If you do an internet search on "metal rub rails for boats" you will find a variety of products which may work for this purpose.  That said, I would recommend against a metal rail because you will have to attach it with screws which over time will loosen and allow water intrustion into the plywood.  Instead, take a look at the rub strip kit that CLC sells.  It works well and is easy to repair with a little epoxy and graphite when needed.  Here it is on three of my boats.

An easier by slightly more expensive option is to use a product called KeelEazy.  It comes in a variety of widths/colors and is easy to install/remove with a heat gun.  I replace with new every couple of years when it gets worn.  If the bow has a sharp bend, you will have to cut a little relief on the sides to get it to conform.  You can see that on the Pygmy that I built last year.

Mark,

I have had horrible luck with KeelEazy. It always starts coming off within weeks of application. This is even on relatively unchallenging shapes like the bottom of my WD12. How do you make yours stick?

Laszlo

Interesting Laszlo, because I have never had a problem.  Possibly you got a bad batch? 

I install with a heat gun, heating it hoy enough that I don't want to touch it with my bare hand.  I then use an oven mitt to smooth.  It has been on the bow of my wife's Freg for 6 years now.  I also place it under the foot brace on the race boats and on the sides to prevent paddle strike damage.

mark,

Maybe it is a bad batch. I also applied it with a heat gun and glove. Maybe I need it to be a bit hotter. The boat is due for some touching up soon, I'll try it again at a hotter setting.

Laszlo