during the end before all eight rocks have come to rest.There are only two reasons to use the six-foot measure during an end:

  1. In Play at the Back of the House
    To determine if a rock, at the intersection of the back line and centerline, is in play.The back line overlaps the back of the house and if the lines were installed properly, a rock that is not within six feet of the center, it is not only out of the house, it is out of play.
  2. Free Guard Zone Measure
    To determine if a rock is in the house.If the free guard zone rule is being played, it can be used during the first four rocks (fifth rock can be removed either way).

The T-Square 

˙Mechanical˙Laser˙6 Foot˙T-Square˙Procedures˙LSD˙

The third measuring device is called the "90 degree" measure.It is an L shaped piece of metal use to determine if a rock is in play around the perimeter of the playing area.

Measuring Procedures 

˙Mechanical˙Laser˙6 Foot˙T-Square˙Procedures˙LSD˙

Measurements are needed when the teams can't agree by eye.A quick note about measuring rocks.The object of the game, of course, is to get closest to the tee, which is an exact spot where the center line intersects the tee line.Measurement by device actually measure s closest to the center of the hole that is drilled over the tee.In some cases, where the hole is drilled improperly, erroneous results could occur.In addition, the standard measure has a cone shaped tip that fits into any size hole.The Laser measure may have a smaller tip and may not fit slush into the hole.Always push the laser toward the rocks being measured.

If officials are not present, the vice skips are responsible for measuring rocks if necessary.The following is the correct procedure for measuring.Rocks are measured clockwise from the back of the house.This is the standard.

Too Close to Call?
If it cannot be determined by device or by eye, the end is considered blanked.Mechanical devices do not give an exact measure.Some interpretation of the dial value is necessary.It is also difficult to determine tie using mechanical device because it is not exact.Since the Laser measure, more ties are recorded since the numeric readout could be the exact same.

Measuring Two Rocks (standard championship procedure)

  1. After retrieving the measuring device, enter the house from the back with the measuring point (the part that goes in the center hole) in your right hand.
  2. You will measure rocks in a forward, clockwise direction to avoid "backing" into a rock.Place the center point in the center hole and put the measuring device on the ice 90 - 180 degrees from the first rock to be measured.This allows you to place the device on the ice away from the rocks to be measured.
  3. As you approach the first rock, determine if any adjustments are needed at the end of device and make them.Adjustments can be made at the far end of the device to accommodate rocks in the twelve foot.Adjust the mechanical sensor to provide an accurate reading.
  4. Measure the front of the first rock (never measure the back of the rock as rocks have different diameters), leave it in place and remember the reading on the device.The opposing vice skip should be looking as well.
  5. Slowly move the device clockwise to the next rock, putting no downward pressure on the device.
  6. Measure the second rock and make a decision as to which one is closer.Point to the closer rock and move the second rock either in or out depending on the result and point to the closer rock for spectators.

Measuring Three Rocks

  1. After retrieving the measuring device, enter the house from the back with the measuring point in your right hand.
  2. You will measure rocks in a clockwise direction.Place the center point in the center hole and put the measuring device to the left of the odd-colored rock.
  3. As you approach the odd-colored rock, determine if any adjustments are needed in the device and make them.
  4. Measure the odd colored rock first, take a reading and leave it in place.
  5. Swing the device clockwise to the next rock and measure it.
  6. After making the decision on the second rock as compared to the odd colored rock, move it either in or out depending on the decision.Indicate with your hand the closer rock.
  7. Move to the third rock and measure it.Again, move it in or out based on your decision.The first rock (odd-colored) will be your reference rock and should not be moved.

In both situations it is acceptable to swing the device back to the first rock for a closer look.If rocks cannot be determined by device, a blank end will result.This is very rare.If the measure is very close, consider moving the mechanical sensor "away" from the rocks.This reduces friction between the sensor arm and the rough rock running surface.If the sensor arm cannot provide a reading, visually determine.

If two or more rocks are so close to the button that the device cannot be used, a decision must be made visually.Find an impartial person to do this for you.

Using the Laser Measure

  1. Locate the laser on turn it on.
  2. Insert the bottom extender into the hole at the Tee.
  3. Put a slight amount of pressure toward each rock for a fair reading.Slowly point the laser at the first rock and note the lowest number.A back and forth motion may be needed.
  4. Point the laser at the other rock(s) and note the lower number.
  5. Make the determination and signal to the fans.

Using the Six-Foot Measure

  1. Enter the house from the rear with the pointer in your right hand.
  2. Place the six-foot pointer in the center hole and rest the device on the ice at 90-180 degrees from the first rock.
  3. Slowly swing the device clockwise until it either contacts the rock or swings past it.Never throw the device at the rock as it may come out of the hole and displace the rock.

If, during a free guard zone measure, another rock is in the six-foot path, a decision must be made visually.

Using the T-Square
The T-Square helps determine perimeter rocks and can determine rocks in play.Since the rocks have an "overhang", the 90-degree angle helps sight the perimeter line by extending the sight downward.


  1. Locate the T-Square device.
  2. Place the vertical flat side against the rock.

Visually check the bottom of the device compared to the line.

LSD and The Formula 

˙Mechanical˙Laser˙6 Foot˙T-Square˙Procedures˙LSD˙

In championship play, where the Last Stone Draw (LSD) is used to determine hammer in most games, rocks are measured from the center of the rock.A tape measure or laser is used for the initial reading from the closest edge of the rock.Then, the radius of the rock is added to complete the distance measure.It may be necessary to measure two rocks that both cover the tee.At the highest level, it is common to cover the tee on more than one shot.The official in charge would take measurements from two spots, one on the tee line at the intersection of the four foot circle and the other on the center line at the intersection of the four foot.With these two numbers a mathematical formula can determine which rock's distance from the tee.