Archimedes Revisited

Bravo! goes to a concrete canoe race

By Chris Horn

For those of us uninitiated in the ways of engineering, the idea of paddling a concrete canoe sounds like a one-way ticket to the bottom of a lake.

But USC civil engineering students this past spring successfully launched a concrete canoe and raced it against similar canoes built by other engineering students in the Carolinas. USC was the host for the three-day Carolinas Conference 2005 that attracted teams from Clemson, N.C. State, UNC Charlotte, and The Citadel, among others.

When I first heard about the event, I thought great, why not have everyone build a cast iron kite, too? Then—along with canoes that don’t float—we could watch kites not fly.

Turns out, though, that concrete canoes really do float, and you can even paddle one around a pond. The secret is in the engineering.

“It’s the Archimedes Principle—a boat floats because it displaces enough water to create a buoyant force,” said David “Mac” McSweeney, a civil engineering student who graduated in May after helping to build USC’s entry in this year’s competition. “Archimedes was sitting in the bathtub when he figured it out.”

So a canoe made of wood, metal—or even concrete—will float if it has the proper shape to displace water. Civil engineering student Stephen Ross used a computer program to design a mold. Other students then added Portland cement, sand, and an aggregate called Dualite to come up with a lightweight concrete mixture, which they poured into the mold and shaped by hand.

The students set up a giant humidifier tent with tarps and misting machines to keep the concrete from drying too quickly and cracking. The 21-foot-long, battleship-gray canoe was taking shape, but the work was far from complete—USC’s team had 73 pages of rules to follow for the official concrete canoe competition.

“These events give students an opportunity to build something as a team and use their ingenuity to overcome engineering challenges,” said Charles Pierce, an associate professor in USC’s civil and environmental engineering department who helped coordinate this year’s Carolinas Conference. “It’s good preparation for what they’ll face after graduation.”

McSweeney and fellow senior Todd Young provided much of the leadership for the canoe construction. McSweeney had completed a two-year apprenticeship with Franz Baichl, a third-generation boat builder in Charleston.

A few days before the race, students put the finishing touches on their boat, which they painted with a faux wood pattern and christened Woody. She weighed in at a svelte 225 pounds and looked like a miniature yacht thanks to the students’ attention to detail.

“This is the best-looking canoe we’ve ever had,” said Steve McAnally, a USC civil engineering associate professor who has seen fleets of concrete canoes in his time.

But while the boat scored points for aesthetics, it didn’t fare well in a critical test. Woody floated like a cork until it was filled with water, whereupon it unceremoniously sank. It seems the students had used too much heavy grout to smooth out several rough spots and that weighed down the otherwise lightweight concrete.

All was not lost, though: In the spirit of cooperative engineering, UNC-Charlotte’s team graciously lent some large styrofoam blocks, which USC’s students duct taped (a standard tool in any engineering endeavor) in place.

At least one other team had to use styrofoam to pass the swamping test, and one of the N.C. teams never even launched its boat. The brittle concrete cracked into pieces during the interstate trek to Columbia.

When the waves had settled, Clemson’s “Aces Wild” canoe took first place, followed by N.C. State’s “Sea Wolf.” USC’s boat held up until the end of the final race when—as most concrete canoes eventually do—it cracked into pieces. USC finished No. 3 in the overall competition, which also included a quiz bowl and water fountain building contest.

USC’s team will be older and wiser in 2006. So to borrow a well-worn phrase from other sports competitions: Wait ’til next year!