Shawn said >snipped<: >>>Why not a VB'ed boat with extra glass that is the same weight as the aforementioned hand-laid kayak....much more stiffness _and_ more strength. And only slightly more cost.<<<<<< "Doug Lloyd" dalloyd_at_telus.net responded: >>>>>>>>Yes, that's the current theory, but take two brand new kayaks >>>>>>>>from reputable manufacturers, flip them over so the hulls are >>>>>>>>face up, then grind through the gelcoat to the underlayer of >>>>>>>>glass with a sharp point on both the individual hulls. Bet the >>>>>>>>hand-laid, bit heavier boat will "fuzz" less at the core than >>>>>>>>the "squeezed-out" VB'ed lay-up. Bet you you will penetrate less >>>>>>>>on the hand-laid hull if the kayak is one made by a skilled >>>>>>>>glasser. <Snip><<<<<<<<<<<<<< I think you are both somewhat mixed up about this subject. For a given weight the hand lay-up will be stiffer (because stiffness is mostly a matter of thickness) and also thicker (because glass weighs more for the same volume than resin does). Vacuum bagging can produce a laminate that, depending on the pressure, can produce a laminate that ranges from resin rich to resin starved. The strongest laminate will be the one with just enough resin to fully bond the glass fibers together without any extra resin. Beyond the ideal extra resin will progressively make the laminate more brittle. The extreme being all resin with no glass. Any less than the ideal amount of resin and the bonds between fibers won't be as good and the laminate will rapidly get weaker with additional pressure/less resin. It is better to error slightly resin rich since resin starved hurts strength much more quickly in that direction. Even the best hand laminators can't get close to the ideal resin to glass ratio because if enough extra resin isn't available during the cure when the glass stiffens as the cure starts the expansion of the weave will suck air into the laminate and weaken it. Vacuum-bagging prevents this by holding the laminate compressed under pressure until it is cured so a higher glass ratio is possible. Of course, you will scrape up more glass fibers scratching through the gelcoat of the VB'd hull than the hand laid one. There are a lot more glass fibers packed more densely in the laminate to scrape up. That's what makes a VB'd laminate so much stronger pound for pound and harder to penetrate (unless resin starved). This is different than saying VB is stiffer. In order to get enough stiffness to hold a rigid enough shape to make a kayak the VB'd hull will be heavier (because of the greater density of the glass in the same thickness of laminate). Remember thicker is stiffer. Once you go beyond just stiff enough to prevent folding then VB will be much stronger (meaning less penetration) pound for pound using the same materials (and also much stronger materials can be used with VB that are unsuitable for hand lay-ups). This is because these heavier weave or unidirectional materials won't hold resins well on vertical surfaces without the VB pressure holding it up in place until it cures). >>>>>>>As for Kevlar composites, its slippery nature means the VB'er >>>>>>>better know what they are doing. <<<<<<< As Shawn said, it is harder to hand-lay Kevlar because of the light fabric tending to float on the resin. Also there is the fact that you can't see as well through Kevlar to chase out the air bubbles with hand lay-ups because it doesn't turn clear when wetted out like glass does. Matt Broze http://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 Sun Mar 02 2003 - 02:42:19 PST
This archive was generated by hypermail 2.4.0 : Thu Aug 21 2025 - 16:31:04 PDT