I wonder if there isn't a practical way to make the underwater section
of the bow/keel stronger on an existing fiberglass boat stronger/more
impact resistant. Surely someone has figured this out, no?

Red

Salty:
Yes. It's often accomplished by the addition of a layer or two of
kevlar cloth during layup.

As I understad it, Kevlar is not only difficult to get a good bond with,
its not all that great for collision protection as it is for puncture
protection.

Besides, your answer doesn't address what I was asking - something that
can be applied on an older existing hull. I believe Kevlar would not
bond well enough on old polyester to make this practical anyway. Is this
correct?

red