A compact German battleship: Ger/BB/1915

I have this design, in the Red Book, for a compact German battleship armed with 12-16in and 20-5in guns. The intended speed was 21 knots with 76,500 SHP. In fact, with almost that much power, 23 knots is achievable. The 45,000 ton Standard displacement was wildly over-optimistic. To achieve adequate strength, I had to increase the normal displacement to 53,500 tons. I have a a cross section and a sideview, to scale, so we knew the citadel length and the armor thicknesses. This is the Springsharp report:

Ger/BB/1915 Short, Germany Enter ship type laid down 1915 (Engine 1927)

Displacement:
    48,961 t light; 51,335 t standard; 53,500 t normal; 55,232 t full load

Dimensions: Length overall / water x beam x draught
    682.10 ft / 680.00 ft x 120.00 ft x 33.00 ft (normal load)
    207.90 m / 207.26 m x 36.58 m  x 10.06 m

Armament:
      12 - 16.00" / 406 mm guns (4x3 guns), 2,048.00lbs / 928.96kg shells, 1915 Model
      Breech loading guns in turrets (on barbettes)
      on centreline ends, evenly spread, 2 raised mounts - superfiring
      20 - 5.00" / 127 mm guns (10x2 guns), 62.50lbs / 28.35kg shells, 1915 Model
      Quick firing guns in turrets (on barbettes)
      on side, all amidships, 6 raised mounts - superfiring
    Weight of broadside 25,826 lbs / 11,714 kg
    Shells per gun, main battery: 90

Armour:
   - Belts:        Width (max)    Length (avg)        Height (avg)
    Main:    18.0" / 457 mm    385.00 ft / 117.35 m    16.00 ft / 4.88 m
    Ends:    Unarmoured
      Main Belt covers 87 % of normal length

   - Torpedo Bulkhead:
        2.00" / 51 mm    385.00 ft / 117.35 m    32.00 ft / 9.75 m

   - Gun armour:    Face (max)    Other gunhouse (avg)    Barbette/hoist (max)
    Main:    18.0" / 457 mm    10.0" / 254 mm        18.0" / 457 mm
    2nd:    5.00" / 127 mm    5.00" / 127 mm        5.00" / 127 mm

   - Armour deck: 8.00" / 203 mm, Conning tower: 18.00" / 457 mm

Machinery:
    Oil fired boilers, steam turbines,
    Geared drive, 4 shafts, 71,191 shp / 53,108 Kw = 23.00 kts
    Range 5,400nm at 15.00 kts
    Bunker at max displacement = 3,897 tons

Complement:
    1,758 - 2,286

Cost:
    £6.895 million / $27.578 million

Distribution of weights at normal displacement:
    Armament: 3,228 tons, 6.0 %
    Armour: 23,247 tons, 43.5 %
       - Belts: 5,137 tons, 9.6 %
       - Torpedo bulkhead: 912 tons, 1.7 %
       - Armament: 7,008 tons, 13.1 %
       - Armour Deck: 9,640 tons, 18.0 %
       - Conning Tower: 551 tons, 1.0 %
    Machinery: 2,247 tons, 4.2 %
    Hull, fittings & equipment: 20,239 tons, 37.8 %
    Fuel, ammunition & stores: 4,539 tons, 8.5 %
    Miscellaneous weights: 0 tons, 0.0 %

Overall survivability and seakeeping ability:
    Survivability (Non-critical penetrating hits needed to sink ship):
      83,710 lbs / 37,970 Kg = 40.9 x 16.0 " / 406 mm shells or 14.4 torpedoes
    Stability (Unstable if below 1.00): 1.02
    Metacentric height 6.8 ft / 2.1 m
    Roll period: 19.3 seconds
    Steadiness    - As gun platform (Average = 50 %): 70 %
            - Recoil effect (Restricted arc if above 1.00): 0.78
    Seaboat quality  (Average = 1.00): 1.40

Hull form characteristics:
    Hull has a flush deck
    Block coefficient: 0.695
    Length to Beam Ratio: 5.67 : 1
    'Natural speed' for length: 26.08 kts
    Power going to wave formation at top speed: 48 %
    Trim (Max stability = 0, Max steadiness = 100): 50
    Bow angle (Positive = bow angles forward): 4.00 degrees
    Stern overhang: -2.00 ft / -0.61 m
    Freeboard (% = measuring location as a percentage of overall length):
       - Stem:        30.00 ft / 9.14 m
       - Forecastle (20 %):    24.00 ft / 7.32 m
       - Mid (50 %):        24.00 ft / 7.32 m
       - Quarterdeck (15 %):    24.00 ft / 7.32 m
       - Stern:        24.00 ft / 7.32 m
       - Average freeboard:    24.48 ft / 7.46 m

Ship space, strength and comments:
    Space    - Hull below water (magazines/engines, low = better): 71.1 %
        - Above water (accommodation/working, high = better): 169.4 %
    Waterplane Area: 65,134 Square feet or 6,051 Square metres
    Displacement factor (Displacement / loading): 100 %
    Structure weight / hull surface area: 235 lbs/sq ft or 1,145 Kg/sq metre
    Hull strength (Relative):
        - Cross-sectional: 0.95
        - Longitudinal: 1.70
        - Overall: 1.00
    Hull space for machinery, storage, compartmentation is excellent
    Room for accommodation and workspaces is excellent
    Ship has slow, easy roll, a good, steady gun platform
    Good seaboat, rides out heavy weather easily