70m Gunboats

[Jefgte]

I'm studying 70m Gunboats for Chilean coasts & Falklands Islands.

- The 40mm belt is for ice protection.
- 6" guns is certainly the best choice but I can instal 120mm guns & increase the speed to 25kts.

Casemates Coastal Gunboat, NUS CGB1400 laid down 1920 (Engine 1916)

Displacement:
   1 400 t light; 1 509 t standard; 1 757 t normal; 1 955 t full load

Dimensions: Length overall / water x beam x draught
   229.66 ft / 229.66 ft x 39.37 ft x 14.17 ft (normal load)
   70.00 m / 70.00 m x 12.00 m  x 4.32 m

Armament:
     2 - 6.00" / 152 mm guns in single mounts, 108.00lbs / 48.99kg shells, 1920 Model
     Breech loading guns in deck mounts with hoists
     on centreline, evenly spread
     4 - 6.00" / 152 mm guns in single mounts, 108.00lbs / 48.99kg shells, 1920 Model
     Breech loading guns in casemate mounts
     on side, evenly spread
     4 - 1.57" / 40.0 mm guns (2x2 guns), 1.95lbs / 0.88kg shells, 1920 Model
     Anti-aircraft guns in deck mounts
     on side, all amidships, all raised mounts - superfiring
     2 - 0.50" / 12.7 mm guns in single mounts, 0.06lbs / 0.03kg shells, 1920 Model
     Anti-aircraft guns in deck mounts
     on side, evenly spread, all raised mounts
   Weight of broadside 656 lbs / 298 kg
   Shells per gun, main battery: 180
   3 - 21.0" / 533 mm above water torpedoes

Armour:
  - Belts:      Width (max)   Length (avg)      Height (avg)
   Main:   1.57" / 40 mm   190.29 ft / 58.00 m   8.99 ft / 2.74 m
   Ends:   1.57" / 40 mm     36.09 ft / 11.00 m   8.01 ft / 2.44 m
     3.28 ft / 1.00 m Unarmoured ends
     Main Belt covers 127 % of normal length

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

Machinery:
   Oil fired boilers, steam turbines,
   Geared drive, 2 shafts, 10 800 shp / 8 057 Kw = 22.27 kts
   Range 7 000nm at 12.00 kts
   Bunker at max displacement = 446 tons

Complement:
   135 - 176

Cost:
   £0.412 million / $1.647 million

Distribution of weights at normal displacement:
   Armament: 82 tons, 4.7 %
   Armour: 145 tons, 8.3 %
      - Belts: 127 tons, 7.3 %
      - Torpedo bulkhead: 0 tons, 0.0 %
      - Armament: 17 tons, 1.0 %
      - Armour Deck: 0 tons, 0.0 %
      - Conning Tower: 0 tons, 0.0 %
   Machinery: 402 tons, 22.9 %
   Hull, fittings & equipment: 666 tons, 37.9 %
   Fuel, ammunition & stores: 356 tons, 20.3 %
   Miscellaneous weights: 105 tons, 6.0 %

Overall survivability and seakeeping ability:
   Survivability (Non-critical penetrating hits needed to sink ship):
     1 628 lbs / 739 Kg = 15.1 x 6.0 " / 152 mm shells or 0.6 torpedoes
   Stability (Unstable if below 1.00): 1.13
   Metacentric height 1.6 ft / 0.5 m
   Roll period: 13.2 seconds
   Steadiness   - As gun platform (Average = 50 %): 70 %
         - Recoil effect (Restricted arc if above 1.00): 0.56
   Seaboat quality  (Average = 1.00): 1.16

Hull form characteristics:
   Hull has rise forward of midbreak
   Block coefficient: 0.480
   Length to Beam Ratio: 5.83 : 1
   'Natural speed' for length: 15.15 kts
   Power going to wave formation at top speed: 68 %
   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:      21.00 ft / 6.40 m
      - Forecastle (18 %):   19.69 ft / 6.00 m
      - Mid (40 %):      19.03 ft / 5.80 m (12.47 ft / 3.80 m aft of break)
      - Quarterdeck (18 %):   12.47 ft / 3.80 m
      - Stern:      12.47 ft / 3.80 m
      - Average freeboard:   15.38 ft / 4.69 m

Ship space, strength and comments:
   Space   - Hull below water (magazines/engines, low = better): 117.8 %
      - Above water (accommodation/working, high = better): 95.6 %
   Waterplane Area: 5 917 Square feet or 550 Square metres
   Displacement factor (Displacement / loading): 103 %
   Structure weight / hull surface area: 62 lbs/sq ft or 303 Kg/sq metre
   Hull strength (Relative):
      - Cross-sectional: 0.82
      - Longitudinal: 5.90
      - Overall: 1.00
   Hull space for machinery, storage, compartmentation is cramped
   Room for accommodation and workspaces is adequate
   Ship has slow, easy roll, a good, steady gun platform

--------------------------------------------
South Coastal Gunboat, NUS CGB1400 laid down 1920 (Engine 1916)

Displacement:
   1 400 t light; 1 470 t standard; 1 643 t normal; 1 782 t full load

Dimensions: Length overall / water x beam x draught
   229.60 ft / 226.38 ft x 39.04 ft x 13.02 ft (normal load)
   69.98 m / 69.00 m x 11.90 m  x 3.97 m

Armament:
     4 - 6.00" / 152 mm guns (2x2 guns), 108.00lbs / 48.99kg shells, 1920 Model
     Breech loading guns in deck mounts with hoists
     on centreline, evenly spread
     2 - 1.57" / 40.0 mm guns in single mounts, 1.95lbs / 0.88kg shells, 1920 Model
     Anti-aircraft guns in deck mounts
     on side, evenly spread, all raised mounts
     2 - 0.50" / 12.7 mm guns in single mounts, 0.06lbs / 0.03kg shells, 1920 Model
     Anti-aircraft guns in deck mounts
     on side, all amidships, all raised mounts - superfiring
   Weight of broadside 436 lbs / 198 kg
   Shells per gun, main battery: 150
   3 - 21.0" / 533 mm above water torpedoes

Armour:
  - Belts:      Width (max)   Length (avg)      Height (avg)
   Main:   1.57" / 40 mm   154.20 ft / 47.00 m   8.01 ft / 2.44 m
   Ends:   1.57" / 40 mm     32.81 ft / 10.00 m   8.01 ft / 2.44 m
     39.37 ft / 12.00 m Unarmoured ends
     Main Belt covers 105 % of normal length

  - Gun armour:   Face (max)   Other gunhouse (avg)   Barbette/hoist (max)
   Main:   1.57" / 40 mm   0.79" / 20 mm      1.57" / 40 mm
   2nd:   0.50" / 13 mm         -               -
   3rd:   0.50" / 13 mm         -               -

  - Armour deck: 0.79" / 20 mm

Machinery:
   Oil fired boilers, steam turbines,
   Geared drive, 2 shafts, 10 000 shp / 7 460 Kw = 21.97 kts
   Range 5 000nm at 12.00 kts
   Bunker at max displacement = 312 tons

Complement:
   128 - 167

Cost:
   £0.347 million / $1.389 million

Distribution of weights at normal displacement:
   Armament: 55 tons, 3.3 %
   Armour: 204 tons, 12.4 %
      - Belts: 100 tons, 6.1 %
      - Torpedo bulkhead: 0 tons, 0.0 %
      - Armament: 19 tons, 1.2 %
      - Armour Deck: 86 tons, 5.2 %
      - Conning Tower: 0 tons, 0.0 %
   Machinery: 373 tons, 22.7 %
   Hull, fittings & equipment: 694 tons, 42.2 %
   Fuel, ammunition & stores: 243 tons, 14.8 %
   Miscellaneous weights: 75 tons, 4.6 %

Overall survivability and seakeeping ability:
   Survivability (Non-critical penetrating hits needed to sink ship):
     2 056 lbs / 933 Kg = 19.0 x 6.0 " / 152 mm shells or 0.7 torpedoes
   Stability (Unstable if below 1.00): 1.10
   Metacentric height 1.5 ft / 0.4 m
   Roll period: 13.5 seconds
   Steadiness   - As gun platform (Average = 50 %): 63 %
         - Recoil effect (Restricted arc if above 1.00): 0.61
   Seaboat quality  (Average = 1.00): 1.21

Hull form characteristics:
   Hull has rise forward of midbreak
   Block coefficient: 0.500
   Length to Beam Ratio: 5.80 : 1
   'Natural speed' for length: 15.05 kts
   Power going to wave formation at top speed: 68 %
   Trim (Max stability = 0, Max steadiness = 100): 52
   Bow angle (Positive = bow angles forward): 9.00 degrees
   Stern overhang: 0.00 ft / 0.00 m
   Freeboard (% = measuring location as a percentage of overall length):
      - Stem:      20.34 ft / 6.20 m
      - Forecastle (20 %):   18.04 ft / 5.50 m
      - Mid (50 %):      17.39 ft / 5.30 m (13.78 ft / 4.20 m aft of break)
      - Quarterdeck (18 %):   13.78 ft / 4.20 m
      - Stern:      13.78 ft / 4.20 m
      - Average freeboard:   16.00 ft / 4.88 m

Ship space, strength and comments:
   Space   - Hull below water (magazines/engines, low = better): 104.3 %
      - Above water (accommodation/working, high = better): 105.3 %
   Waterplane Area: 5 889 Square feet or 547 Square metres
   Displacement factor (Displacement / loading): 113 %
   Structure weight / hull surface area: 64 lbs/sq ft or 313 Kg/sq metre
   Hull strength (Relative):
      - Cross-sectional: 0.81
      - Longitudinal: 6.68
      - Overall: 1.00
   Hull space for machinery, storage, compartmentation is adequate
   Room for accommodation and workspaces is adequate
   Good seaboat, rides out heavy weather easily

[Jefgte]

The last one

1700T-3T2x6", NUS Gun boat laid down 1921 (Engine 1916)

Displacement:
   1 700 t light; 1 799 t standard; 2 076 t normal; 2 298 t full load

Dimensions: Length overall / water x beam x draught
   229.66 ft / 229.66 ft x 43.31 ft x 14.61 ft (normal load)
   70.00 m / 70.00 m x 13.20 m  x 4.45 m

Armament:
      4 - 6.00" / 152 mm guns (2x2 guns), 108.00lbs / 48.99kg shells, 1921 Model
     Quick firing guns in deck mounts with hoists
     on centreline, evenly spread
      2 - 6.00" / 152 mm guns (1x2 guns), 108.00lbs / 48.99kg shells, 1921 Model
     Quick firing guns in a deck mount with hoist
     on centreline aft
      2 - 1.57" / 40.0 mm guns (1x2 guns), 1.95lbs / 0.88kg shells, 1921 Model
     Anti-aircraft guns in deck mount
     on centreline amidships, all raised guns - superfiring
      2 - 0.50" / 12.7 mm guns in single mounts, 0.06lbs / 0.03kg shells, 1921 Model
     Machine guns in deck mounts
     on side, evenly spread, all raised mounts
   Weight of broadside 652 lbs / 296 kg
   Shells per gun, main battery: 150
   3 - 21.0" / 533.4 mm above water torpedoes

Armour:
   - Belts:      Width (max)   Length (avg)      Height (avg)
   Main:   1.57" / 40 mm   157.48 ft / 48.00 m   8.01 ft / 2.44 m
   Ends:   1.57" / 40 mm     39.37 ft / 12.00 m   8.01 ft / 2.44 m
     32.81 ft / 10.00 m Unarmoured ends
     Main Belt covers 105 % of normal length

   - Gun armour:   Face (max)   Other gunhouse (avg)   Barbette/hoist (max)
   Main:   1.57" / 40 mm   0.79" / 20 mm      1.57" / 40 mm
   2nd:   1.57" / 40 mm   0.79" / 20 mm      1.57" / 40 mm
   3rd:   0.79" / 20 mm         -               -
   4th:   0.50" / 13 mm         -               -

   - Armour deck: 0.79" / 20 mm, Conning tower: 1.57" / 40 mm

Machinery:
   Oil fired boilers, steam turbines,
   Geared drive, 2 shafts, 11 760 shp / 8 773 Kw = 22.00 kts
   Range 7 000nm at 12.00 kts
   Bunker at max displacement = 499 tons

Complement:
   153 - 199

Cost:
   £0.482 million / $1.928 million

Distribution of weights at normal displacement:
   Armament: 82 tons, 3.9 %
   Armour: 235 tons, 11.3 %
      - Belts: 105 tons, 5.1 %
      - Torpedo bulkhead: 0 tons, 0.0 %
      - Armament: 28 tons, 1.4 %
      - Armour Deck: 97 tons, 4.6 %
      - Conning Tower: 6 tons, 0.3 %
   Machinery: 438 tons, 21.1 %
   Hull, fittings & equipment: 845 tons, 40.7 %
   Fuel, ammunition & stores: 376 tons, 18.1 %
   Miscellaneous weights: 100 tons, 4.8 %

Overall survivability and seakeeping ability:
   Survivability (Non-critical penetrating hits needed to sink ship):
     2 393 lbs / 1 085 Kg = 22.2 x 6.0 " / 152 mm shells or 0.8 torpedoes
   Stability (Unstable if below 1.00): 1.10
   Metacentric height 1.7 ft / 0.5 m
   Roll period: 13.9 seconds
   Steadiness   - As gun platform (Average = 50 %): 56 %
         - Recoil effect (Restricted arc if above 1.00): 0.58
   Seaboat quality  (Average = 1.00): 1.01

Hull form characteristics:
   Hull has a flush deck
   Block coefficient: 0.500
   Length to Beam Ratio: 5.30 : 1
   'Natural speed' for length: 15.15 kts
   Power going to wave formation at top speed: 69 %
   Trim (Max stability = 0, Max steadiness = 100): 56
   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:      20.34 ft / 6.20 m
      - Forecastle (20 %):   18.37 ft / 5.60 m
      - Mid (50 %):      14.44 ft / 4.40 m
      - Quarterdeck (18 %):   14.44 ft / 4.40 m
      - Stern:      14.44 ft / 4.40 m
      - Average freeboard:   15.97 ft / 4.87 m

Ship space, strength and comments:
   Space   - Hull below water (magazines/engines, low = better): 104.3 %
      - Above water (accommodation/working, high = better): 100.6 %
   Waterplane Area: 6 627 Square feet or 616 Square metres
   Displacement factor (Displacement / loading): 111 %
   Structure weight / hull surface area: 74 lbs/sq ft or 364 Kg/sq metre
   Hull strength (Relative):
      - Cross-sectional: 0.81
      - Longitudinal: 6.02
      - Overall: 1.00
   Hull space for machinery, storage, compartmentation is adequate
   Room for accommodation and workspaces is adequate

25t - fire control
25t - marconi
20t - minen
9t - torpedoes
41t - reserve

[Guinness]

I think all of these, but especially the 6x6" gunned designs are very likely very cramped for the crew. There's not a lot of room for superstructure, etc. It may be a case of NEDS. Each 6" gun is going to be between 7.5 and 8 meters long, then there is working circle to consider, etc. Figure at least 9.5 meters total needed for each. 9.5*6 = 57 meters just for main gun mounts on the 6 gun designs.

[Jefgte]

Drawing in progress   ;)

So,actualy for the 1700t, I have:
6" mounts with 3m x 3.6m for the mount & 7.4m oa with the gun ( 9m free deck space for the centerline mount) Working circle is 120° each side

Working circle is 280° for fore & aft mounts.

90° working circle for the TT between centerline & aft mounts - (turbines are under TT).

( I use too the HNSA guns-turrets catalogue)
http://hnsa.org/doc/guncat/cat-0468.htm


Jef

[P3D]

I don't think ice should be a thing to worry for NUS. Even Patagonia is ice-free year-round.

I don't think squeezing the design into 70m worth it, the artificial length restriction it compromise sea-keeping regardless of what SS2 is telling. The deep draft seriously limits its usefulness in littoral, and make the ship vulnerable to torpedoes.

Then, the ship is just overcrowded with the three gun mounts. Single mounts should be better for small ships, better readiness and ROF.

[Sachmle]

Realistically you're looking at a USS Sacramento type ship. Of course there was the OTL Paraguay class GBs. They're a little ahead of our time, so I'd expect a higher weight or slower speed, but should be 'shrinkable' to 70m (only 70.56m to begin with).

[Jefgte]

I agree, the hull is over loaded   ::)

Here is a lighter type with better seaboat quality inspired by "OTL Paraguay" design.

1000t, NUS Coastal gunboat laid down 1921 (Engine 1916)

Displacement:
   1 000 t light; 1 074 t standard; 1 279 t normal; 1 442 t full load

Dimensions: Length overall / water x beam x draught
   229.66 ft / 229.66 ft x 33.46 ft x 11.20 ft (normal load)
   70.00 m / 70.00 m x 10.20 m  x 3.41 m

Armament:
     4 - 4.72" / 120 mm guns (2x2 guns), 52.72lbs / 23.92kg shells, 1921 Model
     Quick firing guns in deck mounts with hoists
     on centreline, evenly spread
     2 - 4.72" / 120 mm guns (1x2 guns), 52.72lbs / 23.92kg shells, 1921 Model
     Quick firing guns in a deck mount with hoist
     on centreline amidships
     2 - 1.57" / 40.0 mm guns (1x2 guns), 1.95lbs / 0.89kg shells, 1921 Model
     Anti-aircraft guns in deck mount
     on centreline aft, all raised guns - superfiring
     2 - 0.50" / 12.7 mm guns in single mounts, 0.06lbs / 0.03kg shells, 1921 Model
     Machine guns in deck mounts
     on side, evenly spread, all raised mounts
   Weight of broadside 320 lbs / 145 kg
   Shells per gun, main battery: 250
   3 - 21.0" / 533.4 mm above water torpedoes

Armour:
  - Gun armour:   Face (max)   Other gunhouse (avg)   Barbette/hoist (max)
   Main:   1.57" / 40 mm   0.79" / 20 mm      1.57" / 40 mm
   2nd:   1.57" / 40 mm   0.79" / 20 mm      1.57" / 40 mm
   3rd:   0.79" / 20 mm         -               -
   4th:   0.50" / 13 mm         -               -

Machinery:
   Oil fired boilers, steam turbines,
   Geared drive, 2 shafts, 8 300 shp / 6 192 Kw = 21.97 kts
   Range 7 000nm at 12.00 kts
   Bunker at max displacement = 369 tons

Complement:
   106 - 138

Cost:
   £0.285 million / $1.140 million

Distribution of weights at normal displacement:
   Armament: 40 tons, 3.1 %
   Armour: 21 tons, 1.7 %
      - Belts: 0 tons, 0.0 %
      - Torpedo bulkhead: 0 tons, 0.0 %
      - Armament: 21 tons, 1.7 %
      - Armour Deck: 0 tons, 0.0 %
      - Conning Tower: 0 tons, 0.0 %
   Machinery: 309 tons, 24.2 %
   Hull, fittings & equipment: 547 tons, 42.8 %
   Fuel, ammunition & stores: 278 tons, 21.8 %
   Miscellaneous weights: 83 tons, 6.5 %

Overall survivability and seakeeping ability:
   Survivability (Non-critical penetrating hits needed to sink ship):
     1 365 lbs / 619 Kg = 25.9 x 4.7 " / 120 mm shells or 0.6 torpedoes
   Stability (Unstable if below 1.00): 1.10
   Metacentric height 1.2 ft / 0.4 m
   Roll period: 13.1 seconds
   Steadiness   - As gun platform (Average = 50 %): 65 %
         - 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: 0.520
   Length to Beam Ratio: 6.86 : 1
   'Natural speed' for length: 15.15 kts
   Power going to wave formation at top speed: 66 %
   Trim (Max stability = 0, Max steadiness = 100): 54
   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:      18.37 ft / 5.60 m
      - Forecastle (22 %):   15.09 ft / 4.60 m
      - Mid (50 %):      12.80 ft / 3.90 m
      - Quarterdeck (19 %):   12.47 ft / 3.80 m
      - Stern:      12.47 ft / 3.80 m
      - Average freeboard:   13.80 ft / 4.21 m

Ship space, strength and comments:
   Space   - Hull below water (magazines/engines, low = better): 111.5 %
      - Above water (accommodation/working, high = better): 90.8 %
   Waterplane Area: 5 216 Square feet or 485 Square metres
   Displacement factor (Displacement / loading): 123 %
   Structure weight / hull surface area: 57 lbs/sq ft or 279 Kg/sq metre
   Hull strength (Relative):
      - Cross-sectional: 0.83
      - Longitudinal: 4.98
      - 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

---------------
For the moment, I prefer the first one - 1400t with 2M2x6"


Jef  ;)

[P3D]

Why not use one of the interwar sloop designs as a starting point - Black Swan, Erie, Bougainville?
3-6x4-6"+AA guns, <2000t, 20kts speed.

I'd have single mounts for simplicity, if this ship have to engage real cruisers, it's toast anyways.

[Jefgte]

...if this ship have to engage real cruisers...

He'll derusted!
-----------------
Originaly , I reuse armament of Amazonas class cruisers
4x6"+8x90 +4x2TTx457
3 possibilities:
1 ship with 4x6" +8x90
2 ships with 2x6"+4x90 or
4 ships with 1x6" +2x90

[Sachmle]

I'd go 2 w/ 2x6, 4x90.

[Laertes]

What's she built to engage? A 6" armament seems pretty serious given her size, but only having two of them makes it difficult to fight at the higher ranges of a 6" gun.

[Jefgte]

6" guns to be relatively serious for a Gunboat.
Job of this class could be : station ship & South American patrols in heavy sea.


Jef

[Jefgte]

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[Jefgte]

Modif. to carry 30 minen or 30t of material or 30 men in a closed space.



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[Sachmle]

Jean-Francois, you are the King of Multipurpose designs. Very nice.