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Wednesday, 17 June 2015

Chopping up shipwrecks: The science of the saw

By Sara Rich

Contrary to popular opinion, underwater archaeology isn't about gold. It isn't always about amphorae, anchors, bells, or even those brave sailors who succumbed to Davy Jones' locker. Sometimes, it's just about the ship.

In the period known as the Age of Discovery (16th-18th c.), ships were floating forests, composed of wood from thousands of trees. So to study those ship timbers is to study regional and international forest resources, local and long-distance timber trade, the art of training trees to form specific ship elements, and the science of shipbuilding. These fascinating and nuanced aspects of sylvan commerce and construction have helped articulate the globe as we know it today. Essential to this study, undertaken by the ForSEAdiscovery project in a pioneering effort, is dendroprovenance. This term, from the Greek dendros, 'tree', + provenance, refers to several scientific methods developed to determine where the parent tree of a given timber was growing when it was felled.

ForSEAdiscovery is a multi-tiered Marie-Curie Actions project with research areas including GIS, databases, historical cartography, history, dendroprovenance, and maritime archaeology. Research conducted by a team of international scholars in these diverse areas is geared toward answering questions about networks of timber trade, Iberian forestry, the nature of Iberian shipbuilding, and more. While the project historians are tracking down elusive data in archives around Europe, the team's nautical archaeologists are working this field season (June 2015) on three shipwrecks off the coast of Galicia in northern Spain: the corvette Bayonnaise (18th c.) in Fisterra, the frigate La Magdalena (18th c.) in Viveiro, and the galleon (16th or 17th c.) in Ribadeo. Wood from these (and other) shipwrecks will be provided to partner laboratories, whose fellows will furnish the first round of dendroprovenance data.

Of course, in order to perform these laboratory analyses on wood from shipwrecks, samples must be taken from actual ship timbers. Underwater. Using saws, chainsaws, and sheer elbow grease.

These well-preserved pine planks from the shipwreck of La Magdalena are in amazingly good condition for having been submerged since her tragic wrecking event in 1810. But the better the preservation -- and we want high levels of preservation -- the harder it is to cut. This plank took two divers, Sara Rich (above) and Adolfo Martins (photographer), roughly 25 minutes (and about 300 BAR of compressed air) to saw through.

Other samples don't require such effort, even though they represent enormous oak frames from shipwrecks like the Bayonnaise.

Although riddled with holes made by the archaeologist's arch-nemesis, Teredo navalis, this sample is actually invaluable -- not in gold doubloons, but in the currency of scientific data. If you look carefully at the top of the larger piece, you can see the innermost annual growth rings of the tree that this sample was cut from. These rings, and various other anatomical elements of this wood, can provide that provenance information we are seeking in this project.

Whether the wood making up this ship came from the Baltic, the Netherlands, the Americas, or right here in Iberia, the research fellows with ForSEAdiscovery will find it out and keep you posted on our progress ... and our underwater adventures too.

Sara Rich works with old wood from submerged landscapes and shipwrecks at Maritime Archaeology Trust / Maritime Archaeology Ltd. in Southampton, UK.

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