Got skin?

Vinyl

Coton

Nylon

A wooden boat frame is a sight to behold! It is a piece of art, and it could, without a doubt, be used as such. As a matter of fact, it’s a bit of a sad moment when you are about to skin a frame because it dampens the elegance of the work accomplished thus far. But, you can’t escape the fact that the skin is what turns the whole affair into a boat. It completes the metamorphosis from art to a useful object.
The skin has two functions. The first is to keep the water out of the structure to provide flotation. The second is to maintain the structural strength of your boat through compression. In doing so, the skin stiffens the boat quite a bit while permitting the flexibility that makes skin boats so durable and strong.
There are many skin materials to choose from all with their strengths and drawbacks. The strongest has to be ballistic nylon. It is a covering that is both easy to use and very resilient. Its inherent stretch makes it very adaptable to the curved shape of a boat without creating wrinkles. However, it is not moisture stable and it will go from drum tight when dry, but it will become somewhat loose when wet. Nylon also has a nonstick property that limits your choices of waterproofing as most paints and varnishes will not last on this fabric.
I had good results with both light and heavy cotton canvases. It has good stretch when you cover the boat and water tightens it when it is wet. It will take any type of varnish and paint (exterior grades only please). As a skin for your boat, the strength of this fabric is more than adequate, but the arrival to terra firma will require some precautions. Barnacles and sharp rocks might rip the skin and require a few stitches. Ultimately, the skin is repairable and mishaps rarely occur in open water.
The original Sprucedragon was covered with vinyl laminate that was readily available in the Middle East. It is a fairly durable covering and it is waterproof without the use of any applied finish. However, you cannot sew that fabric on. All joints must be glued with special PVC glue. It is also preferable to reinforce with double strips on the high wear areas (you would use the same PVC glue). The biggest drawback of Vinyl laminate is that it has low stretch and wrinkles are hard to avoid. Despite its fault, it is still a viable and cheap option.
A number of other fabrics could be used and I plan to try Sunbrella ™ Linen canvas, blue jeans, and Dacron in the near future. I saw a boat covered with clear PVC on the net recently. That option would have the advantage not to hide all the fine woodwork beneath.
I really believe that any strong fabric can be used for skin-on-frame boats, and one can and should experiment with different options. Remember, if the covering is found unsatisfactory, it can be replaced by another relatively easily.

Cheers.