<<<Can you give us some "light" about Kevlar, carbon/Kevlar, composite, epoxis, etc. As these materials are hard to get for me I could never experience with them. Do you work them the same way as fiberglass? Fernando López Arbarello>>> Yes, they are used as part of a resin/fabric "composite" much like fiberglass. Kevlar was at one time (and still may be) pound for pound the strongest tensile strength fiber known to man. It is used in bulletproof vests and chain-saw chaps because if this quality. It takes a very sharp pair of scissors to cut it. It has a straw like color. In a laminate (a "composite" of fibers and hardened resin) Kevlar's tensile strength allows it to take harder blows without coming apart. Kevlar is lighter than fiberglass for a given thickness of laminate and the laminate can be made thinner (and therefore lighter still) and still stand up well against blows such as from a hammer or rock. But Kevlar has a few downsides as well. Not only is it five to ten times as expensive as glass materials per yard but the manufacturer must work somewhat blind because it is opaque. This makes it more difficult to chase all the bubbles out of the laminate because they are hiding behind the layer(s) of Kevlar. This wouldn't be the case so much if the Kevlar was the layer next to the gelcoat but it should be the layer that is expected to be under the most tension to take advantage of its tensile (stretching) strength. The most likely blow (from the outside of a kayak) will put the inside layer of the laminate under tension. Rarely is Kevlar used alone in a laminate. It is most often mixed with other materials such as fiberglass or carbon fiber (graphite). There are several reasons for this. Cost is one but even if cost were no object it is still usually best to have the outer layers of material be something like glass or graphite which are much better than Kevlar at withstanding compressive forces. In other words an all Kevlar boat will fold up more easily both because the Kevlar compresses easier (and laminate is usually thinner too) and therefore easier to fold. The earliest river kayaks made with Kevlar were all Kevlar and often sported wrinkles and accordion pleated areas due to this easier compressibility. Kayak manufacturers soon learned to combine it with glass is such a way as to take advantage of the best characteristics of each material. That is placing the Kevlar where it is most likely to be put under tension and the glass where it is more likely put under compression. Another downside of Kevlar is that sun degrades it about as rapidly as it does nylon. Sun also darkens the golden straw color of new Kevlar. A Kevlar boat should not be stored in a way that the sun shines a lot on a surface where the straw colored Kevlar is visible. Such as when the kayak has clear (or no) gelcoat. An open cockpit can allow the sun to shine on the Kevlar inside. Since not using gelcoat is another way to keep the weight down this is often used in conjunction with Kevlar when weight savings are the prime goal. This makes sense because weight savings is the main reason consumers are willing to pay the roughly $100 per pound saved by using Kevlar (given roughly equal strength laminates). Marketing savvy and a patent held by Dupont is another reason we pay so much for it. Store a kayak like this out of the sun and don't use it surfing unless it is a heavy duty Kevlar lay-up rather than a super lightweight one. Verlon Kruger's Loon with which he paddled 28,000 miles around the North American continent back in the early 1980's was all Kevlar (Dupont was a sponsor). I watched Verlen drag it out of the water fully loaded and tip it over the edge of a dock buckling the hull somewhat in the middle. I asked him if that wasn't hard on his boat and he told my it was 14 layers of Kevlar thick. Most Kevlar kayaks today use two layers of Kevlar inside a glass layer or two in the hull. Verlen's Loon lasted him the entire 28,000 miles even though he lost it for two weeks once off Cape Blanco on the Oregon Coast and had it stolen for several days during a 68 mile portage in Nebraska when he went down to a culvert to get a drink of water. In Oregon he was rescued by his partner and then a Coast Guard Helicopter. He had built a new craft to continue the trip but then the original was recovered by a fishing boat and returned. I take credit for it being found because I had convinced Verlen he needed to seal off the 1" opening I saw in the bulkheads (near the deck). I was surprised to see in the big gaps when I took a close look at his boat after a slide show he did while passing through Seattle. He had added these semi-bulkheads (and a kayak like lid for the deck of his semi-open canoe/kayak hybrid craft) to use during the open coast legs of his trip. He hadn't thought it was necessary to seal the bulkheads up at the top. In Nebraska he saw it drive by on the top of a truck load several days after he had reported it stolen and gave chase while still managing to write a note to give to a pedestrian to call the police to help him. But I digress. Hey, I'm almost 54 I have a right to digress in my old age. My mind sometimes gets sidetracked by fond memories. Its late again and I'm planning to go skiing tomorrow so the carbon and Kevlar/carbon laminates will have to wait for a later time. Also someone else will have to take on the Epoxy part of the question because I don't think I'm very knowledgeable about that. Matt Broze http://www.marinerkayaks.com *************************************************************************** PaddleWise Paddling Mailing List - All postings copyright the author and not to be reproduced outside PaddleWise without author's permission Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
On Sun, 6 Feb 2000, Matt Broze wrote: > Kevlar was at one time (and still may be) pound for pound the strongest > tensile strength fiber known to man. The last wonder fiber chart that I saw had Spectra as the strongest fiber. Spectra's specific gravity is less than water - it floats. The article went on to say it was a bear to work with because it tended to float in the resin instead of becoming saturated. I can't remember what magazine I read this in, it was several years ago. I wish I still had the article. It had strength graphs comparing fiberglass (possibly E and S glass), carbon, kevlar, and spectra. kirk *************************************************************************** PaddleWise Paddling Mailing List - All postings copyright the author and not to be reproduced outside PaddleWise without author's permission Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
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