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  Sorry, but
  Posted by: CEWilson on Feb-05-13 4:54 PM (EST)
 

Sorry, I'm having a bad day concerning belief verse data based systems.

Common Kevlar, taffeta or crows foot weave, weighs 5oz per square yard. Carbon commonly available weighs between 5.7 and 6.3 oz per sq. yd.

Infused, we would assume ~45% resin content and more for the wet bagging system WeNoNah uses, so lets double fabric weight to arrive at approximate and comparable weights for the Minnesota firm's laminations. Carbon is 5.7X2= 11.4oz/sq yd, Kevlar is 5X2= 10oz/sq yard. A Prism blanket layer will have about 5 sq yards of fabric, so the Kevlar outer skin weighs ~4lbs, the Carbon outer 4lbs 12oz. Yet the carbon boat is lighter. How can that be?

That is because while Kevlar is has great tensile strength it has poor compression resistance. It takes more Kevlar layers to build aqequate thichness to stiffen a hull. Carbon has marginal tensile strength but great compressive strength. Combining the two positive characteristics allows fewer and/or smaller partial inner pieces or layers to construct the boat. So, the half carbon boat weighs less because adequate stiffness is achieved by combining fabrics.

We can design a lamination schedule to any weight or strength we desire, but we cannot max strength and minimize weight at the same time. It is useful to remember that laminate thickness increases stiffness, just like increasing web on an I beam. Cores do this; the lightest being honeycomb, with foams, balsa and various poly mats following in ascending-weight order.


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