Aluminum Frame Details

The Frame When you take it apart does it become a kit? Well, yes. My first designs took several hours to assemble. A very loosely fitting skin was laced over a very loose frame. One could forget about the skin's contribution to frame stability; in my case, this worked only in theory. Maybe this is due to actually very small loads, I don't know. However, some parts of that frame were put loosely together for my inability to do a better design. Some parts even had some sort of interlock that I had to cut away to be able to assemble the boat. In essence, being outdoors gave nature a great chance to get me streamlining my assembly procedure. But it was amazing what loads and abuse that frame was able to bear. This surely is good news for any newcomer. At least in my case even that first design was well good enough to do the job.

Now I am somewhere at under an hour assembly time. But basically, my folding Greenland Baidarka still is somewhat of a construction kit. But that is no real problem. My own design assembles a lot better than the two-place folder I have bought. Joints are a lot more precise and rigid, and the overall stability of my frame is worlds apart from that of the commercial product.

My design routine begins with the gunwales. These are built at the full length of the boat. This is possible because the aluminum factory is not far from here. I make the bow and stern bulkheads and spread the gunwales apart. This only requires the angle between the gunwale and a vertical line (78 degrees), the dimensions of the stem and stern bulkheads and the frames fore and aft of the cockpit. For a better description of this read The Aleutian Kayak by Wolfgang Brinck.

The output of this action is a boat's beam, length, sheer and rigidity against vertical loads. Combined with the given height of any section, this also predefines the boat's amount of rocker. The two gunwales are designed so strong that they can accept all vertical loads that bear on the structure. This is done with two aluminum tubes and stiffening shear plates that creates an efficient and lightweight shear webbing. The next step is to set up the deck stringer and cockpit rim; now this defines a sort of a ''deck frame''. This approach's advantage is the simple building bed (you may just take some sawhorses); the aleuts also built the ''deck frame'' first. The height of the frames and the position of the stringer result out of David Zimmerlys book ''Qajaq: Kayaks of Siberia and Alaska'', page 17 (Aleut Kayak, collected on Atka Island in 1934 by M.Lantis).

If you consult an aluminum structural handbook you will find that compared to wood, aluminum is not necessarily lighter and stronger if you do not change the construction details. I added to the height of the gunwales and the height of the sheer. I designed only one stringer and placed it at about the middle of the two lower original stringers.

Resulting out of the reduction to 6 frames, the large cockpit, and all that Make-It-Foldable-Stuff there is not much left of the original design of a baidarka. Anyhow, for me it is important to realize the idea of such an old design, even if my realization of it is foldable and of aluminum.

The 3-dimensional form of the boat directly results out of the bending of the gunwale tubes, constrained by the already mentioned four gunwale spreaders. Out of this I measure the dimensions of each frame. There are four frames left to make; 2 for the front and 2 for aft. Actually, I cut them out of 2mm aluminum plates. After all, I disassemble the boat and reinforce all frames. I add the tube connectors and after that, I cut all tubes apart. After cutting, the 3-d form changes a bit, because of the changed material stiffness at the position of the connectors. The boat is cut in two areas; so each stringer has three parts. One separation point is before the cockpit, and the other aft of it. At the position of maximum bending moments (the cockpit area), there is no connector that can break. The bag for the parts is about 1.7m long, 0.25m wide and 0.35m high.

So it definitely is worth the extra effort at assembling the Baidarka. At least there is no commercially available folding Baidarka and I think I know why. I designed my foldables against the structural strength of a rigid Baidarka. Problem is, I only have had two rigid aluminum designs of my own deviation from George Dyson's. This deviation makes it difficult to give absolute numbers.

Now that I have made a wooden foldable Baidarka, I can tell that my very first aluminum designs were a lot less flexible than this wooden version. This was due to my usage of tubing with very large outside diameter (20mm). Using 18mm tubing should give better results. Using thin-walled tubing will have the problem associated with it that during transport the tubes will get bent and dented.

The Aleuts fixed their gunwales into the stem and stern deadwood and made sure they would not move within these joints. Gerald and I simply kept to this rule and made sure that all the foldable longitudinals are thoroughly interlocked to prevent them from changing their length, no matter how thick or thin they are. This was a major design problem for us since anything that interlocks is an attraction spot for salt water. This tends to transform a folder into a partly rigid boat that defends itself from being disassembled (as mentioned in Gerald's "bloody fingers" mail).

And don't forget the skin. A good part of the stiffness of the boat is due to the tension of the skin - it limits the motion of loosely assembled parts.