I've used both quite a bit and I'd also use the 650 to do Dynel repair patches/plates. I don't use graphite but I do add black pigment to skids.
I have been using both black pigment and graphite mixed together to achieve the deepest saturation of black. A tiny dab of pigment will saturate new cloth, but even then the graphite powder deepens the black. Wee dab of black pigment, teaspoon of graphite powder (or some amount less than 10% by volume) and that is black as black can be through and through.
Unless the graphite does something other than make my shoddy repairs black I won't be using any.
Graphite powder purportedly makes things slipperier. I can now attest to that “purportedly”, having lost control of a canoe with slick graphite powdered skid plates while rolling it over on the sawhorses. It was akin to squeezing a watermelon seed betwixt my fingers.
How much effect that has in helping slide over rocks I do not know. Probably can’t hurt, takes seconds to add graphite powder while stirring the epoxy mix, and that is your one chance while saturating the cloth.
I doubt your new Dynel layer will be shoddy. Tape (X2; tape, paper mask and tape again at the overlap). When the G/flex starts to set up pull the mask, lay on an oversized piece of release treated peel ply and roller compress atop the peel ply every half hour for the rest of the afternoon, especially along the transition edges.
Pull the release treated peel ply the next morning. Scchweeeet!
Dynel does not set up transparent clear with epoxy, it’s a sickly milky color. Your multi-layers of S-glass may already be sickly scuffed as well. If you want to skip the graphite black you could just pigment the epoxy so the Dynel cloth better matches the hull color, red or green or whatever.
Dammit, I wanna see before and after photos. Mostly I’d like to see the abrasion damage done to multiple layer S-glass skid plates, which, already installed, should provide a hellva impact resistant base layer.
