Milt Baker asked what type of steel is recommended for the keel rub strip.

I would say that if the cost is not prohibitive for the budget that copper nickel would be the best. The main advantage is that is resists biofouling and no antifouling would be needed. Also best corrosion resistance.
I don't think a soft metal would be an advantage. Harder material will resist galling and distribute the load better. The CuNi is soft though, about 30% of the yield strength of 304L. So you would need a thicker section. I would determine thickness by how well the steel is backed up by the hull. If you use the SS you'll have to sandblast it so the paint will stick.
I would purchase plate and have it cut and formed in a channel section with enough radius to match the hull. I'm assuming the keel has a generally rectangular shape and enough meat to through bolt
I think this would be a very wise investment.

John Crowley

If you use bar stock, I would think that 5200 and large diameter,
countersunk screws would be adequate attachment. I say large diameter
because there will be shearing forces if you ground hard. Of course, in such
a grounding those screws could break the fiberglass.

Nordhavn seems to have thought out everything in great detail, I sure would
get their endorsement for this idea. This protective strip might turn into a
liability. Be sure that you are solving a real problem and not creating one.
Ron Rogers