An Investigation Comparing the Efficacy of Different Lubricants for Skis on Artificial Snow

An Investigation Comparing the Efficacy of Different Lubricants for Skis on Artificial Snow

Richard Coupe


Abstract

Whilst the earliest skis were made of wood, modern day ski bases are constructed of high molecular weight polyethylene. Water repellent or hydrophobic surfaces improve the glide of the skis and a significant industry has developed to provide waxes and other additive products to support alpine skiing. Using a method known as glide testing which employs accurate instruments to time skis travelling down an artificial snow slope, the effectiveness of fluorocarbon and Perfluropolyalkylether additives together with combinations of these with hydrocarbon waxes were compared. Skis which were un-waxed were used as a control. Whilst this investigation was not able to demonstrate any firm conclusions regarding the comparative efficacy of products under investigation, it does raise interesting questions relating to waxing, as the ‘skis with wax removed’ were surprisingly faster over the first 10 meters of the test track. A number of improvements to the glide testing method are also suggested.

Introduction

There is evidence from cave painting that hunters and trappers have used forms of skis for over 5000 years. Skis were used by the Swedish army in the 18th century and it was during this period the first reported competitions between these soldiers took place (Lund and Masia, 2003). Skis have evolved over the years, starting out as wood, then moving to laminates in 1893, then to plastic and wood laminates in 1947 and progressing to modern day skis which are comprised of a range of different materials (Lund and Masia, 2003). Frederolf (2005) explains that the base of the modern ski comprises of sintered or extruded polyethylene encapsulated by two steel edges. Above the base layer, a sandwich construction of wood or plastic is enclosed by two metal face layers consisting of aluminium or titanium. Waxing has always been an important issue in both alpine ski racing and recreational skiing; wooden skis were waxed in order to both preserve the wood and to increase water repellency. Water repellent or hydrophobic surfaces improve the glide of the ski and the thin water layer generated between the base of the ski and the snow has a low coefficient of friction. Whilst polyethylene bases do not require waxes as a preservative they are still universally used with the aim of improving performance.

Modern day composite waxes are paraffin (hydrocarbon) based, together with other additives such as graphite, teflon, silicon, fluorocarbons, and molybdenum. Harder waxes are generally used for cold, dry, abrasive conditions and softer waxes are used for warmer and wetter conditions. (SkiWax CA, 2002). All supplying companies offer different waxes for different snow temperatures, air temperatures and humidities (Swix, 2007; Toko, 2007 and Holmenkol Company, 2002). There have been several claims as to which combination of additives produces the greatest speed increase and in which environmental conditions (Traverso and Rinaldi, 2001; Arnold, 2002; Swix, 2007; SkiWax CA, 2002; Jobwerx, 2007; Hashimoto, 1986 and Karydras, 2001).

In this study, a product called NotWax™,which was originally explored for its properties as a waterproofing agent for clothing, is compared with other more conventional waxes. NotWax™ is marketed as a low cost, easy to apply, alternative to conventional hot waxing with paraffin based waxes (Zardoz, 2007). NotWax™ derives from a line of lubricants from Dupont™ called Krytox® with NotWax™ being one of the lowest molecular weight lubricants in the product line (Zardoz, 2007; Dupont, 2007). The Krytox range of lubricants by Dupont are low molecular weight fluorine end-capped homopolymers of hexafluoropropylene epoxide and are widely used in a range of industries as lubricants as it is claimed that they are chemically inert below 400C (GBR Technology Limited, 2007; Dupont, 2007).

For competitive alpine ski racing, high fluorocarbon waxes are usually used (SkiWax CA, 2002). These waxes are the most expensive to buy but according to ski wax manufacturers, do produce the best results (Swix, 2007; Toko, 2007). High fluorocarbon waxes are certainly used by all world class ski racers, depending on the environmental conditions (Raguso, 2000). Fluorocarbon waxes produce a hydrophobic effect on the base of the ski, repelling the water (Raguso, 2000). The more hydrophobic a surface is the more resistant it is to water, which is beneficial in a ski wax. Although a disadvantage of using fluorocarbons is that they are not soluble in the wax matrix which, therefore, limits the level of water repellency that they can deliver (Jobwerx, 2007). When pure fluorocarbon and fluorocarbon additives were introduced they were hailed as a turning point in waxing technology because of their high water hydrophobicity. Blossey (2003) reports that the contact angle, which is a measure of hydrophobicity, for pure fluorocarbons, was 120°. If this is compared with data collected by Kuzmin and Tinnsten (2005), this contact angle is greater than waxes without fluorocarbons or with other additives, but only by a few degrees.

Should a wax have an effect of improving performance by increasing the maximum velocity of a skier, it is suggested that it would have this effect by reducing the coefficient of dynamic friction. Smith (2002) has suggested that a 5% change in the dynamic coefficient of friction would produce a substantial, positive effect on racing performance. Therefore even a small reduction in dynamic friction could affect the outcome of an alpine ski race and this is potentially why waxing skis to their maximum potential is so important. The low coefficient of dynamic friction shown on snow and ice is due to the water films generated through frictional heating (Baurle et al (2006). Colbeck (1994) has identified a number of factors contributing to the overall friction but the minimisation of the influence of friction, due to water lubrication and to surface contamination are, particularly pertinent to the focus of this investigation.

There are several different methods used to measure the effectiveness of a wax including contact angle droplet testing, friction testers, video analysis and glide testing. The contact angle measurement (CA) is a test to determine how hydrophobic a surface is. A liquid of well known properties, for example water, is used and dropped onto the testing surface. A light source then illuminates the droplet and a set of optics is used to magnify the image for observation. A protractor within the optics is then positioned to measure the tangent line from the droplet to where it touches the test surface (Shieh, 2001). Operator subjectivity can affect accuracy but modern day testing machines have overcome this by automating the process. Friction testers use a test slider, of known mass and move it at a constant speed across the test material, the force needed to move the slider is used to calculate the coefficient of friction. However, as in Ellingsen and Torgersen’s (1983) experiment, the accuracy can be as low as +/-5%. Video analysis and digitalization analysis can be used to measure average glide speed of skis over a small (20m) distance (Smith, 2002). One advantage of video analysis is that there is no interference to the athlete and equipment. However over large distances perspective or parallax errors can distort the results (Bartlett, 1997). Williams (1985), suggests that there are numerous instances, in published literature, where errors in video analysis have been made. Glide testing is performed on snow using a skier adopting the same position each time while being timed gliding down a hill using accurate timing gear. This type of test uses a control ski and a waxed ski. The control ski remains un-waxed and unchanged during the experiment and acts as a comparison to the waxed ski. This method is used to determine whether there is any change in the track over the course of the experiment (Styring, 2007). The skis are tested over many runs to achieve a good average. “There is no substitute for testing the skis in real conditions.” according to Styring (2007). However, whilst this type of analysis is performed in a natural snow sport environment it also introduces other variables, such as weather conditions into the experiment. Snowdomes can be used to reduce external variables within the experiment. This approach is supported by Frederolf (2005), who used an indoor snowdome especially for the purpose of reducing external variables. However, the snow produced artificially within a snowdome does differ from natural snow in the mountains. There is also a rather limited length of slope inside a snowdome for conducting such an experiment.

Artificial snow could become a more common appearance in ski resorts with global warming. Widespread use of snow cannons in alpine resorts during poor snow conditions has become common place. This was especially prominent during the 2006/7 season (Cove, 2007). Artificial snow, from modern snow cannons, is usually ‘very wet’ when made. It is allowed to dry out for 24 hours to lose its moisture and then it is compacted down. Whilst fresh natural snow is very different from artificial snow, according to Raguso (2000) it differs little from older, granulated, real snow. The advantage of artificial snow is that it is fairly constant and makes the process of deciding what wax to use easier (Raguso, 2000). There are several types of snow conditions, however, and artificial snow is mostly compared to granulated old snow (Swix, 2007; Toko, 2007 and Skiwax.CA, 2002). Dry snow has a lower coefficient of friction to that of wet snow. The effectiveness of silicone and fluorocarbon additives to hydrocarbon waxes increases with added water content in the snow but so does the negative effect of hydrodynamic drag (Raguso, 2000). Waxing with fluorocarbon and silicone additives helps to overcome hydrodynamic drag, because of the additive’s hydrophobic properties, therefore making the ski go faster. For reasons already outlined the glide testing method was adopted in this study to compare lubricants.

Method

A smooth track was prepared by using a snow shovel with the aim of minimising snow terrain variation errors. Two timing systems were used namely, Tag and Bower. The Tag system is accurate to 0.001 second and included one start wand and one end light gate; these were set at a distance of 50m apart, measured using a tape measure. The second timing system was a Bower system, accurate to 0.01 second, and consisted of 3 light gates at 10m, 40m and 50m from the start wand. This overall setup arrangement was chosen because, as both systems ended at 50m, the times of the two systems could be synchronised with one another. A diagram summarising the timing gate arrangement is shown in figure 1 together with a picture showing the start wand.

Figure 1: Detailing the set up for the experiment and distances of the timing systems.

The start gate was placed on the hill and the skier required to place their ski poles over the start gate. The pole positions were then marked by holes in the snow and these positions where used on all subsequent occasions to ensure minimal variation in the start procedure. The skier was then required to release the poles and ski in a straight line, in a standing up position, to the end of the slope, triggering the start wand and the end light timing gates. Two competent adult skiers were used with matched pairs of skis; one (Skier A) to test the different waxed skis as detailed below and the other (Skier B) to act as a control to detect any changes, for example caused by slope deterioration during the investigation period. Skier A was asked to repeat this procedure five times for each of the four ski preparations. The set of 5 runs conducted at the outset with no wax was performed in order that the times of the two skiers could be compared with one another using the same ski base conditions. Skier B skied down, on the other set of skis which were un-waxed, every other run to evaluate if there was any deterioration in the track.

The wax combinations used were:

  1. No wax – All the wax was cleaned out of the bases with wax remover (Swix, 2007).

  2. Wax (Toko HF Yellow Dibloc High Fluro) - Wax was hot applied to ski and finished in accordance with the methodology of (Chico Cross Country Ski Club, 2007; Swix, 2007; Toko, 2007 and Skiwax.ca, 2002).

  3. NotWax™ only - The wax was removed from the skis using wax remover and then NotWax™ applied according to the method described by Zardoz (2007).

  4. Combination of Wax (Toko S3 Blue Hydrocarbon) and NotWax™- The skis were prepared using the ‘Felix’ method as described by Zardoz, (2007), which involves applying NotWax™, applying hot hydrocarbon wax over the top and then finished using a cork buffer.

The data collected was time pulse data from which the timing of runs can be calculated. Recording of the data was achieved with the use of a laptop inside the snow dome for both timing systems.

Results

The range of run times for the control ski was 0.12s with a standard deviation from the mean of 0.03. There was a small upwards trend during the course of the experiment by a gradient of 0.001 for the total time (0-50m). However the R-squared value was 3.6% suggesting it would be very difficult to predict future values. Analysis using two way ANOVA showed that there was no significant difference between the wax treatments. However, it did show that there were time differences between runs when using the same treatment. Further analysis was performed using the spilt times to explore variations over different phases of the runs.

Figure 2: Graphs showing the run times of the different wax combinations for total distance 0-50m (2a) and middle sector 10-40m (2b).

The lines drawn on the graphs are a guide to the eye only. There is missing time data for Felix and NotWaxTM wax runs due to the failure of the Bower timing system and external influences during one of the runs.

The skis which had been stripped of all their wax seemed to produce the fastest overall series of run times, with high fluorocarbon wax producing the fastest run time (6.40s). It was not possible to draw conclusions from total time analysis alone, therefore further analyses using the spilt times were conducted to investigate where time was lost or gained in each part of the track.

Analysis of the split times indicated that in runs involving treatment 1(no wax), fast times were gained from a rapid start phase, although these runs had a slower middle section. Waxed skis were slower during the first 10m of the track but after 10m the waxed skis seem to gain speed. The Felix method showed some of the slowest starts at 1.78s and 1.68s but appeared to be faster than skis with no wax in the middle section. This indicates that, during this phase, waxing the skis with NotWax™ does indeed produce a beneficial result compared to leaving the skis un-waxed.

Discussion

If total run time averages are compared, the runs with NotWax™ applications were slower in comparison with traditional fluorocarbon waxes. This applied to both of the alternative methods used to apply the NotWax™, namely the ‘Felix’ method and applying NotWax™ alone. Interestingly, however, all types of runs with waxed skis were slower than those with no wax on the skis. Kuzmin (2006) has argued that modern day ski base materials are hydrophobic with contact angle values close to that of modern day high fluorocarbon waxes making the ski base alone, without wax, very effective in its glide ability. The results of this investigation indicated that using skis with wax removed had a beneficial effect over the first 10m of the test track, although it was found that the wax treated skis were faster over the middle (10-40m) phase of the track. The results in this investigation together with Kuzmin’s unexpected findings, that skis with no wax were more effective, certainly merit further investigation and could potentially have significant implications for the skiing industry and for the ways in which skis are prepared. A number of improvements to the glide testing procedure would be implemented in future investigations. These include the avoidance of unnecessary build up of dirt and other contaminants by using the test skis only on the lift track; the matching of control and experimental participants even more closely for weight; the use of cat suits to minimise any differences in the wind resistance of clothing and ensuring that the control was blind. In addition all timing systems used should have an accuracy of +/- 0.001s with the timing gates placed every 10m down the track and with the skier starting the run 3m above the first timing gate to minimise start errors. The number of runs for each waxed ski should be increased to at least 10 and the effectiveness of the removal of wax should be further investigated to ensure that total removal has been achieved.

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