Vårens Färger

Sketch of grotesques accompanied by text about pigments found on Vasa

The time of year has arrived when we begin to think about seeing in color again! The afternoons are lengthening as the equinox approaches, and the city landscape is beginning to turn that new-spring green around the edges. It is easy to miss the early signs from the magazines: apart from the chalky and subdued pinks and browns of the archival boxes, it's white tissue and dark waxy PEG as far as the eye can see. Similarly, one forgets that before her 333 year sleep at the bottom of a muddy harbor, Vasa was actually quite a colorful lady herself. Above is a sketch of one of her transom grotesques accompanied by the wall text listing the variety of pigments that would have been used in her time.   

Snow over Vasamuseet

Of course, it woudn't be a truly Swedish spring without three or four more solid dousings of snow, or so I'm told. Seems that winter was a little slow to catch on this year, but it's making sure we don't forget that Stockholm looks quite elegant in black, white, and silver, too. 



Repslagarmuseet II

End of a recently closed and stretched piece of rope

Yarn - Strand - Rope

I'm still ruminating over my trip to Repslagarmuseet in Älvängen on the west coast of Sweden a few weeks ago. It was amazing to witness the process from start to finish. Though the basic concept behind ropemaking is simple- draw out fibers, add just enough twist and pull to convince them to hold together, reverse the direction of twist with every step up in scale - the execution is both complex and precise. Length comes in hundreds of meters, but subtleties of twist and diameter are discucssed in milimeters.

Spreader drawing yarns from spools through the tube to form a strand

36 yarns being drawn into a single strand

 In ropemaking, you start with "yarns" as the most basic element. The yarn for this project was sourced in China and then tarred in-house at the ropewalk. The addition of tar increases friction, conditions somewhat, and most importantly, staves off rot. Tar accounts for between 15 and 20% of the final weight of the rope. In this case, we were using about 36 yarns for each strand we were producing: 5 strands together to form the core of the strand, and then the remaining 30 or so  anned out in two layers around the core.

Four strands made up of 36 yarns before closing

Four strands being stretched before being "closed" into rope

While I was hanging out in the walk, the team there was making 150 meter lengths of three and four strand rope that ended up being 45, 50 and 55 mm in diameter. The ideal natural hemp rope for rigging traditional ships must be a loose enough lay that it is strong and a little elastic, but not so loose that it will rot too quickly when exposed to water and weather.

Top closing four strand rope

Closing

Three or four strands were then "closed" using a large lozenge shaped wooden "top" to make the rope. The four strand rope also required a core to keep the structure from collapsing, which was essentially an additional, smaller strand consisting of about 16 yarns. Though 150 yards didn't seem like all that much looking down the length of the walk, the final coils piled on pallets dwarfed us folks milling around.

A photograph of a recently closed four strand rope at the ropewalk in Älvängen

The final product

The level of working knowledge necessary to produce rope that will (in this case, for example,) last through a voyage to China and back can only be attained through years of practical experience and countless hours dealing in fiber and tar combined with a solid practical understanding of traditional sails and rigs. If you want to learn more about the process, or the talented folks who were involved with this particular project, or even see it all for yourself, you can find them here and at Repslagarmuseet's website linked above. They are a talented and impressive bunch all in all, and I'm excedingly grateful that they let me tag along for a few days. Additional photos of the process can be found here as well. 

Messing about in boats 3. Forces of nature.

On my way to work, I usually listen to podcasts. The current favorite is “The infinite monkey cage”, hosted by physicist Brian Cox and comedian Robin Ince. It´s hilariously funny, but once and again some really serious and complicated science crops up.

Take gravity for example, one of the fundamental forces that somehow keeps the universe together (or is it expanding?). Tricky stuff anyway. It also works on boats; the center of gravity pulls the boat down into the water.  Luckily, there is also the center of buoyancy, so the water pushes back against the boat and keeps it afloat.

When you’re out sailing all sorts of forces are working on you and on the boat, so you will probably not be too concerned about gravity, unless you are sinking of course. But you will subconsciously take in the force of the wind and adjust your sails accordingly, make sure that hatches and other openings are secured so the boat doesn´t fill with water if it gets rough, try to figure out what the weather is doing and so on. There are hundreds of forces to reckon with, which is partly why sailing is so exciting. (There is also the scenery and nice places to visit).

Forces of nature.

When Vasa sank, something obviously went wrong with gravity and buoyancy. Well, the gravity was still there, but buoyancy went haywire as the water started to fill the hull through the open gun ports.

So, where am I going with this? And how does it relate to Vasa?

Well, Vasa is no longer afloat or at the bottom of the sea. Standing inside our lovely museum she is basically floating in a sea of air. The density of air is small compared to that of water, so the buoyant force is not great. This means that Vasa is depending a lot on her support cradle to remain upright and intact. To complicate things further, Vasa´s wood is also degraded and has far less strength than new oak (or recent oak as our scientists at Uppsala call it). To come to terms with this degradation, or weakening, Vasa has also been chemically modified with polyethylene glycol in the conservation process. This has of course helped to make the wood more stable, but we now know that there are ongoing chemical reactions inside the wood. One thing that seems to slow down these disturbing reactions is the stable climate inside the museum building. So, there are a lot of interacting and also conflicting forces inside and around Vasa, and she is more or less in the hands of an elaborate life support system for survival.

Does this sound really worrying? Perhaps it is, but the thing is that Vasa, despite all her ailments, is fairly stable. We know this because part of the life support system is a really neat geodetic system for measuring movements in the ship. This system is not so easy to explain, but basically we are using an surveying instrument called a “total station” which we direct to a large number of measurement points on the ship. The measurements are then transformed into the actual movements within the ship´s structure.

So why is Vasa moving at all when she is standing in a cradle inside a climate controlled building? Could it be gravity, or is something the matter with the support cradle? A bit of both probably.

When I lift my own boat ashore for the winter and put her in her cradle, things happen. Although she is a fairly modern and strongly built fiberglass yacht, lockers will suddenly stick, doors will be more difficult to open and hatches tend to jam. Gravity at work, because Signe (that´s her name, after my wife´s grandmother) is no longer buoyant, and her winter cradle does not give the same support as water when she´s afloat.

So in a way it´s quite amazing that Vasa is as stable as she is, considering her age and what she has been through. Obviously, we can´t do much about gravity, but we can (among a lot of other things) work with the support cradle.

This is why our latest research project “Support Vasa” is so important, as the results are totally vital for designing and building a state of the art future support system for Vasa. One part (just started) of this project is building a full scale section of Vasa´s hull for testing the strength in joints and various components of the ship. To accomplish this, our shipwrights have just ordered about ten tons of oak, but more about this later…

So who knows where science can take us? Perhaps Vasa really could be floating in a sea of air in the future, or something very like it. What do you think, dear reader?

Floating on a sea of glass. SS Great Britain, Bristol, UK.

Repslagarmuseet

Sketch of the beakhead and bow

This past week, I had the privilege of visiting Repslagarmuseet in Älvängen, just north of Göteborg, where the ropewalk still runs. I was there to take photographs of the rope making process on behalf of Vasamuseet, as one of our forthcoming publications deals with the rigging of Vasa and we need a few illustrations. While the machinery at Repslagarmuseet is from a later period (18th century), the basic elements of the production process are still very much the same. It was quite a privilege to observe the process; there will definitely be more reflections (and photos, and sketches, in all likelihood) coming soon. 

Sketch of Vasas stern profile

In the meantime, here are a few fun sloppy pencil sketches of our girl-