rust on keel
To some extent this depends on the way your boat has been constructed. Assuming that you don''t have an encapsulated keel, the easiest way is to wirebrush the area and remove any loose rust and use something like Ospho or Naval jelly to consolidate the surface oxydation. They you have a couple choices. There are zinc rich epoxies that bond very well to iron. There are also primers such as zinc chromate that also bond very well. Or you can visit the WEST System site and look at thier method of dealing with rusting iron keels.
If you have an encapsulated keel your problem is far more complex and I don''t have the time to answer that one this morning.