The laced boats of Scandinavia, sometimes called sewn boats, consist of overlapping clinker-style wooden planks. Laced boats have been found in Norway, Sweden, Finland, Denmark, and Estonia. In general, widespread use of these vessels predates the 4th century AD. In some parts of Scandinavia, laced vessels existed side by side with the riveted clinker hulls, likely due to specialized function or lack of iron nails (Westerdah, 1985).
At least 14 laced boats have been found in Norway, many of them in the far north. It is very likely that those boats found in northern Norway were built by Saami boat builders, the native people of northern Scandinavia (Westerdah, 1985). Based upon an analysis conducted of the Scandinavian laced boat finds prior to 1985, Christer Westerdahl published a preliminary ethnic classification of laced boat building traditions. He determined that the Scandinavian Iron Age tradition was characterized by lightly built vessels laced in running stitches with bast or gut strings. They were calked with wool or animal hair drenched in tar. The craft were generally used inshore on the Atlantic coast, though could also be found on the inland waterways of the Baltic coast. They date from the 3rd century BC to the 9th century AD and include such famous vessels as the Hjortspring boat from Denmark (ca. 300 BC), Norway No. 12 Valderøy (ca. AD 250) and Norway No. 5 Halsnøy (ca. AD 350).
Treenails do not appear in Scandinavian boat building (though they may have been utilized in other forms of woodworking) until they were used to plug the lacing holes to stop water from leaking into the boat. They may have replaced the lacing entirely, though there is not presently much evidence for this. Alternately, lacing was replaced by iron nails. In some cases, such as with the Sand boat from Norway, iron nails and lacing coexist in the same boat. The transition from lacing to treenails and iron nails was likely varied for different regions in Scandinavia and more boat finds are necessary to shed light on the transitional process (Westerdah, 1985). Though tree roots and branches were used to lace vessels from Sweden, Finland, and Estonia, bast strings, horse hair, cobbler’s thread, reindeer sinews, and gut string were used to lace the boats from Norway. It should be noted that the not all of the boat finds have had their laces analyzed; very few vessels have had their caulking material analyzed. Laced boat Norway No. 5 from Halsnoy had a tar-drenched woolen textile, while tarred animal hair, tarred moss and birch bark, and resin were used in other parts of Denmark.
For more information about the citations, a short bibliography about Norwegian Seafaring can be downloaded here.