The US Navy played with this back in the early '60s for ship salvage but
soon switched to pour-in-place foam.

I realize your referring to using pingpong balls for reserve floation.. The
total volume of these balls would not be efficient.. Balls don't stack
efficiently.. Foam is much more efficient.

You mentioned something about the bilges.. Your floation shouldn't be in the
bilge for a couple reasons.. 1) If the boat fills with water and your
reserve bouyancy is low in the bilge, the boat will capsize.. 2) Filling the
bilge with anything eliminates volume where bilge water would normally
accumulate until the pumps can remove it. Without that volume for the water
accumulation, every bucket of water that comes down the hatch accumulates on
the cabin sole or in the lockers. (shallow bilges is another topic).


--
My opinion and experience. FWIW

Steve
s/v Good Intentions