Expanded log boats, AD 200 - 850 - an experimental archaeological boatbuilding project
The expanded log boat was built by boatbuilders Hanus Jensen and Rasmus Budde JensenThe Björke boat, dating to the year 400, was found north of Stockholm.
The base of the boat (the actual log) is made from linden (lime) and the additional pine planks are attached with iron nails. The frames are of spruce.
Above, you can see the 1:10 model after expansion.
The linden log is from a small-leaved linden, found in Vindeholme skov on Lolland.
Linden bark is carefully removed and laid in the harbour. After a while, the bast from the bark can be removed. When it dries again, it can be used to make linden bast cordage.
Hanus and Rasmus decided to make another model, this time in 1:5. Above you can see the model durring and after expansion.
Hanus cuts the inner shape of the stem and stern with a motor saw: this is quicker and won't make any difference to the finished boat.
The boat is hollowed out. This is done exclusively with axes.
The sides of the boat bow a little upwards in the centre of the boat. This is where the hull will be expanded so that it will be broader than the original log.
It took several weeks to hew the boat into the correct form. In the first picture above you can see the cut marks on the starboard side. On the port side, you can see tool marks from the gouge.In the second picture, you can see the clamps where the frames will lie.
The boats initial shape can also be clearly seen.
Before the boat is expanded, it is sunk in the harbour, here, its stability is tested.
When the boat is finished it will have a broader and therefore more stable base and will also be one plank higher. It should also be possible to row it with two pairs of oars.
The excitement mounts. The boat is warmed up. It will be doused with water if it goes up in flames. The purpose of the stones is to press the bottom of the boat downwards, while at the same time pressing the stem and stern up and the sides out.
Due to various reasons, the sides of the boat cracked and the expansion was stopped! Well, what did we do wrong?
Maybe the boat wasn't warm enough, maybe the sides weren't thin enough, maybe we shouldn't have exerted so much pressure with the stones during the warming-up!
But, you learn from your mistakes.
The original boat apparently also had some problems.
Hanus and Rasmus repair the cracks using the same method as the original boatbuilders. Thin pieces of linden are laid over the crack and secured in place.
Time to try again... Lots of heat and water is required in order to expand the boat. This time the boat is expanded using bracers, and without excessive force.
The whole process took 40 minutes.
Here, you can see the finished form of the expanded part of the boat.
Now an additional plank must be added, but first, the stem and stern must be extended. The stern is adjusted to fit. The stem and stern must be hollowed out and secured.
Afterwards, the planks will be placed in position and attached.
The stem and stern were not as difficult to make as we had feared, but they were still an interesting challenge. They are made of two pieces of pine. First, an inner stem which is hollowed out, so that there is room to attach the ends of the planks.
Then an outer stem, which stabilises and strengthens the inner stem. The stems can be seen as a forerunner of the so-called stepped stem, which is well known from the Viking Age.
Earlier in the summer, we had cleaved a pine log to make planks for the boat. This was done in the proper fashion, using wedges and axes. To prevent them from cracking, the finished planks were lain in water until needed. Unfortunately, the planks proved to be too narrow for the Björke boat's very wide strakes, so we had to find a new tree in Tisvilde.
We cut the two new planks out using a chain saw, to save both time and materials. There was plenty to be hewn afterwards however, before the planks were ready and sat as strakes on the boat. Here, they can be seen as 40mm thick planks, but they would be just 13mm thick when complete.
Using juniper withies or roots, the floor timbers (frames) of the Björke boat are lashed to the clamps that are hewn out of the planks. They can be seen here as small raised areas on the plank's surface.
The half-finished planks are set in position for the first adjustments and the Björke boat suddenly takes on a whole new appearance. From an initial width of 70cm and a depth of 17cm, the boat is suddenly 120cm wide and 47cm deep. The planks are large and heavy in relation to the very soft bottom of the boat, so they must be attached on both sides at the same time in order to prevent the boat becoming uneven.
It can take a long time to adjust the fit of a plank. The planks are made of a single piece all along the boat's length, and that makes them much more time consuming to adjust.
When the plank has aquired the right shape, it must then be adjusted. If they don't fit well together, you risk cracking the planks when they are nailed together - and then the boat will leak.
The planks are riveted using iron nails. The frames are made from spruce roots. A thwart is positioned on each frame. The frames are lashed to clamps, that were fashioned on the planks and the expanded log.
They are lashed in place using juniper withies.
The oar lock is also lashed in place using withies. A hazel withy sits in a hole in the oar lock. It is used to hold the oar in place when rowing. The actual oar locks were not found with the boat. These are reconstructions of those found on the Nydam boat. The boat has three pairs of oars.