I have a cheaper and quicker method than the sandblast and epoxy coat method: moisture cured polyurethane. I don't have any good information on the relative long term durability of this as compared to sandblasting + epoxy, but in my experience it is a durable and long lasting solution if done properly. I did the cast iron swing keel on my Catalina 22 in place underneath the boat, because I didn't have the money or equipment to transport the keel. I just sanded both sides with a large belt sander and wire wheel until nothing was loose, wiped down with paint thinner to clean, and then painted 4 thick coats of moisture cured polyurethane based paint directly over the rusty iron. This stuff is advertised as being capable of "painting over rust" under the brand name POR-15, and also sold by Pettit as "Trailercoat" for boat trailers. I know it sounds crazy to paint over rust in a marine environment- but the keel still looks perfect after 4 years, including one entire year moored in the water. While it can paint over descaled rust, the surface has to be absolutely clean otherwise- with absolutely no oil or loose existing paint. Sincerely, Tyler