AHC: 27000 tonne illustrious class carrier

While still in denial all my sources do seem to place the Implacables at 23000 tons (although my Antony Preston has done a bunk)

I mean how? They were longer, wider, faster, they had 7 additional Deisel generators in water proof compartments and all sorts of extras including a 4th shaft and turbine etc not to mention the extra hanger and nearly twice the storage for expendables spares and avgas.

Did they have less armour?

I am wondering if the 23000 tons was what they were originally going to weigh when laid down in 1939!
Connway’s says they weren’t actually wider or deeper.
 
Best displacements I have is from Friedman.

Illustrious, 23,207t standard
Indomitable, 23,030 standard
Implacable, 23,460 standard

While the Implacable machinery (4 shafts) was 672t heavier than Illustrious, she saved 1,300 on armour - basically the 1.5" thick sides. That's why the designs come out similar.
Remember RN carriers gained around 10% weight over the war due to additions, and more avgas carried means a higher deep load displacement (but not as much effect on standard displacement).
Implacable had a wider flight deck, but about the same dimensions at the waterline.

The 'new' Implacable design they looked at would have been between 25,000t and 27,000t (depending on hangars and armour), and wider beam (and flight deck). She might also have been a little slower than Implacable (same machinery), but would still have done around 31kt.
 
While still in denial all my sources do seem to place the Implacables at 23000 tons (although my Antony Preston has done a bunk)

I mean how? They were longer, wider, faster, they had 7 additional Deisel generators in water proof compartments and all sorts of extras including a 4th shaft and turbine etc not to mention the extra hanger and nearly twice the storage for expendables spares and avgas.

Did they have less armour?

I am wondering if the 23000 tons was what they were originally going to weigh when laid down in 1939!

Went down to 1 1/2" side armour. That saves nearly 1300t.
 
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Best displacements I have is from Friedman.

Illustrious, 23,207t standard
Indomitable, 23,030 standard
Implacable, 23,460 standard

While the Implacable machinery (4 shafts) was 672t heavier than Illustrious, she saved 1,300 on armour - basically the 1.5" thick sides. That's why the designs come out similar.
Remember RN carriers gained around 10% weight over the war due to additions, and more avgas carried means a higher deep load displacement (but not as much effect on standard displacement).
Implacable had a wider flight deck, but about the same dimensions at the waterline.

I still think a longer Illustrious is the way to go maybe with the Implacable 4 shaft plant. The amoured box carriers needed a longer wider deck with longer wider hangar not a cramped poky lower hangar which seemed to do little for strike numbers.

Is there anyone who uses Springsharp who can do a stretched 4 shaft Illustrious 800 ft x 100 foot on the waterline, minimum 16 foot hangar headroom preferably 17' 6", 2 x full size lifts 45 x 45 ft, no round downs on the flight deck and Avgas storage around 120,000 imp gallons. I have never used Springsharp and the only time I tried to download it my security had a fit.
 
Springsharp doesn't have any real rules for Carriers.
There is roughly accepted guide.
By Rick Robinson

"Carriers.

Spring Style is designed for ships armed
primarily with guns, but carriers become important from the end of World War I on. Here is a method for simming carriers:

Design the ship as you normally would. Put in as much
miscellaneous weight" as you can - that will usually
determine how big an airgroup your CV can carry. Now,
get out your pocket calculator. You'll make two pretty simple calculations, each of which gives a possible airgroup limit.

1) Take the square root of miscellaneous weight; e.g., if miscellaneous weight is 10,000 tons, the eight-based limit for your carrier is 100 aircraft. (In addition, allow at least 25 tons per aircraft, i.e., if miscellaneous weight is just 100 tons, your ship can carry 4 planes, not 10.)

2) Multiply length x beam (both waterline) and divide by 750; e.g., if your CV is 900 ft x 100 ft, the space limit is 120 aircraft.

For the metric gang, divide by 70 instead; if your CV is 280 metres x 30 metres, the size limit is also 120 aircraft.

Use waterline dimensions (if available), NOT flight deck dimensions; they can vary a lot more, and we want a consistant rule.

Your carrier's airgroup is whichever number is LOWER.
So in the example above, your CV has an airgroup of 100
aircraft. (That is for WW II or earlier planes. For postwar CVs with jets, I'd estimate about 2/3 of the airgroup calculated by this method.) Usually, the weight rule gives a lower number of planes and thus sets the limit; the size limit will usually apply to CVEs converted from merchant ships with a great deal of miscellaneous weight.

Use a word processor, etc., to adjust your ship report. I list the air group above guns, since it is obviously a carrier's main armament!
Conversions: If you convert a battlecruiser, etc., to a CV, follow the same basic procedure. Start with the original ship, modify main guns, armor, etc., put in miscellaneous weight (i.e., the flight deck), and there is your carrier.
(There is a bit of argument as to how you work in an Armoured Flight Deck, but if you come up with a design that has over 25% of displacement as armour that should cover it?)
I came up with this ...
HMS Illustrious (2 Hangar Deck), Royal Navy Aircraft Carrier laid down 1937

Displacement:
25,509 t light; 26,412 t standard; 28,700 t normal; 30,531 t full load

Dimensions: Length (overall / waterline) x beam x draught (normal/deep)
(801.53 ft / 744.00 ft) x 96.00 ft x (24.00 / 25.21 ft)
(244.31 m / 226.77 m) x 29.26 m x (7.32 / 7.68 m)

Armament:
16 - 4.50" / 114 mm 45.0 cal guns - 55.00lbs / 24.95kg shells, 400 per gun
Anti-air guns in deck and hoist mounts, 1937 Model
8 x Twin mounts on sides, evenly spread

48 - 1.57" / 40.0 mm 39.0 cal guns - 2.00lbs / 0.91kg shells, 2,500 per gun
Anti-air guns in deck mounts, 1937 Model
6 x 2 row octuple mounts on sides, evenly spread

Weight of broadside 976 lbs / 443 kg

Armour:
- Belts: Width (max) Length (avg) Height (avg)

Main: 4.50" / 114 mm 461.28 ft / 140.60 m 11.76 ft / 3.58 m
Ends: 1.00" / 25 mm 282.70 ft / 86.17 m 11.76 ft / 3.58 m
Upper: 4.50" / 114 mm 461.28 ft / 140.60 m 8.00 ft / 2.44 m

Main Belt covers 95 % of normal length

- Torpedo Bulkhead - Additional damage containing bulkheads:
2.00" / 51 mm 461.28 ft / 140.60 m 22.49 ft / 6.85 m

Beam between torpedo bulkheads 76.00 ft / 23.16 m

- Gun armour: Face (max) Other gunhouse (avg) Barbette/hoist (max)
Main: 0.50" / 13 mm 0.50" / 13 mm 0.50" / 13 mm
2nd: 0.50" / 13 mm - -

- Armoured deck - multiple decks:
For and Aft decks: 6.00" / 152 mm
Forecastle: 1.50" / 38 mm Quarter deck: 1.50" / 38 mm

Machinery:
Oil fired boilers, steam turbines,
Geared drive, 3 shafts, 130,678 shp / 97,486 Kw = 31.00 kts
Range 11,000nm at 14.00 kts
Bunker at max displacement = 4,120 tons

Complement:
1,102 - 1,433

Cost:
£8.047 million / $32.186 million

Distribution of weights at normal displacement:

Armament: 180 tons, 0.6 %
- Guns: 180 tons, 0.6 %
Armour: 7,642 tons, 26.6 %
- Belts: 1,885 tons, 6.6 %
- Torpedo bulkhead: 768 tons, 2.7 %
- Armament: 28 tons, 0.1 %
- Armour Deck: 4,962 tons, 17.3 %

Machinery: 3,622 tons, 12.6 %
Hull, fittings & equipment: 8,879 tons, 30.9 %
Fuel, ammunition & stores: 3,192 tons, 11.1 %
Miscellaneous weights: 5,185 tons, 18.1 %
- Hull below water: 1 tons
- Hull above water: 5,184 tons

Overall survivability and seakeeping ability:
Survivability (Non-critical penetrating hits needed to sink ship):
55,996 lbs / 25,399 Kg = 1,229.0 x 4.5 " / 114 mm shells or 8.7 torpedoes

Stability (Unstable if below 1.00): 1.49
Metacentric height 9.3 ft / 2.8 m
Roll period: 13.2 seconds
Steadiness - As gun platform (Average = 50 %): 46 %
- Recoil effect (Restricted arc if above 1.00): 0.03
Seaboat quality (Average = 1.00): 1.02

Hull form characteristics:
Hull has a flush deck,
a normal bow and small transom stern

Block coefficient (normal/deep): 0.586 / 0.593
Length to Beam Ratio: 7.75 : 1
'Natural speed' for length: 29.45 kts
Power going to wave formation at top speed: 54 %
Trim (Max stability = 0, Max steadiness = 100): 42
Bow angle (Positive = bow angles forward): 35.00 degrees
Stern overhang: 35.00 ft / 10.67 m
Freeboard (% = length of deck as a percentage of waterline length):
Fore end, Aft end
- Forecastle: 19.00 %, 32.18 ft / 9.81 m, 20.48 ft / 6.24 m
- Forward deck: 44.70 %, 20.48 ft / 6.24 m, 20.48 ft / 6.24 m
- Aft deck: 17.30 %, 20.48 ft / 6.24 m, 20.48 ft / 6.24 m
- Quarter deck: 19.00 %, 20.48 ft / 6.24 m, 20.48 ft / 6.24 m
- Average freeboard: 21.37 ft / 6.51 m

Ship space, strength and comments:
Space - Hull below water (magazines/engines, low = better): 82.1 %
- Above water (accommodation/working, high = better): 187.1 %
Waterplane Area: 52,855 Square feet or 4,910 Square metres
Displacement factor (Displacement / loading): 138 %
Structure weight / hull surface area: 128 lbs/sq ft or 625 Kg/sq metre
Hull strength (Relative):
- Cross-sectional: 1.09
- Longitudinal: 0.97
- Overall: 1.00

Excellent machinery, storage, compartmentation space
Excellent accommodation and workspace room

(It has an Aircraft Capacity of 72)
 
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Best displacements I have is from Friedman.

Illustrious, 23,207t standard
Indomitable, 23,030 standard
Implacable, 23,460 standard

While the Implacable machinery (4 shafts) was 672t heavier than Illustrious, she saved 1,300 on armour - basically the 1.5" thick sides. That's why the designs come out similar.
Remember RN carriers gained around 10% weight over the war due to additions, and more avgas carried means a higher deep load displacement (but not as much effect on standard displacement).
Implacable had a wider flight deck, but about the same dimensions at the waterline.

The 'new' Implacable design they looked at would have been between 25,000t and 27,000t (depending on hangars and armour), and wider beam (and flight deck). She might also have been a little slower than Implacable (same machinery), but would still have done around 31kt.

Went down to 1 1/2" side armour. That saves nearly 1000t.

Thanks - not sure why I got it into my head that they were much heavier - but - its not the first time I have been wrong and not likely to be the last

Does make you think how much bigger/better they might have been at 27,000 tons Standard!

My own ideal is for a double Ark Royal style hanger (same dimensions as OTL Ark Royal - see here) - not use the single level lifts as used in the OTL Ark Royal (too complicated not sure what they were thinking?) and have a single lift at each end of the main hanger

My guess is that this should allow for 60+ Swordfish sized aircraft in the hangers with room to move stuff about and carry out maintenance etc and does not include deck parking or overhanging outriggers
 
Thanks - not sure why I got it into my head that they were much heavier - but - its not the first time I have been wrong and not likely to be the last

Does make you think how much bigger/better they might have been at 27,000 tons Standard!

My own ideal is for a double Ark Royal style hanger (same dimensions as OTL Ark Royal - see here) - not use the single level lifts as used in the OTL Ark Royal (too complicated not sure what they were thinking?) and have a single lift at each end of the main hanger

My guess is that this should allow for 60+ Swordfish sized aircraft in the hangers with room to move stuff about and carry out maintenance etc and does not include deck parking or overhanging outriggers

That seems quite doable - I'd guess she could take 70-odd aircraft, the later aitrcraft folded more than expected. There would be a full double hangar, and she could be about 50 foot longer than Ark. I think I'd go for a double-level lift at either end with lift to the upper hangar forward of the crash barrier
 
That seems quite doable - I'd guess she could take 70-odd aircraft, the later aircraft folded more than expected. There would be a full double hangar, and she could be about 50 foot longer than Ark. I think I'd go for a double-level lift at either end with lift to the upper hangar forward of the crash barrier

That would serve - so 2 full length hangers each of 568 x 60 x 16 feet - with fore and aft lifts at each end serving both levels - that puts my conservative hanger capacity estimate as 72 x Swordfish sized aircraft
 

Anderman

Donor
That would serve - so 2 full length hangers each of 568 x 60 x 16 feet - with fore and aft lifts at each end serving both levels - that puts my conservative hanger capacity estimate as 72 x Swordfish sized aircraft

I always wonder why Ark Royal was the only RN carrier with such a long hangar. A 568x60 hangar and you have the size of Indomitable in a single hangar.
 
I always wonder why Ark Royal was the only RN carrier with such a long hangar. A 568x60 hangar and you have the size of Indomitable in a single hangar.
I think longer ships have higher hull stresses, it's more efficient ship design to be beamier than to be long and narrow (although there are speed implications), it also allows better torpedo defences and fitted British harbours more easily. The US tended to produce longer carriers for operational reasons (a permanent deck park taking up half the flight deck while having the remaining deck length to fly off or land on planes).

There may also be an effect of an armoured flight deck, but I haven't thought through the implications, except that they implied very careful calculation of stresses since the armour plate carried the stress rather than being added on to the hull as in normal ships
 
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