archaeologists discovered a number of shipwrecks.
During the extension of the seaport of Wismar in Mecklenburg-Western Pomerania, Germany, archaeologists discovered a number of shipwrecks. One of them, the last to be discovered, was resting in only 9.8 feet (3 meters) of water.
The Baltic Sea water and silt of the harbor had almost perfectly preserved the wreck’s timbers, due to the harbor’s seafloor environment being anaerobic, with very low alkalinity, almost no bacteria or rot, and no woodworms.
Measuring approximately 78.7 feet (24 meters) long by 13 feet (4 meters) wide, the large open-decked ship dates back to circa 1188. 3D scanning would later show that it had been constructed entirely with axes and adzes, and dendrochronology revealed that the ship’s oak and pine timbers were from Western Sweden. It had an estimated crew size of 8-12 men.
“It’s a descendent of Viking ships,” said Dr. Jens Auer, maritime archaeologist and project leader, “and it was buried under sand and silt down through the centuries.” He went on, “It was a heavy, load-bearing cargo ship, of Nordic design, built with great care and durability…with overlapping pine planks, clinker-style, with a beautiful curved construction…made during a relatively peaceful period of time, it very likely carried cargoes such as timber, stones, or even heavy shipments of beer.”
“When we lifted the wreck from the sea, we were amazed at how fresh the pine timbers looked, as if they had just been cut the day before,” said Auer.
To compare the three shipwrecks in terms of their original construction styles, the first and second ships had been a flat bottom ship and a pointed, Viking-style ship, respectively, while the third ship, referred to as the “Big Ship,” was an extremely strong cargo ship with a square sail, built for transporting heavy loads around the Baltic Sea region.
The archaeologists’ next step was to fully study and document the shipwreck, both for preserving it as precious cultural heritage, as well as to understand as much as possible about this one-of-a-kind archaeological treasure for modern and future generations of researchers and others.
But it was a race against time. Winter was setting in, and the now-exposed timbers resting below in the silty water would be increasingly vulnerable to damage. They had to act fast, to lift the wreck from the harbor floor and quickly begin the process of studying and documenting the surviving timbers with the highest levels of scrutiny.
When Auer looked at how they had done 3D scanning and documenting in the past, and with what technology, he realized that there was no way they could clean, scan, process, describe, annotate, and photograph all 228 timbers of the Big Ship in even one year’s time.
Auer put together the best team of specialists he could find: he invited 3D recording specialist and maritime archaeologist Thomas Van Damme of Ubi3D, who brought with him a unique workflow for scanning and annotating 3D meshes in Rhino, as explained below, as well as maritime archaeologist Massimiliano Ditta, who was placed in charge of 3D scanning, together with photogrammetry and 3D recording specialist Marie Couwenberg of Belgium, and maritime archaeologist Benjamin Halkier of Denmark.
“We took one week to decide exactly how to do the scan, which processes and methods to use, and in precisely which order,” said Auer.
They had been using the Faro Arm 3D scanner, a contact scanner. By bringing the scanner in direct contact with the object being scanned, individual points are scanned, converted to solids, and finally into 3D models. It’s a long and slow process, and it requires expert technicians for everything to go smoothly.
Past experience showed them that even working all day, they would at most be able to scan and fully annotate only 1.5 timbers/day. With 228 timbers waiting to be scanned, this put their time to project completion at over one year. That was simply too slow, and so they had to find another way.
During his time on the ecological impact assessment and shipwreck preservation work on an earlier project, Auer had been introduced to the professional 3D scanner Artec Eva by the knowledgeable specialists at Artec Gold Certified reseller KLIB. Eva is a lightweight, full-color 3D scanner used across a variety of industries, including archaeology and reverse engineering. Auer was highly impressed by what he saw. As a final test, he tried out Eva on some wet timbers. When he saw how fast and accurately the handheld structured-light scanner captured the full spectrum of detail of the timbers, he made his decision immediately and chose the Eva.
And so upon Auer’s strong recommendation, the team moved ahead with using Eva for working with the Big Ship.
“Normally one year would have been needed to scan and annotate all these timbers the old way, but with Eva, we did everything in just one month!” said Auer
The process of scanning the timbers with Eva went as follows:
The scanning took place in a Schwerin warehouse, not far from the famous Schwerin Castle.
“7 timbers/day, including cleaning, scanning, annotating, describing, photographing...228 timbers in 33 days by a 4-person team,” said Massimiliano Ditta.
Every day, 7 timbers would be readied for scanning, 2 of them would be patted dry and scanned one at a time, while the remaining 5 others would be waiting under wet cloths. The reason for this is that anything more than 20-30 minutes of exposure to dry air would cause the timbers to begin to buckle and rupture.
“Scanning all four sides of each 26.2-foot-long (8 meters), .7-1.1-inch-thick (2-3 cm) timber took only 5-10 minutes,” said Massimiliano Ditta.
“Even though the Eva was new to me, and I had to take a little while to get used to it, I like it so very much…it saved us loads of time and was really comfortable to use, especially compared with the Faro contact scanner,” said Ditta.
He went on, “We scanned some of the timbers on their sides, while others, because of too much bending when we laid them flat, had to be suspended by ropes from the ceiling and we scanned them hanging that way.”
Van Damme explained the entire process, which he created and then refined with Auer and Ditta and the others during the project, and then later presented at an ISBSA conference.
“First, each timber was scanned, all four sides, and the scans were processed and turned into beautiful, full-color textured meshes in Artec Studio. These are the most ideal digital replicas of the timbers possible. From there, these were exported as OBJ files over to Rhino 5 for annotation.”
“Then in Rhino, each characteristic of the timber was fully annotated, via the PolylineOnMesh feature, stored on separate layers, in precisely the location where it was found on the wood. These notes included details on every cut and chop mark, all the nail holes, each and every little scratch, the wood grain itself, what kinds of nails were used, whether they were iron nails or wooden treenails, which tools were used for construction, if there were signs of repairs made, what kind of wood was used, and even which part(s) of the tree that wood had come from, whether trunk or branch, etc.”
“During this annotation process, not only did we have the digital textured meshes with us, but we were actually looking at the real physical timber right in front of us, which we examined extremely closely.”
“Following these two steps, we produced 2D technical drawings for all the timbers, one by one, in full and complete detail. These drawings are basically distilled versions of the 3D models, showing only the interpreted information that is relevant to researchers, including the outline of the timber and cross-sections to show its shape, and the color-coded polylines showing the various characteristics we annotated on the timber in Rhino. By having a 2D technical drawing of the timber, other researchers can ‘understand’ the timber at just one glance,” said Van Damme.
“The great advantage of the Artec Eva was that, in comparison to photogrammetry, it was a lot more user friendly, meaning that even people with relatively little experience working with 3D scanning could carry out the documentation + it was just more ‘fun’ and ergonomic to scan timbers this way, rather than taking 300+ close up pictures of each timber from awkward angles,” Van Damme explained.
These technical drawings, as well as 2D views of the textured meshes of the timber and written descriptions of each one were added to the Timber Catalog at the end of the published report, and this has allowed researchers to examine each timber in detail. The Timber Catalog contains a legend that explains what the various colors on the technical drawing refer to.
“In the past, all edges of timbers had to be traced using a contact digitizer (such as the FaroArm), which was very time consuming. The nice thing in our approach is that Rhino has tools which automatically convert the annotated scan (the textured 3D mesh + layers containing the polylines we drew to interpret the timbers) into a technical drawing. So the 2D line drawings are essentially generated automatically from the annotated scans, without us having to trace all the timber outlines,” said Van Damme.
When it came to later digitally reconstructing the entire ship from the high-resolution meshes of the surviving timbers, there was a bit of a problem: some of the timbers were not as well intact as others. Auer explained what they chose to do, “The port side being almost completely preserved, we simply took the side they scanned with Eva and mirrored that, thereby creating a whole ship from the side that Eva had so beautifully captured.”
Massimiliano Ditta 3D printed all the timbers for creating a small version of the ship. “I 3D-printed the shipwreck at 1/20 scale in gypsum powder, to reconstruct the wreck exactly as it was, as well as to help identify the position of several loose elements.”
The small scale model will be used for various kinds of scientific analyses, such as hydrostatic, CFD (computational fluid dynamics), etc., as well as for public outreach, to show visitors as well as people around the world, via the Internet, how the original ship once looked.
Auer and Ditta scanned the Big Ship model with their newly-acquired Artec Space Spider, an extremely high-resolution color 3D scanner that excels at creating impeccable digital replicas of even the most intricate objects.
Auer said that the entire project has gone so well that the Mecklenburg-Vorpommern Office of Culture and Conservation has recently purchased Artec’s newest professional handheld 3D scanner, Artec Leo, and is expecting delivery soon. Leo is an award-winning, revolutionary 3D scanner that includes a built-in touchscreen and offers a fully wireless scanning experience.