Almost a year ago the Sea Stallion and the crew of 65 people departed Roskilde for a four week long test voyage. But actually the ship and the crew only experienced one time where the forces of nature really competed with the Sea Stallion. That happened in Skagerrak on a sail from Læsø in Denmark to Lysekil in Sweden. With a wind speed up to 15 metres a second and three meter high swells the Sea Stallion showed its strongest – and at the same time the weakest – side; the enormous flexibility of the light construction.
With the swells coming in from abaft the beam (behind and from the side) the ship wriggled and twisted through the water.
”We don't have exact measures of how much the ship gave way when we crossed Skagerrak. But we are going to try and measure that on the test voyage for Dublin. My personal feeling, though, is that the stern and stem gave about 30 centimetres starboard and port side – 60 centimetres all in all, that is” Søren Nielsen, leader of the Viking Ship Museum's boat yard, says.
Final test for the Sea Stallion
And 60 centimetres were a bit much for the boat builders. In the middle of Skagerrak, Søren Nielsen had to knock nails back into the hull of the Seastallion several times. They had wriggled themselves loose from the very flexible hull.
”The knowledge from last year – and especially the trip across Skagerrak – made us choose to reinforce the hull of the Sea Stallion more than we originally planned when we built it back in 2004. When the wind is hard and the water no longer flat as in Roskilde Fjord, but the waves are high and the swells coming from the big Atlantic Ocean… Well, that's where the Sea Stallion has to show it's quality. When the ocean gets rough, the light and flexible hull of the Sea Stallion will show its strengths and weaknesses in earnest,” Søren Nielsen says.
The voyages of last year was not only done to train the crew in handling the Sea Stallion – a wisdom lost over the 900 years separating us from the Viking Age. The purpose of the sails was also to test the reconstruction of the Viking Ship Museum.
”If even a few of the small individual parts of the Sea Stallion doesn't work properly with the ship in its entirety, we have to reevaluate the reconstruction. But if all the small and big parts work together, our interpretations of the original find are made more probable. Then the results can be seen as representative of the original ship as well as the ship type as such. The reconstruction can be seen as an experimental setup, a hypothesis, that mirrors our interpretations of the original ship and all the missing parts. The idea is to test the hypothesis on a 1:1 scale.
Must give in
"The Viking ships and the open clinkerbuilt traditional boats, that are still built today in a few places in Scandinavia, are built on the basic idea that the ship must be able to give in or give way to the strains from the sea and the rigging. All parts of the ship must be equally flexible. If some parts are too rigid, they won´t stand the pressure from the ship wriggling in the water. On the other hand, if the parts are too flexible, they´ll break under the strains. But our idea of the connection between flexibility and strength is probably not the same as that of the Vikings. We have to experiment," says Søren Nielsen.
And that is exactly, what the ship builders on the Viking Ship Museum have done. When the wreck was excavated from the bottom of Roskilde Fjord in 1962 only one fifth of the ship was preserved. Luckily enough central parts of the ship were preserved to allow the reconstruction within very slim margins.
But the Sea Stallion is not an exact copy of the Skuldelev 2 ship.
And after the summer expedition last year and the experiences from Skagerrak, the boat builders of the museum have made some small adjustments and reinforcements of the ship.
"We´ve chosen to add a few parts to the Sea Stallion, because we find them necessary for the ship to behave properly in the water. But also because we´ve scrutinized the original ship again and found the possibility for a new interpretation of the original parts on Skuldelev 2," says Søren Nielsen.
Facts
Reinforcements of the Sea Stallion
• The wooden nails in the caprail - which is the highest reinforcement in the ship's length – have been checked and given new wedges.
• The ship has been provided with a reinforcement - known as a fish - in the middle of the ship, from fore to aft on level with the floorboards. Except midships under the mastfish that holds the mast. Midships the ship has enough strength due to the mastfish and keelson that lies in the bottom of the ship. On the original wreck there is a carving in the only preserved biti - the name for the beams supporting the floorboards. The boat builders interpret the carving as an indication of a fish on level with the floorboards. The fish will brace the ship longships, mostly on the vertical level.
• The second outermost floorboards fore and aft have been fastened with spikes to brace the ship diagonally. The boat builders could see that this was done in the Viking Age as well on the Norwegian Oserbergship. Here most of the floorboards had ben nailed to the beams (biti) supporting the floorboards. The boatbuilders believe that this was done to reduce the ship's flexibility. It hasn´t been possible to ascertain if the same was done on Skuldelev 2, but the boatbuilders think there must have been a need to reduce the longships flexibility here as well.
• Two bitts fore and aft, that - aside from their function as bitts - are also bracing the ship's top 3-4 strakes in both ends of the ship. Right there the ship was very flexible. This area wasn't found on the original ship, therefore not allowing the ship builders to say if the bitts were originally there for certain.
• Finally, the boat builders made extra removable wash strakes in all the ship's length. In this way the shipbuilders enhanced the entire freeboard of the ship. Wash strakes have been mentioned in the sagas for both warships and merchant ships, but the boatbuilders can't see, if Skuldelev 2 had wash strakes. The test sails of last year showed, however, that the comfort on board rose considerably, as the wash strakes helped the ship to take in less water from the leeward as well as the windward side.
"It's difficult to tell how much pressure the ship will see in hard weather. Hopefully the same everywhere. At least the goal is for the ship to even out the pressure and strains. That is exactly the advantage with the clinkerbuilt and flexible hull... contrary to a very rigid hull as for example in a carvel-built galeass, where a small area of the ship has to be strong enough for a heavy beating, because it doesn't give in," Søren Nielsen explains.
When the strakes of the hull overlap each other a bit the ship is klinkerbuilt. This ship-building method was refined to perfection by the Vikings and characterized Scandinavian ship-building for a millenium - as long as wooden ships have been built, and the tradition still shows in every harbour even today.
When a ship is carvelbuilt, the strakes are put on top of each other, usually with much larger timber than the comparatively thin strakes allowed by the clinkerbuild tradition. The two methods are for very different ship types: The clinkerbuilt ship is very flexible - the carvelbuilt ship very rigid.
Not a joke
"The worst sea every ship can experience is a short, chobby sea or in other words a tall, steep wave. This can happen if the direction of the currents are opposite to the wind. The waters between the Orkneys and Scotland, Pentland Firth, are notorious for a very unpleasant and dangerous sea - we don´t want to sail there," Søren Nielsen says, which is the explanation for the Sea Stallion's plan; sailing in between the Orkneys on its way for Dublin.
But also the big ocean can spell trouble for the Sea Stallion:
"Tall and long swells, where up to perhaps a third of the hull can exit the water when the swells roll under the ship or the ship surfs above them, are not something to make jokes of. 10 metres out of the water means a very heavy strain on the hull."
"We don't know for certain how serious the strains were in Skagerrak last year. We didn't notice any leaks in the hull and no strakes had split by the nails. But the wooden nails of the caprail were loose and the ship gave more in in the areas fore and aft from the mastfish. Our purpose with the reinforcements - and we believe the Vikings had this in mind as well, when building ships - was to construct the hull to be equally flexible everywhere. It will spread out the strains by itself, so to speak," the leader of the Viking Ship Museum boat yard says.
From flexibility to collapse
But there is a limit to flexibility - collapse. When a boatbuilder - building the traditional, open clinkerbuilt boats in the Viking tradition - wanted to test a boat, he grabbed the top of the stern or stem and shook the boat. In this way he could see if the flexibility was allright - "absolutely allright." When we´re home from Dublin, hopefully our knowledge and experience will be much greater. And we will probably know much better when the flexibility is "absolutely allright" in a longship like the Sea Stallion," Søren Nielsen concludes.
