I called the original designers of the O'Day. Although they no longer
have any of the original documentation, I spoke with a gentleman that
was working there when the boat was originally designed. He said that
it has a lead keel encapsulated in a fiberglass mold. He wasn't sure
what the the material was that I was moving around, but he said it's
likely that the lead didn't go all the way to the bottom. He suggested
that I could use some spray foam to shore things up. He also said that
I shouldn't need to worry about the boat's center or weight.

Now, I just need to make sure that the patch is good and solid.