IJN, Post-1900

[Logi]

On another note.... I lined up all my recent ship models as well as the historical Fubuki destroyer (for scale) just for curiosity's sake. All the models except Fubuki have their own SS file but I refrained from posting some due to either being slightly too early to post or criterion/requirements of the design having changed.



And the Sakura-class with 1 gun removed for a torpedo tube.



This is the modified SS if we follow Walter's suggestion. Not following the suggestion means +3t misc weight, -0.08 kn top speed, and a higher (more comfortable) block coefficient.

Sakura, Japanese Fleet Destroyer laid down 1904 (Engine 1905)

Displacement:
   500 t light; 525 t standard; 602 t normal; 664 t full load

Dimensions: Length (overall / waterline) x beam x draught (normal/deep)
   (259.19 ft / 259.19 ft) x 23.62 ft x (8.04 / 8.60 ft)
   (79.00 m / 79.00 m) x 7.20 m  x (2.45 / 2.62 m)

Armament:
      5 - 4.72" / 120 mm 45.0 cal guns - 44.97lbs / 20.40kg shells, 100 per gun
     Quick firing guns in deck mounts, 1904 Model
     5 x Single mounts on centreline, evenly spread
      1 raised mount
      Weight of broadside 225 lbs / 102 kg

Machinery:
   Coal and oil fired boilers, steam turbines,
   Direct drive, 2 shafts, 10,000 shp / 7,460 Kw = 26.92 kts
   Range 2,700nm at 10.00 kts
   Bunker at max displacement = 139 tons (90% coal)
     Caution: Delicate, lightweight machinery

Trial Speed: 29.50 kts

Complement:
   59 - 78

Cost:
   £0.075 million / $0.299 million

Distribution of weights at normal displacement:
   Armament: 46 tons, 7.7 %
      - Guns: 46 tons, 7.7 %
   Machinery: 319 tons, 53.0 %
   Hull, fittings & equipment: 133 tons, 22.0 %
   Fuel, ammunition & stores: 102 tons, 16.9 %
   Miscellaneous weights: 2 tons, 0.3 %
      - On freeboard deck: 2 tons

Overall survivability and seakeeping ability:
   Survivability (Non-critical penetrating hits needed to sink ship):
     142 lbs / 64 Kg = 2.7 x 4.7 " / 120 mm shells or 0.2 torpedoes
   Stability (Unstable if below 1.00): 1.29
   Metacentric height 0.9 ft / 0.3 m
   Roll period: 10.4 seconds
   Steadiness   - As gun platform (Average = 50 %): 70 %
         - Recoil effect (Restricted arc if above 1.00): 0.62
   Seaboat quality  (Average = 1.00): 1.01

Hull form characteristics:
   Hull has raised forecastle, rise forward of midbreak,
     a normal bow and a cruiser stern
   Block coefficient (normal/deep): 0.428 / 0.441
   Length to Beam Ratio: 10.97 : 1
   'Natural speed' for length: 16.10 kts
   Power going to wave formation at top speed: 63 %
   Trim (Max stability = 0, Max steadiness = 100): 70
   Bow angle (Positive = bow angles forward): 0.00 degrees
   Stern overhang: 0.00 ft / 0.00 m
   Freeboard (% = length of deck as a percentage of waterline length):
            Fore end,    Aft end
      - Forecastle:   0.00 %,  15.09 ft / 4.60 m,  15.09 ft / 4.60 m
      - Forward deck:   20.00 %,  14.44 ft / 4.40 m,  14.44 ft / 4.40 m
      - Aft deck:   65.00 %,  8.20 ft / 2.50 m,  8.20 ft / 2.50 m
      - Quarter deck:   15.00 %,  8.20 ft / 2.50 m,  8.20 ft / 2.50 m
      - Average freeboard:      9.45 ft / 2.88 m
   Ship tends to be wet forward

Ship space, strength and comments:
   Space   - Hull below water (magazines/engines, low = better): 190.6 %
      - Above water (accommodation/working, high = better): 119.8 %
   Waterplane Area: 3,839 Square feet or 357 Square metres
   Displacement factor (Displacement / loading): 34 %
   Structure weight / hull surface area: 23 lbs/sq ft or 113 Kg/sq metre
   Hull strength (Relative):
      - Cross-sectional: 0.50
      - Longitudinal: 1.28
      - Overall: 0.55
   Cramped machinery, storage, compartmentation space
   Adequate accommodation and workspace room
   Ship has slow, easy roll, a good, steady gun platform

Misc Weight: 2t
2t - 1x46cm rotating ceneterline TTs with 1 reload

[Jefgte]

IMO, for a destroyer, 1TT is not enough, not serious, Sakura is a fast gunboat.
2 TT are the minimum
3 TT are better

Jef  ;)

[Logi]

Single tubs are too worthless (but that is 1900 Destroyer Tech), that is why I had the Sakura class as an all-gun ship.

[Logi]

Here is another destroyer design which ended up being quite similar to the original Kaba proposal.

It dropped 10m of ship length, 1 TT and it's reload, and good seakeeping (1.21->1.01) in exchange for a ship that is much fatter and therefore more comfortable (0.420->0.502) and can fit in T1 docks/slips.

I like this the best out of all the Kaba designs I've done as I'm now fully comfortable with the block coefficient. I also prefer this over the 5-gun Sakura class for much the same reasons (and the short-range wireless it has that the Sakura doesn't).

Umikaze, Japanese Fleet Destroyer laid down 1904 (Engine 1905)

Displacement:
   500 t light; 527 t standard; 613 t normal; 682 t full load

Dimensions: Length (overall / waterline) x beam x draught (normal/deep)
   (229.66 ft / 229.66 ft) x 21.00 ft x (8.86 / 9.60 ft)
   (70.00 m / 70.00 m) x 6.40 m  x (2.70 / 2.93 m)

Armament:
      4 - 4.72" / 120 mm 45.0 cal guns - 44.97lbs / 20.40kg shells, 150 per gun
     Quick firing guns in deck mounts, 1904 Model
     4 x Single mounts on centreline ends, evenly spread
      2 raised mounts - superfiring
      Weight of broadside 180 lbs / 82 kg

Machinery:
   Coal and oil fired boilers, steam turbines,
   Direct drive, 2 shafts, 9,500 shp / 7,087 Kw = 25.84 kts
   Range 3,000nm at 10.00 kts
   Bunker at max displacement = 154 tons (90% coal)

Trial Speed: 28.50 kts

Complement:
   61 - 80

Cost:
   £0.073 million / $0.292 million

Distribution of weights at normal displacement:
   Armament: 37 tons, 6.1 %
      - Guns: 37 tons, 6.1 %
   Machinery: 324 tons, 52.8 %
   Hull, fittings & equipment: 125 tons, 20.4 %
   Fuel, ammunition & stores: 113 tons, 18.4 %
   Miscellaneous weights: 14 tons, 2.3 %
      - On freeboard deck: 14 tons

Overall survivability and seakeeping ability:
   Survivability (Non-critical penetrating hits needed to sink ship):
     131 lbs / 60 Kg = 2.5 x 4.7 " / 120 mm shells or 0.2 torpedoes
   Stability (Unstable if below 1.00): 1.18
   Metacentric height 0.7 ft / 0.2 m
   Roll period: 10.9 seconds
   Steadiness   - As gun platform (Average = 50 %): 70 %
         - Recoil effect (Restricted arc if above 1.00): 0.90
   Seaboat quality  (Average = 1.00): 1.01

Hull form characteristics:
   Hull has rise forward of midbreak,
     a normal bow and a cruiser stern
   Block coefficient (normal/deep): 0.502 / 0.515
   Length to Beam Ratio: 10.94 : 1
   'Natural speed' for length: 15.15 kts
   Power going to wave formation at top speed: 67 %
   Trim (Max stability = 0, Max steadiness = 100): 70
   Bow angle (Positive = bow angles forward): 0.00 degrees
   Stern overhang: 0.00 ft / 0.00 m
   Freeboard (% = length of deck as a percentage of waterline length):
            Fore end,    Aft end
      - Forecastle:   15.00 %,  14.11 ft / 4.30 m,  13.78 ft / 4.20 m
      - Forward deck:   26.00 %,  13.78 ft / 4.20 m,  13.78 ft / 4.20 m
      - Aft deck:   47.00 %,  6.89 ft / 2.10 m,  6.89 ft / 2.10 m
      - Quarter deck:   12.00 %,  6.89 ft / 2.10 m,  6.89 ft / 2.10 m
      - Average freeboard:      9.73 ft / 2.97 m
   Ship tends to be wet forward

Ship space, strength and comments:
   Space   - Hull below water (magazines/engines, low = better): 186.8 %
      - Above water (accommodation/working, high = better): 93.9 %
   Waterplane Area: 3,220 Square feet or 299 Square metres
   Displacement factor (Displacement / loading): 37 %
   Structure weight / hull surface area: 22 lbs/sq ft or 107 Kg/sq metre
   Hull strength (Relative):
      - Cross-sectional: 0.50
      - Longitudinal: 1.93
      - Overall: 0.57
   Cramped machinery, storage, compartmentation space
   Adequate accommodation and workspace room
   Ship has slow, easy roll, a good, steady gun platform

Misc Weight: 14t
10t - Short-Range Wireless
4t - 2x1 46cm rotating centerline TTs with 1 reload each

[Logi]

I prefer releasing the 18 kton limitation on the Tsukaba BC.

Tsukaba, Japanese Fast Battleship laid down 1904 (Engine 1905)

Displacement:
   21,000 t light; 21,898 t standard; 22,585 t normal; 23,135 t full load

Dimensions: Length (overall / waterline) x beam x draught (normal/deep)
   (557.74 ft / 557.74 ft) x 75.79 ft x (30.51 / 31.13 ft)
   (170.00 m / 170.00 m) x 23.10 m  x (9.30 / 9.49 m)

Armament:
      8 - 12.01" / 305 mm 40.0 cal guns - 850.98lbs / 386.00kg shells, 80 per gun
     Breech loading guns in turret on barbette mounts, 1898 Model
     4 x Twin mounts on centreline ends, evenly spread
      2 raised mounts - superfiring
      12 - 5.98" / 152 mm 45.0 cal guns - 108.07lbs / 49.02kg shells, 200 per gun
     Quick firing guns in casemate mounts, 1904 Model
     12 x Single mounts on sides, evenly spread
      Weight of broadside 8,105 lbs / 3,676 kg

Armour:
   - Belts:      Width (max)   Length (avg)      Height (avg)
   Main:   11.0" / 280 mm   557.74 ft / 170.00 m   13.12 ft / 4.00 m
     Main Belt covers 154 % of normal length

   - Gun armour:   Face (max)   Other gunhouse (avg)   Barbette/hoist (max)
   Main:   12.0" / 305 mm   3.15" / 80 mm      9.06" / 230 mm
   2nd:   5.51" / 140 mm         -               -

   - Armoured deck - multiple decks:
   For and Aft decks: 2.56" / 65 mm
   Forecastle: 1.97" / 50 mm  Quarter deck: 1.97" / 50 mm

   - Conning towers: Forward 11.02" / 280 mm, Aft 0.00" / 0 mm

Machinery:
   Coal and oil fired boilers, complex reciprocating steam engines,
   Direct drive, 4 shafts, 49,155 ihp / 36,670 Kw = 24.01 kts
   Range 3,000nm at 10.00 kts
   Bunker at max displacement = 1,237 tons (90% coal)

Complement:
   920 - 1,197

Cost:
   £2.334 million / $9.338 million

Distribution of weights at normal displacement:
   Armament: 1,269 tons, 5.6 %
      - Guns: 1,269 tons, 5.6 %
   Armour: 5,956 tons, 26.4 %
      - Belts: 2,985 tons, 13.2 %
      - Armament: 1,351 tons, 6.0 %
      - Armour Deck: 1,429 tons, 6.3 %
      - Conning Tower: 190 tons, 0.8 %
   Machinery: 7,053 tons, 31.2 %
   Hull, fittings & equipment: 6,421 tons, 28.4 %
   Fuel, ammunition & stores: 1,585 tons, 7.0 %
   Miscellaneous weights: 300 tons, 1.3 %
      - On freeboard deck: 300 tons

Overall survivability and seakeeping ability:
   Survivability (Non-critical penetrating hits needed to sink ship):
     12,773 lbs / 5,794 Kg = 14.8 x 12.0 " / 305 mm shells or 1.5 torpedoes
   Stability (Unstable if below 1.00): 1.09
   Metacentric height 3.9 ft / 1.2 m
   Roll period: 16.2 seconds
   Steadiness   - As gun platform (Average = 50 %): 70 %
         - Recoil effect (Restricted arc if above 1.00): 0.90
   Seaboat quality  (Average = 1.00): 1.20

Hull form characteristics:
   Hull has a flush deck,
     a normal bow and a cruiser stern
   Block coefficient (normal/deep): 0.613 / 0.615
   Length to Beam Ratio: 7.36 : 1
   'Natural speed' for length: 23.62 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 (% = length of deck as a percentage of waterline length):
            Fore end,    Aft end
      - Forecastle:   20.00 %,  18.37 ft / 5.60 m,  18.37 ft / 5.60 m
      - Forward deck:   30.00 %,  18.37 ft / 5.60 m,  18.37 ft / 5.60 m
      - Aft deck:   35.00 %,  18.37 ft / 5.60 m,  18.37 ft / 5.60 m
      - Quarter deck:   15.00 %,  18.37 ft / 5.60 m,  18.37 ft / 5.60 m
      - Average freeboard:      18.37 ft / 5.60 m
   Ship tends to be wet forward

Ship space, strength and comments:
   Space   - Hull below water (magazines/engines, low = better): 125.9 %
      - Above water (accommodation/working, high = better): 119.0 %
   Waterplane Area: 31,290 Square feet or 2,907 Square metres
   Displacement factor (Displacement / loading): 86 %
   Structure weight / hull surface area: 146 lbs/sq ft or 714 Kg/sq metre
   Hull strength (Relative):
      - Cross-sectional: 0.95
      - Longitudinal: 1.57
      - Overall: 1.00
   Cramped machinery, storage, compartmentation space
   Adequate accommodation and workspace room
   Ship has slow, easy roll, a good, steady gun platform
   Good seaboat, rides out heavy weather easily

[Walter]

I prefer releasing the 18 kton limitation on the Tsukaba BC.

Who cares about limits! If someone in the Japanese government should object to that, he should be shot for treason. :)

[Tanthalas]

I conducted similar experiments with a "Fully Functional Fast BB" and ended up about the same place... I decided it was too damn big, but then again I feel I need more capable hulls to patrol my far flung empire.  I will likely wait for the next generation of propulsion to start building BCs.

[Logi]

Another try at the Tenryuu cruiser, this time with a 24 kn max speed to match the Tsukaba BC.

+1,000t Displacement (6,000t -> 7,000t)
+2x203mm/50 main guns
- 6x152mm/45 secondary guns (lose 3x152mm guns on a broadside)

- 50mm Turret Face armor (180mm -> 130mm)
- 20mm Barbette armor (100mm -> 80mm)

- Seakeeping (1.22 -> 1.06)
- Stability (1.09 -> 1.08)
- Misc Weight (65t -> 34t)
+Max speed (23kn -> 24kn)

The broadside weight has increased by 103kg and the extra pair of 20cm guns helps in straddling targets. Since period 15cm and 20cm ROF don't different by all that much the loss of a secondary battery is somewhat mitigated. However, all in all, a fair bit has been given up for the extra knot in speed and pair of 20cm guns. Thoughts?

PS: I can't get the ship any larger without giving up mixed propulsion for full VTE.

Tenryuu, Japanese Cruiser laid down 1904 (Engine 1905)

Displacement:
   7,000 t light; 7,281 t standard; 7,952 t normal; 8,488 t full load

Dimensions: Length (overall / waterline) x beam x draught (normal/deep)
   (492.13 ft / 492.13 ft) x 53.64 ft x (20.28 / 21.32 ft)
   (150.00 m / 150.00 m) x 16.35 m  x (6.18 / 6.50 m)

Armament:
      8 - 7.99" / 203 mm 50.0 cal guns - 275.58lbs / 125.00kg shells, 100 per gun
     Breech loading guns in turret on barbette mounts, 1904 Model
     4 x Twin mounts on centreline ends, evenly spread
      2 raised mounts - superfiring
      Weight of broadside 2,205 lbs / 1,000 kg

Armour:
   - Belts:      Width (max)   Length (avg)      Height (avg)
   Main:   3.15" / 80 mm   492.13 ft / 150.00 m   9.84 ft / 3.00 m
     Main Belt covers 154 % of normal length

   - Gun armour:   Face (max)   Other gunhouse (avg)   Barbette/hoist (max)
   Main:   5.12" / 130 mm   1.50" / 38 mm      3.15" / 80 mm

   - Armoured deck - single deck:
   For and Aft decks: 1.57" / 40 mm
   Forecastle: 1.18" / 30 mm  Quarter deck: 1.18" / 30 mm

Machinery:
   Coal and oil fired boilers, reciprocating cruising steam engines and steam turbines
   Direct drive, 4 shafts, 25,600 ihp / 19,098 Kw = 24.01 kts
   Range 6,000nm at 10.00 kts
   Bunker at max displacement = 1,207 tons (90% coal)

Complement:
   420 - 547

Cost:
   £0.846 million / $3.383 million

Distribution of weights at normal displacement:
   Armament: 539 tons, 6.8 %
      - Guns: 539 tons, 6.8 %
   Armour: 1,312 tons, 16.5 %
      - Belts: 564 tons, 7.1 %
      - Armament: 246 tons, 3.1 %
      - Armour Deck: 502 tons, 6.3 %
   Machinery: 2,682 tons, 33.7 %
   Hull, fittings & equipment: 2,433 tons, 30.6 %
   Fuel, ammunition & stores: 952 tons, 12.0 %
   Miscellaneous weights: 34 tons, 0.4 %
      - On freeboard deck: 34 tons

Overall survivability and seakeeping ability:
   Survivability (Non-critical penetrating hits needed to sink ship):
     3,901 lbs / 1,770 Kg = 15.3 x 8.0 " / 203 mm shells or 0.8 torpedoes
   Stability (Unstable if below 1.00): 1.08
   Metacentric height 2.3 ft / 0.7 m
   Roll period: 15.0 seconds
   Steadiness   - As gun platform (Average = 50 %): 70 %
         - Recoil effect (Restricted arc if above 1.00): 0.68
   Seaboat quality  (Average = 1.00): 1.06

Hull form characteristics:
   Hull has rise forward of midbreak,
     a normal bow and a cruiser stern
   Block coefficient (normal/deep): 0.520 / 0.528
   Length to Beam Ratio: 9.17 : 1
   'Natural speed' for length: 22.18 kts
   Power going to wave formation at top speed: 48 %
   Trim (Max stability = 0, Max steadiness = 100): 66
   Bow angle (Positive = bow angles forward): 0.00 degrees
   Stern overhang: 0.00 ft / 0.00 m
   Freeboard (% = length of deck as a percentage of waterline length):
            Fore end,    Aft end
      - Forecastle:   20.00 %,  18.04 ft / 5.50 m,  18.04 ft / 5.50 m
      - Forward deck:   10.00 %,  18.04 ft / 5.50 m,  18.04 ft / 5.50 m
      - Aft deck:   55.00 %,  9.84 ft / 3.00 m,  9.84 ft / 3.00 m
      - Quarter deck:   15.00 %,  9.84 ft / 3.00 m,  9.84 ft / 3.00 m
      - Average freeboard:      12.30 ft / 3.75 m
   Ship tends to be wet forward

Ship space, strength and comments:
   Space   - Hull below water (magazines/engines, low = better): 134.4 %
      - Above water (accommodation/working, high = better): 90.2 %
   Waterplane Area: 17,915 Square feet or 1,664 Square metres
   Displacement factor (Displacement / loading): 90 %
   Structure weight / hull surface area: 100 lbs/sq ft or 487 Kg/sq metre
   Hull strength (Relative):
      - Cross-sectional: 0.99
      - Longitudinal: 1.00
      - Overall: 1.00
   Cramped machinery, storage, compartmentation space
   Adequate accommodation and workspace room
   Ship has slow, easy roll, a good, steady gun platform

[snip]

I think it really needs some sort of light secondary. I agree that the 152mm was to much, but it needs something.

[Logi]

Like this? I added 2x75cm per side for no cost by changing the hull dimensions slightly.

Tenryuu, Japanese Cruiser laid down 1904 (Engine 1905)

Displacement:
   7,000 t light; 7,287 t standard; 7,958 t normal; 8,495 t full load

Dimensions: Length (overall / waterline) x beam x draught (normal/deep)
   (492.13 ft / 492.13 ft) x 53.48 ft x (20.34 / 21.39 ft)
   (150.00 m / 150.00 m) x 16.30 m  x (6.20 / 6.52 m)

Armament:
      8 - 7.99" / 203 mm 50.0 cal guns - 275.58lbs / 125.00kg shells, 100 per gun
     Breech loading guns in turret on barbette mounts, 1904 Model
     4 x Twin mounts on centreline ends, evenly spread
      2 raised mounts - superfiring
      4 - 2.95" / 75.0 mm 45.0 cal guns - 12.99lbs / 5.89kg shells, 200 per gun
     Quick firing guns in deck mounts, 1904 Model
     4 x Single mounts on sides, evenly spread
      Weight of broadside 2,257 lbs / 1,024 kg

Armour:
   - Belts:      Width (max)   Length (avg)      Height (avg)
   Main:   3.15" / 80 mm   492.13 ft / 150.00 m   9.84 ft / 3.00 m
     Main Belt covers 154 % of normal length

   - Gun armour:   Face (max)   Other gunhouse (avg)   Barbette/hoist (max)
   Main:   5.12" / 130 mm   1.50" / 38 mm      3.15" / 80 mm

   - Armoured deck - single deck:
   For and Aft decks: 1.57" / 40 mm
   Forecastle: 1.18" / 30 mm  Quarter deck: 1.18" / 30 mm

Machinery:
   Coal and oil fired boilers, reciprocating cruising steam engines and steam turbines
   Direct drive, 4 shafts, 25,600 ihp / 19,098 Kw = 24.01 kts
   Range 6,000nm at 10.00 kts
   Bunker at max displacement = 1,208 tons (90% coal)

Complement:
   420 - 547

Cost:
   £0.848 million / $3.394 million

Distribution of weights at normal displacement:
   Armament: 548 tons, 6.9 %
      - Guns: 548 tons, 6.9 %
   Armour: 1,309 tons, 16.5 %
      - Belts: 564 tons, 7.1 %
      - Armament: 244 tons, 3.1 %
      - Armour Deck: 500 tons, 6.3 %
   Machinery: 2,682 tons, 33.7 %
   Hull, fittings & equipment: 2,426 tons, 30.5 %
   Fuel, ammunition & stores: 958 tons, 12.0 %
   Miscellaneous weights: 34 tons, 0.4 %
      - On freeboard deck: 34 tons

Overall survivability and seakeeping ability:
   Survivability (Non-critical penetrating hits needed to sink ship):
     3,870 lbs / 1,755 Kg = 15.2 x 8.0 " / 203 mm shells or 0.8 torpedoes
   Stability (Unstable if below 1.00): 1.08
   Metacentric height 2.3 ft / 0.7 m
   Roll period: 15.0 seconds
   Steadiness   - As gun platform (Average = 50 %): 70 %
         - Recoil effect (Restricted arc if above 1.00): 0.69
   Seaboat quality  (Average = 1.00): 1.05

Hull form characteristics:
   Hull has rise forward of midbreak,
     a normal bow and a cruiser stern
   Block coefficient (normal/deep): 0.520 / 0.528
   Length to Beam Ratio: 9.20 : 1
   'Natural speed' for length: 22.18 kts
   Power going to wave formation at top speed: 48 %
   Trim (Max stability = 0, Max steadiness = 100): 66
   Bow angle (Positive = bow angles forward): 0.00 degrees
   Stern overhang: 0.00 ft / 0.00 m
   Freeboard (% = length of deck as a percentage of waterline length):
            Fore end,    Aft end
      - Forecastle:   20.00 %,  18.37 ft / 5.60 m,  17.72 ft / 5.40 m
      - Forward deck:   10.00 %,  17.72 ft / 5.40 m,  17.39 ft / 5.30 m
      - Aft deck:   55.00 %,  9.84 ft / 3.00 m,  9.84 ft / 3.00 m
      - Quarter deck:   15.00 %,  9.84 ft / 3.00 m,  9.84 ft / 3.00 m
      - Average freeboard:      12.24 ft / 3.73 m
   Ship tends to be wet forward

Ship space, strength and comments:
   Space   - Hull below water (magazines/engines, low = better): 134.6 %
      - Above water (accommodation/working, high = better): 89.4 %
   Waterplane Area: 17,865 Square feet or 1,660 Square metres
   Displacement factor (Displacement / loading): 90 %
   Structure weight / hull surface area: 100 lbs/sq ft or 488 Kg/sq metre
   Hull strength (Relative):
      - Cross-sectional: 0.99
      - Longitudinal: 1.00
      - Overall: 1.00
   Cramped machinery, storage, compartmentation space
   Cramped accommodation and workspace room
   Ship has slow, easy roll, a good, steady gun platform

[snip]

It feels light to me still, but then again I have gone for heavy 5" batteries. This feels like a ship that is going to benefit a lot from better engines, so the future half-sisters or daughters will be much more capable. I would personally try and expand the 75mm battery as large as practical, as I think she would have a hard time fending off small ships.

[Logi]

I feel fending off small ships isn't going to be a significant problem considering:
1) Torpedoes have extraordinarily short range and slow speeds. The max range of torpedoes on the slowest setting (26kn) is 3000m now and 5000m in the future. Full speed (30kn now and 35kn future) cuts the range by more than half. That means a torpedo from the max range (because you simply won't get close enough for the short range launch unless in night conditions and there are no night battle tactics currently) is only 2 knots faster than this cruiser.

2) Contemporary destroyers are quite slow in Navalism are quite slow and fragile. Most destroyer designs I've seen hover at 25-26kn Springsharp speed and have 29-30kn trial speeds. Of course in an actual battle the speeds of the ships are considered at their Springsharp speed, so there is actually only a 1-2kn advantage on the side of destroyers over the cruiser. I think it's unlikely they can close to torpedo launch range before getting destroyed by the secondary/main battery fire from the cruiser and it's squadron, especially if the cruiser & its squadron are heading away from the destroyer's advance.

3) 75mm is actually the size of most destroyer armament in Navalism. Heavy 5" batteries are absurdly larger than the armament on the destroyers they are facing and overkill for tiny 500 ton destroyers. It would only take 1-2 5"(127mm) shells to sink the Nowaki or the Blandin destroyers.

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For some mathematical fun, let's calculate the furthest distance a destroyer can launch those future torpedoes (26kn @ 5000m or 35kn @ 2200m) and have them hit the cruiser.
First I'll considered the case where the two ships are moving in parallel (i.e. same heading) and neither ships makes any course corrections after and during the torpedo run (torpedo speed 26kn).

The destroyer will have to launch the torpedo at an angle ahead of the cruiser's current position in other to hit the cruiser. In other words, the actual range to the cruiser is less than 5000m. Let's do some math to find out that actual range.

We'll need to divide the distance the torpedo travels by it's speed to get how long it took (in time) for the run. Using that time, we can tell how far the cruiser moved in that period and then what the actual distance between DD and CL is.

26 kn = 13.3756 m/s
24 kn = 12.3467 m/s

(5000m / 13.3756 m/s) * 12.3467 m/s = 4615.38174 m
That makes the distance from DD to CL 1920m.

That's terrible. Let's consider the faster run now (2,200nm @ 35kn)

35 kn = 18.0056 m/s
(2200m /18.0056 m/s) * 12.3467 m/s = 1508.5712 m
That makes the distance from DD to CL 1600m.

Still bad, but not as bad as I thought when compared to the slower speed run. Let's do a more realistic scenario now:
Suppose the cruiser is moving away from the DD's launch point at a fixed 45 degrees angle. This would allow the cruiser to still bring all it's guns to bear whilst gaining decent distance.

Let's do the 26kn case:
The cruiser still moves 4615.38174 m but at an angle now. So the distance from DD to CL is 524m.
And for the 35kn case 857m.


To give a sense of scale, in the 45 degrees case that range is about the same as the mean range of tank engagements in WW2 (768m)! The Battle of Tsushima had fire start at 7,000m and close to 4,600m before widening the distance again.

Now's let consider the time under fire of the DD. To make math simple, let's compress it down to 1 axis. The DD heads straight at the the cruiser, the cruiser backs away at a 45 degrees angle. We'll use the horizontal component of the cruiser's speed and ignore the distance generated by the vertical component (So our time-under-fire will be an underestimate, in reality it would take even more time). So we have a DD closing at 26 kn and a CL backing away at 17 kn, a total gain of 9 kn. The goal is for the DD to close the gap between the ships to 857m, so it can launch the 35kn@2200m torpedo and have a possibility of a hit. They start 7000m away from each other since that's when fire starts. The time under fire (not including time after torpedo launch) would be (7000m - 857m) / 4.63 m/s* = 1326.782 sec = 22 minutes and 7 seconds.

20cm ROF is 3-5 per minute and 8cm ROF is 13-20 per minute. Let's go with the lower bound. That's 66 20cm shells and 286 8cm shells per barrel during the whole closing duration. With 8x20cm and 2x8cm on a broadside, that's a total of 528x20cm shells and 572x8cm shells. Each 20cm shell will outright sink the DD and it takes 8-9 8cm shells to sink the DD. Let's go with 1x20cm and 9x8cm respectively. Supposing a 0.01% chance to hit which is really low considering historical examples and the ranges the ships are at in this situation, there will be an average 5x20cm and 5x8cm hits. Not enough 8cm hits to sink, but enough to heavily cripple. There are, however, more than enough 20cm hits to sink the DD before it ever drops it's torpedoes.

*4.63 m/s because that's what 9kn is equivalent to.

[snip]

Very informative math. Couple points, two technical, three theoretical:

1) I think you are overestimating what a 20cm gun is capable of RoF wise for this era. See the US 8"/35 8"/45 and Japanese 8"/45. All those guns about about 2 rounds per minute in combat conditions. Claiming 3-5 is somewhat out of line with what was happening in OTL at this point. The nearest example I can find with a quick search of about your ROF is several Royal Navy 9.2" guns (Mark X best fit IMO), but, those all note 2 RPM for "battle practice". I think 2-3.5 would be a more realistic range.

2) I also think the train speed for 20cm turrets (or just turrets in general) has been overestimated for the period. So while you are correct (pending recalculation for the above) in that the volume of shell is likely sufficient against a single 500t destroyer, I think counting on the 20cm guns to be effective at tracking a small target like a destroyers is being overstated.

3) While we have not gotten to any Fire Control Tech yet, I feel that while the 75mm guns as a caliber are a good anti-destroyer weapon but they will need volume to increase the chance of landing hits. While a 20cm HE shell will outright wreck a Destroyer, I think a increase in the volume of 75mm will increase the number of possible destroyer kills. Which leads me to...

4) I find the scenario of lone destroyer on lone cruiser a little contrived. As previously noted, the math itself is very informative but I feel the scenario needs to account for more destroyers being present. I know beyond a certain point we may as well turn it into a fleet engagement, but I feel there is room to improve the plausibility of the scenario.

5) While I don't think we should ever fully give into hindsight, I think there is some room to anticipate bigger things coming. Within the last 10 game years, torpedo have gone from ultra-close range weapons to ones that are at least triple that. Destroyers have been getting larger (up to our artificial cap, which I know at least the US is close to breaking), and with turbines (a known quantity by N-verse 1904) they will be getting faster. I think the ship is "good enough" to fight what is out there now, but she will not be ready until late 1905(ish). I think there is room to improve the secondary to be "good enough" for an realistically anticipated 1906.

As a final note, this is not a bad ship. Very capable of punching above its weight, something that hostile armored cruisers will not appreciate. As you noted, it is a ship constrained by engines and I think that is going to limit how far you can push the hull. While this is not a ship the USN would build, I think it's a good fit for the IJN. Two curious requests, if you would oblige me:

1) How many 75mm can you cram on while keeping everything else where you want it?

2) How does the ship look as a 6x20cm? My thought here is that six main guns would still be enough to make older ACs think twice and might let you get a cheaper and/or more capable ship out of your tonnage as a ~7000t ship is going to get smacked around by some of the big ACs on the drawing boards.

[Logi]

1) The guns you have lsited are all old types. They were designed in or before 1900 and entered service later. And then, if you looked at the notes, a lot (but not all) are completely manually operated. The 20cm/50 is a new gun with a new turret, it would be absurd to compare it's ROF strictly with others of it's type that are so much older (they're a whole naval gun tech level apart in our sim).

Take the German old mount (even older) which achieves such ROF.
Or this German gun, which has a date of design in 1905, which would be the right tech level as the 20cm/50 gun on this cruiser.
We can look at the Russian guns as well as the
I wouldn't use the British 9.2" figures since they fire a 172kg shell (almost 40% heavier than the 20cm/50 shells) and yet still manage to get a ROF of 2 rounds per minute in battle. If I were to use such a great difference in shell weight and argue their ROF must be similar, I could say the British 7.5"/50 III/IV designed in 1902 achieved a ROF of 5-6 rounds, each weighting 91kg is only almost 30% lighter and therefore the 20cm/50 guns should have a ROF of 5. Clearly this is absurd. In fact, I might argue that because of how the 20cm/50's shells are in between the British 9.2" and 7.5", it's ROF should also be in between, i.e. between 2 to 5 ROF. This would work out to probably being around 3-4 ROF.

The real mystery here is why the USN's 20cm guns achieved a slower ROF than contemporary guns from other nations. I suspect it has to do with the relatively newness of the USN to naval design as well as the seemingly cramped nature of the USN 20cm turret. Of course, "I suspect" means I have no evidence to back up this assertion.


2) The training issue has been brought up from no where. In no historical text have I ever found any mention of this supposed tracking problem, which makes sense considering that math dictates that there is no such problem. Consider a circle, 6000m in radius. Suppose an object, this destroyer, is moving along the edge of this circle at a speed of 26kn (we suppose it doesn't lose any speed from the constant turning) - the cruiser's guns must have at least train faster than 0.11 degrees per second to keep track of the destroyer. Even if we shrink the radius to 2000m, the guns have to train only faster than 0.355 degrees per second. The idea that a ship can't keep it's guns trained on a destroyer is pure nonsense. The problem has never been training the guns to track a destroyer, it's always been (re)finding exactly where the guns are supposed to track to to fire and hit the destroyer (you don't point directly at the target) and not losing the relative headings and distances of the two ships when conducting back-to-back maneuvers.

The only situations which would make the guns not track the target is if the ship with the guns is conducting an extreme maneuver, such as circling to reduce the chance of getting hit by a dive-bomber, or if the ship with the guns is the destroyer maneuvering in to close the distance whilst dodging shots. The larger ship in such an engagement has never AFAIK conducted such maneuvers because the destroyer's torpedo armament is thrown off by the slightest of heading changes from distance and if the destroyer is close enough that such wild maneuvers are necessary, it is likely the ship is lost anyways!

This is not the first time, I've talked about this non-issue - I believe it was a year or so ago that I explained the very same thing to you! I believe you are the only person I have ever met/read about/etc. to have ever mentioned gun training speed as an issue on naval designs. I really don't know why you believe this is an issue. The USN 20cm gun you linked even lists a training rate of 6 degrees per second, more than enough to keep locked on a destroyer by an order of magnitude.


3 & 4) The scenario still stands. In a realistic scenario a few 8cm hits will disable portions of these 500 ton destroyers and slow them down tremendously. Given that their speed margin is only 2 knots faster than the cruisers, they would probably never even make it into range!

The cruisers have the power to focus-fire. Supposing 4 destroyers face 2 cruisers. The two cruisers can focus down the destroyers one at a time, not necessarily to sink the destroyer but simply to slow it down. They fire until they land a few hits and the destroyer slows down, then they switch fire to the next. Each destroyer facing the focused fire suffers from reduced fighting ability. Their ability to close in is heavily impacted by the fact that they need to attempt to dodge and that the mess of splashes breeds chaos on the ship. The unimpeded destroyers still have a very lengthy time required to close in!

Or in an even more clearly cut fashion:
The cruisers head straight away from the destroyers as the destroyers head straight for the cruisers. In this case, there is only a speed margin of 2 kn. I'll assume when the destroyer launches the torpedo, the cruiser moves back to a 45 degrees heading so the distance between ships doesn't change (otherwise the destroyer would need to be even closer) and this is just so I don't have to recalculate the numbers as I'm pretty certain, even in this lenient situation, the numbers will be pretty devastating.
(7000m - 857m) / 1.03 m/s = 5964 seconds = 1 hour, 39 minutes, 24 seconds. Good luck!

And history supports this conclusion. There has never been an engagement in which the cruisers were peeling back, where the chasing destroyers managed to achieve any sinkings via torpedoes. Even in their most successful runs, destroyers have historically barely damaged the cruisers and themselves taken on heavy losses. These successful runs required copious amounts of smoke generate, favorable weather (foggy/rainy, etc. that reduce visibility), confusion on the enemy side (inaccurate target selection, higher value target behind the destroyers, captains unsure whether to press into the destroyers or peel back while firing, extremely poor damage control), and help from other supportive elements (bombers, fighters, etc.).


5) I already did that. NO nation in Navalism currently has or has started researching 5000m@26kn, 2200m@35kn torpedoes (that's 1905 tech) and the next tech up from that 1908 barely adds any range. In fact, in a strictly current time-space, I've already vastly overestimated the ability of torpedoes. The torpedoes that are present in every navy afloat in Navalism as of 1904 are 3000m@26kn, 1500m@15kn torpedoes. They're also in single tubes limited to a grand total of 4 per ship (no nation has the ability to reload torpedoes during battle). In other words, my calculations will hold true until the middle of OTL World War One (that's 1913 torpedo tech which is the big jump in torpedo ability). Therefore IMO torpedoes are worst than worthless, they currently (and for the next decade) only work under the most optimistic battle scenarios, present hazard to the ship in terms of highly explosive material on deck, and I haven't even mentioned all the reliability issues that torpedoes historically had.

Imagine that even in the height of surface-torpedo power in WW2, the German torpedoes were having mechanical issues. The American torpedoes not only didn't work unless it was fired in a very specific wrong (according to the original method to firing it in it's manual) way and even then there was a chance the torpedo wouldn't exploded, run too deep, and even circle around to hit the ship that launched them!

[Logi]

And since I've managed to convince myself that torpedoes are completely unnecessary on the cruisers (and indeed I am now heavily favoring the 5-6 all-gun DD with no torpedoes), I can simply reduce the misc weight of the ship and increase the 8cm battery significantly.

+6x8cm guns (+3 per broadside for a total of 4 per broadside).

That is, a broadside of 1124 8cm shells in the destroyer closing in a cruiser retreating at 45 degrees scenario. Enough to sink a destroyer and then some under the abysmal 0.01% accuracy.

Tenryuu, Japanese Cruiser laid down 1904 (Engine 1905)

Displacement:
   7,000 t light; 7,294 t standard; 7,965 t normal; 8,502 t full load

Dimensions: Length (overall / waterline) x beam x draught (normal/deep)
   (492.13 ft / 492.13 ft) x 53.48 ft x (20.37 / 21.43 ft)
   (150.00 m / 150.00 m) x 16.30 m  x (6.21 / 6.53 m)

Armament:
      8 - 7.99" / 203 mm 50.0 cal guns - 275.58lbs / 125.00kg shells, 100 per gun
     Breech loading guns in turret on barbette mounts, 1904 Model
     4 x Twin mounts on centreline ends, evenly spread
      2 raised mounts - superfiring
      8 - 2.95" / 75.0 mm 45.0 cal guns - 12.99lbs / 5.89kg shells, 200 per gun
     Quick firing guns in deck mounts, 1904 Model
     8 x Single mounts on sides, evenly spread
      Weight of broadside 2,309 lbs / 1,047 kg

Armour:
   - Belts:      Width (max)   Length (avg)      Height (avg)
   Main:   3.15" / 80 mm   492.13 ft / 150.00 m   9.84 ft / 3.00 m
     Main Belt covers 154 % of normal length

   - Gun armour:   Face (max)   Other gunhouse (avg)   Barbette/hoist (max)
   Main:   5.12" / 130 mm   1.50" / 38 mm      3.15" / 80 mm

   - Armoured deck - single deck:
   For and Aft decks: 1.57" / 40 mm
   Forecastle: 1.18" / 30 mm  Quarter deck: 1.18" / 30 mm

Machinery:
   Coal and oil fired boilers, reciprocating cruising steam engines and steam turbines
   Direct drive, 4 shafts, 25,600 ihp / 19,098 Kw = 24.00 kts
   Range 6,000nm at 10.00 kts
   Bunker at max displacement = 1,208 tons (90% coal)

Complement:
   421 - 548

Cost:
   £0.851 million / $3.404 million

Distribution of weights at normal displacement:
   Armament: 558 tons, 7.0 %
      - Guns: 558 tons, 7.0 %
   Armour: 1,308 tons, 16.4 %
      - Belts: 564 tons, 7.1 %
      - Armament: 243 tons, 3.1 %
      - Armour Deck: 500 tons, 6.3 %
   Machinery: 2,682 tons, 33.7 %
   Hull, fittings & equipment: 2,427 tons, 30.5 %
   Fuel, ammunition & stores: 965 tons, 12.1 %
   Miscellaneous weights: 25 tons, 0.3 %
      - On freeboard deck: 25 tons

Overall survivability and seakeeping ability:
   Survivability (Non-critical penetrating hits needed to sink ship):
     3,858 lbs / 1,750 Kg = 15.1 x 8.0 " / 203 mm shells or 0.8 torpedoes
   Stability (Unstable if below 1.00): 1.08
   Metacentric height 2.3 ft / 0.7 m
   Roll period: 14.9 seconds
   Steadiness   - As gun platform (Average = 50 %): 70 %
         - Recoil effect (Restricted arc if above 1.00): 0.70
   Seaboat quality  (Average = 1.00): 1.06

Hull form characteristics:
   Hull has rise forward of midbreak,
     a normal bow and a cruiser stern
   Block coefficient (normal/deep): 0.520 / 0.528
   Length to Beam Ratio: 9.20 : 1
   'Natural speed' for length: 22.18 kts
   Power going to wave formation at top speed: 47 %
   Trim (Max stability = 0, Max steadiness = 100): 66
   Bow angle (Positive = bow angles forward): 0.00 degrees
   Stern overhang: 0.00 ft / 0.00 m
   Freeboard (% = length of deck as a percentage of waterline length):
            Fore end,    Aft end
      - Forecastle:   20.00 %,  19.03 ft / 5.80 m,  17.39 ft / 5.30 m
      - Forward deck:   10.00 %,  17.39 ft / 5.30 m,  17.39 ft / 5.30 m
      - Aft deck:   55.00 %,  9.84 ft / 3.00 m,  9.84 ft / 3.00 m
      - Quarter deck:   15.00 %,  9.84 ft / 3.00 m,  9.84 ft / 3.00 m
      - Average freeboard:      12.24 ft / 3.73 m
   Ship tends to be wet forward

Ship space, strength and comments:
   Space   - Hull below water (magazines/engines, low = better): 134.8 %
      - Above water (accommodation/working, high = better): 88.9 %
   Waterplane Area: 17,859 Square feet or 1,659 Square metres
   Displacement factor (Displacement / loading): 90 %
   Structure weight / hull surface area: 100 lbs/sq ft or 489 Kg/sq metre
   Hull strength (Relative):
      - Cross-sectional: 0.99
      - Longitudinal: 1.00
      - Overall: 1.00
   Cramped machinery, storage, compartmentation space
   Cramped accommodation and workspace room
   Ship has slow, easy roll, a good, steady gun platform