Removing Black Streak marks


for years I had trouble removing these black streak marks on the freeboard
of my sailboats.

The only thing that work was to use a mild compound and wax after.

Other people and professional boat cleaners are using a strong soap like
Spay 9 and waxing after.

All that require some elbow crease and I wonder if there is something else
that can be done.

This morning I saw a product (made in the US) in the RV section of Canadian
Tire that is labelled Black Streak remover. I am a little apprehensive to
use this product and I wonder if anyone had some experience or other way to
remove these black streak marks.