For the area under the regular headliner, that adds up to about 5 cubic feet of flotation. Eventually, I plan to line the whole underside of the deck to reduce condensation inside the boat when we sleep on board. Eventually, it will add up to probably 7-10 cubic feet.
That's really good placement for the foam, very high up. It will tend to right the boat in the event of a roll over with the boards open.
Another benefit is that I can remove some of the foam under the v-berth to increase the available storage space. My target for total foam is about 35-36 cubic feet (the boat displaces several cubic feet with the cored deck, fiberglass, etc). That should float a 1300 pound boat, 500 pounds of gear and 600 pounds of passengers quite nicely... right side up too!
But, I don't worry about knocking the P19 over... That's pretty hard to do. Mainly, I'm putting the foam in to protect our heads from the bolts and to reduce condensation when we sleep on board.
Best,
Judy B