A 1916 British 8-in gun cruiser

I tried a 1916 British 8-in gun cruiser, but the armour situation seems very strange. Even with a complete belt, I was not able to satisfy Springsharp, so I shorted the belt to a more modest length. The armament is 8-8in BLR, 8-4.7in QF, 2-4in AA, and 12-2pdr AA guns. There are no torpedo tubes, even though there could have been. The belt is still 4in and the deck is 2in. The maximum speed is 31 knots with a 15 knot cruising speed for a range of 4,800nm. I suspect that there is some design flaw, but I do not see what it is. This is the Sprinsharp report:

GB/CA/1916, Great Britain Heavy Cruiser laid down 1916

Displacement:
 12,989 t light; 13,529 t standard; 14,550 t normal; 15,367 t full load

Dimensions: Length overall / water x beam x draught
 615.89 ft / 614.00 ft x 62.00 ft x 22.00 ft (normal load)
 187.72 m / 187.15 m x 18.90 m  x 6.71 m

Armament:
      8 - 9.20" / 234 mm guns (4x2 guns), 389.34lbs / 176.60kg shells, 1916 Model
   Breech loading guns in turrets (on barbettes)
   on centreline ends, evenly spread, 2 raised mounts - superfiring
      8 - 4.70" / 119 mm guns in single mounts, 51.91lbs / 23.55kg shells, 1916 Model
   Quick firing guns in deck mounts with hoists
   on side, all amidships
      2 - 4.00" / 102 mm guns in single mounts, 32.00lbs / 14.51kg shells, 1916 Model
   Anti-aircraft guns in deck mounts with hoists
   on side, evenly spread
      12 - 1.57" / 40.0 mm guns (3x4 guns), 2.00lbs / 0.91kg shells, 1916 Model
   Anti-aircraft guns in deck mounts 
   on side ends, majority aft
 Weight of broadside 3,618 lbs / 1,641 kg
 Shells per gun, main battery: 120

Armour:
   - Belts:  Width (max) Length (avg)  Height (avg)
 Main: 4.00" / 102 mm 545.00 ft / 166.12 m 16.00 ft / 4.88 m
 Ends: Unarmoured
   Main Belt covers 137 % of normal length
   Main belt does not fully cover magazines and engineering spaces

   - Torpedo Bulkhead:
  1.00" / 25 mm 545.00 ft / 166.12 m 21.00 ft / 6.40 m

   - Gun armour: Face (max) Other gunhouse (avg) Barbette/hoist (max)
 Main: 4.00" / 102 mm 3.00" / 76 mm  4.00" / 102 mm
 2nd: 2.00" / 51 mm       -   2.00" / 51 mm
 4th: 1.00" / 25 mm       -         -

   - Armour deck: 2.00" / 51 mm, Conning tower: 4.00" / 102 mm

Machinery:
 Oil fired boilers, steam turbines, 
 Geared drive, 4 shafts, 96,834 shp / 72,238 Kw = 31.00 kts
 Range 4,800nm at 15.00 kts
 Bunker at max displacement = 1,838 tons

Complement:
 662 - 861

Cost:
 £2.192 million / $8.768 million

Distribution of weights at normal displacement:
 Armament: 452 tons, 3.1 %
 Armour: 3,472 tons, 23.9 %
    - Belts: 1,393 tons, 9.6 %
    - Torpedo bulkhead: 423 tons, 2.9 %
    - Armament: 566 tons, 3.9 %
    - Armour Deck: 1,038 tons, 7.1 %
    - Conning Tower: 51 tons, 0.4 %
 Machinery: 3,608 tons, 24.8 %
 Hull, fittings & equipment: 5,457 tons, 37.5 %
 Fuel, ammunition & stores: 1,561 tons, 10.7 %
 Miscellaneous weights: 0 tons, 0.0 %

Overall survivability and seakeeping ability:
 Survivability (Non-critical penetrating hits needed to sink ship):
   15,698 lbs / 7,121 Kg = 40.3 x 9.2 " / 234 mm shells or 2.0 torpedoes
 Stability (Unstable if below 1.00): 1.14
 Metacentric height 3.1 ft / 0.9 m
 Roll period: 14.8 seconds
 Steadiness - As gun platform (Average = 50 %): 53 %
   - Recoil effect (Restricted arc if above 1.00): 0.87
 Seaboat quality  (Average = 1.00): 1.06

Hull form characteristics:
 Hull has rise forward of midbreak
 Block coefficient: 0.608
 Length to Beam Ratio: 9.90 : 1
 'Natural speed' for length: 24.78 kts
 Power going to wave formation at top speed: 57 %
 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:  27.00 ft / 8.23 m
    - Forecastle (20 %): 24.00 ft / 7.32 m
    - Mid (67 %):  24.00 ft / 7.32 m (16.00 ft / 4.88 m aft of break)
    - Quarterdeck (15 %): 16.00 ft / 4.88 m
    - Stern:  16.00 ft / 4.88 m
    - Average freeboard: 21.60 ft / 6.58 m
 Ship tends to be wet forward

Ship space, strength and comments:
 Space - Hull below water (magazines/engines, low = better): 153.9 %
  - Above water (accommodation/working, high = better): 175.8 %
 Waterplane Area: 28,053 Square feet or 2,606 Square metres
 Displacement factor (Displacement / loading): 102 %
 Structure weight / hull surface area: 120 lbs/sq ft or 586 Kg/sq metre
 Hull strength (Relative):
  - Cross-sectional: 0.97
  - Longitudinal: 1.32
  - Overall: 1.00
 Hull space for machinery, storage, compartmentation is cramped
 Room for accommodation and workspaces is excellent