Manufacturing of the planks

Treatment of a plank piece over fire; it is getting flat all by itself, without spreading bars.

Side strakes were also done with fire treatment, for experiment purpose. Pine log was split by means of wedges into halves, which were then hollowed until they became half-round in crossection with 12-13mm thick walls. They were flattened into planks in the same way as bottom part was expanded over fire. The technique was powerful enough to to turn 27cm diameter pieces into completely flat planks without applying any external force, i.e. without using any spreading bars or clamps. But tensions appeared to be too high, and ready planks cracked too much when drying; still, they were used for the boat's strakes, cracks stopped with melted spruce gum, bigger ones patched with sewn lathes. Advantage of this technique is that planks become much wider then diameter of trunk they were made of -- the trunk was from 35 (bottom) to 27(top) cm thick, while ready planks width was from 47 to 35cm respectively. Total volume of wood reduced into chips while making planks of a given width is about twice (that is, about π²/4 times) less in comparison with ordinary technique, when trunk is split into halves and two flat planks are carved out of them. So the technique with expanding over fire can be less labour consuming, especially when tools are small and light, and quality of steel and whetstones are low, as it was in 8^th century. Original boat strakes, however, were not sufficiently preserved to judge about the technique, but implementation of fire and steam is very doubtful in this case.

One can see ready planks left to dry, their wave-like crossection pattern clearly visible. Planks are tied flat with a plenty of sticks, to prevent further waving and cracking.

An interesting question is if planks were ever made this way; for example, in Hjortspring boat, linden planks were so wide -- up to 80cm, that it appeared to be impossible to find trees of sufficient dimensions in whole northern Europe for a replica building. At the same time planks were incredibly thin -- only 1cm; these dimensions, (as well as the material -- linden, which must have far higher cracking tension threshold then pine), match the steam-and-fire expanding supposition very good, these planks could be made of only 50cm thick trees, and if these trees were old and had rotten core, it could even make the job easier.