: Bryan, Please do this for all of us and "end the Madness!" Make
: some test panels, use two layers of woven smooth 3oz glass on 3mm ply. One
: layer on each side. Make another panel with 6oz glass on either side.
: Break them. Which one's lighter ? which one's stronger? ok, ok, ok, well
: then how about two layers of woven smooth 3oz on either side of the 3mm,
: which one's lighter? which one's stronger? hmmmmm

Just a SWAG with no analysis (number crunching) what so ever, but I'll go with the (2) 3 oz over the (1) 6 oz PROVIDED that the (2) 3 oz are layed up at 0/90 and +45/-45. The one thing I never hear any talk about is that you get fibers in more directions for out of plane loads.

The 6oz would be stronger if you laid it up with the cloth at 0/90 and then loaded the panel by supporting it at the ends and pushing down in the middle (with the direction of the 0 fibers). But what if the 6oz cloth were at +45/-45 to the load. Not very strong at all.

Take a piece of cloth and pull in the direction of strands (STRONG), then pull in the other direction at 90 degrees to the first (STRONG). Now pull at 45 degrees (weak). It's the same in compression. Of course you can't push on the cloth (like pushing on a rope), that's one of the jobs of the resin. It stabilizes the cloth so it can take compression. In compression the resin would be entirely in compression, and if the fibers were at an angle they would be in compression and bending which is much higher stress on the fibers.

The thing about your kayak hitting a rock is that it is not loaded like a board held at each end and loaded in the middle, it's loaded more like if the board were held on all 4 sides and loaded in the middle (actually more like disk supported all around with a load in the middle, like a truck driving over a round manhole cover). The fibers in the +45/-45 direction help to take the load that are out of plain to the fibers in the 0/90 direction and vice versa.

It's like a piece of plywood versus a board of the same thickness. Hold them on 2 ends (the strong direction of the board) and load them in the middle and the board should win. Hold them on all 4 sides, or in the bad grain direction of the board, and the plywood should win.

So I guess I'm saying George is ri..., sorry I can't bring myself to saying it. My problem with George has always been, not whether he is right or wrong, but that if he say's he is right and everyone else is wrong, then prove it (show me). Don't ask others to prove your own point for you.

I am not saying that the 6oz cloth layups are bad (especially since they have been proven by years of tests on the water), I myself even used it on the deck. They are probably more than adequate to do the job. I am saying that there are stronger, lighter (but more expensive) layups than the standard 6oz.

By the way, satin weave is better than plain weave because there are a lot more fibers that are not bent so they can take the compression better.

: What I'm getting at is lighter is not stronger, they are two different
: things. But good building practices can make something stronger per unit
: of material, and that is different from lighter and stronger. Just to be
: cantankerous about the whole issue there's no way that a 30lb strip built
: kayak is going to be stronger than a 45 lb kayak built of the same
: materials, make the boat and test it. All I can tell you in my experience
: is that when lightness is the goal then strength and durability are
: compromised. That's true whether the forces are between a well built Honda
: and a chevy suburban or kit kayak and a boutique ultralight. We all live
: in the same reality.

My guess would be (again no analysis) that if you put (1) layer of 3 oz at 0/90, (1) 3oz at 30/-60 and (1) layer 60/-30 you would have a stronger layup (loaded with support all the way around) than (1) 6oz at 0/90 and (1) 6oz at +45/-45. You'd also have only 9 oz of cloth rather than 12 oz.

Lesson for George: See I am giving my opinion of which I may believe I am right, but I am not saying (YOU ARE WRONG!!!). To do that, I should prove it with numbers and provide reasoning for any assumptions, not "I'm right, now you go look at these books and prove it to me".

How's all of my info above, but then again, you got what you paid for.

Dale