> Why would 3 layers of 2oz glass be stronger than one layer of 6oz glass.
> Wouldn't the weight come out to the same? Is there anywhere on the net to
> see why this is so?

> JC

I'm not a composite materials specialist and I never could figure out the engineering data that was posted here when this topic was first presented.

It is not particularly intuitive, and there has been a lot of blood spilt on this ground over this matter before. One camp says it doesn't make a difference. Another camp says it is the ONLY way to go. Again, check the archives for the combat reports.

Here is MY take on the matter:

As I see it, 2 ounce cloth is not merely 1/3 rd the strength of 6 ounce cloth. It must be slightly stronger. Lets say that instead of it being 33% as strong as 6 ounce fabric it is 35% to 38% as strong. If this is the case, you add up the three layers and you get 105% to 114% of the strength. So you pick up a little strength.

Because each layer of the thinner cloth is woven from finer fibers, it will be more likely to stretch, rather than snap under an impact. This would make the material more flexible and pliant, as well as more impact resistant. It would be more likely to bend under impact, not break.

With three layers, you have three boundaries to penetrate when you encounter a sharp rock. This may increase the ding resistance a bit.

Think of extremely thick fabric. The warp and weft have to cross each other. The thicker they are, the more extreme the change in the fiber's direction each time it has to go over or uunder the next cross fiber. They are stronger when aligned straighter. The thinner fabrics have more material that is straighter because the fibers aren't passing over thick crossfibers. They are passing over very thin ones, instead.

Beyond this I start getting confused by claims and counter claims. What I know is that people who have tested the process are happy with it, and that if I stock 2 ounce material I'll be able to use as many layers as I like to make the glass layer as thick as I like. I have some plans that call for using 4 ounce fabric, and other plans tha call for 6 ounce. If I get 2 ounce material I get a quantity discount and I can use it for either project.

I may be able to sandwich scraps between two sheets to get the thickness of 6 ounce, and have a smooth, easily sandable outer layer, mwanwhile using up the odds and ends. This could be a good way to add ding resistance to the center of the hull bottom, while using up the odd sized scraps. Cutting a rectangular piece of cloth to fit over a mostly rounded boat leaves a lot of odd shaped pieces.

Hope this helps. You should be able to get a better engineering discussion of this matter when someone posts a rebuttal to my delusions.

Paul Jacobson