WesWorld

The following design is based on the Brazilian Ceara which was equiped with a central circular caisson dock 216 feet long that can dock subs up to 198 feet long and 23.25 feet in beam between the double hulls and two slavage cranes at the stern capable of lifting 400 pounds of dead weight. She is also equiped with two 150 kw charging dynamo's, air compressors, workshops pumps to empty the dock in roughly 2 hours and carries spare battery's, torpedo's and stores for 6 submarines.
My design will closly resemble this ship seeing as my knowledge on exactly how she is laid out is limited at this point by what janes say's about her.

Any area's of improvement?

Efficax, Atlantis Sub repair,depot,docking and salvage laid down 1923

Displacement:
6,588 t light; 6,736 t standard; 6,909 t normal; 7,019 t full load
Loading submergence 409 tons/feet

Dimensions:
325.00 ft x 62.00 ft x 20.00 ft (normal load)
99.06 m x 18.90 m x 6.10 m

Armament:
2 - 4.00" / 102 mm guns
4 - 3.00" / 76 mm guns
6 - 1.00" / 25 mm guns
Weight of broadside 121 lbs / 55 kg

Machinery:
Diesel Internal combustion motors,
Geared drive, 2 shafts, 3,666 shp / 2,735 Kw = 14.00 kts
Range 4,000nm at 10.00 kts

Complement:
378 - 492

Cost:
£0.758 million / $3.031 million

Distribution of weights at normal displacement:
Armament: 15 tons, 0.2 %
Machinery: 123 tons, 1.8 %
Hull, fittings & equipment: 3,450 tons, 49.9 %
Fuel, ammunition & stores: 321 tons, 4.6 %
Miscellaneous weights: 3,000 tons, 43.4 %

Metacentric height 2.6

Remarks:
Hull space for machinery, storage & compartmentation is excellent
Room for accommodation & workspaces is adequate
Excellent seaboat, comfortable and able to fight her guns in the heaviest weather

Estimated overall survivability and seakeeping ability:
Relative margin of stability: 1.02
Shellfire needed to sink: 11,484 lbs / 5,209 Kg = 358.9 x 4.0 " / 102 mm shells
(Approx weight of penetrating shell hits needed to sink ship excluding critical hits)
Torpedoes needed to sink: 2.6
(Approx number of typical torpedo hits needed to sink ship)
Relative steadiness as gun platform: 62 %
(Average = 50 %)
Relative rocking effect from firing to beam: 0.01
Relative quality as seaboat: 1.87

Hull form characteristics:
Block coefficient: 0.600
Sharpness coefficient: 0.45
Hull speed coefficient 'M': 5.22
'Natural speed' for length: 18.03 kts
Power going to wave formation at top speed: 40 %
Trim: 33
(Maximise stabilty/flotation = 0, Maximise steadiness/seakeeping = 100)

Estimated hull characteristics & strength:
Underwater volume absorbed by magazines and engineering spaces: 55.6 %
Relative accommodation and working space: 101.0 %
(Average = 100%)
Displacement factor: 205 %
(Displacement relative to loading factors)
Relative cross-sectional hull strength: 2.12
(Structure weight / hull surface area: 166 lbs / square foot or 811 Kg / square metre)
Relative longitudinal hull strength: 4.63
(for 14.00 ft / 4.27 m average freeboard, freeboard adjustment -0.06 ft)
Relative composite hull strength: 2.29

Heres a slightly modified design.


Efficax, Atlantis Sub repair,depot,docking and salvage laid down 1923

Displacement:
6,449 t light; 6,598 t standard; 6,953 t normal; 7,209 t full load
Loading submergence 422 tons/feet

Dimensions:
325.00 ft x 64.00 ft x 19.50 ft (normal load)
99.06 m x 19.51 m x 5.94 m

Armament:
2 - 4.00" / 102 mm guns
4 - 3.00" / 76 mm guns
6 - 1.00" / 25 mm guns
Weight of broadside 121 lbs / 55 kg

Machinery:
Diesel Internal combustion motors,
Geared drive, 2 shafts, 3,699 shp / 2,759 Kw = 14.00 kts
Range 3,500nm at 14.00 kts

Complement:
380 - 494

Cost:
£0.744 million / $2.976 million

Distribution of weights at normal displacement:
Armament: 15 tons, 0.2 %
Machinery: 124 tons, 1.8 %
Hull, fittings & equipment: 3,310 tons, 47.6 %
Fuel, ammunition & stores: 504 tons, 7.2 %
Miscellaneous weights: 3,000 tons, 43.1 %

Metacentric height 2.7

Remarks:
Hull space for machinery, storage & compartmentation is excellent
Room for accommodation & workspaces is adequate
Ship has slow, easy roll, a good, steady gun platform
Excellent seaboat, comfortable and able to fight her guns in the heaviest weather

Estimated overall survivability and seakeeping ability:
Relative margin of stability: 1.03
Shellfire needed to sink: 11,812 lbs / 5,358 Kg = 369.1 x 4.0 " / 102 mm shells
(Approx weight of penetrating shell hits needed to sink ship excluding critical hits)
Torpedoes needed to sink: 2.7
(Approx number of typical torpedo hits needed to sink ship)
Relative steadiness as gun platform: 71 %
(Average = 50 %)
Relative rocking effect from firing to beam: 0.01
Relative quality as seaboat: 1.91

Hull form characteristics:
Block coefficient: 0.600
Sharpness coefficient: 0.45
Hull speed coefficient 'M': 5.21
'Natural speed' for length: 18.03 kts
Power going to wave formation at top speed: 40 %
Trim: 37
(Maximise stabilty/flotation = 0, Maximise steadiness/seakeeping = 100)

Estimated hull characteristics & strength:
Underwater volume absorbed by magazines and engineering spaces: 55.3 %
Relative accommodation and working space: 103.7 %
(Average = 100%)
Displacement factor: 206 %
(Displacement relative to loading factors)
Relative cross-sectional hull strength: 1.99
(Structure weight / hull surface area: 157 lbs / square foot or 768 Kg / square metre)
Relative longitudinal hull strength: 4.29
(for 14.00 ft / 4.27 m average freeboard, freeboard adjustment -0.08 ft)
Relative composite hull strength: 2.15

Why would such a vessel be armed? What is the armamend good for?

Otherwise a useful design...

HoOmAn

Well as I said she was based on another design, which is similarily armed, but I do see your point of her being armed, at least in peace time.

Even at wartimes I can hardly see her armed that way. See, for those guns you need ammonition to be stored in magazins, you need lots of crew to man and handle all the stuff. For those men you need a place to sleep, eat and bathrooms etc.

Together I think this would mean too much weight and room is wasted on a vessel with a very special task. The space is needed to fulfil her original mission, I assume.

Of course some light AA machine guns can be easily added and manned by her original crew but for 10,2cm and 7,6cm guns you need more than that.

Just my opinion of course...

HoOmAn

The Brazilian Ceara was armed with 4x4" janers saying two of the 4" were smaller? (I assume barrel length), the Efficax would be armed with a similar number of mounts with the 3" in twin mounts.
The Ceara looks very bulky forward and reminds me of the British aviation training ship Argus with a bulky superstructure forward. I may remove the 4" guns anyway because as you say it will still eat up much space.