SWEEPING ANGLE

Sweepers are always looking for ways to maximise their effectiveness, often with the aim of lengthening stone trajectory. A simple performance factor to address is the sweeping angle, and it may be having a greater impact than you think.

This article will break down two key studies which have investigated this variable and suggest how to implement the findings of their research.

study 1

The first investigation of optimal sweeping angles in curling was carried out by Marmo et al. [2006]. Their research analysed how different sweeping angles impacted thermal increases in the ice surface.

The researchers found that having sweeping strokes overlap on each area of ice leads to greater ice heating. This then reduces the ice-stone friction coefficient, decreasing the rate of stone deceleration, and allowing stone trajectory to be lengthened.

A greater overlap in sweeping stroked was observed when sweeping along the axis of stone motion. This leads to the ice temperature post-sweeping being ≈0.4°C higher than when sweeping across the axis of motion.

However, the researchers also suggested that by sweeping across the the axis of motion, overlapping brush strokes occur closer to the stone than when sweeping along the axis of motion. This means that there will be less time for heat to dissipate from the ice before coming into contact with the stone’s running band. At this location, ice temperature was measured as ≈0.2°C higher in the sweeping across the axis of motion condition.

Using a numerical model, it was predicted that sweeping across the axis of motion would lead to a stone traveling 5% further, based on these thermal differences between sweeping angles

study 2

A more recent study was performed by Kim et al. [2021], investigating the effects of different sweeping conditions in Korean national curling athletes. The researchers also compared sweeping across the axis of stone motion to along this axis.

The results of this investigation showed that stones travelled significantly further when sweeping along axis of motion. This was the the case with both male and female sweepers. The increase in stone distance was found to be 33% higher than sweeping across the axis of motion.

This research was completed in 2021, later than when World Curling [2016] enforced the use of a single fabric for sweeping devices. This likely makes this study more relevant to the game at present, compared to earlier research. However, the study did not explicitly state what kind of broom or pad materials were used in this study. It can be assumed that differences here could directly impact results.

mechanism vs outcome

The measurement of outcome data is very important, even when the full mechanisms determining changes in outcome are not fully understood.

The research of Kim et al. [2021] measured actual stone trajectory distance outcome data in differing sweeping conditions. Marmo et al. [2006] used a numerical model based on their mechanistic thermal data to predict the effects of differing sweeping conditions, which led to contrasting findings. This suggests that other factors, other than thermal, are likely also important in fully explaining how sweeping affect eventual stone distance. Research that determines outcomes of altered sweeping conditions will likely be more useful in practice to apply to you own performance.

asymmetry

Another factor to consider when discussing sweeping angles is the impact of differing sweeping power throughout the sweeping cycle. The point at which maximum power is created during is at the start of the push phase, having the greatest effect on stone-ice friction changes.

When sweeping across the axis of stone motion, sweeping power varies across the path of the stone, creating friction asymmetry. Sweeping along the axis of stone motion, however, ensures that there is no friction asymmetry laterally. The full running band will pass over the area of ice receiving maximum sweeping power.

How these friction asymmetries impacts stone trajectory is not yet fully understood. There is much debate surrounding directional sweeping, and many theories based on anecdotal evidence will exist until improved research data is published.

summary

Based on the results of these studies, these are my recommendations to maximally increase stone trajectory length:

Sweep along axis of stone motion.
Sweep with a high frequency to increase overlapping strokes. This leads to greater ice temperature increases.
Sweep as close to the stone as possible to reduce heat dissipation.

references

Kim, T.W., Lee, S.C., Kil, S.K., Choi, S.H., & Song, Y.G. [2021] A Case Study on Curling Stone and Sweeping Effect According to Sweeping Conditions. International journal of environmental research and public health, 18[2], 833. link
Marmo B.A., Farrow I.S., Buckingham M.P., & Blackford J.R. [2006] Frictional heat generated by sweeping in curling and its effect on ice friction. Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications, 220[4], 189-197. link
World Curling [2016] Specifications for Sweeping Devices. link