So what do you guys think about the core Kjell is using ? Some construction foam 70kg/cum, which showed that can handle compression better than Corecell I believe. If the foam can't handle shear stress as good as "marine" foams, then he might get local delamination during the boat's life.

I assume shear stress in the laminate can be reduced with scoring the foam ? Indeed that will add some resin weight but will it improve shear stress handling ?