: I will glass only and add "strategic" second layers of same
: as required.

You can probably wait a year or two before you add these, as well. First take your boat out and paddle it for a while. Let it get scratche dup for an entire season or two. About that time you'll need to refinish the varnish, so when you are sanding off the varnish you'll find if you have any deep scratches.

Before then, though, you'll get a clear pattern scratched into the resin showing where on the hull you get the most abuse. When it comes time to refinish the boat, you can put on an extra layer of glass that would overlap those poinst a bit.

In my case, I launch my canoe at a river and the starboard side gets scratched against the rock-lined walls at the entry point. I also get scratches under the bow as I beach the boat. The only scratches I get in the middle of the boat are from where I hit submerged rocks that I can't see. Those river rocks tend to have somewhat rounded edges, so there is little chance they'll poke through or break anything, but they are noisy to slide off of, and I cringed for a while at every new scratch.

PGJ