January 1999
THE CONTROL OF RACKET COVERINGS
Rufford Harrison (USA) and Odd Gustavsen (Norway)
ITTF Equipment Committee
As everybody must know by now, there is concern about the lack of attractiveness of our sport. When most rallies last only two or three strokes, there is very little opportunity for the spectator to see what is happening, to understand the tactics employed by each player, even to know why a player lost a particular point. A possible reason for this situation is that the ball is so fast that virtually every return is a stroke in desperation; the player just has time to reach the ball, but very little time in which to think about making a good return. Even if he does get the ball back, his opponent will have exactly the same problem, so that the probability of the ball going of or of winning the point is probably higher than that it will be returned. This is not a good situation and it has resulted, of course, from the development of spinny, speedy racket coverings. The obvious solution is to control those racket coverings so as to reduce the speed and spin slightly, but not too much; we do not want to change the character of the sport entirely. How can we do this?
Because this is such a complicated subject we decided first to try a different approach. That is why the 40 mm ball is under study, since that does slow the ball somewhat, and similar thoughts are behind the higher net concept. Another idea was interjected at this point: if we increase the size of the ball, and slow it a little, will not the players work harder and increase the speed by means of more physical exertion, so that the ball becomes just as fast as it is today? With that in mind, the ITTF Council at its last meeting instructed the Equipment Committee to develop control methods for limiting the properties of the racket coverings. But that is all that the Council said, and it is our job to determine how best to do it. We believe that there are at least four phases to such a project:
1) First, we have to determine what properties must be controlled. This has the unexpected difficulty that we have no control over exactly what the racket covering really is. Even though natural rubber is the main ingredient, there are many types of additives and after the vulcanisation process it is difficult, if not impossible, to know what the starting point was. In addition, there is nothing to prevent a player from buying "sandwich rubber" from supplier A, removing the sponge layer and replacing it with a sponge layer from supplier B. So although it is the combination of the layers that governs what the player can do with the ball, it is pointless for us to measure all possible combinations, unless we can give referees devices for making the same measurements. Thus we can either measure properties of the combination, and give referees a means for making the same measurements, or we can measure the properties of the pimpled rubber and the sponge separately, and apply control at the supplier level.
2) The second phase is to develop suitable test procedures, which will depend on whether they are being conducted by a testing laboratory or by a referee. Let's think about testing the covering as a whole, so that the referee could make the ultimate control. Some tests appear deceptively simple:
Resilience: Just drop a ball on the racket, and see how far it bounces. A referee could do that, but it isn't a very meaningful test because it measures the bounce only from a ball that is impacting the racket slowly. Most balls in actual play don't; they hit the racket very rapidly and forcefully. How could a referee duplicate that?
Friction: Just put a standard weight on the racket, gradually tilt the racket upwards, and measure the angle at which the weight slips. A referee could do that, but again it does not mimic what happens under the dynamic conditions of play.
Hardness: Perhaps a test could be devised for the referee's use, but does it have the same disadvantage of not duplicating what happens during play?
Elasticity: The tangential elasticity of the covering is of the utmost importance - but it doesn't look like something a referee could measure.
Our thinking at this stage is that there is little likelihood of our developing control tests for the referee. So let us turn our thoughts to separate laboratory tests on the outer layer of normal or inverted pimpled rubber and the sponge layer.
Pimpled rubber: Dynamic friction is important. There is a device for measuring this which projects a ball rapidly, with controlled spin, at a controlled angle on to the sheet of rubber. The speed, spin and angle of the reflected ball are measured automatically and the friction - and other properties - computed. Unfortunately, the only such device we know of is owned by its developer, who happens to have close ties to a rubber manufacturer. We are uncomfortable with this situation. We are aware of the various "robots" that are available in the marketplace but these were developed as training tools, not as scientific instruments, and we do not believe they have sufficient accuracy for our purposes. Hardness, density and perhaps other properties are important, and could be measured by fairly simple methods. That leaves elasticity, which would have to be measured dynamically, and standard items of equipment are available for doing this.
Sponge: Pore volume, density and hardness can be measured simply, but what is of more importance, perhaps, is the elasticity, measured dynamically as for the top sheet. However, there is another complication with sponge. Is it adequate to measure the sponge as it comes out of the wrapper? That is not what most players use; they use sponge that has been wetted with a solvent. Is that how we have to measure it? What solvent should we select? How much of it? How long should we wait between wetting the sponge and measuring it? When we think of all these complications an alternative method of reducing the speed of the ball rapidly becomes more attractive. Why not simply reduce the maximum thickness of the racket covering? For instance, should the total thickness of the rubber/sponge combination be limited to 3 mm instead of 4 mm?
3) Thirdly, we must relate the measured properties to actual play and determine suitable limits. We may measure many things, but we should make clear when we select an item to be measured what is important to our sport. This may very well turn out to be rather complicated. We can, perhaps, be certain that friction will play an important role, but when it is added to other properties who can decide how much influence is due to one single element like friction? And if one considers the numerous combinations possible of only the proposals mentioned here, how can we find some clear-cut and easily comprehensible answers? When we believe we have some of these answers there will still be the question as to what kind of table tennis we want; in other words which limits should be established to achieve an objective that is not yet defined. Should we slow down the average speed by 10%? Compared to what? Should the average number of returns per rally be doubled? What is our aim? These are subjects on which we can offer opinions, but the decisions will have to be made by the Council or the BGM.
4) Finally we must determine control procedures. As stated above there is a choice on where to measure this, on the playing floor and/or at the source of supply. On the floor there will be a demand for cheap, lightweight equipment with high accuracy for referees. Will such equipment be available, and what will it cost? For the rubber manufacturers also there will be economic considerations and not all suppliers have the means, or expertise, to go deeply into the question. Will this affect all suppliers fairly? Probably the suppliers will have to pay initially, but eventually the cost will be transferred to our players. How great will the impact be? For the suppliers it may also be important that the "time to market" will be longer as a result of prolonged testing.
As we have said before, our sport has become far too technical, but it is the way things have grown around us. We must now face the problems, and meet the challenges involved. We firmly believe we must have an objective measurement scheme where results can be controlled and repeated. There are many players who have their own feelings here which probably assist them, but this could be of little help to others. There was a proposal once that players should receive their racket when entering the hall and should play with that one only; that is, all players would play with identical rackets. This implausible idea would be most unattractive to both players and suppliers, so we are left with finding some way to keep the many coverings available within some boundaries to be determined. We hope that these notes give some idea of the complexity of this problem. We are looking for advice, and would welcome any suggestions. Any proposals or comments may be sent to Odd Gustavsen (
[email protected])
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