mr.b wrote:
2 questions.
Has anyone ever heard of this procedure being done from the interior
rather than the exterior of the boat?

Also, can anyone give a ballpark estimate as to the expected cost of
loosening the lead ballast on a fin-keel and re-sealing/repairing the
joint between the two?

I see you have many good replies, but let me add that duplicating the
non-skid is rather easy if you choose to do it from above. You make a
mold from the pre-repair non-skid and use that as a template for the new
gel coat. Were I do do it, I'd remove all non-skid left after the repair
and use the paint / sand route for the new non-skid.

Re-coring isn't simple or cheap so you need to evaluate the value of
your boat before and after the repair, but it's possible (like almost
anything marine).

I have also heard rumor of injections which will, in situ, repair
defective cores. I'd run those rumors down to earth before embarking on
such a task.

-paul