This has been discussed a couple of times here and I think you have captured the key points

Plywood is harder to install but provides opportunites to serve as a foot brace or a structural member to mount a pump. Some have sugested that the structural stiffness could be a problem if the hull hits a rock. Foam pesumably gives and lets the hull flex some while plywood doesn't. There is not unaimous agreement that the "hard spot on the hull" is an issue.

I don't think the buoyancy provided by a 3 inch thick bulkhead is significant. Having float bags and a water tight compartments provided by the bulkheads provides the buoyancy

Jack
>

What are advantages and disadvantages of plywood bulkheads against foam
> ones?

> plywood - more difficult to install but works as structural element ?

> foam - additional buoyancy ?