The age of Iron
According to Christian Thomsen, the Iron Age is the third principal period of the three age system that classifies ancient societies and prehistoric stages of progress. Roughly lying from 1200BC to 700AD with the earliest use of Iron dating to at least 3200BC with the discovery of 9 small beads from burials in Gerzeh in northern Egypt. These were a primitive form of a Iron–Nickel alloy classified as Meteoric Iron which required no smelting of ores. Smelted Iron appears sporadically in the middle Bronze Age. The true Iron Age is classified as such do to the mass production of Iron and the collapse of the Bronze Age do to the lack of Tin and disruptions in trade in the Mediterranean around 1300 BC, forcing metalworkers to seek an alternative to Bronze.
The introduction of Iron into everyday life proved to be a catalyst for evolution in the Middle Ages. With the advancement of Iron came advances in farming allowing humans access to a more nutritious diet advancing brain capacity. This led to introduction of alphabetically characters, and the consequent developement of the written language, which enabled literature and historic record. It also allowed for advancement in weaponry and hardware, this is where the Vikings come in.
Irons role in the Viking Age
So I hope I haven't lost you yet......
The Iron Age made way for the Viking Age. Advancements in Iron and Steel made it possible for the Scandinavian expansion. Allowing for stronger tools for farming, war, and boatbuilding. The ability to fasten the planks on a ship using Iron made it possible to build bigger and faster ships and to spread across the North Sea and eventually the North Atlantic.
One of the earliest finds of the use of Iron in a Norse boat is the Nydam Boat found around the 1860s in Southern Denmark. Believed to be built around 300 AD. She was Oak on Oak and clinker built. But the most prevalent time of the use of Iron in Viking Age ships is from 700 AD on.
Fastening The Plank
Step 1. Having a good fit.
Obviously the key to keeping water out of your boat is to have a good, tight fit on your plank. Making sure the marring edges of the overlaps are nice and tight is very important. You can add all the tar and caulking you can to fill a gap but over the long run it just won't hold up. This can be quite a hard task when you are shaping your plank with an axe. Getting an even plane and thickness takes time and practice. We do use planes reconstructed from the Viking Age when working on the Gislinge Boat but we try to use the axe as much as possible. Holding the blade of the axe in your hand and using it like a "slick" or wide chisel works really well. The versatility of an axe is amazing. Don't just think of it as something you swing, try out different techniques. (More on that in a later post. Stay tuned)
Take your time in this step. It will payoff in the end.
After your plank is fit go ahead and fit the scarfs. One into the stem and in most cases one to connect the next plank. Before I go ahead and do this and after the marring edge on the overlap is finished I drill two holes where rivets will go and I put a small nail in to keep my plank in place for fitting the scarfs. This will also help a lot when it comes to installing the plank.
Also don't forget to check the angles of the plank. Theres no point to having a good fit if your plank bevels on the overlap aren't correct.
Step 2. Adding the Profiles and The Caulking Cove.
Most of the Viking Age ships found were quite ornamental. Incredible carving on the stem and stern, colorful paint, and dramatic designs were just a few of the details. The Gislinge boat was found with profile covings both on the inside and the outside of the planks. Details to the edges of the boards allowed for aligning the fastenings as well as a nice look. This is archived by using reperductions of scrapers that were found on the island of Gotland in Sweden in the "Mastermyr Chest." There is also a cove added to the overlapping plank for the caulking to set in.
Step 3. Laying Some Serious Caulk
The most common question I get while working at the Viking Ship Museum is "Where are you from?" This is probably because I don't speak Danish and have no Danish accent oh and I'm not from Denmark. But a close second is "How do you keep the water out of the boat?" This is a good question.
A tight fit can only go so far. A "clinker-built" boat has overlapping planks so having just wood on wood will only do so much no matter how well they are fit. A ship will exspand and contract in the water and during the seasons. It is also meant to flex while sailing so it's bound to open up at the seams. This is where caulking comes in. It's the gasket between the planks that allows the ship to act correctly and still keep water out.
During the reconstruction of the Gislinge Boat we are using the same materials and building methods that would of been used during the Viking Age. Iron, pine tar, oak, linseed oil, seal skin rope, flax sails, and lambs wool. The caulking used in the Gislinge Boat is spun from pure lambs wood native to Denmark from a species of sheep thought to be from the Viking Age. The caulking is combed from raw, untreated wool from lambs. Wool as a wicking agent it self is a remarkable material. It's ability to repel water and moisture has made it the top choice for clothing for 1000s of years. This is also why it is so useful as a caulking between the planks of a boat. As the planks swell the wool will act a gasket and will repel any water that enters. This will also stop the wood from rotting between the planks
After the wool is spun and made ready to become caulking it time to lay pine tar on the plank. Pine tar is applied to both marring faces and to the scarfs. Be sure to apply as much as you need and not miss any spots. You really won't get a second chance after the planks up nor will you want one. Shits messy!
After we apply the tar to the overlap we do the scarfs. Loose, matted wool is applyed here. Only on the plank face. You don't want to over do it with the wool here unless its a crappy fit. Then load it up. A slight cove is hewn into the scarf to accept the wool.
After this is set we can put the plank on. This is where you're going to be happy that you per-drilled the holes to line up the planks. I replace the small nails with a rivet hammered through half-way. Trying to clamp on a tarred plank is a real pain in the ass. And normally I have 20 Italian tourists standing behind me watching. Don't add the caulking to the over lap yet. Just put the plank up in its place and lightly clamp her down. Make sure you check all your marks when you have it lined up. You made marks right?
Once you have the plank on and on the marks lined up you can go along and lay in the spun caulking. This is done with a FID that I made earlier that's set to the depth of the coving with a notch cut in to stop it on the top of the overlap. This prevents me from pushing the caulking to far down. I use a small wedge to open the plank up to make it a bit easier to lay in the caulking. You don't want to push it to hard and chop it up.
Step 4. Install and Rivet
After the caulking is laid up you can go ahead and really clamp her down making sure that the bottom edge on the underside is completely closed. It's better to have a gap up top than on the bottom but ideally you want a nice flush joint throughout. Check your angles one more time then it's time to rivet.
The term "clinker-built" is more of a referral to the sound that is made by riveting then the overlapping planks. A rivet is essentially a nail thats put through the two planks with a washer or "rove" on the other side. The nail or "rivet" is cut off above the rove and hammered flat. This tightens the fastening and lockes the overlap in place. We use over 400 hand made rivets and roves in the reconctruction of the Gislinge Boat.
As I have mentioned before, during the reconstruction of the Gislinge Boat we are using the materials and methods that would of been used during the Viking Age. All the holes drilled for the rivets are done with a bow drill. You would think this is a pretty time consuming method but we found that's it's actually pretty fast. After you get finished fussing with dead batteries and broken drills it takes just about the same amount of time.
With the holes drilled it's time to rivet. This might seem simple but it's actually a really important step. If done wrong you can really screw up the plank. There's a whole method for doing this that I could write a whole other post about, but I'm not going to. The only real way to lean is to do it. A lot. What I can say is that you need to stay inline with the rivet when you peen over the head. Going off to one side will bend it and this is "very not good." It will inlarge the hole preventing it from being water-tight and could even crack the plank. I really hate the word finesse. I just think it's a cop-out for not knowing how to do something. But, you really need to finesse this. Which will only come with practice.
After about 450 of these you'll be done and an expert. Good luck.