All the ventilating ports were naturally ventilated, i.e., they relied on the afterbody suctions to provide tile necessary ventilating air. The method of construction is illustrated in Fig. 4. Each port was connected to a porthole in the side of the hull by way of a light-alloy duct. The duct inlets were flush with the skin plating, i.e., no use was made of ram pressure to provide additional flow. To enable the effect of varying ventilation area to be investigated, each port was provided with a flush-fitting sealing cover which could be screwed to the afterbody skin plating. The interior ducts on the port side of the hull had provision for measuring the total flow of ventilating air.