Abstract: A fibrous ply forming apparatus unit or module, which can be assembled with at least one additional essentially identical fibrous ply forming apparatus to form a multiply paperboard making machine, comprising four horizontally positioned spaced-apart rolls equally spaced from a vertical plane normal to the axes of the rolls, with said rolls being a tail roll, head roll, foot roll and guide roll, parallel to each other, a fibrous ply forming endless fabric belt wound over the four rolls, a low-vacuum box beneath a run of the fabric belt extending from the tail roll to the head roll for dewatering a forming fibrous ply deposited on said fabric run, and a high-vacuum box behind a run of the fabric belt extending from the head roll to the foot roll.