jwd_at_acm.org wrote: >> Their justification was that gelcoat provides no structural benefit to the boat, and going without it saves 5-8 lbs of essentially useless weight. [snip] Now I know that finishing the boat's exterior with gelcoat doesn't improve the structural rigidity of the craft. [snip] I also know that some in the industry, Tom Derrer of Eddyline among them, have staked their reputation (and their business) on foregoing gelcoat. But even Eddyline's high-end "modulus" boats, which are vacuum bagged glass/kevlar composites, still use a Carbonlite (polycarbonate?) shell on the outside.>> 1. Adding a thick layer of gel coat will stiffen the laminate __a little__, because the modulus of elasticity of the gel coat is different from the underlying FRP. "Structural rigidity" = stiffness, I guess. However, in my limited experience with FRP boats, too-flexible hull/deck sections flexed like hell when pressed too hard, and cracked the gel coat. The gel coat was not useful in preventing flex. I bet Matt Broze has better data than I do. 2. The main value of gel coat is two-fold: A. It protects the underlying resin (whether polyester-, polyvinylester- or epoxy-based) from degradation from UV. Coat a plank with a generous layer of epoxy and lay on a 6 oz of glass and then apply more epoxy to wet out the glass. Let sit in the sun for 6 months, and then see if you want that to happen to your boat. B. It protects the underlying FRP from __abrasion__ damage. B. Is very important -- any time you cut into the glass/resin layer, you are damaging both the rigidity and the strength of the boat. On an extended trip, it would be easy to eat all the way through the glass from running the boat onto the beach. Even boats with gel coat can have this happen. I've seen it in abused rental boats. 3. The quote from Derrer is somewhat out of context. In one case, he uses a polycarbonate layer __in place of__ gel coat ("A Carbonlite 2000 skin replaces the gel coat in a composite kayak"). See: http://eddyline.com/kayaks.cfm Note that none of their "Legacy Composite" (= FRP) models are in normal production any more. They would have needed a UV protector, as do their Modulus versions. Those Modulus boats must be heavier than FRP boats of equivalent rigidity (note: I did not say strength, because the Carbonlite 2000 layer is strucural). -- Dave Kruger Astoria, OR *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************Received on Fri Jun 06 2003 - 03:00:30 PDT
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