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Wednesday, August 01, 2007

Springsharp doesn't handle an Elswick cruiser very well

I thought that designing an Elswick cruiser would be an interesting exercise. Little did I know that Springsharp doesn't handle such a ship very well. My ship has 2-8in and 10-6in guns and a speed of 23 knots. I had to increase the size of the ship too much and increase the draft, as well. The protection is primarily a 4in protective deck. The ship uses coal-fired boilers, of course, and has reciprocating engines. Presumably, if I had lightened the machinery enough, the design would have worked better. This is the Springsharp report:
Elswick cruiser, Great Britain Protected Cruiser laid down 1892 (Engine 1904)

Displacement:
 8,154 t light; 8,465 t standard; 9,183 t normal; 9,757 t full load

Dimensions: Length (overall / waterline) x beam x draught (normal/deep)
 (432.00 ft / 425.00 ft) x 48.00 ft x (23.00 / 24.25 ft)
 (131.67 m / 129.54 m) x 14.63 m  x (7.01 / 7.39 m)

Armament:
      2 - 8.00" / 203 mm 45.0 cal guns - 250.00lbs / 113.40kg shells, 150 per gun
   Breech loading guns in deck and hoist mounts, 1892 Model
   2 x Single mounts on centreline ends, evenly spread
      10 - 6.00" / 152 mm 45.0 cal guns - 100.00lbs / 45.36kg shells, 150 per gun
   Quick firing guns in deck and hoist mounts, 1892 Model
   10 x Single mounts on sides, evenly spread
      Weight of broadside 1,500 lbs / 680 kg
      5 - 18.0" / 457 mm, 18.00 ft / 5.49 m torpedoes - 0.497 t each, 2.484 t total
 In 5 sets of deck mounted carriage/fixed tubes

Armour:
   - Gun armour: Face (max) Other gunhouse (avg) Barbette/hoist (max)
 Main: 6.00" / 152 mm 3.00" / 76 mm  6.00" / 152 mm
 2nd: 4.00" / 102 mm 3.00" / 76 mm  4.00" / 102 mm

   - Protected deck - single deck: 4.00" / 102 mm For and Aft decks
 Forecastle: 4.00" / 102 mm  Quarter deck: 4.00" / 102 mm

   - Conning towers: Forward 6.00" / 152 mm,  Aft 0.00" / 0 mm

Machinery:
 Coal fired boilers, complex reciprocating steam engines, 
 Direct drive, 2 shafts, 26,401 ihp / 19,695 Kw = 23.00 kts
 Range 3,800nm at 12.00 kts
 Bunker at max displacement = 1,292 tons (100% coal)

Complement:
 468 - 609

Cost:
 £0.980 million / $3.921 million

Distribution of weights at normal displacement:
 Armament: 426 tons, 4.6 %
    - Guns: 424 tons, 4.6 %
    - Torpedoes: 2 tons, 0.0 %
 Armour: 1,574 tons, 17.1 %
    - Armament: 314 tons, 3.4 %
    - Armour Deck: 1,203 tons, 13.1 %
    - Conning Tower: 57 tons, 0.6 %
 Machinery: 3,882 tons, 42.3 %
 Hull, fittings & equipment: 2,271 tons, 24.7 %
 Fuel, ammunition & stores: 1,029 tons, 11.2 %
 Miscellaneous weights: 0 tons, 0.0 %

Overall survivability and seakeeping ability:
 Survivability (Non-critical penetrating hits needed to sink ship):
   3,961 lbs / 1,797 Kg = 15.5 x 8.0 " / 203 mm shells or 0.7 torpedoes
 Stability (Unstable if below 1.00): 1.22
 Metacentric height 2.4 ft / 0.7 m
 Roll period: 13.0 seconds
 Steadiness - As gun platform (Average = 50 %): 61 %
   - Recoil effect (Restricted arc if above 1.00): 0.58
 Seaboat quality  (Average = 1.00): 1.22

Hull form characteristics:
 Hull has rise forward of midbreak,
   a ram bow and a cruiser stern
 Block coefficient (normal/deep): 0.685 / 0.690
 Length to Beam Ratio: 8.85 : 1
 'Natural speed' for length: 20.62 kts
 Power going to wave formation at top speed: 55 %
 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 (% = length of deck as a percentage of waterline length):
    Fore end,  Aft end
    - Forecastle: 25.00 %,  20.00 ft / 6.10 m,  17.00 ft / 5.18 m
    - Forward deck: 30.00 %,  17.00 ft / 5.18 m,  17.00 ft / 5.18 m
    - Aft deck: 30.00 %,  15.00 ft / 4.57 m,  15.00 ft / 4.57 m
    - Quarter deck: 15.00 %,  15.00 ft / 4.57 m,  16.00 ft / 4.88 m
    - Average freeboard:  16.48 ft / 5.02 m
 Ship tends to be wet forward

Ship space, strength and comments:
 Space - Hull below water (magazines/engines, low = better): 151.9 %
  - Above water (accommodation/working, high = better): 104.2 %
 Waterplane Area: 16,133 Square feet or 1,499 Square metres
 Displacement factor (Displacement / loading): 85 %
 Structure weight / hull surface area: 92 lbs/sq ft or 450 Kg/sq metre
 Hull strength (Relative):
  - Cross-sectional: 0.95
  - Longitudinal: 1.63
  - Overall: 1.00
 Hull space for machinery, storage, compartmentation is cramped
 Room for accommodation and workspaces is adequate
 Good seaboat, rides out heavy weather easily

4 comments:

Chris K said...

That's interesting. I got quite a good result for 'Esmerelda' - the composite strength is quite low at 0.59 but I don't think that's unreasonable for a protected cruiser.

I encountered a bit of a problem with Tone, the last big Japanese protected cruiser, and had to shave half an inch off her armoured deck to make her work - but that could be justified as representing a relatively fast taper on the armoured deck...

Jim said...

Chris, I guess that I want a composite strength of 1.0, or I consider that the design does not work well. My standard is that a ship larger than a destroyer or torpedo boat is too weak with a composite strength less than 1.0. I am open to the possibility that Springsharp complains about strength, when the strength is actually adequate, then I would agree with what you say. All of this is very arbitrary, I suspect. I would be interested to know more about the various stress factors for real ships to have a better idea of what is really acceptable and what is not.

Jim said...

I think that the Esmeralda and ships of her type were lightly built and did in fact a lower standard for hull strength so as to achieve a higher speed for displacement. I was just rereading William Hovgaard's assessment in his book, Modern History of Warships. My copy of D. K. Brown's book Warrior to Dreadnought got packed away (not by me) in the last few weeks, so I can't consult it (sadly).

Jim said...

I seem to not be able to write complete sentences this morning. Sorry about that!

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