Ship Theory

Viking ships have held peoples’ interest for centuries. Since the very late 1800’s that interest turned to how well they really performed at sea. Many groups, organizations, government agencies, and individuals, have built replicas of Viking ships since then. They have been, and are still being, built in many counties around the world. They are to be found in all the different sizes, and categories of the Viking ship finds. It’s almost redundant to say hull design is one area we understand a good bit about, with all the work that has been done in that area. There are other problem areas in the “How did they do that”, but hull design and construction is not really one of them. One item that has caused the most difficulty is the sail. None of the surviving ships have been found with a mast that is intact. With no mast the sail size and dimensions can only be guessed at. Another area is how do you make a ship like Skuldeve 6 stable in deep water, or running against the wind. Theory is all we have had to this date. Some of the theory just does not fit in producing a stable ship. Loading the hold full of ballast, to make a stable ship, is a good idea. Is ballast the only way to make a stable ship? The answer to that question is no. Take many sail boats made today and look for the ballast in them. In many a case you will not find any, because they don’t use any. Ship design does not remain stagnant. If it did we would still be using dugout, or skin, boats. Mankind has always looked to better ways to make a boat, or even improvise with the ones they had. With that in mind, think of the Viking ships. Would it be logical that a boating society, such as theirs, would stagnate in the design of its ships? The logical answer, when looking at all the different ship designs of the finds, is no.
When read most papers on ships you normally find it loaded with terms that you don't know what they mean. I will try to describe those terms, as I use them, or avoid them. The intent here is to help non sailing people understand the content presented here. Those with a sailing background will, I hope, find information useful to them.
Where do we go to get new theories on how the Vikings made their ships design the most focal design of its day. There is evidence in documents and art work of the period that we can look at, and make some good guesses, based on that information. Lets start with the sail. Today just about every Viking ship replica uses a square sail, but why? There is no evidence to prove that they used a square sail, so why use it? In the late 1890’s a replica of a Viking ship was sailed to the US. The ship, to meet its sailing deadline, had to be fitted with any sail that they could find. The sail that they found was from a schooner, and it was a square sail. From their ‘use what we can get’ situation we have adopted the use of the square sail ever since. Is it right? Probably not, and for several reasons. Square sails will limit the abilities of Viking designed ships to perform many sailing maneuvers with efficiency. Square sails also make the ship very top heavy, and that means ballast, or weight in the bottom (hold) of the ship. One more problem with a square sail is that it catches the wind up high in the sail. Catching wind high in a sail will push the stem (front of the ship) into the water, and increase drag on the hull. The idea of a sail is to make the ship move without other forms of power, and in the Viking age that meant rowing. Another duty for the sail was to move the ship faster than rowing by the power of the wind. Sailing into the wind was, and is, a problem. To do this you have to tack into the wind. What that means is you sail in a zig zag fashion into the wind. In this way your sail can always catch wind to push you toward your objective. With square sails, on a Viking ship, tacking is very poor at best. Rowing the ship might even prove faster then tacking when using a square sail. Square sails equal; poor performance into the wind, top heavy, extra weight in the form of ballast, and increased drag. Use of the square sail does not equal the period reports of its speed and handling.
If the square sail is not the answer, what is? Using a rectangle sail is one answer. The short and wide sail concept proves to make for a very maneuverable ship. Tacking is improved dramatically, and the need for ballast is gone, or almost gone. If this is true, what evidence is there to back it up? Research of drawings and rune stones have shown Viking ships with a different form of sail, and that sail is rectangular in shape. Coins from the Viking age provided images of the same sail shape, and help support the idea of a rectangular sail. Håkan Larsson, of Sweden, more than did a bit of work in this area. He and several others worked out the design for this new sail theory. They worked out a formula of 3:1, or width is 3 times the height. This formula produces a sail that resembles the sails that are found on period evidence. The Yard (the pole that the sail is attached to) length is based on the length of the ship. To use this theory you must first figure out how long the Yard needs to be based on the length of the ship, or about 2/3 its length. From Yard length you can now come up with the height of the mast, based on the 3:1 formula. Sigrid Storåda is a copy of the Gokstad ship, and their test bed for their theories. She comes in at about 76 1/2 feet long and 17 3/8 feet wide. Weight is about 15 tons (US), and caries 818 square feet of sail. The mast is only 36 feet in height, and almost half as short as other masts used on replica Viking ships. This would make the Yard about 51 feet long. At 51 feet wide and 16 feet high you now have about the 818 square feet of sail that they used. Their actual dimensions have to vary a bit from the formulas to get 818 square feet, but not to much to have only 2 square feet of difference. All of this data is needed for one important reason, does it make a logical argument. Their work is summed up very nicely by how it tacks. They have achieved a speed of almost 6 mph when sailing into a wind of 18 mph at a 45 degree angle of approach. Very impressive for such a large ship with only one sail. They report that it sails much like a modern catamaran. All this sounds good but there is one more thing that supports this theory. With out a boom, the cross pole that the bottom of the sail is attached to, you have to have to secure the bottom of the sail to the hull in some way. On the original Gokstad ship they have 3 securing points that no one knew what they were for. They didn't know because they were using a square sail. Using a yard made for a rectangular sail, and 36 foot mast, the sail lines now mate perfectly to those securing points in the original Gokstad ship. The theory of a rectangular sail, put forward by Håkan Larsson, would seem to the most logical of any of the theories to date. Thanks should be given to Håkan for his dedication in Viking ship research.
The second problem is how do sail a ship like Skuldeve 6? The hull design of Skuldeve 6 would make for a very fast ship,as she has very low drag in the water. Under sail though she is not very stable in deep water, or any depth water. Skuldeve 6 is a very shallow draft ship that is very long and narrow. At 117 feet long and 11.5 feet wide, with a draft of only 3 feet, she is very prone to roll over under sail. Even with a sail like Håkan Larsson’s she will still want to roll over. Under sail the wind would have to be at her back, or she rolls over. The point is, she wants to roll over under sail. This would suggest that under all but perfect conditions she would have to rowed. The warriors on board would not be in good battle form after rowing any great distance. If she were to be used close to shore, why have a sail? Skuldeve 6 was meant to be a war ship for long range use, and under sailing conditions. If you can't sail it, why build it to sail. No shipwright would ever risk his name, and reputation, to building a ship that wouldn't work. So, how do you make a ship like Skuldeve 6 work? From the sagas we know that the Vikings went into sea battles with their ships tied together, like large platforms. We know that they did that because Olav Trygvason did that in the battle at Svold. There are several reasons for this. One is you now have a platform to fight from. Another would be to give rest to your fighters before the battle. A third is that it keeps your ships from drifting apart in a battle. On several ship finds they have found long wood poles that no one has any idea as to what they were used for. Could they have been used to tie the ships together in combat? How does this fit in with making Skuldeve 6 a useful ship? Here I would like to put forward the only theory I have come in contact with that makes a logical argument, the theory of Kirk Solberg. Kirk has studied Viking ship design and theory for many years. He has also traveled to Scandinavia to get first hand information on Viking ships. To back up the mountain of information from modern study sources, he has also read all the sagas that had any information on Viking ships. Kirk also presented the theory of a rectangular sail to me several years back, and before Håkan put the same theory into operation. This is not meant to detract from Håkan’s work, but to give you an idea of Kirk’s understanding of Viking ships, and why I'm willing to put it forward. His theory on ships of the Skuldeve 6 design is that they were secured together in pairs. The wooden poles that were found, that no one knows what they were used for, were used to hold the ships together. The configuration would be much like a catamaran, but with two sails instead of one. This would instantly provide deep water (blue water) stability to Skuldeve 6 designed ships. The use of twin sails would provide interesting theories on how they could be set under different sailing conditions. Deck space would increase also by using this theory, and provide for more men and/or equipment. While this may seem to be a far reach for the Vikings to do this, what about the battle platform. Tying your ships together, to make that platform, also seems to be a bit far reaching, but they did that. With the knowledge that ships could be tied together, to gain stability in battle, a good shipwright could well use that information in other ways. Travel to other parts of the world would also give them access to other ship designs. Designs that they may use in their own ships. Shipwrights were businessmen that sold their talents to the highest bidder. The better you were at your designs, the higher the bid. Should you come up with a radical idea, that worked, your fee could be very high. Should this catamaran theory prove to be correct, the design was doomed. The idea would come late in the Viking age, and the Viking ship was soon to be replaced by a new design - the Square Sail tall ships.
Source:
Sigrid Storåda, a sailing replica, by Håkan Larsson.
Viking Ship Museum, Roskilde, Denmark.
Vikingskipshuset, Oslo, Norway.