The Reconstruction and Conservation of Belle

From February to late April 1997, the Texas Historical Commission (THC), under the Direction of Dr. James Bruseth, carefully documented and disassembled the remains of the barque-longue Belle.  The fourth vessel added to the colonizing fleet of René-Robert Cavelier, Sieur de La Salle, Belle, sank in the Texas coastal waters of Matagorda Bay, in the winter of 1687.  The loss of the vessel deprived the La Salle and the French settlers under his command, an opportunity of water-borne escape or resupply, and the colony failed within a few short months.

Although the location of wreck site was discovered in 1995, it was not until large pumps had drained the Matagorda Bay waters from a double-walled cofferdam in September of 1996 that the THC archaeologists could fathom the scope and breadth of the discovery.  All totaled, over the next eight months, more than a million artifacts of varying sizes, shapes, and composition emerged from the bog at the bottom of the cofferdam.  The largest artifact, comprising approximately 35% its original volume was the remains of Belle.  All of the finds, discovered after September 1996, were shipped to the Conservation Research Laboratory (CRL) at Texas A&M University.  The similar missions, but varying expertise of the two state agencies, formed an extraordinary partnership that bolstered the stabilization of both the “colonial-kit” of small material cultural finds, and the vessel herself.

During the course of the four month disassembly, twice weekly, a shipment of timbers made the 200 mile trip from Matagorda Bay to the CRL.  By the date that the final timbers were delivered in early May, 384 principal timbers weighing in excess of 23,000 pounds were in the lab’s storage vats awaiting stabilization.  CRL Director, Dr Donny L. Hamilton tasked his staff to develop a plan to stabilize the timber in toto instead of individually.  His concern was that the multi-degraded state of the waterlogged timber would inhibit alignment of plank to frames in a post stabilization reconstruction.  Since the final goal for the artifact was a elaborate museum display, an equally difficult challenge was to overcome the physics that impact the display of any watercraft structure, at sea level – air is 784 times less dense than water, the medium for which the structure was designed, and those forces can generate considerable stress and strain on already degraded elements.  Modern museum practice seldom employs rows of artifact cases with rigidly ordered object dichotomies, and few museums abide by the classical notions of kunstkammer, or “cabinet of curiosities”. The modern museum endeavors to educate and inspire its audience toward further discovery, all the while competing with alternative suppliers of entertainment for a limited amount of leisure revenue (Casey: 80). Cast against the backdrop of this theory, the display of Belle, or any archaeological ship remains represent somewhat of a paradox: a large, static, often seemingly lifeless object, but one possessing a certain vitality and characteristics and project of a sense-of-place that can easily pique visitor curiosity.

To bring hundreds of friable, fragmented, and waterlogged pieces into a well supported meaningful unit, pre-stabilization, while balancing representation of the artifact’s significance required an elaborate decision making process that could have only been achieved by drawing on aspects of “whole systems engineering”.  It was this “whole thinking” approach that lead to the creation of an endoskeleton of individually cast, carbon fiber laminates, the ability to modify that support structure to allow the hull to again be laid at 69 degrees, and ultimately a methodology to freeze-dry the timbers.  The initial timber and structural stabilization plan called for a “two-step” procedure to imbibe low and high molecular weights of Polyethylene glycol (PEG) into the timber before a controlled dehydration (Hoffman:1986).  Reconstruction of the timbers commenced in 2000 and the reconstruction and laminate casting had been completed by 2004.  In 2008, with the cost of PEG skyrocketing (a hydrocarbon based product its production cost mirrors fluctuations in crude oil prices) and having only completed 70% of the first aqueous bath with the low molecular weight PEG, our partners at the THC asked if there was a procedure that could be instituted to reduce costs.  Four alternative methods were proposed and subjected to peer review.  The unanimous consensus was to follow a protocol of freeze-drying the individual timbers in a chamber large enough that no individual element had to be intentionally broken or cut.  That way, less low molecular weight PEG would be needed, and once disassembled again, the timbers could be consolidated in vats that would reduce the quantity of required high molecular weight PEG by 85%.

Having first been considered a viable stabilization method for wet organic archaeological materials in the mid to late 1960s, freeze-drying is not a new stabilization procedure (Ambrose: 1971). Yet, application of the methodology has to date been generally limited to small or medium sized items, not large integrated structures with complex curves.  Several smaller craft have been successfully freeze-dried.  The reconstruction of a Sixteenth-Century Basque Chalupa (1998), freeze-dried by Parks Canada (Moore: 1998) and the Bronze-Age Dover Boat freeze dried by the Mary Rose Trust in Portsmouth, UK have both yielded satisfactory results.  The difficulty in freeze-drying larger ship timbers are the twists and compound curves of the hull and ceiling planks.  When both free and bound water is driven off, or desorbed, during the lyophilization process the physical properties of the wood shifts along the ductility scale from malleable to brittle.  In other words, the shape that the plank holds entering the process will be its final shape upon completion.  Timbers not placed on molds that accurately mimic the curves and twists of the hull shape may never again fit the hull shape.  If placed in the freeze-dryer flat any attempt to recreate, or force the curve after the process would most likely result in cracking or splitting of the timber.  Fortunately, three-dimensional recording technologies have made considerable advances in the last decade and following a reconstruction of Belle in the Lab’s 60’ x 20’ x 12’ vat it was digitally recorded in order to delineate the lines and loft molds that hold to the proper shape of the hull curvature.

On molds in the 40’ long and 8’ diameter product chamber the timbers, imbibed water and PEG are rapidly frozen to temperatures that exceed minus 40o C.  Thermal couples placed on the surface and situated in the interior of the timber, monitor the temperature and sublimation of the ice.  Once completely frozen, a vacuum is applied to the product chamber and reduced to pressures as low as 150 millitorr.  The low temperature and pressure allow the ice in the wood to sublimate, or shift from a solid to a vapor, skipping the liquid phase.  Once all the timbers have completed the freeze-drying process the hull will be reconstructed once again, this time in the public-eye on the main floor of the Bob Bullock Texas State History Museum in Austin, TX.  Scheduled starting date is November 2013.

Read the rest of the Tech Week posts, all about public archaeology and underwater archaeology!

References

  • Ambrose, W.
    • 1971      “Freeze-drying of swamp degraded wood” in Conservation of Wooden Objects:  New York Conference on Conservation of Stone and Wooden Objects, preprints of the contributions, 7-13 June, 1970.  New. York: The International Institute for the Conservation of Historic and Artistic Works, 53-58.
  • Casey, Valarie.
    • 2005    “Staging Meaning; Performance in the Modern Museum”.  TDR 49 (3) 2005: 78-95.
  • Clark, P.
    • 2004      The Dover Bronze Age boat in context: society and water transport in prehistoric Europe.  Oxford, UK: Oxbow.
  • Hoffman, Per.
    • 1986      “On the Stabilization of Waterlogged Oakwood with PEG.  II Designing a Two-Step Treatment for Multi-Quality Timbers,” Studies in Conservation Vol. 31. N3 Aug: 103-113.
  • Moore, C.
    • 1998      “Reassembly of a Sixteenth-Century Basque Chalupa” Material History Review 48 (Fall 1998) 38-44.

What Purposeful Public Engagement Means for Archaeology

The term “public outreach and engagement” is a popular, credence-lending industry buzzword, but do we know what that actually means in archaeology today? And are we as a profession committed to using these components of our work to their greatest advantage in our field? Unfortunately, the answer to both of these questions, far too often, is: No.

Public outreach and engagement in archaeology should be holistic, meaningful and a primary component of our scientific research design—and this includes all projects, from the beginning.  Unfortunately, fully integrated public engagement in our collective archaeological work is a rarity.  When we do see purposeful engagement, it is often uni-directional, refusing to engage the public in an equal exchange of information. At best, the public is often an “add-on” instead of a meaningfully-planned, integral part of the process.

There are, of course, notable exceptions to learn from in our quest to meaningfully improve our public engagement.  One such example is the California Gold Rush shipwreck Frolic, lost along the rugged northern California coast in 1849.  Although known to wreck divers, the ship’s association with the history of the area was brought to the public’s attention when Chinese artifacts excavated in a Native American contact site in the coastal range led to the identification of the gold rush shipwreck on the coast.  This identification spurred local residents of Mendocino to explore the connection between the Frolic and the founding of their city.

This exploration originated from a diverse set of voices from throughout the community. A complex exhibit of the shipwreck spanned three museums, exploring many community voices and the rise of lumbering in the Redwoods.  Research on the ship’s manifest revealed a sizeable cargo of ale, leading a local microbrewery to replicate the drink.  Community interest in heritage led to a theater production about the shipwreck’s historical significance, as well as the return of many salvaged artifacts to local museums.  And all this in addition to a series of historical books by Thomas Layton, regarding the ship, the cargo, her history, the people, and the places associated with the ship’s career.  Years later, the collections and collected stories helped inform the underwater archaeologists who finally studied the submerged remains, and reconstructed the final moments of the fateful voyage.

The defining public engagement variable in this project was the community’s active participation at each stage from the start—from the research design phase all the way through public presentation, including interpretation and implementation of both the outreach and the archaeological investigation.  In other words, the “public” was not just an outreach activity. Instead, the public became an active member of the research team that impacted both design and outcomes.  The engagement was meaningful because there was a clear role for the public to be an active participant, not just an observer.

We live in an exciting age for archaeology. Technology is changing the very nature of our work, and increasing accessibility to large volumes of knowledge. More crucially, these changes allow us to actively engage the public with far less friction than ever before. It’s time to move beyond measuring public outreach and engagement only in terms of “site visits”: lectures, tours, school visits, streaming video and websites. It’s time to make meaningful engagement—in which the public is a fully contributing member of our research team—a standard for every stage of the process.

The good news is that this trend is changing – share with us your examples of the public as part of the science.

Read the other Tech Week posts, all about public archaeology and underwater archaeology!

AUV Camera Capabilities for Deep-Water Archaeology

Autonomous Underwater Vehicles (AUVs) are built for a variety of purposes and come in many shapes and sizes with near limitless combinations of sensors and payloads.  Some are built solely for oceanographic uses, collecting water column data salinity, dissolved oxygen content, etc., while commercial survey AUVs are designed to collect geophysical (e.g. side scan sonar or seismic, ect.) or hydrographic data. Camera systems are a relatively new addition to deep AUV systems. Currently, there are only a few companies, institutions, or government agencies that operate AUVs equipped with digital still cameras capable of survey to 1,000 meters or deeper.

/C-Surveyor-III/ AUV Being Launched (Courtesy of C & C Technologies, Inc.)

I am writing here primarily about C & C Technologies’ C-Surveyor AUVs, because I have the most access to these systems (a HUGIN 1,000, two 3,000, and a 4,500 meter systems).  Although the sensor payload of each of these AUVs may be slightly different, the basic payloads include an EM 2000 multibeam bathymetry system, Chip Edgtech subbottom profiler system, and duel frequency side scan sonar (120 kHz or 230 kHz dynamically focused and 410 kHz, or synthetic aperture). C & C’s has equipped three of these AUVs with digital still cameras (George 2009a).

In 2001, C & C began using the first commercial deep-water AUV in the Gulf of Mexico.  C & C surveyed the first of several shipwrecks with their AUV in January 2001 when the AUV passed the SS Robert E. Lee during a pipeline survey for BP and Shell. The SS Robert E. Lee was a passenger freighter sunk by the German submarine, U-166 during World War II. A continuation of the project led to the startling discovery of the U-166 in March of 2001. During the course of the survey two other historic shipwrecks, the Mica Wreck and the later designated Mardi Gras Wreck were imaged with sonar as well as four of SS Robert E. Lee’s lifeboats. Between January 2001 and January 2012, C & C collected over 246,000 line kilometers of deep-water AUV data, enough to circle the earth more than six times at the equator. These have included surveys of over 30 deep-water shipwrecks many of which are historically significant.

Photo Mosaic of /U-166/ Conning Tower and Deck Guns (Courtesy of C & C Technologies, Inc.)

Integration of digital still camera

In 2009, C & C began integrating digital cameras into their AUV fleet. The AUV photography system provides black and white still photographs of the seafloor while the vehicle travels at a speed of 3.7 knots. An image is taken approximately every 1.75 seconds which equates to one photo every 3.5 meters of travel at normal survey speeds (George 2009b). The length of the camera footprint is equal to 0.75 times the AUV with an aspect ratio of 4:3. The AUV is typically flown at 6 to 10 meters altitude during camera surveys with a typical tracklines spacing of 5 meter or less allowing for overlap of photos.

The first shipwreck imaged with the C & C AUV camera was the Ewing Banks Wreck in 2,000 feet of water. The near immediate success of the camera provided archaeologists with another tool to quickly assess and ground truth potential archaeological sites in deep-water. Soon other wrecks were imaged with the AUV camera including the Mardi Gras Wreck in 4,000 feet of water and the U-166, in 4,800 feet of water.

AUV Photo Mosaic of the Ewing Banks Wreck Draped Over Bathymetry (Courtesy of C & C Technologies, Inc.)

Advantages and Challenges

Three of advantages of the AUV camera system are a) the ability to take the collected images and efficiently mosaic the photos into larger geo-referenced images; b) the ability to combine those images with the other geophysical data to aid in interpretation and site analysis; and c) the ability to quickly ground truth targets detected with the geophysical sensors.

Several hundred photographs are collected during a typical camera survey and it is important to know what portion of the seafloor each photo represent. C & C developed a software application to sync the photos with the AUV navigation/positioning system and convert each photograph to a geo-referenced image. In addition, a post processing routine was developed to equalize the repetitive flash pattern produced on each photograph, adjust for spherical light spreading, linear attenuation, and flash scattering resulting from water column particulates. The result of this processing is nice evenly lighted geo-referenced images that can then be more easily mosaiced and imported into a GIS system.

Having the photo mosaic and geophysical data (e.g. side scan sonar, multibeam bathymetry, and subbottom profiler) collected simultaneously allows all the site data to be analyzed in conjunction. The photo mosaic can also be draped over the swath bathymetry to provide a three-dimensional photographic perspective of the site. Although individual photographs and ROV investigation may be required for detailed analyses of specific areas or features of a wreck site, being able to quickly see the bigger picture along with the geophysical data offers a larger perspective of a site for assessing site formation, artifact distribution, and other aspects of the site.

The AUV camera is also an excellent tool for ground truthing unidentified targets. Often potentially significant targets are detected with side scan sonar during an archaeological survey and a recommendation has to be made based solely on the geophysical data. Having the option to collect photos over select targets, helps remove most of the ambiguity in the interpretation.

Conclusion

AUV cameras are advantageous to both the survey industry and the advancement of deep-water marine archaeology.  Since the introduction of digital still camera systems into survey class AUVs, the technology has repeatedly proven its value, efficiency, and effectiveness.  Although the technology is still in its relative infancy, it has immediately demonstrated its benefit for deep water AUV surveys in ground truthing unidentified targets, inspecting previously known sites, and creating geo-referenced photo mosaics to analyze historic shipwreck sites.

What other potential archaeological uses or advantages are there for this type of technology?

References

  • George, A Robert
    • 2009a.  Sensor Upgrades for Deep-water Survey AUVs.  International Hydrographic and Seismic Search, (August): 32-33.
  • George, A Robert
    • 2009b.  Integrated High Resolution Geophysical and Photographic AUV System.  Oral presentation given at the IMCA Annual Seminar, Rio De Janeiro Copacabana, Brazil (November).

All images courtesy of C & C Technologies, Inc.