Abstract: A construction element having a high strength to weight ratio, particularly useful in the fabrication of a boat hull, the construction element comprising:A first face layer of resin impregnated glass fiber cloth or glass fiber matting;An intermediate stiffening member comprising a laminate of:A. a flexible top sheet, preferably of paper;B. an intermediate foam layer, bonded to the top sheet; andC. a flexible bottom sheet, preferably of paper, bonded to the intermediate foam layer on the side opposite the top paper sheet; the laminate having:I. a first series of spaced slits extending through the top sheet and intermediate foam layer but not through the bottom sheet;Ii. a second series of spaced slits parallel to the first series of spaced slits and extending through the bottom sheet and intermediate foam layer but not through the top sheet, the second series of spaced slits being offset from the first series of spaced slits;Iii.