: I've seen the bottoms of my strip boats with a couple layers of glass vs. the
: boat with the graphite/epoxy/silica coating, no comparison in resistance
: to scratching.

: Bill H.

I'll defer to your experience but I wonder how much of what you're describing is cosmetic as opposed to actual depth a gouge takes into that ablative layer and how far the gouge is going before it starts into the glass. Also I wonder if your graphite/epoxy/silica coats are substantially thicker than comparable clear coated boats. Is it possible what you interpret as resistance to scratching is actually low visibility of scratching with less ability to discern damage to the underlying glass laminate and wood?

In other words line up three test panels all with the same thickness of epoxy/glass. One with 6oz glass and three thick fill coats then sanded and varnished. One with glass then graphite/silica fill coats of the same thickness. One with glass plus lighter glass and minimal fill coats and varnish to approximate the same thickness/weight of the other two. I'm assuming your graphite/silica mix is thicker than regular epoxy and that you are putting on at least two coats. Basically ensure the thickeses of epoxy above the glass is the same as on the thicker graphite mix. With the double layer with lighter glass and thin fill coats can ensure the thicker glass layer panel isn't over weight.

Then get a big cinderblock and slide it back and forth some set period of times followed but suspending the brick and repeating some glancing/gouging blows.

I could see the graphite sliding over rocks with a more slippery layer could pass you over and not stop on the rock or in the case of sand that it would slide over more easily but when it comes to the kind of sliding impacts that dig into glass and depress the wood I wonder how different the actual depth of the gouge is. With a varnished surface every scratch of any kind shows up and the varnish begins to peel of along the keeline leaving an obvious wear strip. With the graphite you're never going to see that whitened scratch or strip of missing varnish, it's just more black stuff but that isn't exactly a measurment of wear, ie. depth of the scratch/gouge.
Also any kind of gouge that dings the wood but doesn't tear into the glass won't be visible on the graphite anywhere as much as varnished epoxy.

When I made a kayak for a friend I wanted the bottom to be as maintence free as possible but she lived where it got very hot and it was likely the kayak would be sitting outside in the sun upside down. In 95 degree sunlight things get too hot to touch. So I did the bottom with two layers of 4oz s-glass, two thin fillcoats, lightly sanded then three white tinted fill coats with a bit of silica. Sanded and painted yellow. That way there would be a depth gauge for scratches but there would still be some UV protection where the paint peeled on the bottom. Basically I went for thick ablative tint coats on the very bottom and not much on the sides.

Like I said my experience with graphite is minimal on two boats where it was just along the center strip on an s&g kayak about 2"-3" at the widest and it looked like it got scratched just like the varnish except it wasn't as noticable next to the varnished wood scratches.