> I'd never though about converting the Guillemot design to skin-on-frame.
> It would undoubtably be a beautiful boat and one that I would have a hard
> time resisting building---

> But I'd have serious reservations about it's ability to take the high
> point impact loads that collisions with river rocks produce. Is there
> anyone out there with skin-on-frame experience who could comment on this?

Mike,

I've shared this before but in case you didn't see it, here is a quote from Peter Franz about his nylon skinned boat "This boat is absolutely indestructible.  I am convinced that it will continue to be a kayak when I am long forgotten. I once committed the unspeakable atrocity of driving my car over the bow-line with the kayak strapped into the roof rack. The Yakima rack collapsed under the load, and the boat slammed down onto the roof of my Trooper.  Trashed the rack, yet I was unable to detect the slightest damage to the boat. We also surfed this boat onto a mussel bed on Round Island in the Gulf of Mexico with a week's worth of gear inside. We must have skidded 8 feet without water underneath us, with only cosmetic scratches in the neoprene coating on the hull."

I have a skin boat and a wood/fiberglass boat, when I hit rocks in each the wood/fiberglass boats is more likely to get scraped up. Mine is canvas, not as tough as nylon, but it still gives when there is an impact upon it. The skin stretches and distributes the force over a large section of the frame. Very sharp rocks and freshly broken glass are the enemies of my canvas kayak, but balistic nylon can deal with sharp items much better. If you paint it with neoprene paint it becomes almost indestructable.

Here is some other information from a page on Nick's site about selecting a skin. It is very long, but it shows how tough the nylon with neoprene is.

"5. Selecting an Adequate Covering

Before describing the process I followed in building the baidarka, I want to share some considerations regarding selection of an adequate covering. I reflected at length on this point. The skin had to be sufficiently firm; I didn't want to be constantly afraid of a stone or anything else that might cause a hole in the covering during use of the boat. It also had to be applicable in such a way that folds could be avoided, a precondition which soon led to the exclusion of finished materials. Finally, it had to correspond with the historical appearance of the entire construction. Although attractive, I soon rejected the idea of using leather since no adequate material was available and even if it had been, its durability is inadequate. Only the use of textiles proved to be realistic, which had to be impregnated after the sewing process. Textiles I had available were 1.) a canvas-like, firmly woven cotton (450 g/m2), 2.) a linen fabric (315 g/m2), 3.) a polyester fabric (230 g/m2), and 4.) a nylon textile offered by G. Dyson (510 g/m2). The cotton and linen textiles had the best aesthetic appearances, the others looked somewhat "artificial" and synthetic. The most important characteristic, however, appeared to be the material's mechanical strength. In order to evaluate this feature, I tested its resistance to tearing. If a sharp object such as a rough stone or a shell comes into contact with the boat's skin and penetrates the surface, the object will continue to tear at the fibers and extend the initial hole into a tear. This effect appears to correspond best with the forces to which the fibers are exposed when the fabric as a whole is torn apart. Therefore, I prepared samples of about 20 cm 10 cm and made a longitudinal incision of about 5 cm in each. One corner was fixed with a tie at a firm point; a second string was fixed at the other corner. Then I stood on a pair of scales which I had placed exactly below the fixing point and, while looking at the scale, I pulled at the free string until the fabric began to tear. The final value was calculated by subtracting my body weight from the weight indicated on the scale at that point. The following data (refering to uncoated fabric) were obtained: 1.) the canvas-like cotton: 9 kg, 2.) the linen fabric: 16.5 kg, 3.) the polyethylene material: 6 kg, and 4.) the nylon fabric: more than 80 kg. Before definitively selecting a material, I had to choose an appropriate impregnation. G. Dyson experienced the most success with a neoprene coating. However, it was impractical to have his material sent because of the flammable solvent. Therefore, I had to run my own experiments. I tested the following agents: 1.) linseed oil, 2.) linseed oil primer, 3.) Latex primer, 4.) Acrylic primer, 5.) Coelan ``Bootsbeschichtung®, 6.) and 7.) two ``GummilösungenÔÔ, neoprene-based: Patex®, Henkel, and the polychloroprene kautschuk, GXGQ 8802, Conti-Tech, Breslauerstr.14, D-37154 Northeim, Germany. The first finding I made was that these liquids penetrated the fabrics to significantly varying degrees. The low-viscosity solutions 1, 2, and 4 penetrated completely, agents 3 and 5 to a lesser degree and 6 and 7 to the lowest degree. The latter compounds formed a layer in direct contact with the material, however, they could not diffuse into the closely packed bundles of fibers. On first sight, the latter effect appeared to be disadvantageous but testing the tensile strength of the impregnated tissues revealed an unexpected result: The strength of the materials treated with the completely penetrating liquids declined greatly. For example, the canvas' resistance to tearing was reduced from 9 to 4 kg, that of the nylon fabric from over 80 kg to 40 kg after impregnation with Coelan. On the other hand, application of the neoprene coating to the nylon yielded a result no less than 80 kg. The most plausible explanation is the following: In the untreated fabric, the tearing force applied causes a shifting in the arrangement of the fibers at the point of incision such that tearing can only occur when a greater number of fibers are torn at a point in time. In contrast, when the fabric is impregnated, such a shift in the weaving cannot occur. At a point in time the external force affects only a few fibers, which tear under much less effort, one after the other. A different characteristic of a boat's skin is its resistance to abrasion. In principle, this feature depends on the elastic properties of the material: An elastic material yields when it comes in contact with abrasive particles and the latter elements lose their energy. In contrast, firm material is affected by the undamped energy of the abrasive object. The effect is most evident when sanding a piece of rubber and a piece of varnished wood - the differences in the amount of material sloughed off are exteme. Regrettably, I did not find a method for quantifying this factor simply. On a qualitative basis resistance to abrasion was expected to be best in the elastic materials, the Neoprene-based elastomeres (Patex and GXGQ). Linseed oil and linseed-oil based varnish are much less elastic. When exposed to greater deforming forces, they become plastic, retract no more and soon tear. This characteristic applies to Latex primer as well and is even worse in this respect. Based on these findings and the observation that the material doesn't undergo a reduction in resistance to tearing, I decided to use one of the neoprene-based glues. Since only the compound GXGQ formed a smooth surface when dry, I finally used the latter material. "

I don't know for certain if it would be an ideal whitewater kayak, but it appears to have quite a bit of potential.

Mike Hanks