We have archeological evidence of longboat construction methods from which we can guess how they built their ships, but my research has not yet uncovered who did the work
As a matter of fact building a Viking longboat is now a lost art. At some places we can only guess or speculate, but for the basic construction we have solid archeological evidence, save for the sail and rigging. Say I am an ambitious young Norseman with a lot of friends who would follow me to sea if I had a longboat, and that I am from a family where the knowledge of how to build such boats has been passed down to me. This is a fictional account of how I would proceed to build myself a longboat.
First I would go to a large forest where I could find a suitable tree for my keel. The keel log has to be about half again as long as I want my ship to be when finished because the Keel is going to bend high above the boat in the front and the rear. Working with an axe, an adze, and a plane I'm going to shape the new fallen tree into a long "T" with the long downward portion of the "T" being the part that will protrude below the hull and cut the water. The (concave) two top sides of the "T" being where I will attach my first two planks or "strakes" (garboard strakes to be exact in modern English) to start my hull by overlapping the "T" and riveting them in place at close intervals with iron passed through drilled holes and hammered into a rivet shape by pounding both sides at once. The resulting overlapping klinker joint will be sealed with cow or reindeer hair shaved from hides and mixed with thick tar. This sealing will go on as each new strake is installed. Vertical joints in the strakes must be carefully staggered, overlapped, tapered outside lap toward the stern, and sealed and riveted as well.
If I am the heir to truly profound sea lore, I may soak my keel for a month or two in the semi-salt water at the bottom of a fjord and let it dry thoroughly before shaping it. This may reveal any weakness in the wood, and also infuse the wood's cellular structure with salt which will aid in sealing out salt water later on. While all this is going on me and my friends are going to seek and harvest many more trees with long straight trunks, using a froe or a broad axe and hammers and wedges we will split long straight grained boards for our hull strakes from the trunks of these trees, only using the straightest strongest grain and discarding the rest to insure we use only the strongest boards, because our lives, and more importantly, our fame and fortune, are going to rest on the strength of this ship. These rough split boards can then also be sunk in the fjord and then dried.
Then using adzes we will shape the keel and attach the garboard strakes as mentioned above. Adzing the salted wood before planing gives the added benefit of compressing the cellular structure of the wood (now infused with salt) into a more water resistant exterior. Then rivet by rivet, drilling a hole every eight or ten inches or so, and sealing between planks with animal hair and tar, we can finally assemble the hull by pounding the iron rivets flat from both ends. There is a significant amount of overlap in the strakes of a klinker hull. Steaming and bending are a hugely important part of this process. The Keel must curve just right, and rise high in both the front and the rear, and if I am building a warship, I will also want to provide for a dragon head on the front keel, for a merchant ship I may just taper it, and bend it into a graceful spiral. The klinker on the prow and stern must rise high to save the ship in high seas, no wave will defeat our mighty prow. In or just below the final upper strakes (sheer strakes) I must provide square oar holes so that we can power ourselves up rivers, and on the seas, when the wind is contrary to our designs.
Now the ribs are bent and shaped from single young trunks, and tied securely within the already formidable iron riveted hull. There is room for flexing in every part of the longboat's design. It is not a rigid ribbed ship, it lives in the water and becomes one with the sea and waves. Now for removable decking, seats, and oars. Finally a mast, Grandfather said the mast should not be longer than can be lowered into the stern. The mast is seated and secured by many guy ropes stem and stern and along the gunwales, it can be lowered at will. The sail is square linen.
To Father's mead hall, tonight we revel, and tommorrow we launch.
Like a new made barrel the new longboat leaks like a sieve when first put in the water, but the boards expand in a few days and a watertight hull results. In only days we can sail out to trade or raid, and make our name in the world like men.
Life is truly glorious, kiss your sweethearts well and lustily tonight for tommorrow we sail!
The whole process could take many months using green wood (maybe years if time for salt soaking and drying the wood is included) and untold man-hours to complete, but the reward in the centuries on both sides of 800 A.D. was to be the owner of one of the best sea-going craft in the world.
This is romanticized and fictional, there may or may not have been professional boatwrights building longboats in 800 A.D., and in advanced Norse culture Thralls may have done the bulk of the hard work. However there was likely a time when a story like this was true. Anyway, it makes a better story this way, and I am still seeking the answer to who actually built the longboats.
Sources:
http://home.online.no/~joeolavl/viking/norse-shipbuilding.htm
wikipedia
assorted assimilated general knowledge
UPDATE: I have read other sources that discuss not drying the wood after soaking, but working it wet, maybe being green going in it retains its "greenness". I'm a little unsure on this point. Also, very early, and some later eastern longboats used wooden "nails" consisting of a dowel pin with a wooden wedge driven in its center to lock it in instead of iron rivets.
Also, Drakkar, or dragon headed ships may have belonged primarily to important chieftans, and the heads may very well have been a removable ornament.
