The GB/PG/1915 design

The GB/PG/1915 design does not work as I had hoped, due to the poor performance of the Springsharp empirical equation for small, fast ships. Frankly, for a 900 ton vessel, it should not take 37,962 tons to reach even 34 knots. The 36 knot speed specified should be easily achievable. All we need to do is to look at the S-class to see that 36 knots is very feasible. I had sort of thought that the 3 guns were 5in, but I suspect that the plan was just for 3-4in QF guns for this design. In any case, this is the Springsharp report:

GB/PG/1915, Great Britain  Gunboat laid down 1915 (Engine 1950)

Displacement:
 909 t light; 938 t standard; 1,030 t normal; 1,104 t full load

Dimensions: Length overall / water x beam x draught
 276.21 ft / 275.00 ft x 28.00 ft x 11.00 ft (normal load)
 84.19 m / 83.82 m x 8.53 m  x 3.35 m

Armament:
      3 - 4.00" / 102 mm guns in single mounts, 32.00lbs / 14.51kg shells, 1915 Model
   Breech loading guns in deck mounts with hoists
   on centreline ends, majority forward, 1 raised mount
 Weight of broadside 96 lbs / 44 kg
 Shells per gun, main battery: 150

Machinery:
 Oil fired boilers, steam turbines, 
 Geared drive, 2 shafts, 37,962 shp / 28,320 Kw = 34.00 kts
 Range 3,200nm at 15.00 kts
 Bunker at max displacement = 166 tons

Complement:
 90 - 118

Cost:
 £0.174 million / $0.696 million

Distribution of weights at normal displacement:
 Armament: 12 tons, 1.2 %
 Machinery: 556 tons, 53.9 %
 Hull, fittings & equipment: 341 tons, 33.1 %
 Fuel, ammunition & stores: 121 tons, 11.7 %
 Miscellaneous weights: 0 tons, 0.0 %

Overall survivability and seakeeping ability:
 Survivability (Non-critical penetrating hits needed to sink ship):
   271 lbs / 123 Kg = 8.5 x 4.0 " / 102 mm shells or 0.2 torpedoes
 Stability (Unstable if below 1.00): 1.28
 Metacentric height 1.2 ft / 0.4 m
 Roll period: 10.9 seconds
 Steadiness - As gun platform (Average = 50 %): 51 %
   - Recoil effect (Restricted arc if above 1.00): 0.35
 Seaboat quality  (Average = 1.00): 1.03

Hull form characteristics:
 Hull has rise forward of midbreak
 Block coefficient: 0.426
 Length to Beam Ratio: 9.82 : 1
 'Natural speed' for length: 16.58 kts
 Power going to wave formation at top speed: 74 %
 Trim (Max stability = 0, Max steadiness = 100): 50
 Bow angle (Positive = bow angles forward): 3.00 degrees
 Stern overhang: 0.00 ft / 0.00 m
 Freeboard (% = measuring location as a percentage of overall length):
    - Stem:  23.00 ft / 7.01 m
    - Forecastle (20 %): 21.00 ft / 6.40 m
    - Mid (34 %):  21.00 ft / 6.40 m (13.00 ft / 3.96 m aft of break)
    - Quarterdeck (15 %): 13.00 ft / 3.96 m
    - Stern:  13.00 ft / 3.96 m
    - Average freeboard: 15.88 ft / 4.84 m

Ship space, strength and comments:
 Space - Hull below water (magazines/engines, low = better): 183.1 %
  - Above water (accommodation/working, high = better): 150.2 %
 Waterplane Area: 4,820 Square feet or 448 Square metres
 Displacement factor (Displacement / loading): 54 %
 Structure weight / hull surface area: 27 lbs/sq ft or 133 Kg/sq metre
 Hull strength (Relative):
  - Cross-sectional: 0.41
  - Longitudinal: 5.12
  - Overall: 0.52
 Hull space for machinery, storage, compartmentation is cramped
 Room for accommodation and workspaces is excellent