Peter T said: > Couple of questions: > 1. Is there any value in a kayak builder post-curing the kayak when deck and hull are joined, with the aim that the resin in the join is raised to a sufficient temperature to bond with the hull and deck more effectively? > 2. Why do not more kayak manufacturers use the QCC type overlapping join? See http://www.qcckayaks.com/kayaks/hulltodeck.asp. Is that a superior joint? Doug Lloyd responded: >>>>>2. Looks superior to me. New glues are incredible powerful. How about this joining method and a taped seam inside and out? 1. Here's a quote from your neck of the woods from Sisson kayaks (who make the Nordkapp down-under): "The hull / deck joins are cross-linked solid: All kayaks are joined within hours of the original hull and deck lay-up. All kayaks are joined the same day they are laid up using the same materials used to form the hull and deck. No 'bog' here! All boats keep their design shape - unlike other brands that are joined out of the mould. All 'joined' kayak hull / decks are 'Post Cured' in the mould. This demands 'cooking' overnight with heat for optimised hull and deck strength. Which means that the hull / deck unit is cross linked (chemically fused - not just bonded) together into a solid unit. This sometimes means extra hours must be worked into the evening. No substitution or compromise. Which means your kayak hull to deck join is the strongest in the business." No affiliations<<<<<< 1. It looks like mostly a "red herring" from my viewpoint. The only time I've seen a seam bond that came unbonded was because the smooth fully cured vacuum bagged surface wasn't sanded well. Most of the few broken seams I've seen have been due to folding or tearing at the joint itself rather thant he fiberglass bond failing. and in most of those cases the rest of the kayak suffered serious damage as well. Even that folding damage is very rare but could be prevented by making the seam heavier or using a higher tensile strength material such as Kevlar for one of the seam layers. The trouble with making seams too heavy (and not tapering in thicknesss/stiffness towards the edges-- #2?) is that the sudden transition creates a stress riser at the seam's edge that may create a fold line. Post curing may make a better bond but I think the advertising is taking advantage of the seaming inside the mold they use (that is easier to do with a hand lay-up--which is weaker pound for pound than vacuum-bagging). Also with hand lay-ups the seam's chemical bond is already stronger than the mechanical bond (to a rough sanded surface as with a vacuum-bagged part). If a hand laid part is not contaminated with something like a petroleum product (oil, wax, grease) the air inhibited surface that makes this so would bond very well with resin years later. The rush to join the parts likely has more to do with production efficiency or maybe curing evenly and more quickly in the mold to get the parts out so it can be used again. Without sufficient heat the resin won't set but I doubt an even higher heat is making a really significant difference in the bond strength. Do a lot of seams come apart in Oz? If by: "no 'bog' here" the manufacturer is referring to the better alignment of the parts and the curing together of the seams and parts (to cause the shrinkage to be even and leave the parts a little less likely to be deformed by uneven curing--because it is held firmly inside the molds while this takes place) there is a little something to that. It certainly makes it easier to get a smoother join between parts. 2 Overlapping glued joints--time will tell if they hold up. Gluing is a lot cheaper to build with so I assume many manufacturers will tend go that way. That's how most thermoformed kayaks are put together. I believe Epic uses an overlapping joint and also I remember one local builder that used it as well. The reality is that the seams are the strong point of kayaks that use an adequate thickness and strong materials in the joint. I couldn't tell you how good or bad QCC seams are because I've seen very few of them and have not heard of any problems. I'd be willing to bet that they are a lot cheaper to build than inside and outside fiberglass seams though and I suspect that is a major motivator for any company to use them. Anyone out there in Paddlewise land who has seen or had problems with overlapping or glued joints? Matt Broze www.marinerkayaks.com *************************************************************************** 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 Apr 06 2007 - 20:25:30 PDT
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