8 Nova Cannon firing at a BB, 3.33 target the escort screen instead, 3.11 direct hits accounting for scatter, 1.556 partial hits, 12.4 hits total. 4 absorbed by shields, braced, 4.22 hits past shields and saves.
Note that 45cm is also well within torpedo range, with the torpedos able to be fired all but unavoidably into the path of the battleship. 48 torps, the equivalent of 8 Nova Cannons, would do 6 hits past shields and bracing, not including damage to other ships caught in the path.
Also, 8 Nova Cannons would only be found in a fleet of 2000pts, in which you could have two battleships squadroned together and taking perhaps 2 hits each without even having to brace.