Bischoff, V. 2010. Hull form of the Oseberg ship.

Maritime Archaeology No. 25 • Summer 2010 from Denrrtark Vaaler Moor and more ·-" Archaeology and the Sea in Scandinavia and Britain J_ \_ ~ A pecsonal account More and more students in mari time archaeology, that mea ns more and more opportunity for maritime archaeo logica l projects, now and in the future. Such projects can take very different forms as th e Newsletter, including this 25th ed ition, shows . Submerged landscapes and fasc inating f li nt are more than ever at the centre of attention, as An ders Fi scher reports. Others, such as the gra nd o ld man of D anish maritime archaeo logy, O le Crum lin Pedersen do not think fl ints are fasci nating at all. At least, that was one of the things he sa id whi le presenting his new book Archaeology and the Sea, in Roskilde - w here else? - in the beginn ing of May this year. lt is a fasc inating book, conso lidating more than fifty years of research in many fasc in ating aspects of mari time archaeo logy in northern Europe, center ing on D enmark and the place of its people in space and ti me. Flint is not incl uded, or hardl y. But there is much to read on ships and ships graves, nava l prowess and defence, trade and exp loration as well as detailed work on finding sources and starting (re-)constructing protoh istori c ships, pub li shed in many books and articl es . lt is all conven ientl y brought together as num ber 3 in the Viking Ship Museum 's series Maritime Cu lture of the North . it is, as usual, given pride of place. Th e book is also a personal account. On th e very first page, it relates how CrumlinPedersen consul ted prehistory professor C.J. Becker in Copenhagen on the prospects of studying archaeo logy and do 'someth ing' with boats. Not an option, accordin g to th e then authority, no way to earn a liv ing. So Crumlin-Pedersen decided to study nava l arch itecture and tackle hi story and archaeo logy from that angle, indirectly or direct ly providing a living for a w hol e generation of maritime archaeo logists. More than a decade later, I experi enced a different attitude in Becker's contemporary, friend and counterpart in Leiden, P.j.R. Modderman. His early career had made him excavate 'M 107', a high medieval ship site in recently reclaim ed land. That was in many ways by chance. He saw its importance, however, and felt that spec iali sed technical understanding needed to be developed, just as this is the case with flint or pottery. lt was an understanding he did not see himself developing. But he certain ly encouraged the combine archaeo logy and idea to try ~ nd maritime technology. Boats are, after all, at least as fascinating as flints or pottery in bogs. Every second year Modderman organised an excu rsion to different parts of Europe. 1978 brought us to Denmark and back in two minibuses, and archaeo logica l shipfinds were high on the agenda. Ladby, Lejre, Roskilde, and Amose were some of the stops with boat connotations. Moesgard, Vorbasse, and Vedbaok were not forgotten, and neither was Vandkunsten in Copenh agen, to pay respects to, C.J. Becker. But first we visited Schleswig and th e Landesmuseu m in Gottorp Slot. it was the last time in many years that I saw the Vaaler Moor 'boat' that adorns the cover of this issue. After many yea rs of storage, it was recently put back on display; a good occasion to visit it with students, in two minibuses actua lly (yes, the Maritime Archaeology Programme acquired a second second-hand car!). Moreover, it could be taken as starting point for the students to dive into a wealth of archaeological questions: how does the boat compare to logboats in their respective countries, from Portugal to Sweden? What are the different research traditions? How is the boat supposed to fit into th e ' development of ships'? But equa ll y: how ca n this boat or group of boats be interpreted in the wider archaeological context? What are the different archaeo logi cal contexts along the North Sea in th e relevant time period? How, do these relate to geology and waterlevel change? A maritime archaeologist, like every archaeologica l specialist, should after all be ab le to work with a wider archaeologica l understand ing. Th e mu seum's director, Cl aus von CarnapBornheim, vice-director Ralf Bleil e and their staff are thanked for the warm welcome that we received, com ing back for the students to experiment with different techniques in documenting the construction. The work will be conso lidated in a booklet, as we did earli er with the Gredstedbro ship as starting point. But there is more than Vaaler Moor. Work on the find materi al of the St Ceorge, the British maritime pearl on the Danish west coast has seriously started. Paul Montgomery reports in this issue. Two other theses follow, and a detailed study of the rudder is nearly ready for publication. Two reports were published as a resu lt of last year's fi eldwork, on w hich a short note by )ens Auer. just like a report on the excavation of th e logboat-find 'Kadoe lerveld' the full reports are avai lab le on the internet (www. mariti mearchaeo logy. dk). Vibeke Bischoff has a fine contributi on on th ~ Oseberg ship. lt is yet one furth er step in a tradition of detailed technical analys is that Crumlin-Pedersen started . j an H ammer Larsen reports on an area survey in the Kattegat. And then, in April, the pipelaying barge Castoro Se i started its work on the Nordstream pipeline, the first transnationa l maritime construction project that included archaeologica l co nsideration over its fu 11 trajectory through the maritim e zones of five individual co untri es . Will construction work be as consciousl y considerate with cu ltural heritage as promised? lt would be a novum, but why not. Thijs }. Maarleveld 3 Hull form of the Oseberg ship The Oseberg ship, built in AD 820 and buried in a grave mound 13 years later, was excavated in 1904. Shortly after, the ship was re-assembl ed for exhibi t at th e Viking Ship Museum, in Bygd0y, Os lo (Br0gger 1917). For almost 100 yea rs, the ship, of which almost 95% of the original wood is present in an amazing state of preservation, was rega rded as a truthful reconstruction. lt is 21.5 m long with a breadth of 5.0 m. However, when the ship was assembled in 1906-07, a series of decisions were made, that deserve ca reful scrutiny. In 1987, a full-scal e reconstru ction, baptised Dronningen, was built in Norway. lt was based on drawings of the ex hibited ship. Dronningen caps ized during its very first sea tri al, sa il ing on a close reach in a 4 Beaufort 5 wind. Her speed was about 8-10 knots. An alyses of the sailing tri al, as we ll as a subsequent test of a 1 :10 sca le mode l in a hyd rodynam ics laboratory, showed that th e bow water shipped over the sheer, when the vessel reached a speed of approx imately 9 knots and a heel angle of approx imately 10 degrees (Goda l 1988). There have been many hypotheses about what went wrong. Was it tbe keel rocker, the shape of the bow, too small a crew, too li ttl e ballast, or too large a sail (Bischoff 2007)? Would the orig in al ship have done better? The onl y way to find out was a thorough The well preserved Oseberg Ship in the Viking Ship Museum in Oslo, Norway. Photo: Th e Viking Ship Museum, Oslo. examination of the exhibited remains. With the firm belief that new methods and new expertise would bring new answers, the Oseberg Project 2006 aimed to evaluate and reconstruct the hull form of the Oseberg ship anew, through new documentation methods and a reconsidered interpretation of the preserved parts (Bischoff et al. 2007). Recording and modelling In 2006, the interior was systematica lly photographed, and two different scann ing methods were used to document both the interior and exterior of the vessel. The outs ide was documented with a photo scanner, 10 points/mm2 and with minimum 0.5 mm accuracy. The inside was scanned by laser, 0.3 points/mm2 with 6.0 mm accuracy. Photo scanning is a very time-consuming process and creates large digital files, but it is much more detailed and accu rate than laser scanning, which is rougher and more blurred. Both scanning processes were comp limentary to each other and a great help in the reconstruction process. On the basis of the scans, 2D drawings of all parts The elements were cut in cardboard and assembled in a 3-0 reconstruction model at 1: 10 scale in which all preserved parts were taken into account. Photo: W Karrasch, The Viking Ship Museum, Roskilde. . were made. Cracks and deformations in the individual elements were scrutinised in order to reconstruct the hull form reliably. The drawings and photographs that had been made during excavation and assembly formed additional information . Each part was then cut out of cardboard and assembled in a 1:10 scale model. For this purpose, the 1 :10 scale drawings were printed on paper and then glued onto cardboard with the same scaled thickness as the ship parts, ensuring that the planks can be assemb led correctly, and that all preserved parts are taken into accou nt. By creating a physical 3-D model in this way, a reliable hull form ca n be estab lished. As the hull form is a coherent structure, o ne ca nnot make alterations in one dimension without influencing changes in other dimensions. If a large percentage of the ship is preserved, 5 the model thereby will present a reasonably precise image of the original sh ip (Ravn et al. forthcoming). Adjustments to hull form The outs ide of the ship as exhibited appears smooth and coherent and shows no visible signs of irregularities. The inside of the ship, however, is more irregular, with several cracks and fragmentary pieces. The interna l structure and planking show the results of manipulation. When found, the ship was deformed and broken in 2000 fragments. In the grave mound, the sides had been pressed down, so that the bottom of the hull was at the same height as the sheer. During the excavation in 1904, all ship parts were measured and documented in situ, before they were removed and stored for about 2 years. During assembly, the reconstructors During the assembly of the ship the reconstructors did not have sufficient control of the angle of the stem. Photo: The Viking Ship Museum, Oslo. 6 understandably faced problems on which they took radical decisions. Photographs from the storage show very fragmentary, deformed and driedout hull parts, and it is obv ious that the reconstructors had a tremendous task. In the 1917 publication, it is noted that some parts had to be steamed up to three times in order to press them into their original shape (Bmgger 191 7: 86-87). A photo taken during the assembly of the ship shows, that the reconstructors did not have sufficient contro l of the angle of the stem. The top strakes were not attached to the stem, and there were major problems in connecting the planking in that area. These problems most likely resulted from the very start of the reconstruction process. The keel had been laid slightly too straight. lt was broken in many fragments when found, so its rocker is unknown. Equally, the stem was made to heel a b it too much forward. Difficulties then occurred when the upper strakes- where the ship is broadest- did not reach the rabbet. In conseq uence, the reconstructors had to press the ship's sides inward. For this to be possible, the beams were shortened. Also, the floor timbers are very fragmentary. Th e lower edges of th e floor timbers and the protruding cleats upon wh ich they sit had collapsed. Thi s problem caused the planks to appear up to 7 cm closer to the floor timbers than they originally were. The lines drawing used for building the full-scale reconstruction Oronningen did not take this collapse into consideration . Furthermore, the top ends of severa l floor timbers in the forward part of the ship were broken at the eighth strake. While putting the ship together for display in. Bygd0y, the reconstructors pressed the top ends of the floor timbers further into the ship than they would have been initially, ca using th e bow to be more narrow and more flat in cross-section than it would have been originally. By superimposing a simplified sketch of an excavated floor timber on a cross-section of the recent laser scan of the timber as displayed, it was clear that during discovery, the floor timbers in the bow were wider than they appear today. This is supported by the in the bow seem to have fact, that the ~earns been shortened, although it wasn't possible to determine by how much. During reassembly, some were cut or were put together from parts that did not fit. The fact that several of the supports between the floor timbers and the beams in the bow were skewed, instead of vertical, as are other supports in the aft of the ship, supports this observation. On the basis of these observations, it was possible to stipulate some changes in the hull form that might be cruci al to the sailing performance of the ship. Adjusting the shape of the floor timbers and reconstructing the co llapsed cleats and frame edges gives the hull more fullness and lifts the stem. Correctin g the shape of the floor timbers by making them wider gives the bow area a concave cross-section and more hollow water lines below the bilge. Sailing performance After completion of the cardboard model, its dimensions were recorded. This was done with a digitising tool (Faro Arm), and the measurements were directly entered into the drafting programme Rhinoceros (Hocker 2000, 2002). On the basis of this, a 3-D lin es drawing and a 3-D solid model were produced. Physical waterproof models were then made of the lines that had been used in 1987 and of the new lines in order to see, if th e sa iling performance had changed after readjustment of the hull form. The models were tested in the laboratory of the Norwegian Marine Technology Research Below left: The lower edge of the floortimbers and the protruding cleats were collapsed. Below right: Th e top parts of the floortimbers in the bow area were pressed in during the installation. Photos: V. Bischoff, Th e Viking Ship Museum, Roskilde. 7 Several bities in the bow area were shortened or assembled in correctly during reconstruction for exhibition in 7906-07. Photo: V Bischoff, The Viking Ship Museum, Roskilde. In stitute (MARTINEK) in Trondh eim, w ith different displacements, different heel angles, and different leeway angles. Th e engin eers then measured th e sa iling performance of the ship under conditions up to 20 knots and up to 15 degrees of heel angle and 10 degrees of drift angle. The flow of water around the hull was remarkabl y different in the two sca le models. The old model pressed the water to the sides rather than guiding the fl ow under the hull. This meant that the bow dived instead of ga ining lift, w hen speed in creased. The new model created bow water that guided th e flow under th e hull, w hi ch made th e bow lift remarkably when ga ining speed. The tank tests showed two comp letely different ships w ith very different performance leve ls. 8 Conclusions This research has led to a better insight into the ori ginal hull form of the Oseberg ship and has provided more know ledge of th e sa iling capab iliti es of a Nordic ship of around AD 800. The project showed that the ship origin al ly had more fu lln ess in the submerged part of the hull, and th at it has been broader above the waterline in its forward part than it appears on displ ay today. The new reconstruction of th e Oseberg ship has a more concave cross-section in the bow area w ith its stem lifted a littl e more out of the water. The reco nstruction revea ls that this Iift gives the vessel a more rockered kee l than was assumed and realized in the exhib ited ship. Al l these factors are of vita l importance for the water flow around the hull, affecting the ship's overa ll sai ling performance. The corrected reconstruction of the bow shape all ows the conclusion that the Oseberg reconstruction Dronningen actual ly had less buoyancy below the bilge and a different run of the strakes in the bow than the original ship, wh ich may have been the ca use for the bow water to ship over the sheer so unfortunately resu lting in th e sinking of the vesse l in 1987. Although the new hu ll form was tried in a tank test, it remains to be seen if a new ful l-scale reconstruction wi ll all ow for a more seaworthy, more stab le, and better-sa i Iin g vesse I. Vibeke Bischoff References Bischoff, V., 2007, Gaden Osebergskibet. Kysten 2007, Nr. 3, 36-40. Bischoff, V. Paasche, K. & R0vik, G., 2007, Rekonstruksjon av Osebergskipets form . Unpubli shed report. Bonde, N . & Christensen, A.E., 1993, Dendrochrono logical dating of the Viking Age ship burials at Oseberg, Gokstad and Tune, Norway. Antiquity 67: 575-583 . Br0gger, A.W., Fa lk, Hj. and Shetelig, H ., 191 7, Osebergfundet. Bind I. Kristia nia. Goda l, )., 1988, Rapport am Pnwesegling. Unpubl ished report. Hocker, F., 2000, New too ls - for maritime archaeology. Maritime Archaeology Newsletter from Roskilde, Denmark, No.14, 27-30. Rosk il de. Hocker, F., 2002, New too ls - for maritime archaeo logy. Maritime Archaeology Newsletter from Roskilde, Denmark, No. 18, 50. Roski lde. Ravn, M ., Bischoff, V., Englert, A. & Nielsen, S., forth coming, Recent Advances in Post-Excavation Documentation, Reconstruction and Experimental Maritime Archaeology. In: Catsamb is, A., Ford, B. ; nd Hamilton, D. (eds.), Oxford Handbook of Maritime Archaeology. New York. Bonde, N. & Stylegar, F.A. Fra Avaldsnes ti l Oseberg. Dendrokronologiske unders0kelser av skipsgravene fra Storhaug og Gr0nhaug pa Karm0y. Viking, Norsk arkeologisk arbok Bind LXXII - 2009, Oslo 2009. Rhinoceros, a 3-D design software package, is suitable for making a surface modeling of the hull, which is required to produce a solid test model for a hydrodynamics laboratory. Drawing: Vibeke Bischoff 9