the art of keeping a ball off your sand

A pre-Olympic post

 

Now a bit on one of my favorite sports - beach volleyball.   It's played on a sixteen by eight meter rectangular court on fine grained loosely compacted sand that's at least 40 cm deep.  The net is 2.43 meters high for me and 2.24 meters for women.  From there it's mostly similar to indoor volleyball.  Rather than going into rules it's more interesting to take a look into what's happening. (as with most sports there's much more going on than can be described in a few paragraphs, so just a few points - the videos give a better sense)

 

First a short segment featuring Canadians Sarah Pavan and Melissa Humana-Paredes. 

 

As the blocker, Sarah tends to stay near the net removing attack options from the other side.  Her height and jump gives her a larger set of options for placing the ball close to the net on the other side in very difficult to return locations.  Melissa's job is to cover the rest of the court - not exactly the easy task.  At 1.75m (5'9) Melissa is considered undersized, but makes up for it with amazing athleticism.  In the past decade both positions have become taller.  Six foot female and six foot six male blockers are considered undersized.  Blockers, like basketball players, often have wingspans that are longer than their height.  Defenders are usually smaller as shorter limbs tend to accelerate faster.

 

Some women can serve the ball around 90 km/h (about 55 mph)  and men are about twenty percent faster.  The fastest serves deliver about 8,000 watts of power in the women's game and over eleven in the men's.   Putting things in perspective eight kilowatts is about eleven horsepower and a good reason for serious weight training.  Or consider that an electric cooking element on a range is about 1,800 watts.   But thanks to the fluid dynamics of the ball in flight and a need to test the other team the highest speeds aren't used all of the time.

 

Calculating the power of a jump is difficult - particularly in the sand - but the most athletic women probably generate an average power of 2,000 to 2,500 watts in their greatest efforts.   This is only for a few tenths of a second, but for reference Usain Bolt averaged about 2,600 watts for nearly a second at the beginning of his record race.  (These power levels are unsustainable - if you could average 500 watts for thirty minutes you could probably win the Tour de France.)  Near the net a player sometimes adjusts their center of gravity in a jump giving them hang times similar to that of a ballet dancer performing a grand jeté.  It's part of extending the window of being where you need to be and deception. 

 

You've probably noticed putting spin on a ball can add curve to its path.  It's called the Magnus effect and the size and low weight of the volleyball gives a more pronounced effect than most of the other sports (table tennis is the exception). Topspin is most commonly used and will drop the ball short of the expected flightpath - sometimes up to a meter with a lot of spin at an optimal speed.   And like baseball there's a narrow airspeed window with little or no spin on the ball where knuckleballs can occur.¹  The airspeed window for beach volleyball  is usually somewhere around 50 km/h  - a speed that is much more common in the women's game.   Like baseball it's difficult to master, but properly done the ball can unpredictably deviate from its normal path by as much as a ball  diameter by the time it makes it to the other side of the net making reception more difficult.

Sand wind sun and heat. 

The elements are part of the game.  Try running around in the sand,  particularly deep sand, changing directions and jumping.  Walking in the sand takes  at least one point six times as much energy as a solid surface. Running and jumping can take more - up to three times as much.  Agility is difficult without a lot of practice.  On the other hand diving into the sand is much safer than diving onto a harder surface.

 

Since the ball has only weights about five eights as much as a soccer ball (football for most of the word), wind is an issue.   Players watch flags around the court to gauge the wind and will  drop sand to gauge it closer to the court. Windspeed and direction lead to "good" and "bad" sides of the court.  To even things out players switch sides at regular intervals.  As with other outdoor games heat, humidity, sunlight and shadows are issues. Moderate rain won't stop a game, but nearby lighting or heavy gusts associated with a storm will.

 

Games like baseball, volleyball, cricket and tennis share a feature based in our neurology.  Court size and ball speed are such that the fastest points average about four tenths of a second. Recognizing what's going on and reacting chews up a good deal of that time so players need to react without thinking.²   In beach volleyball deception is a common weapon.   Melissa "reads" the dynamic posture of her opponent and might notice a shift of weight to one leg.   She might change her own movement to make the other player think their intended move is correct.   Then, at the last moment, she'll make a small change and put the ball slightly out of reach on the other side of her opponent causing them to lose balance and miss the ball.   

 

You'll notice  most points see the receiving side touch the ball three times.  It can be done one or two, but usually the ball is carefully set and the two touches before the final touch allow time to read the other side and more accurately place the ball.  The best sets have incredible precision - usually within a few centimeters of where they need to be when the team is playing well.  

 

Sarah will tell you what separates the elite game is the mental component dealing with short term tactics and longer term strategies.  Communication between players and being able to "read" what the other side is doing - properly used it's probably the most powerful weapon they have.  Sarah and Melissa read simultaneously and have a sense of what the other sees.  Each has to have a lot of trust in the ability and judgement of their teammate.

 

Here's another look at some long rallies where each team is reading well and reacting

 

 

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¹ There's a critical speed for a ball traveling through a fluid like the air at the boundary between turbulent and laminar flow.  Turbulent flow dominates at higher speeds, laminar at lower speeds.  Part of a spinning ball at this critical speed will be faster than the other so the drag on that part of the ball will be lower.   A zero spin an instability in airflow wanders oscillates around the edge of the ball somewhat unpredictably giving the swerving path of a knuckleball. 

² This is a very rich area in neurology.   Physical Intelligence by Scott Grafton is a great non-technical introduction to the neurology of movement.