Some info on the strength of foam, honey-comb, marine ply, and balsa - shear & compressive
But don't forget about good ol Marine grade ply!
Marine Plywood: Compressive strength is 5000 psi- more than 5 times better than the best foam (at 10# density).
Marine Plywood: Shear (transverse) strength is 4500 psi- more than 5 times better than the best foam.
End grain Balsa (10# density): Compressive strength is 4000 psi- 4 times better than the best foam (at 10# density).
End grain Balsa (10# density): Shear strength is 433 psi- here is the weakness of Balsa, this is at the low-mid range of foams, many foams will outperform balsa in transverse shear. This is significant if a cored bottom skin is supported by a bulkhead or stringer, the pressure load will put the core material into shear at the bulkhead connection. Easily managed by tabbing, etc, if the builder knows about this characteristic.
Just remember this is comparing just the core alone, the strength on the foam comes from the glass laminated to it. But wood gains from the lambent too once glassed just the same but just is heaver and can rot if not sealed 100%.
This below is another good diagram backing up what was being said about the core thickness and strength by bushwacker on my 25' seafari thread, the thicker the core the stiffner it will yield with the same inner and outer lambent:
