QUOTE "From this you will note that quoting "displacement" is pointless as it is the same as the mass of the board."
I think the original poster means the displacement not with just the board weight and not with the board fully submerged (because at that point the displacement just equals the volume anyway!!!) but I think he means with a standard average rider weight. Say 75kg. Then you have a more accurate assessment of the flotability that takes into account length, width, rail shape, etc.