What Makes a Pool Fast?

This is one of those questions that makes non-swimmers look at you kinda funny. How can you have a fast pool or a slow pool. It’s water. And the formula for that has been known for a while.  H₂O.

But as any swimmer can tell you, there are definitely fast pools, and definitely slow pools. So what makes them that way?

Swimmers will come up with more reasons that you can imagine, and I have to admit that some of them are pretty creative.  But let’s stick with more conventional thinking.  There are 4 main factors that affect the swimming speed of a pool:  turbulence (surface waves), pool depth, water circulation, and starting blocks.

Turbulence

This is the big one – the major factor that affects speed, and the major factor that has impacted on pool design over the years. If you’ve ever swum in the ocean, you know what swimming in waves can be like.  Although pool waves aren’t as high, we do create our own waves as we swim. After all, we’re basically shoving water out of way so we can get down the pool. And those waves will slow a swimmer down when they hit them.

Turbulence comes in 2 forms:  Direct, and Reflected.  Direct turbulence is basically swimmer to swimmer. Without lane ropes separating swimmers, the pool would become one big choppy mess, slowing everyone down.  So besides separating the swimmers, the lanes ropes are there to absorb the waves that swimmers create. They’ve improved tremendously over the years.  I remember swimming in meets years ago where the lane ropes were just ropes with a little donut-shaped plastic piece every metre or so. These days all big meets will use the best ones available to absorb the turbulence.  But in many smaller meets, the pools may be using older, less-effective designs. That makes a big difference.

Reflected turbulence comes when waves bounce off the side or end walls and comes back at a swimmer.  And its usually the same swimmer that created the waves in the first place.  Handling these waves actually has taken a lot more pool design and technology than any other factor.  On the sides of the pool, level gutters can take good care of surface waves.

But two other methods are often used to handle side reflections as well.  Additional lane ropes can be put right by the walls on the sides of newer pools in order to cut down on waves before they even reach the wall.  Big international meets even call for two additional lanes (from 8 to 10) with nobody in the outside lanes.  This minimizes the impact of side reflections on all swimmers in the water. The major problem here is that 10-lane pools cost a lot more than 8-lane pools. A lot more.

End-reflected waves are much harder to control. Level gutters are less desirable as swimmers like to have a visual indicator of the end wall, timers need some place dry to stand, and starting blocks need to go somewhere.  The Milton Sports Centre shows the newest thinking in having level end gutters inset into the wall, with the wall continuing above the gutters.

Another problem with end walls are that the solid walls will very effectively reflect waves back out.  Concrete walls are very bad that way, but bulkheads can be built with many holes that can help absorb part of that incoming wave.  That is, unless they have a touch pad on the wall.  In other words, end-reflected waves are a problem for most pools, and really good solutions have yet to be found.

Pool Depth

Pool depth affects speed in pretty much the same way that turbulence does, except these waves are underwater.  As the swimmers moves through the water, they send out waves in pretty much every direction, including down. These waves fan out and lose strength the farther they travel. If the pool is shallow enough, the waves will bounce off the bottom and come back and hit the swimmers relatively hard.  The deeper the pool, the weaker these waves will be when they get back to the surface.

But there’s another way that the pool bottom can affect speed. The transition from the deep end to the shallow end can be handled in many ways in a pool, and in most designs, waves will bounce off that transition right back at the swimmer. The best transition appears to be a gentle slope. The worst is usually a large step.

Water Circulation

Those ubiquitous water jets are in every pool, and they have to go someplace. Often right at the ends of the pool.  As swimmers come into the wall, the jets push them back, sometimes very energetically.  And while the jets will help the swimmer when they push off the wall, they are going much quicker so the jets are of very little benefit. To make things worse, the jets aren’t placed in each lane, so some lanes will be more affected than others.

Even jets placed on the sides of the pool can make a big difference if you swim in an outside lane. Our Drury pool is a good example of that. Swimming against the wall is actually difficult since the jets want to push you out.

The newest technology being used at big competition pools are up-flow jets evenly spaced on the bottom of the pool so that they don’t impact any one lane more than another.

Starting Blocks

Starting blocks have evolved tremendously over the years.  Milton is a perfect example.  The old Drury pool has starting blocks that are level, slippery and incredibly high above the water.  You cannot get a good start on those no matter what you do.  The next pool built in Milton was the Leisure Centre. These blocks are slanted, a good height, but the surface material is still a little on the slippery side. You can still get good practice in starts, but they will be a little inconsistent.  The newest pool is the Milton Sports Centre. Only a few years old, these blocks are slanted, have the new movable wedge, and a surface on which it is impossible to slip.  There is no question that the fastest starts can be done at this pool.

Other Factors

Those 4 factors make the biggest difference in swimming speed.  But there are a few other factors that can possibly, maybe, conceivably impact on performance.

• Water temperature – FINA mandates competition water temperatures to be between 25 and 28C, and by far most competitions are within this range.  However, on occasion pools can be too hot (saps energy, swimmers may overheat), or too cold (shocks the swimmer, sometimes too  cold to get muscles working smoothly)
• Wall slipperiness – The Etobicoke Olympium had notoriously slippery touch pads.  It was not uncommon to see backstrokers slip off the wall at the start, or see horribly slow turns for the same reason.  Even world champions have slipped on walls during major competitions.
• Air Quality – This seems like a strange one, but if you’ve ever spent 4-7 days at a pool with horrible air quality (e.g. Nepean Kanata pool) you’d understand. Bad air can affect breathing, induce coughing, and leave you with headaches. Definitely not a good environment for swimming fast.
• Water Treatment – Now we’re pushing it a little. There are some who insist that chlorination through salt creates more dissolved solids in the water, which makes the water more dense.  As a result, slower swimming.  And others insist that the additional salt creates buoyancy that raises the body, reduces water resistance. Meaning faster swimming. The reality seems to be that there is very little difference.
• Bright Sun – Whether swimming outdoors, or swimming inside with large windows, a bright sun shining in your eyes when you’re swimming backstroke can be a problem.

Some swimmers claim that wall light brightness, lane widths, familiarity with the pool, elevation above sea level, number of screaming fans and a host of other things affect swimming speed. The bottom line is that if they firmly believe this, they may end up making it true.