The "BBX" design revisited yet again: GB/BB/1915

I was looking at the specification for the GB/BB/1915, which my friend Cliff called the "BBX". I noticed that the intended SHP/ton was 30, so I took that and started working in Springsharp. I kept lowering the date, as the SHP/ton was "too good" for later dates. I finally ended up with 1921, which actually produced too low a number, but not too bad, either. The final figure was 29.04 SHP/ton. The specifications that I started with were:

• Displacement: 70,000 tons
• Length: 800 ft
• Beam: 135 ft
• Draft: 36.5 ft
• Belt: 18 inches
• Deck: 7 inches
• Speed: 20 knots, but expecting to reach 24 knots
• SHP: 90,000
• Armament: 9-20in/45, 24-5in/45 QF

The final Springsharp report is pretty glowing:

GB/BB/1915 (BBX), Great Britain Enter ship type laid down 1915 (Engine 1921)

Displacement:
 64,918 t light; 68,245 t standard; 71,879 t normal; 74,785 t full load

Dimensions: Length overall / water x beam x draught
 803.01 ft / 800.00 ft x 135.00 ft x 38.00 ft (normal load)
 244.76 m / 243.84 m x 41.15 m  x 11.58 m

Armament:
      9 - 20.00" / 508 mm guns (3x3 guns), 4,000.00lbs / 1,814.37kg shells, 1915 Model
   Breech loading guns in turrets (on barbettes)
   on centreline ends, majority forward, all raised mounts - superfiring
      24 - 5.00" / 127 mm guns (12x2 guns), 62.50lbs / 28.35kg shells, 1915 Model
   Quick firing guns in deck mounts 
   on side, all amidships, all raised mounts - superfiring
 Weight of broadside 37,500 lbs / 17,010 kg
 Shells per gun, main battery: 90

Armour:
   - Belts:  Width (max) Length (avg)  Height (avg)
 Main: 18.0" / 457 mm 535.00 ft / 163.07 m 17.00 ft / 5.18 m
 Ends: Unarmoured
   Main Belt covers 103 % of normal length

   - Torpedo Bulkhead:
  3.00" / 76 mm 535.00 ft / 163.07 m 34.00 ft / 10.36 m

   - Gun armour: Face (max) Other gunhouse (avg) Barbette/hoist (max)
 Main: 18.0" / 457 mm 9.00" / 229 mm  18.0" / 457 mm
 2nd: 2.00" / 51 mm       -         -

   - Armour deck: 7.00" / 178 mm, Conning tower: 11.00" / 279 mm

Machinery:
 Oil fired boilers, steam turbines, 
 Geared drive, 4 shafts, 92,297 shp / 68,853 Kw = 24.00 kts
 Range 7,500nm at 15.00 kts
 Bunker at max displacement = 6,540 tons

Complement:
 2,194 - 2,853

Cost:
 £9.679 million / $38.718 million

Distribution of weights at normal displacement:
 Armament: 4,688 tons, 6.5 %
 Armour: 26,673 tons, 37.1 %
    - Belts: 7,185 tons, 10.0 %
    - Torpedo bulkhead: 2,019 tons, 2.8 %
    - Armament: 6,706 tons, 9.3 %
    - Armour Deck: 10,354 tons, 14.4 %
    - Conning Tower: 410 tons, 0.6 %
 Machinery: 3,178 tons, 4.4 %
 Hull, fittings & equipment: 30,379 tons, 42.3 %
 Fuel, ammunition & stores: 6,961 tons, 9.7 %
 Miscellaneous weights: 0 tons, 0.0 %

Overall survivability and seakeeping ability:
 Survivability (Non-critical penetrating hits needed to sink ship):
   102,978 lbs / 46,710 Kg = 25.7 x 20.0 " / 508 mm shells or 19.2 torpedoes
 Stability (Unstable if below 1.00): 1.03
 Metacentric height 8.3 ft / 2.5 m
 Roll period: 19.7 seconds
 Steadiness - As gun platform (Average = 50 %): 73 %
   - Recoil effect (Restricted arc if above 1.00): 0.85
 Seaboat quality  (Average = 1.00): 1.45

Hull form characteristics:
 Hull has a flush deck
 Block coefficient: 0.613
 Length to Beam Ratio: 5.93 : 1
 'Natural speed' for length: 28.28 kts
 Power going to wave formation at top speed: 44 %
 Trim (Max stability = 0, Max steadiness = 100): 50
 Bow angle (Positive = bow angles forward): 2.00 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 %): 25.00 ft / 7.62 m
    - Mid (50 %):  25.00 ft / 7.62 m
    - Quarterdeck (15 %): 25.00 ft / 7.62 m
    - Stern:  25.00 ft / 7.62 m
    - Average freeboard: 25.32 ft / 7.72 m
 Ship tends to be wet forward

Ship space, strength and comments:
 Space - Hull below water (magazines/engines, low = better): 74.5 %
  - Above water (accommodation/working, high = better): 173.5 %
 Waterplane Area: 79,953 Square feet or 7,428 Square metres
 Displacement factor (Displacement / loading): 102 %
 Structure weight / hull surface area: 285 lbs/sq ft or 1,394 Kg/sq metre
 Hull strength (Relative):
  - Cross-sectional: 0.95
  - Longitudinal: 1.64
  - Overall: 1.00
 Hull space for machinery, storage, compartmentation is excellent
 Room for accommodation and workspaces is excellent
 Ship has slow, easy roll, a good, steady gun platform
 Good seaboat, rides out heavy weather easily