Re: [Paddlewise] British Heavies "crumple"

I think that what Brian is saying is: the solar heating and positive pressure due thereto held off the "crumple" until the boat was placed in water and the interior pressure fell. This argument relies heavily on very good thermal conduction by hull resin, as the entire interior volume has to cool off to effect a great pressure change (irrespective of kayak cargo, not expected to shrink). Consider instead, that the resin itself is a very _poor_ thermal conductor, and thus shrank itself only in the bits that were immersed.   Very like cutting a glass bottle by tying an alcohol-soaked string around it, lighting on fire, and dousing it in ice.     Kevlar and fiberglass are actually pretty heat resistant (notice that your fireplace glass doors are very likely sealed with fiberglass, and that a bulletproof vest converts mechanical energy to thermal).   So, resin is really the issue, as we could expect the fiberglass to actually act more like rebar inside concrete, spreading stress out over a greater area.  In this scenario, parti-colored hulls (white underneath, black on top?), kayak loading (oops stressing the weak 'glass free resinous bit) all contribute to the failure.    So: either the resin was weak with pinholes in it, or (restarting a tired hare) vacuumbagging is the true ticket to durability.  P. Gudac

Brian Curtiss <bc_at_asdi.com> wrote:>...the color has little to do with the failure. The issue is
>probably a combination of a bad batch of resin, air tight hatches, and moving
>from 7500 ft. elevation to sea level plus the color and sun.

Actually, the dark color (at least in part) helped.

If moving the boats from 7500' to sea level really caused the 
problem, the color may have both helped and hurt. If you assume a 50 
deg F (10 deg C, 283 deg K) temperature at altitude, the pressure 
difference relative to ambient (at sea level) varies between -7.3 psi 
(with no internal temperature change) to -4.1 psi (with an internal 
temperature of 120F = 49C = 322K). If heated up enough (to about 
213F in this example) the pressure difference would be zero.

Where the color may have hurt is in the strength of the hull. Does a 
fiberglass (or carbon fiber or kevlar) layup get weaker when heated 
to 100-120 degrees or so?

I converted these pressures into feet of water to put it into a 
context to which most of us can relate: 7.3 psi == 16.5 feet of 
water, 4.1 == 9.4 feet of water.

Brian Curtiss



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