'Sometimes students will create something that is super stable but becomes too heavy and laborious to even move it," says Leonard Perry, professor of industrial engineering at the University of San Diego. "They'll have a structure that is really wide and heavy and sturdy, and you can stand on it and not fall, but they'll forget about the idea that they have to move that [structure] across an entire 25-meter swimming pool." This weekend USD hosts the 16th Annual Walk on Water Competition, in which participating high school and college students design and build a pair of water-walking "shoes" and then demonstrate the efficacy of their creations. "It takes 20 to 30 hours to make a pair of shoes," says Martin Teachworth, physics teacher and science team coach for La Jolla High. "That's from 'Let's sit down and talk about it' to getting shoes that are completely finished. At the end of that 30 hours, they're ready to put them in the pool and practice walking."
Judges will be looking for three things: buoyancy, stability, and propulsion. Shoes must be less than eight feet long, and the cost of the materials cannot exceed $100. "There are design restrictions, just like you'd have in the real world," explains Perry. "[Students are] incorporating engineering principles using the whole engineering design process -- coming up with sketches, figuring out propulsion, stability, and flotation."
Most of the entries are made from Styrofoam and duct tape. "One of the better designs was Styrofoam wrapped in fiberglass," says Perry. Perry has seen shoes made with inner tubes, two-liter plastic bottles, PVC piping, metal, and cardboard. His favorite design incorporated a paddle wheel for propulsion, "like the ones you see on old riverboats."
Teachworth describes most shoes as "two fat skis, eight feet long, a foot wide, and about four inches thick." Propulsion is particularly difficult to achieve. "You need to design a shoe so it will glide forward, but as soon as you move your foot back, you need it to grab the water, otherwise your feet will go back and forth, like on an elliptical machine -- a lot of work but no motion. You have to design things to grab the water underneath."
The first year that students of Teachworth's participated in the competition (1996), their design consisted of wooden shoes with wooden flaps affixed beneath. "They were 12 inches long, so they floated," Teachworth remembers. "When they'd go forward, great, but when they went backward, they didn't go down and grab the water." To solve the problem, students filled empty dog food cans with rocks and affixed them to the flaps. To seal the wood they used leftover purple house paint. "They were the godawfulest-looking shoes you've ever seen, but darned if they didn't win," says Teachworth. The team took first place in the high school division; in the overall competition, they were second to a college team. One of those students is now an electrical engineer, another an aeronautical engineer, and a third just received a doctorate for geophysics.
Mishaps do occur. "The ratio is: If you make shoes shorter than you are tall, you're probably going to fall over front or back," says Teachworth. "Anything that can go wrong, does. Kids will get partway across, and then their shoes will fill with water and sink." One student accidentally put his foot through one of his cardboard shoes before the competition. His winning shoes of the same design from the year before had been kept at the USD campus and had been thrown in a trash bin earlier that morning, so the student fished one of his old shoes from the trash to replace the damaged one. The same design, as long as it is one's own, can be used year after year.
Though there have been many patents for water-traversing shoes (the first of which was filed by Bostonian H.R. Rowlands in 1858), Perry does not yet see practical uses for water-walking technology. "It's more of a way to get high school students interested in science and engineering," he says, "which has always been labeled dull and boring and for nerds." -- Barbarella
Walk on Water Competition
Saturday, April 21, and Sunday,
April 22, 10 a.m.
USD Sports Center Pool
5998 Alcalá Park
Info: 619-260-7518 or www.sandiego.edu/engineering/walkonwater