thanks Will.Welcome to SBO, Anemone. That is a sad sight for you, I'm sure, but the good news is you've joined an amazing crew of skilled and knowledgeable sailors ready to help.
That looks like Winter ice. What caused the initial crack that allowed the water infiltration, I can't say, but I'm inclined to think 'flaw in the original poor.' @dLj is a materials engineer and might have a better idea.
I'm not that experienced with metals. I'd grind it out to see what's going on better, then figure out what was best to fill it with. Not sure if cast iron is easy to weld, I think not. Then, I'd fill the crack with something like JB Weld and epoxy barrier coat it over.
Not so sure about that. If it was rust on cast iron, there would be stains present; I see it on my cast iron keel every few years on haulout. As you stated, no big thing, grind down to bare metal & recoat with epoxy & apply antifouling paint.That is a Cast Iron /Steel keel - that is DEFINATELY a bit of corrosion that has permeated the filler and the rust has lifted the filler and epoxy fairing.
will do and thanks for your help!OK, hold on here. I have a B331 with the shoal keel in Nova Scotia. These were made of lead (which is a real plus). The deep draft had the typical iron keel. At the same place as you are showing, my lead keel has a funny ridge. It looks like some material that has deteriorated, but it is not lead. I think it was some fairing compound on that part. It looks like someone was poking around at it. It is not smooth like yours.
You will have to scrape and poke around a bit to see exactly what you are dealing with. Take it one step at a time and get back to us with what you find.