Pre-Dreadnought to Coastal BB in 1920's

[Jefgte]

When the pre-dreadnought use for coastal protection "ll be too old, they could be replace by new coastal BBs.
This new kind of ships could be laid down in the 20's.

First type with 2T3x275

11500T coastal BB, Peru 2T3x275 laid down 1923 (Engine 1920)

Displacement:
   11 500 t light; 12 129 t standard; 12 715 t normal; 13 183 t full load

Dimensions: Length overall / water x beam x draught
   524.93 ft / 524.93 ft x 72.18 ft x 20.43 ft (normal load)
   160.00 m / 160.00 m x 22.00 m  x 6.23 m

Armament:
      6 - 10.83" / 275 mm guns (2x3 guns), 661.39lbs / 300.00kg shells, 1923 Model
     Breech loading guns in turrets (on barbettes)
     on centreline ends, evenly spread
      12 - 6.00" / 152 mm guns in single mounts, 108.00lbs / 48.99kg shells, 1923 Model
     Breech loading guns in deck mounts with hoists
     on side, evenly spread
      8 - 3.00" / 76.2 mm guns in single mounts, 13.50lbs / 6.12kg shells, 1923 Model
     Quick firing guns in deck mounts
     on centreline, all amidships, all raised mounts - superfiring
      4 - 0.50" / 12.7 mm guns in single mounts, 0.06lbs / 0.03kg shells, 1923 Model
     Machine guns in deck mounts
     on side, evenly spread, all raised mounts
   Weight of broadside 5 373 lbs / 2 437 kg
   Shells per gun, main battery: 120
   6 - 21.0" / 533.4 mm above water torpedoes

Armour:
   - Belts:      Width (max)   Length (avg)      Height (avg)
   Main:   9.45" / 240 mm   354.33 ft / 108.00 m   9.84 ft / 3.00 m
   Ends:   3.15" / 80 mm   144.36 ft / 44.00 m   8.01 ft / 2.44 m
     26.25 ft / 8.00 m Unarmoured ends
     Main Belt covers 104 % of normal length

   - Torpedo Bulkhead:
      1.57" / 40 mm   354.33 ft / 108.00 m   20.28 ft / 6.18 m

   - Gun armour:   Face (max)   Other gunhouse (avg)   Barbette/hoist (max)
   Main:   9.45" / 240 mm   3.94" / 100 mm      9.45" / 240 mm
   2nd:   0.79" / 20 mm         -               -
   3rd:   0.79" / 20 mm         -               -
   4th:   0.50" / 13 mm         -               -

   - Armour deck: 2.76" / 70 mm, Conning tower: 9.45" / 240 mm

Machinery:
   Oil fired boilers, steam turbines,
   Geared drive, 2 shafts, 36 000 shp / 26 856 Kw = 24.14 kts
   Range 5 500nm at 12.00 kts
   Bunker at max displacement = 1 054 tons

Complement:
   598 - 778

Cost:
   £3.275 million / $13.102 million

Distribution of weights at normal displacement:
   Armament: 651 tons, 5.1 %
   Armour: 4 180 tons, 32.9 %
      - Belts: 1 544 tons, 12.1 %
      - Torpedo bulkhead: 419 tons, 3.3 %
      - Armament: 727 tons, 5.7 %
      - Armour Deck: 1 380 tons, 10.9 %
      - Conning Tower: 111 tons, 0.9 %
   Machinery: 1 259 tons, 9.9 %
   Hull, fittings & equipment: 5 059 tons, 39.8 %
   Fuel, ammunition & stores: 1 215 tons, 9.6 %
   Miscellaneous weights: 350 tons, 2.8 %

Overall survivability and seakeeping ability:
   Survivability (Non-critical penetrating hits needed to sink ship):
     17 963 lbs / 8 148 Kg = 28.3 x 10.8 " / 275 mm shells or 3.3 torpedoes
   Stability (Unstable if below 1.00): 1.11
   Metacentric height 3.7 ft / 1.1 m
   Roll period: 15.7 seconds
   Steadiness   - As gun platform (Average = 50 %): 70 %
         - Recoil effect (Restricted arc if above 1.00): 0.66
   Seaboat quality  (Average = 1.00): 1.21

Hull form characteristics:
   Hull has a flush deck
   Block coefficient: 0.575
   Length to Beam Ratio: 7.27 : 1
   'Natural speed' for length: 22.91 kts
   Power going to wave formation at top speed: 51 %
   Trim (Max stability = 0, Max steadiness = 100): 58
   Bow angle (Positive = bow angles forward): 0.00 degrees
   Stern overhang: 0.00 ft / 0.00 m
   Freeboard (% = measuring location as a percentage of overall length):
      - Stem:      23.62 ft / 7.20 m
      - Forecastle (18 %):   19.36 ft / 5.90 m
      - Mid (50 %):      15.75 ft / 4.80 m
      - Quarterdeck (18 %):   15.75 ft / 4.80 m
      - Stern:      15.75 ft / 4.80 m
      - Average freeboard:   17.28 ft / 5.27 m
   Ship tends to be wet forward

Ship space, strength and comments:
   Space   - Hull below water (magazines/engines, low = better): 103.3 %
      - Above water (accommodation/working, high = better): 127.9 %
   Waterplane Area: 27 070 Square feet or 2 515 Square metres
   Displacement factor (Displacement / loading): 104 %
   Structure weight / hull surface area: 133 lbs/sq ft or 649 Kg/sq metre
   Hull strength (Relative):
      - Cross-sectional: 0.96
      - Longitudinal: 1.39
      - Overall: 1.00
   Hull space for machinery, storage, compartmentation is adequate
   Room for accommodation and workspaces is excellent
   Ship has slow, easy roll, a good, steady gun platform
   Good seaboat, rides out heavy weather easily

----------------------------------
Second type with 2T3x340

14000T coastal BB, Peru 2T3x340 laid down 1923 (Engine 1920)

Displacement:
   14 000 t light; 14 759 t standard; 15 424 t normal; 15 956 t full load

Dimensions: Length overall / water x beam x draught
   551.18 ft / 551.18 ft x 75.46 ft x 21.63 ft (normal load)
   168.00 m / 168.00 m x 23.00 m  x 6.59 m

Armament:
      6 - 13.39" / 340 mm guns (2x3 guns), 1 199.24lbs / 543.97kg shells, 1923 Model
     Breech loading guns in turrets (on barbettes)
     on centreline ends, evenly spread
      12 - 4.72" / 120 mm guns in single mounts, 52.72lbs / 23.91kg shells, 1923 Model
     Breech loading guns in deck mounts with hoists
     on side, evenly spread
      8 - 3.00" / 76.2 mm guns in single mounts, 13.50lbs / 6.12kg shells, 1923 Model
     Quick firing guns in deck mounts
     on centreline, all amidships, all raised mounts - superfiring
      4 - 0.50" / 12.7 mm guns in single mounts, 0.06lbs / 0.03kg shells, 1923 Model
     Machine guns in deck mounts
     on side, evenly spread, all raised mounts
   Weight of broadside 7 936 lbs / 3 600 kg
   Shells per gun, main battery: 100

Armour:
   - Belts:      Width (max)   Length (avg)      Height (avg)
   Main:   9.45" / 240 mm   393.70 ft / 120.00 m   9.84 ft / 3.00 m
   Ends:   3.15" / 80 mm   144.36 ft / 44.00 m   8.01 ft / 2.44 m
     13.12 ft / 4.00 m Unarmoured ends
     Main Belt covers 110 % of normal length

   - Torpedo Bulkhead:
      1.57" / 40 mm   393.70 ft / 120.00 m   21.42 ft / 6.53 m

   - Gun armour:   Face (max)   Other gunhouse (avg)   Barbette/hoist (max)
   Main:   9.45" / 240 mm   3.94" / 100 mm      9.45" / 240 mm
   2nd:   0.79" / 20 mm         -               -
   3rd:   0.79" / 20 mm         -               -
   4th:   0.50" / 13 mm         -               -

   - Armour deck: 2.76" / 70 mm, Conning tower: 9.45" / 240 mm

Machinery:
   Oil fired boilers, steam turbines,
   Geared drive, 2 shafts, 40 000 shp / 29 840 Kw = 24.10 kts
   Range 5 500nm at 12.00 kts
   Bunker at max displacement = 1 197 tons

Complement:
   691 - 899

Cost:
   £4.419 million / $17.677 million

Distribution of weights at normal displacement:
   Armament: 992 tons, 6.4 %
   Armour: 4 787 tons, 31.0 %
      - Belts: 1 684 tons, 10.9 %
      - Torpedo bulkhead: 491 tons, 3.2 %
      - Armament: 934 tons, 6.1 %
      - Armour Deck: 1 551 tons, 10.1 %
      - Conning Tower: 126 tons, 0.8 %
   Machinery: 1 399 tons, 9.1 %
   Hull, fittings & equipment: 6 522 tons, 42.3 %
   Fuel, ammunition & stores: 1 424 tons, 9.2 %
   Miscellaneous weights: 300 tons, 1.9 %

Overall survivability and seakeeping ability:
   Survivability (Non-critical penetrating hits needed to sink ship):
     19 613 lbs / 8 896 Kg = 16.4 x 13.4 " / 340 mm shells or 3.4 torpedoes
   Stability (Unstable if below 1.00): 1.07
   Metacentric height 3.7 ft / 1.1 m
   Roll period: 16.4 seconds
   Steadiness   - As gun platform (Average = 50 %): 72 %
         - Recoil effect (Restricted arc if above 1.00): 0.88
   Seaboat quality  (Average = 1.00): 1.20

Hull form characteristics:
   Hull has a flush deck
   Block coefficient: 0.600
   Length to Beam Ratio: 7.30 : 1
   'Natural speed' for length: 23.48 kts
   Power going to wave formation at top speed: 50 %
   Trim (Max stability = 0, Max steadiness = 100): 60
   Bow angle (Positive = bow angles forward): 0.00 degrees
   Stern overhang: 0.00 ft / 0.00 m
   Freeboard (% = measuring location as a percentage of overall length):
      - Stem:      24.61 ft / 7.50 m
      - Forecastle (18 %):   19.69 ft / 6.00 m
      - Mid (50 %):      16.40 ft / 5.00 m
      - Quarterdeck (18 %):   16.40 ft / 5.00 m
      - Stern:      16.40 ft / 5.00 m
      - Average freeboard:   17.87 ft / 5.45 m
   Ship tends to be wet forward

Ship space, strength and comments:
   Space   - Hull below water (magazines/engines, low = better): 108.9 %
      - Above water (accommodation/working, high = better): 144.4 %
   Waterplane Area: 30 420 Square feet or 2 826 Square metres
   Displacement factor (Displacement / loading): 97 %
   Structure weight / hull surface area: 153 lbs/sq ft or 748 Kg/sq metre
   Hull strength (Relative):
      - Cross-sectional: 0.96
      - Longitudinal: 1.42
      - Overall: 1.00
   Hull space for machinery, storage, compartmentation is adequate
   Room for accommodation and workspaces is excellent
   Ship has slow, easy roll, a good, steady gun platform
   Good seaboat, rides out heavy weather easily

[Korpen]

I cannot say i like them, think you try and do too much and end up with a compromise that cannot really do anything.
What the two designs really are, is slow battlecruisers; their armour is excellent against older cruisers with <25cm guns, but not so impressive against even older BC with 30cm guns, and insufficient against BBs and later BCs (35cm+ guns).
Similar wit the speed, it is not fast enough to catch anything smaller, and not fast enough to run from larger things (something a CBB should never do IMO).

You could reduce speed to 18kts without and real impact on the CBB function. Similar with the armour, reducing the belt to 18-20cm will still give the ship reasonable protection against cruiser fire, while the threat from first rate guns is unaffected (drop the TB while you are at it as well to save weight). This would allow you to shrink the 34cm version to around 10kton and perhaps add a third gun tower (around 8000ton with just six guns).

The 27,5cm armed version is pointless IMO as the main function of a defence ship is to hurt the enemy, that version lacks that ability.

[Korpen]

Think something like this is better value for money.

Enter ship name, Enter country Enter ship type laid down 1920

Displacement:
   8 400 t light; 9 259 t standard; 9 765 t normal; 10 170 t full load

Dimensions: Length overall / water x beam x draught
   360,89 ft / 360,89 ft x 68,90 ft x 19,69 ft (normal load)
   110,00 m / 110,00 m x 21,00 m  x 6,00 m

Armament:
      6 - 13,39" / 340 mm guns (2x3 guns), 1 199,24lbs / 543,97kg shells, 1920 Model
     Breech loading guns in turrets (on barbettes)
     on centreline, evenly spread
      12 - 4,72" / 120 mm guns in single mounts, 52,72lbs / 23,92kg shells, 1920 Model
     Breech loading guns in deck mounts with hoists
     on side, all amidships
   Weight of broadside 7 828 lbs / 3 551 kg
   Shells per gun, main battery: 150

Armour:
   - Belts:      Width (max)   Length (avg)      Height (avg)
   Main:   7,87" / 200 mm   236,22 ft / 72,00 m   9,84 ft / 3,00 m
   Ends:   Unarmoured
     Main Belt covers 101 % of normal length

   - Gun armour:   Face (max)   Other gunhouse (avg)   Barbette/hoist (max)
   Main:   9,45" / 240 mm   3,15" / 80 mm      7,09" / 180 mm
   2nd:   2,95" / 75 mm   0,98" / 25 mm      1,97" / 50 mm

   - Armour deck: 2,76" / 70 mm, Conning tower: 9,84" / 250 mm

Machinery:
   Oil fired boilers, steam turbines,
   Geared drive, 4 shafts, 11 999 shp / 8 952 Kw = 18,00 kts
   Range 5 500nm at 12,00 kts
   Bunker at max displacement = 911 tons

Complement:
   490 - 638

Cost:
   £2,777 million / $11,106 million

Distribution of weights at normal displacement:
   Armament: 979 tons, 10,0 %
   Armour: 2 621 tons, 26,8 %
      - Belts: 825 tons, 8,4 %
      - Torpedo bulkhead: 0 tons, 0,0 %
      - Armament: 684 tons, 7,0 %
      - Armour Deck: 1 015 tons, 10,4 %
      - Conning Tower: 97 tons, 1,0 %
   Machinery: 420 tons, 4,3 %
   Hull, fittings & equipment: 4 081 tons, 41,8 %
   Fuel, ammunition & stores: 1 365 tons, 14,0 %
   Miscellaneous weights: 300 tons, 3,1 %

Overall survivability and seakeeping ability:
   Survivability (Non-critical penetrating hits needed to sink ship):
     9 628 lbs / 4 367 Kg = 8,0 x 13,4 " / 340 mm shells or 1,6 torpedoes
   Stability (Unstable if below 1.00): 1,12
   Metacentric height 3,6 ft / 1,1 m
   Roll period: 15,3 seconds
   Steadiness   - As gun platform (Average = 50 %): 53 %
         - Recoil effect (Restricted arc if above 1.00): 0,84
   Seaboat quality  (Average = 1.00): 1,12

Hull form characteristics:
   Hull has a flush deck
   Block coefficient: 0,698
   Length to Beam Ratio: 5,24 : 1
   'Natural speed' for length: 19,00 kts
   Power going to wave formation at top speed: 52 %
   Trim (Max stability = 0, Max steadiness = 100): 47
   Bow angle (Positive = bow angles forward): 0,00 degrees
   Stern overhang: 0,00 ft / 0,00 m
   Freeboard (% = measuring location as a percentage of overall length):
      - Stem:      18,04 ft / 5,50 m
      - Forecastle (20 %):   13,12 ft / 4,00 m
      - Mid (50 %):      13,12 ft / 4,00 m
      - Quarterdeck (15 %):   13,12 ft / 4,00 m
      - Stern:      13,12 ft / 4,00 m
      - Average freeboard:   13,52 ft / 4,12 m
   Ship tends to be wet forward

Ship space, strength and comments:
   Space   - Hull below water (magazines/engines, low = better): 94,6 %
      - Above water (accommodation/working, high = better): 101,5 %
   Waterplane Area: 19 899 Square feet or 1 849 Square metres
   Displacement factor (Displacement / loading): 84 %
   Structure weight / hull surface area: 155 lbs/sq ft or 755 Kg/sq metre
   Hull strength (Relative):
      - Cross-sectional: 0,91
      - Longitudinal: 2,27
      - Overall: 1,00
   Hull space for machinery, storage, compartmentation is adequate
   Room for accommodation and workspaces is adequate

[Jefgte]

Thanks for your comments & suggests.

Here is an other study with 2T3x6" for secondary armament:
- The disposition of the turrets is similar to BC Von der Tann.
- With this disposition, I could install 2x4 TTx533 protected by the upper deck.
- I increase the protection to 300mm.
- I decrease the speed to 22.2kts.
- Survivability approach 10 000kg.


14000T coastal BB, Peru 2T3x340+2T3x152 laid down 1923 (Engine 1920)

Displacement:
   14 000 t light; 14 758 t standard; 15 426 t normal; 15 960 t full load

Dimensions: Length overall / water x beam x draught
   535.83 ft / 531.50 ft x 78.74 ft x 20.94 ft (normal load)
   163.32 m / 162.00 m x 24.00 m  x 6.38 m

Armament:
      6 - 13.39" / 340 mm guns (2x3 guns), 1 200.00lbs / 544.31kg shells, 1923 Model
     Breech loading guns in turrets (on barbettes)
     on centreline ends, evenly spread
      6 - 6.00" / 152 mm guns (2x3 guns), 108.00lbs / 48.99kg shells, 1923 Model
     Breech loading guns in turrets (on barbettes)
     on side, evenly spread
      8 - 3.00" / 76.2 mm guns in single mounts, 13.50lbs / 6.12kg shells, 1923 Model
     Quick firing guns in deck mounts
     on side, evenly spread, all raised mounts
      4 - 0.50" / 12.7 mm guns in single mounts, 0.06lbs / 0.03kg shells, 1923 Model
     Machine guns in deck mounts
     on side, evenly spread, all raised mounts
   Weight of broadside 7 956 lbs / 3 609 kg
   Shells per gun, main battery: 100
   8 - 21.0" / 533.4 mm above water torpedoes

Armour:
   - Belts:      Width (max)   Length (avg)      Height (avg)
   Main:   11.8" / 300 mm   341.21 ft / 104.00 m   10.17 ft / 3.10 m
   Ends:   2.36" / 60 mm   144.36 ft / 44.00 m   8.01 ft / 2.44 m
     45.93 ft / 14.00 m Unarmoured ends
     Main Belt covers 99 % of normal length

   - Torpedo Bulkhead:
      1.57" / 40 mm   341.21 ft / 104.00 m   20.80 ft / 6.34 m

   - Gun armour:   Face (max)   Other gunhouse (avg)   Barbette/hoist (max)
   Main:   11.8" / 300 mm   3.94" / 100 mm      11.0" / 280 mm
   2nd:   3.15" / 80 mm   1.57" / 40 mm      2.36" / 60 mm
   3rd:   0.79" / 20 mm         -               -
   4th:   0.50" / 13 mm         -               -

   - Armour deck: 2.95" / 75 mm, Conning tower: 11.81" / 300 mm

Machinery:
   Oil fired boilers, steam turbines,
   Geared drive, 2 shafts, 30 000 shp / 22 380 Kw = 22.21 kts
   Range 5 500nm at 12.00 kts
   Bunker at max displacement = 1 202 tons

Complement:
   691 - 899

Cost:
   £4.282 million / $17.126 million

Distribution of weights at normal displacement:
   Armament: 994 tons, 6.4 %
   Armour: 5 229 tons, 33.9 %
      - Belts: 1 891 tons, 12.3 %
      - Torpedo bulkhead: 414 tons, 2.7 %
      - Armament: 1 070 tons, 6.9 %
      - Armour Deck: 1 697 tons, 11.0 %
      - Conning Tower: 158 tons, 1.0 %
   Machinery: 1 049 tons, 6.8 %
   Hull, fittings & equipment: 6 428 tons, 41.7 %
   Fuel, ammunition & stores: 1 426 tons, 9.2 %
   Miscellaneous weights: 300 tons, 1.9 %

Overall survivability and seakeeping ability:
   Survivability (Non-critical penetrating hits needed to sink ship):
     21 010 lbs / 9 530 Kg = 17.5 x 13.4 " / 340 mm shells or 3.9 torpedoes
   Stability (Unstable if below 1.00): 1.10
   Metacentric height 4.2 ft / 1.3 m
   Roll period: 16.2 seconds
   Steadiness   - As gun platform (Average = 50 %): 72 %
         - Recoil effect (Restricted arc if above 1.00): 0.68
   Seaboat quality  (Average = 1.00): 1.20

Hull form characteristics:
   Hull has rise forward of midbreak
   Block coefficient: 0.616
   Length to Beam Ratio: 6.75 : 1
   'Natural speed' for length: 23.05 kts
   Power going to wave formation at top speed: 48 %
   Trim (Max stability = 0, Max steadiness = 100): 60
   Bow angle (Positive = bow angles forward): 10.00 degrees
   Stern overhang: 0.00 ft / 0.00 m
   Freeboard (% = measuring location as a percentage of overall length):
      - Stem:      24.61 ft / 7.50 m
      - Forecastle (19 %):   20.34 ft / 6.20 m
      - Mid (50 %):      19.49 ft / 5.94 m (11.48 ft / 3.50 m aft of break)
      - Quarterdeck (18 %):   11.48 ft / 3.50 m
      - Stern:      11.48 ft / 3.50 m
      - Average freeboard:   16.10 ft / 4.91 m
   Ship tends to be wet forward

Ship space, strength and comments:
   Space   - Hull below water (magazines/engines, low = better): 97.7 %
      - Above water (accommodation/working, high = better): 116.2 %
   Waterplane Area: 31 068 Square feet or 2 886 Square metres
   Displacement factor (Displacement / loading): 99 %
   Structure weight / hull surface area: 155 lbs/sq ft or 757 Kg/sq metre
   Hull strength (Relative):
      - Cross-sectional: 0.96
      - Longitudinal: 1.35
      - Overall: 1.00
   Hull space for machinery, storage, compartmentation is adequate
   Room for accommodation and workspaces is adequate
   Ship has slow, easy roll, a good, steady gun platform

[mentat]

The last design is the strongest - but still very expensive for an essentially single purpose ship?

  DK - what PDNs you have - but why not make them last another 10 years - with sensible but lmtd modernisation (as long as well protected but very slow ships have a function vs. ever increasing torpedo threat (from Sub, DD and Aircraft) )


   - and invest all this $$$$$ - in  proper (multi-purpose) ships - with 1916 Engine Tech - you can now build sexy BBCs   -   sorry I don't understand  :D  .....

[maddox]

The Dantons are an example of a recently refitted PDN.

The lack of reasonable secundaries worries the admiral who has to work with those;

[P3D]

The ships are rather second-class battleships and a waste of BP, IMHO.

[miketr]

The question is can Peru afford a modern DN at all?  If we assume No or with great difficulty then you start having to look at making accepting weakness in whatever you do build.

Michael