My It/CL/1928 design

I have been writing about the Second Battle of Sirte that involved the Italian 6in gun cruiser Giovanni della Bande Nere. I thought that I would try a Springsharp design for a similar ship. The Springsharp design is disappointing. My design can only make 34.5 knots with 94,136 SHP on with a Standard displacement of 6,554 tons. The real ship could supposedly make 37 knots with 95,000 SHP on a displacement of 6,571 tons standard:

It/CL/1928, Italy Light Cruiser laid down 1928 (Engine 1950)

Displacement:
 6,312 t light; 6,554 t standard; 7,076 t normal; 7,494 t full load

Dimensions: Length (overall / waterline) x beam x draught (normal/deep)
 (555.00 ft / 555.00 ft) x 51.00 ft x (17.50 / 18.28 ft)
 (169.16 m / 169.16 m) x 15.54 m  x (5.33 / 5.57 m)

Armament:
      8 - 6.00" / 152 mm 55.0 cal guns - 116.57lbs / 52.88kg shells, 150 per gun
   Quick firing guns in turret on barbette mounts, 1928 Model
   4 x Twin mounts on centreline ends, evenly spread
  2 raised mounts - superfiring
      6 - 4.00" / 102 mm 45.0 cal guns - 32.27lbs / 14.64kg shells, 150 per gun
   Anti-air guns in deck and hoist mounts, 1928 Model
   6 x Single mounts on sides, aft deck forward
  6 raised mounts
      8 - 1.46" / 37.0 mm 55.0 cal guns - 1.67lbs / 0.76kg shells, 150 per gun
   Anti-air guns in deck mounts, 1928 Model
   8 x Single mounts on sides, evenly spread
      Weight of broadside 1,140 lbs / 517 kg
      4 - 21.0" / 533 mm, 22.00 ft / 6.71 m torpedoes - 1.453 t each, 5.813 t total
 In 2 sets of deck mounted side rotating tubes

Armour:
   - Belts:  Width (max) Length (avg)  Height (avg)
 Main: 1.00" / 25 mm 370.00 ft / 112.78 m 12.00 ft / 3.66 m
 Ends: Unarmoured
   Main Belt covers 103 % of normal length
   Main belt does not fully cover magazines and engineering spaces

   - Gun armour: Face (max) Other gunhouse (avg) Barbette/hoist (max)
 Main: 1.00" / 25 mm 1.00" / 25 mm  1.00" / 25 mm

   - Armoured deck - multiple decks: 1.00" / 25 mm For and Aft decks
 Forecastle: 1.00" / 25 mm  Quarter deck: 1.00" / 25 mm

Machinery:
 Oil fired boilers, steam turbines, 
 Geared drive, 2 shafts, 94,136 shp / 70,225 Kw = 34.50 kts
 Range 3,800nm at 18.00 kts
 Bunker at max displacement = 940 tons

Complement:
 385 - 501

Cost:
 £2.534 million / $10.137 million

Distribution of weights at normal displacement:
 Armament: 324 tons, 4.6 %
    - Guns: 318 tons, 4.5 %
    - Torpedoes: 6 tons, 0.1 %
 Armour: 614 tons, 8.7 %
    - Belts: 180 tons, 2.5 %
    - Armament: 82 tons, 1.2 %
    - Armour Deck: 352 tons, 5.0 %
 Machinery: 2,252 tons, 31.8 %
 Hull, fittings & equipment: 3,122 tons, 44.1 %
 Fuel, ammunition & stores: 764 tons, 10.8 %
 Miscellaneous weights: 0 tons, 0.0 %

Overall survivability and seakeeping ability:
 Survivability (Non-critical penetrating hits needed to sink ship):
   6,371 lbs / 2,890 Kg = 59.0 x 6.0 " / 152 mm shells or 1.0 torpedoes
 Stability (Unstable if below 1.00): 1.05
 Metacentric height 2.0 ft / 0.6 m
 Roll period: 15.2 seconds
 Steadiness - As gun platform (Average = 50 %): 67 %
   - Recoil effect (Restricted arc if above 1.00): 0.73
 Seaboat quality  (Average = 1.00): 1.33

Hull form characteristics:
 Hull has raised forecastle,
   a normal bow and a cruiser stern
 Block coefficient (normal/deep): 0.500 / 0.507
 Length to Beam Ratio: 10.88 : 1
 'Natural speed' for length: 23.56 kts
 Power going to wave formation at top speed: 60 %
 Trim (Max stability = 0, Max steadiness = 100): 50
 Bow angle (Positive = bow angles forward): 0.00 degrees
 Stern overhang: -2.00 ft / -0.61 m
 Freeboard (% = length of deck as a percentage of waterline length):
    Fore end,  Aft end
    - Forecastle: 27.00 %,  29.00 ft / 8.84 m,  28.00 ft / 8.53 m
    - Forward deck: 30.00 %,  20.00 ft / 6.10 m,  20.00 ft / 6.10 m
    - Aft deck: 28.00 %,  20.00 ft / 6.10 m,  20.00 ft / 6.10 m
    - Quarter deck: 15.00 %,  20.00 ft / 6.10 m,  20.00 ft / 6.10 m
    - Average freeboard:  22.27 ft / 6.79 m

Ship space, strength and comments:
 Space - Hull below water (magazines/engines, low = better): 119.7 %
  - Above water (accommodation/working, high = better): 182.3 %
 Waterplane Area: 18,859 Square feet or 1,752 Square metres
 Displacement factor (Displacement / loading): 112 %
 Structure weight / hull surface area: 90 lbs/sq ft or 439 Kg/sq metre
 Hull strength (Relative):
  - Cross-sectional: 0.91
  - Longitudinal: 2.51
  - Overall: 1.00
 Hull space for machinery, storage, compartmentation is cramped
 Room for accommodation and workspaces is excellent
 Good seaboat, rides out heavy weather easily