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A Lesson in Nylon and Urethane

The Gossamer Muskellunge is an East Greenland style kayak made to fit lines developed by Bj√∂rn Thomassen. Instead of building the boat with stitch and glue or strips and glass, I retrofitted the hydrodynamically modern design to ancient technology. 

Wanting nothing but the best for the frame, which looked as if it would be a lovely boat, I chose extra durable ballistic nylon for the skin (first mistake). I then used a two part urethane goo from an online skin-on-frame boat supplier to seal the skin (second mistake.)

The nylon was tight as a drum when it was stretched. Initially, the urethane was clear as can be, creating a translucent nylon shell, which looked stunning on the boat. I was quite happy.

The Gossamer Muskellunge, prior to her maiden voyage.

This is what happened. 

  1. The urethane yellowed QUIKCLY, and unevenly.
  2. The nylon stretched, A LOT. Only to be tight again during prolonged drought conditions.
  3. Every bit of crud, muck, sand and silt that got into the boat ended up visible in the bow and stern. 
What happens with nylon and urethane…

Here is the bow immediately after the skin was removed. My helper is smiling since she found a living slug in there.

Look, Blake, I see a slug! The bow and stern looked awful after removing the skin.
The tung oil that was rubbed liberally into the frame prior to skinning did a great job of minimizing rot. No penetrating decay!

The appearance after removing the skin was no less than disgusting. I was certain that I would have to rebuild the bow and the stern due to rot. Once fully dried out and brushed off, however, it was apparent that there was no significant decay. The frame had been liberally coated with tung oil prior to skinning, which seemed to halt the mold to the surface. 

A stitch and glue boat would not have fared anywhere near as well. The plywood would have delaminated and the high surface area veneers rapidly rotted. This is one of the reasons that skin-on-frame is a wonderful way to build personal watercraft. 

Once brushed off, some penetrating oil stain was applied to even out the color again and to add more resistance to mold and mildew. A darker color was selected in case the skin is translucent. The dirt that inevitably accumulates in the bow and stern won’t be as apparent. I’ll probably seal the frame again with more tung oil for good measure, since it worked so well the first time around. 

The skin this time around will be polyester. I will seal the skin with oil-based paint or marine varnish.

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