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Measurement. Playability 2

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Javier Méndez Lorente
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Table of contents: Measurement. Playability 2

Following on from the previous entry, in this article we will look at different physical characteristics that affect turf quality and what options we have for measuring them.

Ball rolling

In football, ball rolling is a crucial parameter for assessing the quality of pitches. In order to perform the test, the ball is rolled along the lane of a standard rampwhich is one metre high and has an inclination of 45 degrees. The acceleration of the ball is generated solely by gravity.

Once the ball comes into contact with the turf, you wait for it to come to a complete stop. Then, the distance between the end of the ramp and the final position of the ball is measured. Additionally, the horizontal displacement of the ball can be noted, which helps to assess the uniformity and consistency of the turf in different areas of the field.

There are many variables that can affect the results of this measurement. Among these factors are turf cutting height, cutting direction, soil moisture, turf density, and weather conditions at the time of the test. Optimum values for rolling the ball on a football pitch are typically between 6 and 9 metres.

Balloon Canister

The ball bounce is another crucial parameter on football pitches. The recommended range of values for the bounce of the ball is between 0.6 and 1 metre.

There are two main types of ball bounce meters: analogue and digital.

Analogue Meters

At the top of a structure 2 metres, there is a stop where the ball is manually placed to let it fall freely. The height of the bounce is displayed by means of a ruler fixed to the structure, which allows the height reached by the ball after bouncing on the turf to be measured. This method may be subject to human error due to the need for manual observation.

Digital Meters

Digital gauges are more accurate and advanced instruments that also use a two-metre high structure. However, instead of a manual release mechanism, these devices have an automatic balloon release mechanism, such as an electromagnet or a vacuum machine.

When the ball lands and bounces on the turf, an ultra-sensitive microphone, laser or other electronics measure the time between the first and second bounce. This time is used to accurately calculate the height of the bounce.

Digital ball bounce measuring instrument

Hardness and Firmness

In sports surface management, the terms "...", "..." and "..." are used to refer to the management of sport surfaces.firmness" y "hardness"are used to describe surface compactness, depending on the sport in question. For golf, one speaks of firmness, especially on the greens, while for other sports such as football, rugby and cricket, one speaks of hardness.

TruFirm:

The TruFirm is the standard instrument used by the United States Golf Association (USGA) to measure the firmness of greens. This device is widely known and used by greenkeepers. The TruFirm works with a hammer that has a hemispherical head, simulating the impact of a golf ball falling from a fixed height. The penetration of the hammer into the surface of the green is measured in thousandths of an inch. The smaller the indentation, the firmer the green.

Greens Firmness (USGA) Value
Very soft > 430
Soft 380-430
Normal 350-380
Sign 300-350
Very firm 250-300
TruFirm

Clegg's hammer:

The Clegg's hammer is a high-precision instrument used to measure the firmness of sports surfaces. This device measures the deceleration of a free mass falling from a fixed height onto the test surface. The impact generates an electrical pulse which is converted into units of gravities (G). Depending on the value of the suspended mass, the Clegg hammer can be used for different sports, such as golf or football.

For football, FIFA recommends that acceptable scores should be between 60 and 90 gravities. For golf, the values considered optimal vary according to the type of course: for Parkland courses, the values should be between 80 and 100 gravities, while for Links courses, the optimal values range between 100 and 130 gravities, according to the Sport Turf Research Institute (STRI).

Clegg's hammer

Bunker Firmness Measurement

The firmness of the sand in the bunkers is a crucial parameter affecting the playability and consistency of the course. To avoid undesirable situations such as the "fried egg", where the ball is excessively buried in the sand, the following are used penetrometers of bunkers. These devices are specifically designed to measure the firmness of the sand, helping course managers to adjust bunker maintenance to maintain the quality of the playing surface.

Fried egg" potentialPenetrometer Reading
Little tendency to bury itself> 2,4 Kg/cm2
Slight tendency to bury2,2-2,4 kg/cm2
Moderate tendency to bury1,8-2,2 kg/cm2
High tendency to bury itself<1.8 kg/cm2,
Bunker penetrometer

Compaction

In addition to measuring hardness or firmness at surface level, it is essential to obtain information about the different strata of the soil profile. The penetrometer is the right tool for the task. Using the fundamentals of the cone index, the penetrometer measures the pressure required to drive a conical tip into the soil profile.

Penetrometers use pressure units such as PSI (pounds per square inch) or KPa (kilopascals).

Some models of digital penetrometers have integrated data loggers, and the more advanced ones can record both pressure and depth simultaneously using depth sensors. This allows for more accurate and detailed data collection, facilitating analysis of the compactness of underlying layers and helping to implement more effective maintenance practices.

Digital penetrometer
Measuring Compacity in Depth

Measuring compactness in depth is essential for deciding the depth required for decompaction work. This practice ensures that sports surfaces maintain their integrity and optimal playability. One of the critical aspects to consider is the high inverse correlation between volumetric moisture percentage and hardness or firmness values. It is crucial to test under constant moisture conditions to obtain comparable and accurate results.

Uniformity Tester

The uniformity tester is used to detect non-uniform areas on football pitches, golf tees and other sports surfaces. This device is essential for surface homologation, as it allows the quality of the pitch to be determined and ensures that it meets the required standards. The measurement process generally involves passing the device over different areas of the surface, recording any variations in elevation or ground texture.

To maintain the quality of the surface, deformation values should not exceed 10 mm and in no case more than 20 mm. These parameters ensure that the surface provides a fair and high quality playing experience. Measuring surface uniformity and controlling these values ensures that the course meets playability and safety standards.

Ruler or level with measuring wedge

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