foam under the deck

[Waterman]

Hey guys just reading an old post about foam under the deck I had an old 78 manatee 19ft i ripped apart as a project it did have foam and yes it was waterlogged but i think it still would of helped in an emergency. I was under the impression all boats under 23ft were foamed to keep the boat from completley sinking in an emergency any thoughts?
Im lookin at an 89 right now and is there any other spots on the v20s that are foamed?
THANKS