On sailboats you can sometimes find galvanized keels. Galvanization is a process where steel or iron is protected by a layer of zinc to prevent rust.

It is important to use the correct type of antifouling on these otherwise there is a risk for a galvanic reaction between the zinc and the copper in the antifouling. Use an antifouling compatible with aluminium which contains no copper or copper thiocyanate. Make sure to have a good layer of primer before applying the antifouling.