How Waterskiing Works
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It’s not exactly walking on water. But it’s close — and you might even say it’s better. Gliding across the surface of a lake at 20 miles per hour (32 kilometers per hour) with the wind in your hair is definitely a unique feeling. And you can thank water skis for giving it to you.
Waterskiing is pretty simple. A person, wearing what looks like snow skis, is pulled behind a motorboat across the water. The water sport has about a century’s worth of history. Its development has paralleled the development of motorized water crafts. You can’t waterski behind a canoe; you must be pulled by a motorboat going at least 20 miles per hour. So, technological advancements in motor crafts have only contributed to waterskiing’s evolution. The faster the boat, the faster the skier. And speed also translates to new tricks and maneuverability.
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Aside from being a popular recreational sport enjoyed by thousands, waterskiing is also an ever-growing competitive sport. USA Water Ski guides over 900 tournaments, ranging from small events for beginners to world-level competitions each season. Skiers of all ages can compete in slalom, tricks and jumping tournaments. The International Water Ski Federation hosts several world-level competitions each year, including categories for the elite, veteran, under 21, junior and disabled water ski championships.
But before we get to the expert skiers, we need to start at the beginning. Who invented the sport? And how can you stand up on those skis?
Although very little information remains on the record, it seems that waterskiing could have originated in Sweden, given that the term vatternskida, a verb meaning to ski on a body of water, can be found in Swedish dictionaries dating back to 1921.
But, officially, the sport’s origins are anchored to two teenagers in Minnesota. The story goes that in June of 1922, 18-year-old Ralph Samuelson, who lived near Lake Pepin in Lake City, Minn., got the bright idea that if you could ski on snow, you also could ski on water. Samuelson and his brother Ben worked on their idea for a few days, and in early July of 1922, Samuelson was able to stand up on two skis while being pulled by a boat his brother was driving.
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Their equipment was very basic. Samuelson first experimented with staves of a barrel and lengths of woods held together by leather strips to form his skis. He used a window sash as a ski rope. Samuelson found that if you leaned back with the tips of your skis facing up, you could successfully glide over the water.
Although he never patented his invention, Samuelson is recognized as the father of the water sport, and the American Water Ski Association credited him in 1966 as the first on record to attempt the sport. In 1925, while Samuelson was occupied touring the East Coast of the United States, fellow American Fred Waller became the first person to patent a water ski. He dubbed his product Dolphin AquaSkees.
It didn’t take long for waterskiing to catch on. In North America and Europe, the sport increased in popularity throughout the 1920s and 1930s. In 1939, the first national waterskiing championship was held at Jones Beach in Long Island, N.Y. At the 1972 Summer Games in Kiel, West Germany, waterskiing became an Olympic sport. Today, there are more than 650 waterskiing clubs and 11 million active participants in the United Sates alone.
So, we know that after experimenting, the inventor of waterskiing found that pointing the tips of your skis up improved your skiing abilities. Why is that? On the next page, we’ll take a look at the physics of waterskiing.
In order to understand how waterskiing works, it’s helpful to know the principles of physics underlying the sport. In order to waterski, several factors come into play.
First of all, you should acquaint yourself with the basic characteristics of water. Fluids in motion can be characterized as turbulent and laminar. While turbulent water in motion has a rough surface and irregularities in its flow, laminar water is smoother. The formula, called the Reynolds number, used to compare the two types of water is:
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Re = P (density) x L (obstacle length) x V (flow speed) / v (viscosity or internal friction)
A higher Reynolds number indicates a more turbulent fluid. A lower number suggests laminar water, which is optimal for water skiing because it’s smoother and maintains a certain flow.
Before you take off, make sure the tips of your skis are kept out of the water. By lifting the tips of the skis out of the water, your position will apply pressure that will counter the force of the boat when it begins to pull you. The tilt of the ski is the source of the lift that will pull you out of the water. With the ski tip tilted up, the water will strike your ski as you move forward, creating a rebound downward from the ski. This will create an upward force on the ski and you. As long as the force of the upward water is equal to the downward force of gravity, and accordingly the weight of the skier, you’ll stay afloat. Gravity is a constant force that determines the weight of the skier, skis and the air above the water. Water counterbalances the weight above its surface.
Newton’s Third Law of Motion states that for every action there is an equal and opposite reaction. When the boat accelerates, it’ll begin to pull you. Accordingly, you will supply the equal and opposite pull against the boat. That is, you’ll lean back to counter the force of the boat. Since the force of the boat is much greater than your own, it will pull you up and out of the water.
There’s more to learn about the laws of motion on the next page.
Another important element of the physics of waterskiing is the speed at which the boat tows you. The average speed needed for a 150-pound person is 20 to 25 miles per hour (32 to 40 kph). However, when skiers use one ski, the speed needs to increase because there’s less surface for pressure to build up on in the water.
When you’re being towed in a straight line behind a boat, the two main forces acting on you are the force of the tow rope, which is created by the forward movement of the boat, and the force of the water on the skis. If there’s constant tension in the tow rope, you’ll travel at the same speed as the boat.
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When you move in a direction perpendicular to the boat across the wake, the wave created by the boat and its engine, a centripetal force also comes into play. A centripetal force happens when a body moves in a circular path around another object, based on the fact that some force is pulling the body toward the center object. For example, think about a satellite circling the Earth. In that case, the gravitational pull keeps the satellite moving in a circular path around Earth. With waterskiing, the rope keeps the water-skier traveling in a circular path around the boat. When an object moves on a curve, it accelerates. Hence, when a water-skier starts to move on a curve around the boat, he or she accelerates. When centripetal, water and boat forces act on you at once, you’ll move faster than the tow boat. The diagram above displays these forces at work.
Now that you know the physical principles behind waterskiing, you’ll learn about the basics of standing up on those skis.
Before you start waterskiing, it’s important to have a method of communication worked out between you and the people on your boat. Here are a few generally accepted hand signals.
To waterski, you should start in a sitting position in the water with your knees bent and weight shifted to the back of your skis — so the front tips of your skis will poke out of the water. Make sure to maintain your balance; the forces pushing and pulling will make balance a little tricky. As the boat accelerates, it will begin to pull you. At that point, all you need to do is stand up. To do this, keep your arms straight out in front of you and your back straight as well, but bend your knees. If you want to get some practice before you hit the water, you can try stretching your arms out straight and lowering yourself in a chair at home a couple of times to get the feel for this motion before you hit the water.
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After you’ve begun gliding along, you should keep your knees bent. This will help to absorb any of the bumps you might encounter. While you’re skiing, be sure to stay behind the boat as it turns. That way you’ll be inside the boat’s wake, the waves created by the boat. If you’re following to the side of the boat, outside the wake, you’ll whip around pretty quickly as it turns. Once you become more advanced, you can try to maneuver, cut and jump outside the wake.
When you need to stop, sit on your skis and let go of the rope. That way, you’ll glide for a while and come in for a smooth landing. Don’t try to ski into the dock. Rather, come in for a safe landing away from any object you could collide with.
Since water-skiers can reach speeds of about 50 miles per hour (80 kph), if you take a tumble, it can have pretty serious repercussions. Knee and facial injuries are the highest percentage of waterskiing injuries. Injuries can also be sustained to the arms and upper bodies as well [source: Roberts]. Executing jumps and twists can put a lot of tension on the knees in particular, so be sure to keep your knees bent at all times to prevent awkward angles or points of collisions with the water. There are some preventative measures you can take to prevent knee injuries. You can work on strengthening your calf muscles by doing lunges or squats to help you to control your knees’ flexion and extension, and thus your balance on the water.
Now that you know how to get yourself up and going, we’ll take a look at the equipment you’ll need to waterski. First, you’ll need a life jacket. This is a no-brainer. Safety always comes first. Next, you’ll need a boat that can reach speeds of at least 20 to 25 miles per hour (32 to 40 kph).
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You’ll also need skis made of fiberglass. The length of the ski depends on what kind of skiing you’ll be doing and how experienced a skier you are. If you’re a beginner, you should use longer skis because their flat bottoms will help you remain stable and allow you to turn more easily. Skis with sharp edges allow you to move more quickly, and large tips cause quicker pull up. Fins located on the bottom of the ski add to maneuverability, while the size of rockers, the curve at the bottom of the ski, allows for varying degrees of acceleration.
What other equipment do you need for water skiing?
There are a couple of different types of skis to choose from.
Combination pairs are the most common and easiest skis to learn with. They have wider tips for better control. Slalom skis, used for skiing with one ski, are good for making sharp turns and going faster. Beginner slalom skis have wider tails and flat bottoms to make it easier to get up and stay straight. But intermediate and advanced skis feature tapered tails, beveled edges and a concave bottom. Although they’re more difficult to use, once you get the hang of them, you’ll go faster and make sharper turns. Trick skis are used for jumping, spinning and doing tricks (hence the name). They’re short and wide with no fins. This makes them more difficult to control but easier to turn and slide. Jump skis are designed for jumping off ramps and are very long but light so that you can jump across large distances. When choosing skis, you should also consider the bindings, which should be made of gummed rubber or neoprene with adjustable hold-down straps and reinforcing pieces across the heel.
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Next, you’ll need to choose a rope. Look for the following characteristics:
Here are some things to keep in mind when choosing a handle:
On the next two pages, we’ll look at the many ways to waterski.
Aside from recreational water skiing, there are several types of competitive water skiing events. Let’s take a closer look at each type of waterskiing.
Trick skiing is just like it sounds; skiers perform tricks on the water. Trick skiers use short, finless skis instead of the usual gear in order to perform tricks akin to gymnastics. You can do tricks on one ski or two. Using one ski, you can do surface and wake tricks holding the rope in one or two hands. Most skiers use two hands, while more advanced skiers can even slide their back foot into the handle. In trick ski competitions, skiers have two 20-second passes to attempt as many tricks as they can. Before the competition begins, skiers must outline their routine and present it to judges. Usually, advanced skiers perform the first pass with their hands and the second with their back foot in the handle. Judges watch the skiers and award points for each completed trick. Tricks that earn the largest amount of points are wake flips and multiple turns with the handle attached to the foot. The winner is the skier with the most points.
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In slalom skiing, a skier uses only one ski with two foot bindings to negotiate a course of six zigzagged buoys. Boat speed increases by increments of 2 miles per hour (3.2 kph) until a maximum speed — set by the competition’s rules — is reached. Then, the rope is shortened in measured lengths. The winner is the contestant who rounds the most buoys without falling or missing. Skiers with slalom proficiency are those who don’t miss until the rope is shorter than the distance from the boat to buoy. This is pretty difficult; in fact, to do this, you have to round the buoy by leaning over it with your body.
What about ski jumping and racing? Learn about those next.
The object of ski jumping is to optimize distance. It’s performed on two long skis with short, wide tail fins designed to support your weight while on the ramp. There’s a rule for the maximum boat speed for each competitive division, so it’s up to the skier to increase the distance they jump. You can do this by making a single, three-quarter, or double cut in order to increase your speed and give you a longer jump. Male jumpers have approached speeds of more than 60 miles per hour (96 kph) at the very base of the ramp, causing them to jump more than 240 feet (73 meters) off a 6-foot (1.8-meter) ramp. Female skiers have jumped more than 170 feet (51.8 meters) from a 5-foot (1.5-meter) ramp.
Show skiing is a form of water skiing in which teams of skiers choose a theme, music, multiple boats or other elements of entertainment to put on a show for a crowd. This is the kind of waterskiing you might associate with TV shows and movies where people stand on each other’s shoulders in the shape of a pyramid. They’re judged according to difficulty and showmanship.
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Ski racing, the fastest type of water skiing, takes place when several water skiers race around a set course. A team consists of a boat driver, an observer, and either one or two skiers. The driver tows the skier at varying speeds, taking into account water conditions, while an observer watches the skiers’ signals and relays them to the driver.
For more information on waterskiing and other water sports, look through the links on the next page.
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How Waterskiing Works
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