Here are a couple of sites with info on resins and additives etc.It would seem that the gouging resistance is a property of the resins(hardness/softness) and not the glass layers.Multiple layers of glass and resin will certainly slow the violation of the core material but the resin determines the resistance to gouging.
Regards
Ron

http://www.eagerplastics.com/cab.
htmhttp://www.mrfiberglass.com/westfill.html

420 Aluminum Powder

420 Aluminum Powder provides limited protection from ultraviolet light in areas that will not be protected with other coatings. Can be used as a base for subsequent painting. 420 will increase the hardness and abrasion resistance of the coated surface and improve its moisture resistance. Cures to a metallic gray color. Add to mixed resin/hardener at the rate of 5 to 10% by volume (approximately 6 oz. per B group).

422 Barrier Coat Additive

A proprietary blend designed to improve cured epoxy's moisture-exclusion effectiveness. 422 is used as a barrier coating additive to help prevent gelcoat blistering. 422 also increases the epoxy's abrasion resistance. Cures to a light gray color. Add to mixed resin/hardener at the rate of 15 to 20% by weight - 3 tablespoons per 8 fl. oz. epoxy (approximately 32 oz. per B group).

423 Graphite Powder

423 Graphite Powder is a fine black powder that can be mixed with WEST SYSTEM epoxy to produce a low-friction exterior coating with increased scuff resistance and durability. Epoxy/graphite is commonly used as a bearing surface, and as a coating on rudders and centerboards, or on the bottoms of racing craft that are dry sailed. It does not provide antifouling qualities. The epoxy/graphite mixture can also be used in teak deck construction to simulate the look of traditional seams and to protect the epoxy from sunlight. Cures to a black color. Add to mixed resin/hardener at the rate of up to 10% by volume (approximately 5.7 oz. per B group

: Basically you have a standard layup. This has plenty of strength for
: "normal" conditions. If you need more strength you can add more
: layers. You will get all sorts of controversy considering whether two 4
: oz. layers are actually that much stronger than a single 6 oz. layer. What
: about 6 oz s-glass, or some other weave, or combination. There are many
: variables for strength. I just added two layers of 6 oz...for a total of
: three on the outside and two on the inside of my kayak...but I have a
: "need" for added strength and I'm trying to make the best of
: what I currently have. The future will see different types of layups for
: my specific use kayaks. However...your question concerns two different
: things. It really doesn't matter how many layers of glass you put
: on...you're still gonna get scratches and gouges...IF you paddle in areas
: where such can occur. Resistance to scratches and gouges CAN be a function
: of the material...ie: e-glass, s-glass, kevlar, dynel, etc....that you are
: using, BUT it might be said that the hardness of the epoxy and/or the
: additives to the epoxy are more important to scratch and gouge resistance.
: If you, or I, or anybody, can come up with a good formula for scratch
: resistance, then we'll be sitting on easy street. As it is we...or maybe
: just I...will have to continue experimenting with additives (such as
: cabosil, graphite, rock flour, etc.) to the fill coats on the hull for
: scratch and gouge resistance. The problem with additives is that it
: usually will dull, or completely cover, the beauty of the wood. Not too
: much of a problem in my case on the hull...but some people want the wood
: completely exposed to show the inherent beauty. I don't find scratches or
: gouges very difficult to repair after a season....but then, I'm not trying
: to maintain museum pieces. I will someday though. Decide what your
: requirements are, then build to fit those requirements.