The definition used here requires a fast battleship to maintain contact with the cruiser line. A battlecruiser must be able to exceed that line's speed. Cruiser reconnaissance formations are described as commonly operating at about 28 knots, which establishes the benchmark. At 27 knots, the Yamato class falls short under this definition. The comparison is less favorable still against a Japanese cruiser line described as faster than 28 knots.
Notable Point · 1:22:28-1:23:41
Why 28 knots defines a fast battleship here
Cruiser-line speed supplies the operational benchmark used to distinguish fast battleships from slower designs.