Which foam for stringers

[Mshugg]

These threads always seem to devolve into two camps:

You need the foam for flotation or the foam will break down; skip it. The foam for flotation croud goes a bit far sometimes suggesting billets of EPS, empty soda bottles even ping pong balls as a sub for foam.

The thing is, the foam was there not just for flotation. It also provided structure in the same way that the center web of an Ibeam provides structure. Original spec for your stringers was 4lb. 2 pound everywhere else. Some folks leave the flotation foam out, but I would never leave it out of a box beam stringer.

Yes, the foam will eventually absorb water if subjected to prolonged water exposure. But it doesn't have to. Just protect it from water. The foam in the stringers of my 1978 Aquasport was dry.

Replace the foam or not, but it does provide more than flotation.