Old DD conversion

[Jefgte]

I test a SS for the conversion of the 15 yo Caravani class to a troop transport

I remove 2/3 of the 120mm guns, remove all TT, remove too 3 of the 4 boilers.
Add bulges to maintain stability.

Here is the original SS

750T, Peru DD laid down 1905 (Engine 1906)

Displacement:
   750 t light; 782 t standard; 909 t normal; 1 010 t full load

Dimensions: Length overall / water x beam x draught
   288.71 ft / 288.71 ft x 29.53 ft x 9.24 ft (normal load)
   88.00 m / 88.00 m x 9.00 m  x 2.82 m

Armament:
     2 - 4.72" / 120 mm guns in single mounts, 52.72lbs / 23.91kg shells, 1905 Model
     Breech loading guns in deck mounts
     on centreline, evenly spread
     1 - 4.72" / 120 mm guns in single mounts, 52.72lbs / 23.91kg shells, 1905 Model
     Breech loading gun in deck mounts
     on centreline, all amidships, 1 raised gun
     2 - 3.00" / 76.2 mm guns in single mounts, 13.50lbs / 6.12kg shells, 1905 Model
     Quick firing 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, 1905 Model
     Machine guns in deck mounts
     on side, evenly spread
   Weight of broadside 185 lbs / 84 kg
   Shells per gun, main battery: 120
   4 - 21.0" / 533.4 mm above water torpedoes

Armour:
  - 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,
   Direct drive, 2 shafts, 8 773 shp / 6 545 Kw = 24.79 kts
   Range 5 000nm at 10.00 kts
   Bunker at max displacement = 229 tons

Complement:
   82 - 107

Cost:
   £0.102 million / $0.406 million

Distribution of weights at normal displacement:
   Armament: 23 tons, 2.5 %
   Armour: 9 tons, 1.0 %
      - Belts: 0 tons, 0.0 %
      - Torpedo bulkhead: 0 tons, 0.0 %
      - Armament: 9 tons, 1.0 %
      - Armour Deck: 0 tons, 0.0 %
      - Conning Tower: 0 tons, 0.0 %
   Machinery: 399 tons, 43.9 %
   Hull, fittings & equipment: 249 tons, 27.4 %
   Fuel, ammunition & stores: 159 tons, 17.5 %
   Miscellaneous weights: 70 tons, 7.7 %

Overall survivability and seakeeping ability:
   Survivability (Non-critical penetrating hits needed to sink ship):
     307 lbs / 139 Kg = 5.8 x 4.7 " / 120 mm shells or 0.3 torpedoes
   Stability (Unstable if below 1.00): 1.36
   Metacentric height 1.4 ft / 0.4 m
   Roll period: 10.5 seconds
   Steadiness   - As gun platform (Average = 50 %): 95 %
         - Recoil effect (Restricted arc if above 1.00): 0.33
   Seaboat quality  (Average = 1.00): 1.69

Hull form characteristics:
   Hull has a flush deck
   Block coefficient: 0.404
   Length to Beam Ratio: 9.78 : 1
   'Natural speed' for length: 16.99 kts
   Power going to wave formation at top speed: 56 %
   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:      17.72 ft / 5.40 m
      - Forecastle (18 %):   13.45 ft / 4.10 m
      - Mid (50 %):      11.48 ft / 3.50 m
      - Quarterdeck (18 %):   10.83 ft / 3.30 m
      - Stern:      10.83 ft / 3.30 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): 169.5 %
      - Above water (accommodation/working, high = better): 97.7 %
   Waterplane Area: 5 260 Square feet or 489 Square metres
   Displacement factor (Displacement / loading): 65 %
   Structure weight / hull surface area: 25 lbs/sq ft or 123 Kg/sq metre
   Hull strength (Relative):
      - Cross-sectional: 0.50
      - Longitudinal: 1.64
      - Overall: 0.56
   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
   Excellent seaboat, comfortable, can fire her guns in the heaviest weather

Caravani-1905 - El Alto-Sucre-1906 - Cochabamba-1907
Potosi-1908 - Oruro-Montero-1909 - Trinitad-1910
- 25T: fire control
- 25T:  Marconi
- 13T:  Weight reserve
- 7T: 20 Depth Charges or 6 Mines
---------------------------------------------------------
The conversion SS
870T, Peru 1920 troop transport laid down 1905 (Engine 1906)

Displacement:
   869 t light; 894 t standard; 1 030 t normal; 1 139 t full load

Dimensions: Length overall / water x beam x draught
   288.71 ft / 288.71 ft x 29.53 ft (Bulges 33.46 ft) x 9.24 ft (normal load)
   88.00 m / 88.00 m x 9.00 m (Bulges 10.20 m)  x 2.82 m

Armament:
     1 - 4.72" / 120 mm guns in single mounts, 52.72lbs / 23.91kg shells, 1905 Model
     Breech loading gun in deck mount
     on centreline forward
     2 - 1.57" / 40.0 mm guns (1x2 guns), 1.95lbs / 0.88kg shells, 1905 Model
     Breech loading guns in deck mount
     on centreline aft
     2 - 0.50" / 12.7 mm guns in single mounts, 0.06lbs / 0.03kg shells, 1905 Model
     Quick firing guns in deck mounts
     on side, evenly spread
   Weight of broadside 57 lbs / 26 kg
   Shells per gun, main battery: 120

Armour:
  - Gun armour:   Face (max)   Other gunhouse (avg)   Barbette/hoist (max)
   Main:   0.79" / 20 mm         -               -

Machinery:
   Oil fired boilers, steam turbines,
   Direct drive, 2 shafts, 2 193 shp / 1 636 Kw = 16.90 kts
   Range 5 000nm at 10.00 kts
   Bunker at max displacement = 245 tons

Complement:
   90 - 118

Cost:
   £0.056 million / $0.225 million

Distribution of weights at normal displacement:
   Armament: 7 tons, 0.7 %
   Armour: 2 tons, 0.2 %
      - Belts: 0 tons, 0.0 %
      - Torpedo bulkhead: 0 tons, 0.0 %
      - Armament: 2 tons, 0.2 %
      - Armour Deck: 0 tons, 0.0 %
      - Conning Tower: 0 tons, 0.0 %
   Machinery: 142 tons, 13.8 %
   Hull, fittings & equipment: 420 tons, 40.8 %
   Fuel, ammunition & stores: 161 tons, 15.6 %
   Miscellaneous weights: 298 tons, 28.9 %

Overall survivability and seakeeping ability:
   Survivability (Non-critical penetrating hits needed to sink ship):
     1 684 lbs / 764 Kg = 31.9 x 4.7 " / 120 mm shells or 0.8 torpedoes
   Stability (Unstable if below 1.00): 1.00
   Metacentric height 0.8 ft / 0.2 m
   Roll period: 15.7 seconds
   Steadiness   - As gun platform (Average = 50 %): 100 %
         - Recoil effect (Restricted arc if above 1.00): 0.08
   Seaboat quality  (Average = 1.00): 2.00

Hull form characteristics:
   Hull has a flush deck
   Block coefficient: 0.404
   Length to Beam Ratio: 8.63 : 1
   'Natural speed' for length: 16.99 kts
   Power going to wave formation at top speed: 38 %
   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:      17.72 ft / 5.40 m
      - Forecastle (18 %):   13.45 ft / 4.10 m
      - Mid (50 %):      11.48 ft / 3.50 m
      - Quarterdeck (18 %):   10.83 ft / 3.30 m
      - Stern:      10.83 ft / 3.30 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): 82.1 %
      - Above water (accommodation/working, high = better): 131.5 %
   Waterplane Area: 5 260 Square feet or 489 Square metres
   Displacement factor (Displacement / loading): 161 %
   Structure weight / hull surface area: 42 lbs/sq ft or 204 Kg/sq metre
   Hull strength (Relative):
      - Cross-sectional: 0.90
      - Longitudinal: 2.47
      - Overall: 1.00
   Hull space for machinery, storage, compartmentation is excellent
   Room for accommodation and workspaces is excellent
   Ship has slow, easy roll, a good, steady gun platform
   Excellent seaboat, comfortable, can fire her guns in the heaviest weather

- Bulges added to increase stability
- 3 boilers remove ;  from 8773shp to 2193shp - from 399t to 142t

Weigh economised affected to material & troop transport


Any thoughts on this?

[Guinness]

Bulges on a DD? Ay caramba! You do get it to 1.0 overall strength, so I guess that's ok.

Bulges would change the B/C of the hull, strictly speaking. I'm interested in opinions from others about how that relates to simming a modified ship in SS. My guess is the conclusion may be that SS's BC is for the non-bulged part of the hull maybe?

Otherwise, I'm not sure I'd want to deploy a ship with only one boiler. Whenever that boiler has to be inactivated to cleaning and maintenance, this ship would have no steam for ship service, much less going anywhere.

[Sachmle]

The boiler part I agree with, I'd keep 2. As to the BC/Bulge thing, I think the BC of the bulged version should be increased to represent the 'fatter' hullform due to the bulges. As to bulges on DDs, I believe the RN bulged some V&W class DDs to use them as fast troop craft similar to this idea. They used the bulge to store extra fuel oil.

[P3D]

You remove 3/4rd of the machinery, not only the boilers. The turbine weights are not negligible.

You are already spending over 200t of materials on the ship ( 170t for the hull strengthenings plus reconstruction). A newbuilt 800-1000t merchant standard transport would be cheaper, more reliable and have higher capacity.

[Jefgte]

A newbuilt 800-1000t merchant standard transport would be cheaper, more reliable and have higher capacity.

I agree totaly. This concept is just a test.


Jef