The secret to better performance, for underperforming ships, is light-weight machinery

The underperforming 1923 design can be improved by using light-weight machinery. The sad fact is that Springsharp does not allow for very light machinery. The Japanese light cruisers built in the 1920's had very light machinery, but that cannot be duplicated in Springsharp. At least, I cannot duplicate it simply by manipulating the date. I should be able to achieve SHP/ton of machinery of over 60. Instead, I was just limited to something on the order of 40 SHP/ton or so. I have been trying not to change the machinery date, but that is the only way to fix this design. My modified fast British light cruiser now becomes more interesting. I was able to increase the speed to 35 knots and increase the armour to 3.5in belt and turrets, with a 2in deck. This is the modified Springsharp report:

GB/CL/1923, Great Britain Light Cruiser laid down 1923 (Engine 1950)

Displacement:
 10,595 t light; 10,983 t standard; 11,650 t normal; 12,183 t full load

Dimensions: Length overall / water x beam x draught
 619.03 ft / 615.00 ft x 60.00 ft x 20.00 ft (normal load)
 188.68 m / 187.45 m x 18.29 m  x 6.10 m

Armament:
      6 - 8.00" / 203 mm guns (3x2 guns), 256.00lbs / 116.12kg shells, 1923 Model
   Breech loading guns in turrets (on barbettes)
   on centreline ends, majority forward, 1 raised mount - superfiring
      4 - 4.70" / 119 mm guns in single mounts, 51.91lbs / 23.55kg shells, 1923 Model
   Anti-aircraft guns in deck mounts with hoists
   on side, all amidships
      24 - 1.57" / 40.0 mm guns (6x4 guns), 2.00lbs / 0.91kg shells, 1923 Model
   Breech loading guns in deck mounts 
   on side, evenly spread
 Weight of broadside 1,792 lbs / 813 kg
 Shells per gun, main battery: 150
 4 - 21.0" / 533.4 mm above water torpedoes

Armour:
   - Belts:  Width (max) Length (avg)  Height (avg)
 Main: 3.50" / 89 mm 560.00 ft / 170.69 m 15.00 ft / 4.57 m
 Ends: Unarmoured
   Main Belt covers 140 % of normal length

   - Gun armour: Face (max) Other gunhouse (avg) Barbette/hoist (max)
 Main: 3.50" / 89 mm 2.00" / 51 mm  3.50" / 89 mm
 3rd: 1.00" / 25 mm       -         -

   - Armour deck: 2.00" / 51 mm, Conning tower: 6.00" / 152 mm

Machinery:
 Oil fired boilers, steam turbines, 
 Geared drive, 4 shafts, 134,726 shp / 100,506 Kw = 35.00 kts
 Range 5,400nm at 15.00 kts
 Bunker at max displacement = 1,200 tons

Complement:
 559 - 728

Cost:
 £2.938 million / $11.753 million

Distribution of weights at normal displacement:
 Armament: 224 tons, 1.9 %
 Armour: 2,477 tons, 21.3 %
    - Belts: 1,164 tons, 10.0 %
    - Torpedo bulkhead: 0 tons, 0.0 %
    - Armament: 291 tons, 2.5 %
    - Armour Deck: 955 tons, 8.2 %
    - Conning Tower: 66 tons, 0.6 %
 Machinery: 3,223 tons, 27.7 %
 Hull, fittings & equipment: 4,671 tons, 40.1 %
 Fuel, ammunition & stores: 1,055 tons, 9.1 %
 Miscellaneous weights: 0 tons, 0.0 %

Overall survivability and seakeeping ability:
 Survivability (Non-critical penetrating hits needed to sink ship):
   13,683 lbs / 6,206 Kg = 53.4 x 8.0 " / 203 mm shells or 1.5 torpedoes
 Stability (Unstable if below 1.00): 1.17
 Metacentric height 3.1 ft / 1.0 m
 Roll period: 14.3 seconds
 Steadiness - As gun platform (Average = 50 %): 53 %
   - Recoil effect (Restricted arc if above 1.00): 0.48
 Seaboat quality  (Average = 1.00): 1.06

Hull form characteristics:
 Hull has a flush deck
 Block coefficient: 0.553
 Length to Beam Ratio: 10.25 : 1
 'Natural speed' for length: 24.80 kts
 Power going to wave formation at top speed: 61 %
 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:  29.00 ft / 8.84 m
    - Forecastle (20 %): 22.00 ft / 6.71 m
    - Mid (67 %):  22.00 ft / 6.71 m
    - Quarterdeck (15 %): 22.00 ft / 6.71 m
    - Stern:  22.00 ft / 6.71 m
    - Average freeboard: 22.56 ft / 6.88 m

Ship space, strength and comments:
 Space - Hull below water (magazines/engines, low = better): 104.9 %
  - Above water (accommodation/working, high = better): 179.0 %
 Waterplane Area: 25,813 Square feet or 2,398 Square metres
 Displacement factor (Displacement / loading): 109 %
 Structure weight / hull surface area: 106 lbs/sq ft or 519 Kg/sq metre
 Hull strength (Relative):
  - Cross-sectional: 0.94
  - Longitudinal: 1.68
  - Overall: 1.00
 Hull space for machinery, storage, compartmentation is adequate
 Room for accommodation and workspaces is excellent