Johnny Boat Dude said:
What meant by a balsa core?
With the Balsa core, or sandwich construction, the skin of the boat is made up of an outer laminate of say 4, 5, or 6, 8 or 10mm (depending on which boat, and where on the boat) and an inner laminate of maybe half, or a third of the thickness of the outer, and these inner and outer layers of glass/kevlar, are separated by a thickness (again depending on many things) of end grain Balsa wood, that is, many, many 1" square pieces of balsa cut so the grain is running from one laminate to the other. In that plane, (grain end on) it is almost imposible to crush, and adhears very well with the laminates.
in my boat, the balsa is either 1/2 inch thick, (in the bottom, and deck king plank) 1/4 inch thick (topsides and outer deck)
This construction forms a very stiff structure indeed, and it's extremely rare to find a boat build in this way that has any cracks or crazing in the gelcoat, as so little flexing occurs.
In some of the OCR boats, the Balsa core in the running surface is 1" thick, which makes for a very stiff bottom indeed, and this maintains the desired hull form in the most extreme conditions.
Apparently, the big Buzzi's have as much as 1.5-2" of balsa in their running surface.