Piece in the floor is definitely plastic (I scraped it with a screwdriver to be sure). Looks like it had a flange on it at some point and it broke off, there still a bit of a groove around the outside in places.
Thanks for the call Rusty
Rusty, this is a boating web site, he needs to use "Sea Going Poxy Putty".... 
GT
Dont you tempt me GT, I was already thinking about something like that, "Sea Going Poxy Putty" fixes everything !!
So anyway, there should be some kind of slip in / glue in repair piece for this broken plastic flange (the one in the floor), kinda like what GT posted but for plastic. Then drop some new cement around it to keep it from breaking again and I'll be good ?
I'll plug up the hole GT, just had it open for the pics.