Coating the keel
While I am sure there are other methods, I think a good proceedure for coating the keel after bringing it down to bare metal, is to first coat it with Petit's 6980 which is a very good rust prevention coating able to stand up underwarter.Following this, I think faring with a good two part material, such as that 3M product whose name escapes me, is appropriate.Finally, coat the whole thing with a gel coat barrier, like Interlux 2000. At least two coats. This gel coat barrier, which is the same thing you use on fiberglass, is an excellent water barrier to keep water from rusting out the keel and it is an excellent barrier preventing the copper in antifouling paint from corroding the iron keel.However, depending on the particular gel coat barrier used, you will need to apply anti-fouling to the gel coat barrier within a certain time period. Outside of these limits, you will have to sand the barrier coat before applying anti-fouling paint otherwise the anti-fouling may come off too easily.Further, on the C-22, when the keel is lifted, the aft part may press too hard against the keel trunk which will crack the barrier coat and the 6980 causing rust to form. So, if possible without ruining a smooth suface, it may be good to apply more barrier coats to this part of the keel.