Whatever Boats They Float

Engineering analysis confirms feasibility of ancient maritime trading.

Dorothy Hosler, professor of archeology and ancient technology, has long known that ancient peoples from Ecuador and western Mexico had contact with one another. In 1986 she published research demonstrating that Mexican metalworkers adopted South American metalworking techniques around the year 700 c.e. But she's been trying to confirm ever since that they connected over water, not land--and to determine how much cargo they were capable of transporting.

Dorothy Hosler (far left) and Leslie Dewan ’06 (standing) on their “ancient” raft. Credit: Donna Coveney/MIT

A pair of sailors has twice tried to navigate from South America to Mexico in replicas of Ecuadorian sailing vessels. But shipworm infestations and lack of engineering expertise thwarted their efforts. "Professor Hosler told the class about this problem, and I found it completely fascinating," says Leslie Dewan '06, who took Hosler's Materials in Human Experience class as a sophomore.

Dewan and three other students were especially intrigued by the steering mechanism used in Ecuadorian sailing craft: three sets of centerboards and curved sails, rather than the conventional rudder and keel. "We wanted to see how close to the wind you could go, how quickly you could turn," says Dewan. "It's difficult to model that mathe­matically. You really have to build one of the boats and try it out."

So they did. During the summer of 2004, the four students built a three-meter boat, following early European explorers' written accounts of Andean crafts. Because their $600 budget didn't allow them to import balsa logs from Ecuador, the students took apart old docks at the Dorchester Yacht Club, reclaiming the pieces of Styrofoam that had kept the docks afloat. Then they planed the Styrofoam and covered it with plywood to mimic the density and elasticity of balsa. In two days at the MIT boathouse, they lashed the planks of faux balsa together with hemp rope. They also made a mast from a young oak tree, centerboards out of pine boards from Home Depot, and sails out of fabric left over from Daedalus, the human-­powered aircraft built at MIT in the 1980s. Then they set sail on the Charles, gathering data about how well the sail and centerboard handled, how close to the wind the raft could sail (about 60º), and whether it could tack and jibe successfully (it could).

The following fall Dewan, who earned degrees in both mechanical engineering and nuclear engineering, used computer-aided design software, a finite-element analysis program, and software she wrote herself to try to identify the size limits of the crafts, the times of year at which they were most likely to sail, and the constraints on the amount of cargo they could handle. The data allowed Dewan and Hosler to draw anthropological conclusions; by showing that the ­Ecuadorian rafts were capable of navigating between Ecuador and Mexico and that they could carry between 10 and 30 metric tons of cargo, the researchers strengthened the argument that the South American metallurgical technology was transmitted to Mexico by maritime routes. The findings were published in March 2008 in the Journal of Anthropological Research.

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"No archeologist has ever attempted this kind of problem before, because we've never had the mechanical-engineering expertise and enthusiasm," Hosler says.

As for the raft, it met a decidedly modern fate late one night a year after its construction, when a group of undergraduates took it apart and used the material to construct paddleboats. But Dewan didn't mind. She's planning to build another raft--this time with real balsa.