[Editors] Floating a big idea: MIT demos ancient use of rafts to transport goods

[Jen Hirsch]

MIT News Office
Massachusetts Institute of Technology
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Floating a big idea: MIT demos ancient use of rafts to transport goods
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For Immediate Release
WEDNESDAY, MAR. 19, 2008
Contact: Elizabeth A. Thomson, MIT News Office -- Phone: 617-258-5402  
-- Email: thomson at mit.edu

PHOTOS, DRAWING AVAILABLE


CAMBRIDGE, Mass.--Oceangoing sailing rafts plied the waters of the  
equatorial Pacific long before Europeans arrived in the Americas, and  
carried tradegoods for thousands of miles all the way from modern-day  
Chile to western Mexico, according to new findings by MIT researchers  
in the Department of Materials Science and Engineering.

Details of how the ancient trading system worked more than 1,000  
years ago were reconstructed largely through the efforts of former  
MIT undergraduate student Leslie Dewan, working with Professor of  
Archeology and Ancient Technology Dorothy Hosler, of the Center for  
Materials Research in Archaeology and Ethnology (CMRAE). The findings  
are being reported in the Spring 2008 issue of the Journal of  
Anthropological Research.

The new work supports earlier evidence documented by Hosler that the  
two great centers of pre-European civilization in the Americas-the  
Andes region and Mesoamerica-had been in contact with each other and  
had longstanding trading relationships. That conclusion was based on  
an analysis of very similar metalworking technology used in the two  
regions for items such as silver and copper tiaras, bands, bells and  
tweezers, as well as evidence of trade in highly prized spondylus- 
shell beads.

Early Spanish, Portuguese and Dutch accounts of the Andean  
civilization include descriptions and even drawings of the large  
oceangoing rafts, but provided little information about their routes  
or the nature of the goods they carried.

In order to gain a better understanding of the rafts and their  
possible uses, Dewan and other students in Hosler's class built a  
small-scale replica of one of the rafts to study its seaworthiness  
and handling, and they tested it in the Charles River in 2004. Later,  
Dewan did a detailed computer analysis of the size, weight and cargo  
capacity of the rafts to arrive at a better understanding of their  
use for trade along the Pacific coast.

“It's a nontrivial engineering problem to get one of these to work  
properly,” explained Dewan, who graduated last year with a double  
major in nuclear engineering and mechanical engineering. Although the  
early sketches give a general sense of the construction, it took  
careful study with a computerized engineering design program to work  
out details of dimensions, materials, sail size and configuration,  
and the arrangement of centerboards. These boards were used in place  
of a keel to prevent the craft from being blown to the side, and also  
provided a steering mechanism by selectively raising and lowering  
different boards from among two rows of them arranged on each side of  
the craft.

Although much of the raft design may have seemed familiar to the  
Europeans, some details were unique, such as masts made from flexible  
wood so that they could be curved downward to adjust the sails to the  
strength of the wind, the centerboards used as a steering mechanism,  
and the use of balsa wood, which is indigenous to Ecuador.

Dewan also analyzed the materials used for the construction,  
including the lightweight balsa wood used for the hull. Besides  
having to study the aerodynamics and hydrodynamics of the craft and  
the properties of the wood, cloth and rope used for the rafts and  
their rigging, she also ended up delving into some biology. It turns  
out that one crucial question in determining the longevity of such  
rafts had to do with shipworms-how quickly and under what conditions  
would they devour the rafts? And were shipworms always present along  
that Pacific coast, or were they introduced by the European explorers?

Shipworms are molluscs that can be the width of a quarter and a yard  
long. “Because balsa wood is so soft, and doesn't have silicates in  
it like most wood, they are able to just devour it very quickly,”  
Dewan said. “It turns into something like cottage cheese in a short  
time.”

That may be why earlier attempts to replicate the ancient rafts had  
failed, Dewan said. After construction, those replicas were allowed  
to sit near shore for weeks before the test voyages. “That's where  
the shipworms live,” Dewan said. “One way to avoid that is to  
minimize the amount of time spent in harbor.”

Dewan and Hosler did a simulation of the amount of time it would take  
for shipworms to eat one of the rafts and concluded that with proper  
precautions, it would be possible to make two round-trip voyages from  
Peru to western Mexico before the raft would need replacing.

The voyages likely took six to eight weeks, and the trade winds only  
permit the voyages during certain seasons of the year, so the  
travelers probably stayed at their destination for six months to a  
year each trip, Dewan and Hosler concluded. That would have been  
enough time to transfer the detailed knowledge of specific  
metalworking techniques that Hosler had found in her earlier research.

While Hosler's earlier work had shown a strong likelihood that there  
had been contact between the Andean and Mexican civilizations, it  
took the details of this new engineering analysis to establish that  
maritime trade between the two regions could indeed have taken place  
using the balsa rafts. “We showed from an engineering standpoint that  
this trip was feasible,” Dewan said. Her analysis showed that the  
ancient rafts likely had a cargo capacity of 10 to 30 tons-about the  
same capacity as the barges on the Erie canal that were once a  
mainstay of trade in the northeastern United States.

Hosler said the analysis is “the first paper of its kind” to use  
modern engineering analysis to determine design parameters and  
constraints of an ancient watercraft and thus prove the feasibility  
of a particular kind of ancient trade in the New World. And for  
Dewan, it was an exciting departure from her primary academic work.  
“I just loved working on this project,” she said, “being able to  
apply the mechanical engineering principles I've learned to a project  
like this, that seems pretty far outside the scope” of her work in  
nuclear engineering.

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Written by David Chandler, MIT News Office