The J/CL/1937 design is a 37-knot ship

The only improvement in the J/CL/1937 design is that the maximum speed is now 37 knots. The other changes are more beam, a foot more draft, and a small increase in length, which improved seakeeping and lowered the power required for the extra knot. I considered increasing the main armament to 15-6.1in guns, but decided to defer that for the next interation. This is the Springsharp report:

J/CL/1937, Japan Light Cruiser laid down 1937 (Engine 1947)

Displacement:
 12,084 t light; 12,579 t standard; 13,600 t normal; 14,417 t full load

Dimensions: Length overall / water x beam x draught
 663.80 ft / 659.00 ft x 62.00 ft x 21.00 ft (normal load)
 202.33 m / 200.86 m x 18.90 m  x 6.40 m

Armament:
      12 - 6.10" / 155 mm guns (4x3 guns), 113.62lbs / 51.54kg shells, 1937 Model
   Quick firing guns in turrets (on barbettes)
   on centreline ends, evenly spread, 2 raised mounts - superfiring
      8 - 5.00" / 127 mm guns (4x2 guns), 62.50lbs / 28.35kg shells, 1937 Model
   Dual purpose guns in deck mounts with hoists
   on side, all amidships
      32 - 2.24" / 57.0 mm guns (16x2 guns), 5.65lbs / 2.56kg shells, 1937 Model
   Anti-aircraft guns in deck mounts 
   on side, all amidships, 12 raised mounts - superfiring
 Weight of broadside 2,044 lbs / 927 kg
 Shells per gun, main battery: 180
 8 - 24.0" / 609.6 mm above water torpedoes

Armour:
   - Belts:  Width (max) Length (avg)  Height (avg)
 Main: 3.00" / 76 mm 475.00 ft / 144.78 m 12.00 ft / 3.66 m
 Ends: Unarmoured
   Main Belt covers 111 % of normal length
   Main belt does not fully cover magazines and engineering spaces

   - Torpedo Bulkhead:
  1.00" / 25 mm 475.00 ft / 144.78 m 19.00 ft / 5.79 m

   - Gun armour: Face (max) Other gunhouse (avg) Barbette/hoist (max)
 Main: 3.00" / 76 mm 2.00" / 51 mm  2.00" / 51 mm

   - Armour deck: 1.00" / 25 mm, Conning tower: 3.00" / 76 mm

Machinery:
 Oil fired boilers, steam turbines, 
 Geared drive, 4 shafts, 179,924 shp / 134,223 Kw = 37.00 kts
 Range 7,500nm at 15.00 kts
 Bunker at max displacement = 1,839 tons

Complement:
 629 - 818

Cost:
 £6.872 million / $27.488 million

Distribution of weights at normal displacement:
 Armament: 256 tons, 1.9 %
 Armour: 1,839 tons, 13.5 %
    - Belts: 699 tons, 5.1 %
    - Torpedo bulkhead: 334 tons, 2.5 %
    - Armament: 239 tons, 1.8 %
    - Armour Deck: 530 tons, 3.9 %
    - Conning Tower: 37 tons, 0.3 %
 Machinery: 4,445 tons, 32.7 %
 Hull, fittings & equipment: 5,545 tons, 40.8 %
 Fuel, ammunition & stores: 1,516 tons, 11.1 %
 Miscellaneous weights: 0 tons, 0.0 %

Overall survivability and seakeeping ability:
 Survivability (Non-critical penetrating hits needed to sink ship):
   12,534 lbs / 5,685 Kg = 110.3 x 6.1 " / 155 mm shells or 1.6 torpedoes
 Stability (Unstable if below 1.00): 1.23
 Metacentric height 3.6 ft / 1.1 m
 Roll period: 13.8 seconds
 Steadiness - As gun platform (Average = 50 %): 51 %
   - Recoil effect (Restricted arc if above 1.00): 0.49
 Seaboat quality  (Average = 1.00): 1.03

Hull form characteristics:
 Hull has rise forward of midbreak
 Block coefficient: 0.555
 Length to Beam Ratio: 10.63 : 1
 'Natural speed' for length: 25.67 kts
 Power going to wave formation at top speed: 62 %
 Trim (Max stability = 0, Max steadiness = 100): 50
 Bow angle (Positive = bow angles forward): 5.00 degrees
 Stern overhang: 2.00 ft / 0.61 m
 Freeboard (% = measuring location as a percentage of overall length):
    - Stem:  32.00 ft / 9.75 m
    - Forecastle (20 %): 26.00 ft / 7.92 m
    - Mid (67 %):  26.00 ft / 7.92 m (18.00 ft / 5.49 m aft of break)
    - Quarterdeck (15 %): 18.00 ft / 5.49 m
    - Stern:  18.00 ft / 5.49 m
    - Average freeboard: 23.84 ft / 7.27 m

Ship space, strength and comments:
 Space - Hull below water (magazines/engines, low = better): 178.6 %
  - Above water (accommodation/working, high = better): 169.9 %
 Waterplane Area: 28,642 Square feet or 2,661 Square metres
 Displacement factor (Displacement / loading): 106 %
 Structure weight / hull surface area: 112 lbs/sq ft or 546 Kg/sq metre
 Hull strength (Relative):
  - Cross-sectional: 0.95
  - Longitudinal: 1.62
  - Overall: 1.00
 Hull space for machinery, storage, compartmentation is cramped
 Room for accommodation and workspaces is excellent