Reconstructed boat near Waxholm.

Table of contents:

• Stages of "aspering" building in Finland
• Manufacturing of the bottom part
• Expanding of the bottom piece over fire
• Sewn lath in the original boat
• Manufacturing of the planks
• Compare reconstructed Tuna of Badelunda boat with other boats
• Testing of the reconstructed boat on water
• Reconstruction
• Getting spruce roots for sewing
• Tensions in expanded dugout and cracking threshold

Original find (see reference in the paper) was excavated in 1952-53 by Erik Nylen, Bengt Schönbäck, Harald Åkerlund in Tuna gård, parish of Badelunda, Västmanland; now exposed at Västerås Länsmuseum.

It was the only preserved boat from among several boat graves of a large grave field. A women of considerable wealth and social position was buried in it; some arabic silver coins issued in 731-743 AD were found in her necklace, which, together with radiocarbon date 1225± 65 BP, puts the burial event to late 8^th century.

Only the lower part of the boat was preserved &ndash it consisted of a dugout bottom piece some 90cm wide and 18cm deep amidships, with one ca. 30cm wide strake on each side. These parts were of pine wood; five comparatively well preserved ribs were of juniper. False keel and fragments of false stems were also found. Upper edge, gunwales, fore and after ends were completely rotten away, so the total length can only be estimated between 6 and 7 meters. The boat had no metal fastenings, strakes (as well as thin wooden lathes over several cracks) were sewn fast with withes or tree roots (sewing material have not been identified reliably).

Bottom part was extremely thin &ndash only 7mm at the thickest and best preserved spot, it could hardly be thicker then 20 mm originally -- suggesting that it was so called "soft" dugout, expanded after hollowing.

Reconstruction was undertaken in June - September 2000, at Södertörns Högskola in collaboration with Sjöhistoriska Museet, in Stockholm. The work took some 2.5 month, together with a number of preliminary expanding experiments.

Sewing technique was chosen to be the same as in previously built boats , characteristic for Russian Karelia. Spruce roots were taken for sewing material, but as the dimensions of planking were thinner now, sewing holes were also made smaller -- ca. 6 mm instead of 8, and roots were accordingly chosen thinner. In the original boat stitches are best preserved and visible in some of the thin (~6mm) repair lathes, which were sewn onto several leaking cracks in its bottom part.

Inside view of the boat.

The challenge of this experimental reconstruction was to find the technique of expanding hollowed pieces, such as the bottom part. This was in all probability achieved by means of especial treatment with with steam and heat over a fire. The technique is known and described only for expanding of aspen wood dugouts, and even then different variations of the technique existed: while in Northern Russia and Siberia just hot water and steam were used to soften the wood, while in Finland they used to treat the boat inside with tar during expanding (Eino Nikkilä , 1935). But the bottom part of Tuna boat was of pine wood, which is much harder and crisper, and less "steamable". Of course, as a boat material, aspen is a lot worse then pine -- weaker, softer, it soaks in more water, gets heavy and rots rapidly. Many experiments in smaller scale resulted in failure before a satisfactory technique for pine wood was finally found. It was also useful to calculate tensions in a sample being expanded, and estimate their "craking threshold". For the experiment sake, planks for the side strakes were also made this way, but it was not a complete success, they cracked too much when drying; anyway it was useful to know limits of the technique before expanding of the main bottom part, and, after the cracks were patched and stopped with spruce gum, the planks still were used for the strakes. Due to the poor preservation state of the original, many details were unclear, and their reconstuction could only be guided by common sense and by "ideology" of the technique itself. Another helpful information source was different archaeological boat finds of similar design, and some boatbuilding techniques documented by ethnographists in modern time.

Testing of the ready boat on water was rather an unusual experience, she behaves quite differently from modern crafts.