Mine doesn't have a zinc.
I just bought it a few months ago and the keel was pretty ragged (a lot of flaky rust and paint). I wire brushed it and did some grinding with an angle grinder, and then applied POR 15 paint (using their prep chemicals as well). Seemed to work well, but we'll see in the fall when I haul it. I will need to do some fairing with epoxy and filler at that time, as the POR 15 layer is still kind of pocked from the rust pitting.
This is a fresh water only boat, by the way.