The J/CL/1914 design

From the beginning the Japanese light cruiser design depends on lightweight machinery. The J/CL/1914 design is pretty conservative with just a 30-knot speed and 6-5.5in QF guns. The armour basis is 3in with a 1in deck. The displacement is driven in part by the 30-knot speed and the desire to have a substantial freeboard for good seakeeping. This is the Springsharp report:

J/CL/1914, Japan Light Cruiser laid down 1914 (Engine 1921)

Displacement:
 4,727 t light; 4,891 t standard; 5,340 t normal; 5,699 t full load

Dimensions: Length overall / water x beam x draught
 458.31 ft / 455.00 ft x 42.00 ft x 16.00 ft (normal load)
 139.69 m / 138.68 m x 12.80 m  x 4.88 m

Armament:
      6 - 5.50" / 140 mm guns in single mounts, 83.19lbs / 37.73kg shells, 1914 Model
   Quick firing guns in deck mounts with hoists
   on centreline ends, evenly spread
      2 - 3.00" / 76.2 mm guns in single mounts, 13.50lbs / 6.12kg shells, 1914 Model
   Anti-aircraft guns in deck mounts with hoists
   on side, all amidships
      4 - 2.24" / 57.0 mm guns in single mounts, 5.65lbs / 2.56kg shells, 1914 Model
   Anti-aircraft guns in deck mounts 
   on side, all amidships
 Weight of broadside 549 lbs / 249 kg
 Shells per gun, main battery: 180
 4 - 21.0" / 533.4 mm above water torpedoes

Armour:
   - Belts:  Width (max) Length (avg)  Height (avg)
 Main: 3.00" / 76 mm 385.00 ft / 117.35 m 12.00 ft / 3.66 m
 Ends: Unarmoured
   Main Belt covers 130 % of normal length

   - 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, 
 Direct drive, 2 shafts, 51,336 shp / 38,297 Kw = 30.00 kts
 Range 4,500nm at 15.00 kts
 Bunker at max displacement = 809 tons

Complement:
 312 - 406

Cost:
 £0.599 million / $2.396 million

Distribution of weights at normal displacement:
 Armament: 69 tons, 1.3 %
 Armour: 901 tons, 16.9 %
    - Belts: 555 tons, 10.4 %
    - Torpedo bulkhead: 0 tons, 0.0 %
    - Armament: 65 tons, 1.2 %
    - Armour Deck: 261 tons, 4.9 %
    - Conning Tower: 20 tons, 0.4 %
 Machinery: 1,768 tons, 33.1 %
 Hull, fittings & equipment: 1,990 tons, 37.3 %
 Fuel, ammunition & stores: 613 tons, 11.5 %
 Miscellaneous weights: 0 tons, 0.0 %

Overall survivability and seakeeping ability:
 Survivability (Non-critical penetrating hits needed to sink ship):
   5,212 lbs / 2,364 Kg = 62.7 x 5.5 " / 140 mm shells or 0.9 torpedoes
 Stability (Unstable if below 1.00): 1.17
 Metacentric height 1.8 ft / 0.6 m
 Roll period: 13.0 seconds
 Steadiness - As gun platform (Average = 50 %): 72 %
   - Recoil effect (Restricted arc if above 1.00): 0.52
 Seaboat quality  (Average = 1.00): 1.43

Hull form characteristics:
 Hull has rise forward of midbreak
 Block coefficient: 0.611
 Length to Beam Ratio: 10.83 : 1
 'Natural speed' for length: 21.33 kts
 Power going to wave formation at top speed: 61 %
 Trim (Max stability = 0, Max steadiness = 100): 50
 Bow angle (Positive = bow angles forward): 3.00 degrees
 Stern overhang: 2.00 ft / 0.61 m
 Freeboard (% = measuring location as a percentage of overall length):
    - Stem:  25.00 ft / 7.62 m
    - Forecastle (20 %): 22.00 ft / 6.71 m
    - Mid (67 %):  22.00 ft / 6.71 m (14.00 ft / 4.27 m aft of break)
    - Quarterdeck (15 %): 14.00 ft / 4.27 m
    - Stern:  14.00 ft / 4.27 m
    - Average freeboard: 19.60 ft / 5.97 m

Ship space, strength and comments:
 Space - Hull below water (magazines/engines, low = better): 117.7 %
  - Above water (accommodation/working, high = better): 146.0 %
 Waterplane Area: 14,124 Square feet or 1,312 Square metres
 Displacement factor (Displacement / loading): 107 %
 Structure weight / hull surface area: 71 lbs/sq ft or 345 Kg/sq metre
 Hull strength (Relative):
  - Cross-sectional: 0.90
  - Longitudinal: 2.73
  - Overall: 1.00
 Hull space for machinery, storage, compartmentation is cramped
 Room for accommodation and workspaces is excellent
 Ship has slow, easy roll, a good, steady gun platform
 Good seaboat, rides out heavy weather easily