Eight years ago this weekend, the World Curling Federation—since rebranded as World Curling—convened a hastily arranged “sweeping summit” just outside of Ottawa, Ont. in an attempt to scientifically research the effects of the Broomgate scandal and mitigate an immediate solution. While the summit led World Curling to succeed on a key front—the announcement of a common brush pad fabric to be used throughout sanctioned competition—questions remained about what effects “directional sweeping” actually have on a curling stone. The brush—a curler’s essential tool—had been fixed, but what about the brusher? Those questions led Saskatchewan curling veteran Eugene Hritzuk to partner with university professor Dr. Sean Maw and launch a series of scientific experiments to challenge the thinking of many post-Broomgate curling athletes. Hritzuk wrote a March 2020 cover story for The Curling News which eventually led to World Curling commissioning the duo (in April of 2023) for another scientific study aimed “to help clarify the role that sweeping plays in curling … as it affects the ice and the behaviour of the stones.” Here, on the anniversary weekend of the first sweeping summit, is a reprint of Hritzuk’s March 2020 cover story in The Curling News. The question, once you finish reading, is this: are curling athletes ready for another dose of reality, similar to the bombshells that were dropped in 2015 and ’16? <em>The Curling News Mar. 2020 issue cover story</em> [https://www.thecurlingnews.com/.image/c_fit,h_600,w_600/MjA2NjY2MTY3MDE0NjYzMzcy/mar2020-cover_social.jpg] <em>The Curling News Mar. 2020 issue cover story</em> YOU’RE DOING IT ALL WRONG: Are sweepers directionally confused? By Eugene Hritzuk, March 2020 I’ve been annoyed for a while. As I watch today’s curling athletes on television, I can’t believe what I’m seeing. It’s the sweeping. I see teams use two different methods of brushing the stones. I can tell some think they’re scratching the ice surface, just because of the way they’re brushing. Some think they’re polishing. The problem is that curlers who are unaware of which effect their broom has on the ice may be sweeping in a way that inadvertently directs their stone in a very unintended manner. “There’s a lot of bad technique, bad positioning, bad understanding of what sweeping does,” I thought to myself. “We’ve got to fix that. We’re putting our junior curlers at such a disadvantage by not doing this properly.” It all goes back to the “Broomgate” scandal of 2015-16. Specifically, the eventual fix. Ben Hebert and Niklas Edin in Kemptville • NRC/Dan Gamache [https://www.thecurlingnews.com/.image/c_fit,h_600,w_600/MjA2NjY1NTc4NjA0MTQzODIw/sweeping-summit-hebert-edin_nrcdan-gamache.jpg] Ben Hebert and Niklas Edin in Kemptville • NRC/Dan Gamache The “Sweeping Summit” in May of 2016 was supposed to sound the death knell of Broomgate. An impressive lineup of elite curlers, high performance experts, curling administrators and curling equipment manufacturers gathered in Kemptville, Ont. where World Curling had commissioned the National Research Council of Canada to resolve several issues around sweeping. One of the summit objectives was to determine how to eliminate or significantly reduce the ability of a broom to have directional influence on a swept stone. Readers can check out the multitude of stories in various editions of The Curling News from that season, but the basic furor was that some teams had discovered that a sweeper’s brush pad could microscopically scratch the ice— depending on the pad fabric and sweeping style—such that the stone would follow the direction of the scratches, even to the extent of making rocks go in the opposite direction of the curl. The Curling News Feb. 2016 issue cover story [https://www.thecurlingnews.com/.image/c_fit,h_600,w_600/MjA2Njg3MjM1OTc2NzM0MTQy/tcn-feb-2016-cover_sm.jpg] The Curling News Feb. 2016 issue cover story To the chagrin of icemakers, pebble was also being sandpapered off the ice after just a few ends. Not only was the integrity of the ice being destroyed by these “Frankenbrooms” but many felt the integrity of the sport was also being destroyed. The Frankenbrooms affected another change. With the abrasive effectiveness of the now illegal brushes, sweepers had to alter their sweeping technique. Scratching the ice had the opposite effect of the traditional sweeping effect of cleaning/polishing/heating the ice when sweeping a stone; instead of diminishing stone-ice friction, the Frankenbrooms augmented stone-ice friction. (Editor’s note: The following video was posted online by Team Howard in Oct. 2015. The description reads: “With directional fabric and by altering the sweeping technique to more of a snowplow stroke, we achieved even more extreme alterations in direction. Rocks that should curl six feet could be backed up four feet against the curl.”) Team Howard Negative Curl (Oct 2015) After the athletes and researchers tested more than 50 different types of brooms and sweeping methods in Kemptville, standards for brush head design and construction were defined. Also, as stated in the summit’s NRC Executive Summary, “The athletes were able to identify a fabric which they tested in a multitude of different situations and they unanimously agreed that the fabric did not exhibit any signs of directional sweeping.” Consequently, a 420-denier nylon weave yellow fabric supplied by J. Ennis Fabrics Canada was to be exclusively used on all brush heads in competitive i.e. high-performance curling. This is the status quo maintained today. Or so we thought With that, directional sweeping had come to an end … or so we thought. While the athletes were forced to embrace the new standards for brushes which reverted sweeping effectiveness back to cleaning/polishing/heating the ice, many did not cease their directional sweeping technique. In the years since the WCF decrees, competitive curlers are still observed reaching across the path of a running stone from the high side and sweeping on the low side, trying to augment curl. In addition, we see reaching from the low side sweeping position to the high side, thus attempting to diminish curl. If the new fabric only cleans/polishes/heats and does not scratch, the sweeper is causing the opposite effect to what was intended. Sweeping or scratching? • Anil Mungal-Sportsnet [https://www.thecurlingnews.com/.image/c_fit,h_600,w_600/MjA2Njg3MjM1OTc2Nzk5Njc4/17national_kor-sweep_am.jpg] Sweeping or scratching? • Anil Mungal-Sportsnet After repeatedly watching this, I figured I must be missing something about the science of sweeping. I spent considerable time delving into literature and research on sweeping and could not find anything—not one item of evidence—to support what many sweepers are doing out there. I asked several elite competitors why they were employing directional sweeping techniques when, according to the NRC report, “(the curlers) unanimously agreed that the fabric did not exhibit any signs of directional sweeping.” The majority of the players I spoke to simply said that the top curlers were sweeping that way, so “that was good enough” for them. What? Future curling boss Nolan Thiessen at the summit • NRC-Dan Gamache [https://www.thecurlingnews.com/.image/c_fit,h_600,w_600/MjA2Njg3MjM1OTc2NzMzOTAw/sweeping-summit-nolan-thiessen_nrc-dan-gamache.jpg] Future curling boss Nolan Thiessen at the summit • NRC-Dan Gamache While some indicated they felt this was not an effective way to sweep, they suggested they were “not going to go against the grain.” Others, when pressed to explain the science behind sweeping by reaching across the stone, suggested they felt the brushes still had some kind of directional scratching effect. This provided no understanding as to why curlers were still doing what they were doing. So I contacted NRC, Curling Canada, the World Curling Federation and a couple of people whom I would regard as top scientists on sweeping, Dr. Glenn Paulley and Dr. John Newhook. No one could tell me if—or to what extent—the now legal fabric was scratching the ice. Serendipitously, I encountered Dr. Sean Maw, a professor from the U of S College of Engineering in Saskatoon, Sask. who had undertaken studies on the impact of curling stones on pebble at Nutana Curling Club. He was the perfect connection to collaborate with, as he also had a background in research and studies in the area of ice friction and its relation to speed skating, bobsleigh and curling. Team Gushue with one frankenbrusher in fall 2015 • Anil Mungal-Sportsnet [https://www.thecurlingnews.com/.image/c_fit,h_600,w_600/MjA2Njg4MDEyODI4OTQzNTY0/15tourchallenge_gushue-one-sweeper_am.jpg] Team Gushue with one frankenbrusher in fall 2015 • Anil Mungal-Sportsnet We embarked on a new study to determine the extent that sweeping with three different types of brush head would have on scratching the ice surface. The brush heads chosen were 1) new legal Goldline, 2) used legal Goldline and 3) new illegal “Norway” by Goldline. We engaged four competitive curlers—Rianna Kish, Josh Mattern, Kirk Muyres and Colton Flash—to participate. I should state at this point that the equipment rules that came out of the summit only affect high-performance curling athletes, not recreational curlers. As such, the Norway pad and many others deemed “illegal” simply cannot be used in any competition that leads to a domestic or world championship—or which has been declared as such by the competition’s organizing committee. This means chances are good that it’s fine for you to use any sort of broom in your league night at the curling club. If you have any questions about that, you should discuss it with your league/bonspiel convenor or club manager. PT-2 Smartbroom [https://www.thecurlingnews.com/.image/c_fit,h_600,w_600/MjA2NjY1Mjk5NDMxMjY5NTgw/smartbroom_hritzuk-maw-feature.jpg] PT-2 Smartbroom Using the PT-2 Smartbroom equipment, we realized average maximum recorded brush head pressures amongst the four curlers ranging from 48 to 119 pounds. They each swept four times with each of the three different brush heads for a total of 48 sweeping samples. There were 48 virgin marked points on freshly prepared and “nipped” curling ice running the length of the sheets. Each sweeper took a turn to brush through a virgin spot at a typical 15-second draw weight speed. Close-up photos were taken of a marked two-inch by two-inch square area of ice before and after each sweep. Then all 48 images were subjected to computerized image analysis to compare any changes in the before and after characteristics. Visually, something was immediately apparent … there was very little evidence of scratching with the legal brush heads. The subsequent image analysis revealed only an average of 1% change in the before and after photos. Also, there were no significant differences between the new and used brush heads. Pebble secrets exposed [https://www.thecurlingnews.com/.image/c_fit,h_600,w_600/MjA2Njg3MjM1OTc2Nzk5NDM2/hritzuk-maw-pebble-closeup.jpg] Pebble secrets exposed The now-illegal Norway pad manifested significantly more scratching than both legal Goldline heads, meaning the sweeping summit got it right. Conclusively, we found that sweeping with legal brushes—up to an average maximum recorded PT-2 Smartbroom pressure of 119 pounds—did NOT create significant scratches. Respect it deserves Curling is the only sport in the world where an athlete propels an object (the curling stone) towards a target (the skip’s boom) where the trajectory can be influenced by impacting the field of play (sweeping the ice) rather than by touching the object itself. Yet the stakeholders in this sport—coaches and high-performance curlers—seem to disregard the importance of understanding all aspects of sweeping. Darryl Horne, a highly regarded curling coach for 43 years, states “Without doubt sweeping is the most under-coached, under-practiced, under-appreciated and under-rated aspect of the game” and I couldn’t agree more. Perhaps it’s time the sport stakeholders invest time and effort to treat the science behind sweeping with the respect it deserves. (Editor’s note: Obviously, World Curling did just that—and the commissioned Hritzuk/Maw study results are due later in 2024 or early 2025.) This should mark the end of this story … but if scratching is not a determining factor in affecting the curl of a stone it begs the question; what does affect it? This is yet another rabbit hole into which I seem to have jumped. The Hritzuk-Maw camera setup [https://www.thecurlingnews.com/.image/c_fit,h_600,w_600/MjA2Njg3MjUyMDgyODYxMjYw/hritzuk-maw-1_setup.jpg] The Hritzuk-Maw camera setup After researching the topic coupled with countless personal observations, I would suggest what causes a stone to curl more or curl less is asymmetrical stone-ice friction. In working with competitive teams this past winter on sweeping technique and after collecting data on several dozen sweeping bouts with the PT-2 Smartbroom, it was not out of the ordinary to record the maximum average pressure in a typical six- to seven-inch stroke to vary from 120-130 pounds at the start of each stroke and diminish to 30-40 pounds at the end. Other instrumented curling brooms other than the PT-2 have recorded the differential in pressures to be as much as 10 times greater at the start of the brush stroke then at the end of the stroke. The science says both sweeping techniques augment curl; some curlers believe otherwise [https://www.thecurlingnews.com/.image/c_fit,h_600,w_600/MjA2Njg3MjM1OTc2OTMwNTA4/hritzuk-maw-brushes-with-stone-rotation.jpg] The science says both sweeping techniques augment curl; some curlers believe otherwise As such, if one accepts that sweeping cleans/polishes/heats the ice and more pressure increases those variables, the start of a typical stroke decreases the stone-ice friction of the near side of the running path significantly more than the far side of the running path. This differential across the length of a typical brush stroke would cause the rock to glide more easily on the side nearest the sweeper and grab more on the side further away from the sweeper. This glide-grab effect will cause a stone to curl more or curl less, depending on a) the side you are sweeping from and b) the rotation of the stone. Above all one must be mindful that all sweeping only affects the five inches of the diameter of the running surface of the stone. In other words, there are only two and a half inches on either side of the centre of the stone where sweeping will have any effect on the curl. Stay in our lane, please [https://www.thecurlingnews.com/.image/c_fit,h_600,w_600/MjA2Njg3MjM1OTc2ODY0OTcy/hritzuk-maw_cones-on-ice.jpg] Stay in our lane, please I have observed, countless times, where sweepers are only marginally or not even sweeping over the running surface of the stone that affects the curl. Even the average TV curling fan can spot this, and it is maddening that so many top-level high-performance curling athletes are employing such poor and ineffective mechanical form. If anyone is interested in exploring this further, there are literally dozens of articles and studies on curling and sweeping. I suggest a good starting point would be The Sport Science of Curling: A Practical Review by John L. Bradley. The references at the end of the article can take one in a number of directions to further understand the science behind curling and sweeping.
