 During refits in 1923 – 25, the fore funnel was rebuilt in a serpentine shape in an unsuccessful effort to prevent smoke interference with the bridge and fire-control systems. The rebuilt fore funnel was eliminated during the ships' 1930s reconstructions when their boilers were replaced by 10 oil-fired Kampon boilers, which had a working pressure of 313 psi (2,158 kPa; 22 kgf / cm2) and temperature of 300°C (572°F). The turbines were also replaced by lighter, more modern, units and their propellers were replaced by larger 4.3-meter (14 ft 1 in) ones. When the ships conducted their post-reconstruction trials, they reached a speed of 24.98 knots (46.26 km / h; 28.75 mph) with 82,300 shp (61,400 kW). Additional fuel oil was stored in the bottoms of the newly added torpedo bulges, which increased their capacity to 5,560 long tons (5,650 t) and thus their range to 8,560 nmi (15,850 km; 9,850 mi) at 16 knots.
