How Do You Build the World’s Tallest Water Slide?

From the moment that Jeff Henry, owner of Schlitterbahn Waterparks in Kansas City, Kansas, looked at his partner John Schooley and told him that he wanted to build the world's tallest water slide, the two men knew that they were venturing into uncharted territory.

"Water slides, like boats, are an evolutionary technology, in which you do one thing and then you learn something, and then you take another step and learn another thing. In this particular ride we jumped a few steps," Schooley explains. The ride, dubbed Verrückt (which translates to "insane" in German) measures 168-feet tall, approximately 17 stories high—taller than Niagara Falls—and was officially verifed by Guinness World Records as the tallest water slide in the world.

"We pretty much built the ride in house, from start to finish, with some outside consulting from safety experts and engineers," Schooley says of the Kansas City, Kansas attraction. "A project like this is really a group effort."

So how does one go about building the world's tallest water slide—and more importantly, ensuring it's safe? Amazingly, it's little more than trial and error.

Henry has over a dozen waterpark-related patents to his name, like the Master Blaster, an uphill water coaster technology that uses water canons to propel riders up slopes. Schooley is a designer with a degree in biology and a background building yachts, and when Henry asked him for help designing the Master Blaster, Schooley found moving from yachts to water slides an easy transition. But when Henry decided to build the world's tallest water slide, the pair realized their ride might have more in common with roller coasters than with the traditional water park slide.

"The Verrückt water slide was to be a crossover fusion design between water slides and roller coasters. In some ways it was evolutionary in that we already had experience with steep speed slide geometry, rafts and uphill water coaster technology. In others it was revolutionary in that we had to invent and develop several new systems to operate this very large jump from existing technology," Schooley explains. To begin, they started by calculating the height, dictated by the requirement that the slide snatch the title of "World's Tallest Water slide" away from the 134-foot tall Insano Water slide in Brazil. Then they plotted the steepness—at what angle would riders plummet down the slide's first drop? Schooley and Henry settled on 60 degrees, a fairly steep angle that would send riders zipping down the first drop at nearly 65 miles per hour (the typical water slide has a more gentle slope closer to 45 degrees). For the Verrückt, 60 degrees was deemed steep enough to achieve a sense of weightlessness in the rider, but gradual enough that a raft could still maintain good contact with the slide.

"The second bump is what makes it much more than just a high speed drop slide. Roller coasters have valleys and hills and we wanted this element," Schooley explains. "We invented uphill water coasters and felt we could ramp up that technology to make a truly spectacular ride experience. As it turned out this decision made the ride vastly more difficult to develop."

After the height and slope were decided upon, the design team went to work building models. They built two initially, both near Schlitterbahn's corporate headquarters in New Braunfels, Texas. The first model was only 1/20th the size of the eventual slide—the team sent a tiny model car down the slide as a tester. They then scaled up to a half-size model, built from fiberglass, which still stood at an impressive 90-feet. 

Friction and gravity are the two principle forces that dictate how thrilling a ride down a water slide can be (but they're not the only forces—a rider's weight, air resistance and the material of the slide, among other things, all come into play). Riders at the top of a water slide begin the ride at rest; once they begin to plummet down the water slide, gravity pulls them downward, increasing their speed. The rider, or in the case of Verrückt, the rider atop a raft, encounters friction with the slide, slowing them down. The key is to balance a rider's momentum and friction so that they are able to race down the slide at an exhilirating speed without risking their lives.

Schooley's models could predict some of the friction and G-forces that would act on a rider plummeting down the Verrückt, but drawing precise conclusions from these calculations is tricky because of the as-of-yet unmentioned major component: water.

"What’s really difficult on these slides is that we can know something about friction with the size of the raft and how much weight will be in it, but when you start adding water into the equation, there’s actually no way to really know what’s going to happen in terms of hydraulic friction forces on it other than testing it," he explains.

So they tested it—first the 90-foot model, with sandbags and accelerometers and, eventually, Schooley and Henry themselves. When they made it down the half-scale slide with no problems, they scaled the model to full-size. The process took months, mainly because the designers spent much of their time testing raft models, trying to discern the best raft for the ride. But early tests of the full-scale slide sent sandbags catapulting off the slide's second bump—the sandbags had gained too much momentum on the way down the first drop that they weren't slowing down the way they should have been when they made it to the second hump. After watching sandbag after sandbag approach the second bump with far too much speed, and land almost 150 feet away from the water slide, Schooley knew they needed to make some serious changes in their design. 

"We were sailing rafts out into space, basically," Schooley explains. So he and Henry went back to the drawing board—literally—tearing down two-thirds of the slide and rebuilding it from a new model, based on tests from the trials that measured the ride's speed and g-force at every point on the ride. Understanding how these forces work on the raft, with water, was crucial to the team's understanding of the ride as a whole: once they knew how water impacted the raft's speed and acceleration (due to weight), they had a better sense of how to design the slide's second bump.

Using this information, Schooley rebuilt the slide's second hump higher, but longer with a shallower descent, decreasing the angle from almost 45 degrees to 22.5 degrees.

Rebuilding the slide forced Schlitterbahn to push the water slide's opening by almost a month—and set the media ablaze with concern that the insane slide was unsafe. Water park safety regulations vary from state to state, and rarely concern themselves with water slide geometry—instead they're more guidelines for the swimming areas, requiring clean water and ample warning signs. In the absence of concrete safety regulations, Schlitterbahn worked under Texas' waterpark standards, with Schooley says are some of the most stringent in the country, and third-party consultants, to ensure the ride's safety. But Schooley can also personally advocate for his ride, having been the very first human—after hundreds of sandbag tests—to take the plunge. "If you’re designing something like this that is very scary and potentially dangerous, we feel like it’s right to ride it ourselves first," he explains, adding that without riding through the ride, "you can’t really tell what’s happening for a human going through it, the G-forces and the experience."

Building the slide was only part of the project, however. The slide also required custom-built rafts, and the use of Master Blaster technology, which Schlitterbahn pioneered in the 1990s—think of it as the water slide version of the motorized chain that helps pull rollercoaster cars up hill. In order to help the raft accelerate over Verrückt's second hump, air-pumps blast water out of nozzles, which force the raft toward the second hump's crest. For Verrückt, Schooley and Henry took their tried-and-true Master Blaster technology a step further, using specially pressurized air pumps to emit blasts of air and water only when the rafts need to be pushed up the second bump (about seven seconds of the two-minute ride). This helps the ride save energy, since nozzles don't need to be emitting air continuously, and gives operators better control of the ride. "It’s really a very different type of experience," says Schooley of the feeling of a second acceleration from the Master Blaster technology. "You can’t get that type of thing happening on a roller coaster."

The water slide finally opened to the public on July 10—since then, Schooley says, thousands of thrill seekers have climbed Verrückt's 264 stairs, including the mayor of Kansas City.

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Schlitterbahn Waterparks and Resorts in Kansas City, Kansas. Day tickets start at $34.50; season passes available. Open through September 1, 2014.

Natasha Geiling | | READ MORE

Natasha Geiling is an online reporter for Smithsonian magazine.