I know that cottage manufacturers and experienced posters to this forum seem to favor the heavier styles of cuben (CT2K.08, for example) for large tarps for the sake of durability, but I can’t help but wonder if lighter styles might be serviceable. So, I thought I would see if I could come up with a tarp that uses a light cuben but has robust enough seams, edges, and tie-outs to be durable.
I purchased 9m of the 0.48oz CT0.6K.08 material in “black” from cubic tech, and I decided on a 9’ x 9’ design. One of the things I plan to try is a sandwich-style seam along the ridgeline.
Also, it seems to me that some of the tensile forces on the material in a square tarp, due to the positions of the tie-outs, are on the diagonal (not aligned with the fibers). If the material were to actually burst under load, it is more likely to happen when the load is borne mostly by the film (when the forces are not aligned with the fibers). In a sail, the cuben would be cut into a series of panels and oriented so the fibers are better aligned with the tensile forces. I guess we don’t do that with tarps because we have an interest in minimizing the number of seams (also we don’t need a curvacious 3D shape). However, back when Cuben Fiber Corporation and North Sails were in competition, North made paneled laminate sails in which a tape of Kevlar, Vectran, UHMWPE, PBO, or carbon would be laid across the joined panels, radiating outward from the corners. I think these tapes were just bonded down onto the surface of the laminate, on top of the film. A similar method might make for a good tarp experiment, I thought.
I purchased some Vectran HT tow (an untwisted, parallel bundle of fibers) on Ebay. It has a breaking strength of about 130 lbs and has about the same thickness as lightweight braided fishing line. I chose Vectran instead of UHMWPE (spectra or dyneema) for two reasons: I don’t want it to elongate (creep) under the constant load of a taught tarp, and individual Vectran fibers have high surface energy and a flattened, tape-like cross-section, which in combination means excellent adhesion to glues.
Vectran is very sensitive to UV, however. The laminating adhesive used by Cubic Tech is also sensitive to UV, and they protect it by mixing in a small amount of finely powdered titanium dioxide. I decided to do the same. So, I bought some nanoparticle (10-30 nm particle size) 99.95% rutile titanium dioxide powder, mixed it with Hysol U09-LV, saturated a couple of short lengths of Vectran HT tow, and layed them down on a piece of the CT0.6K.08, clamping it tightly. The result was a piece of cuben reinforced on the diagonal by imperceptibly thin Vectran tapes.
Clamping forced the parallel Vectran fibers to spread out a bit and lay flush against the cuben. The adhesive was pressed into a very thin film tapering to the surface of the cuben along the sides of the tows. The result is that the Vectran tapes are not only extremely flat, but they also have no edges. It is actually difficult to tell whether they are above or below the mylar. I tried to scratch at them with my nails but there is nothing for a sharp edge to catch on. They are completely flush. My plan is to make a geometric pattern on the tarp, passing over the ridgeline seam and connecting all of the tie-out points to all of the others. I also plan to bond a continuous length of tow under the folded-over catenary edges along the periphery of the tarp. I have yet to settle on a design for the tie-outs.
I apologize for the long post. Any feedback is appreciated.