WesWorld

Folks:

I'm contemplating the merits of retaining some Colombo class cruisers in service into the early '40s. The class was laid down between 1917 and 1919, and received a mid-life refit ten years afterward.

What I'm considering is rebuilding three into anti-aircraft cruisers, along the lines of historical British rebuilds of similar cruisers in WW2. They would be paired off with a battleship, having received the following modifications:

-The main armament and heavy AA would be replaced by four twin 12.5 cm DP deck mounts.

-Existing light AA would be supplemented by another ~8 to 10 35mm guns.

-The bow would be reshaped for improved seakeeping and to make her less wet.

-Machinery would be updated, with a target speed of 30 knots, and bunkerage improved modestly.

Think this would be a useful conversion? Or is the hull going to be too old/small/inefficient for such work to be economic?

Current stats are below...



Top: Columbo as built
Bottom: as refitted, 1927-1929

As Refitted, 1927-1929

Colombo, laid down 1917

Length, 152.4 m x Beam, 15.2 m x Depth, 4.6 m
5158 tonnes normal displacement (4561 tonnes standard)

Main battery: 6 x 15.0-cm (3x2 deck mount w/hoist)
Secondary battery: 4 x 10.5-cm (1x2, 2x1)
AA battery: 6 x 3.5-cm (6x1)
Light battery: 8 x 1.5-cm (2x4)

Weight of broadside: 349 kg

8 TT, 55.0 cm (2x4)

Main belt, 7.5 cm; ends unarmored
Armor deck, average 3.5 cm
Conning tower, 7.5 cm

Battery armor:
Main, 5.0 cm shields / secondary, 3.0 cm
AA, 2.0 cm shields / light guns, 2.0 cm shields

Maximum speed for 30006 shaft kw = 29.02 knots
Approximate cruising radius, 9000 nm / 12 knots

Typical complement: 304-396


Estimated cost, $3.205 million (£801,000)

Remarks:

Oil firing.

Relative extent of belt armor, 110 percent of 'typical' coverage.

Ship has slow, easy roll; a good, steady gun platform.

Main deck secondary guns subject to being washed down
in a seaway.


Distribution of weights:
Percent
normal
displacement:

Armament ......................... 96 tonnes = 2 pct
Armor, total ..................... 814 tonnes = 16 pct

Belt 366 tonnes = 7 pct
Deck 389 tonnes = 8 pct
C.T. 19 tonnes = 0 pct
Armament 40 tonnes = 1 pct

Machinery ........................ 1474 tonnes = 29 pct
Hull and fittings; equipment ..... 1934 tonnes = 38 pct
Fuel, ammunition, stores ......... 764 tonnes = 15 pct
Miscellaneous weights ............ 75 tonnes = 1 pct
-----
5158 tonnes = 100 pct

Estimated metacentric height, 0.8 m

Displacement summary:

Light ship: 4394 tonnes
Standard displacement: 4561 tonnes
Normal service: 5158 tonnes
Full load: 5615 tonnes

Loading submergence 1428 tonnes/metre

+++++++++++++++++++++++++


Estimated overall survivability and seakeeping ability:

Relative margin of stability: 1.27

Shellfire needed to sink: 2533 kg = 54.1 x 15.0-cm shells
(Approximates weight of penetrating
shell hits needed to sink ship,
not counting critical hits)

Torpedoes needed to sink: 1.1
(Approximates number of 'typical'
torpedo hits needed to sink ship)

Relative steadiness as gun platform, 72 percent
(50 percent is 'average')

Relative rocking effect from firing to beam, 0.16

Relative quality as a seaboat: 1.14

+++++++++++++++++++++++++


Hull form characteristics:

Block coefficient: 0.48
Sharpness coefficient: 0.32
Hull speed coefficient 'M' = 8.85
'Natural speed' for length = 22.4 knots
Power going to wave formation
at top speed: 54 percent


Estimated hull characteristics and strength:

Relative underwater volume absorbed by
magazines and engineering spaces: 109 percent

Relative accommodation and working space: 110 percent


Displacement factor: 112 percent
(Displacement relative to loading factors)


Relative cross-sectional hull strength: 0.99
(Structure weight per square
metre of hull surface: 385 kg)

Relative longitudinal hull strength: 1.12
(for 4.60 m average freeboard;
freeboard adjustment +0.56 m)

Relative composite hull strength: 1.01

+++++++++++++++++++++++++


[Machine-readable parameters: Spring Style v. 1.2.1]

499.87 x 49.86 x 15.09; 15.09 -- Dimensions
0.48 -- Block coefficient
1917 -- Year laid down
29.02 / 9000 / 12.00; Oil-fired turbine or equivalent -- Speed / radius / cruise
75 tons -- Miscellaneous weights
++++++++++
6 x 5.91; 0 -- Main battery; turrets
Central positioning of guns
Gun-shields
:
4 x 4.13; 0 -- Secondary battery; turrets
Main deck battery
:
6 x 1.38 -- Tertiary (QF/AA) battery
Gun-shields
:
8 x 0.59 -- Fourth (light) battery
8 / 0 / 21.65 -- TT / submerged / size
++++++++++
2.95 / 0.00 / 0.00 / 0.00; 110 -- Belt armor; relative extent
1.38 / 2.95 -- Deck / CT
1.97 / 1.18 / 0.79 / 0.79 -- Battery armor


(Note: For portability, values are stored in Anglo-American units)


+++++++++++++++++++++++++++++++++++++++++++++++++++++++

I think it's a good idea. The ships were recently refit, so they're still good material to work with IMO. An AA rebuild would be relatively cheap as well.

Are you going to keep the aircraft facilities? Torpedoes? I think you might be able to squeeze in another twin 12.5cm mount if you drop either.

I'm not sure you need to reshape the bow, myself. It looks pretty seaworthy, for what it's worth...

I figured on keeping both the torps and the aircraft, so there's an ASuW and scouting capability. A fifth 12.5 would be awkward to locate, I think, so better to keep the ship multi-functional.

The original springstyle tells me the secondaries are subject to being washed down in a seaway, but I'm not sure if the bow will change that or if it's more an average freeboard issue.

This is what I can do with a new-build on similar tonnage; since the cost of rebuilding a Colombo is 2200 t, and scrap value is ~650 t, net difference in cost is about 1,400 t:

CLAA laid down 1934

Displacement:
4,211 t light; 4,425 t standard; 5,434 t normal; 6,242 t full load

Dimensions: Length overall / water x beam x draught
543.94 ft / 524.93 ft x 49.21 ft x 16.73 ft (normal load)
165.79 m / 160.00 m x 15.00 m x 5.10 m

Armament:
10 - 4.92" / 125 mm guns (5x2 guns), 59.59lbs / 27.03kg shells, 1934 Model
Dual purpose guns in deck mounts with hoists
on centreline ends, majority aft, 3 raised mounts - superfiring
14 - 1.38" / 35.0 mm guns (7x2 guns), 1.31lbs / 0.59kg shells, 1934 Model
Anti-aircraft guns in deck mounts with hoists
on side, evenly spread
16 - 0.59" / 15.0 mm guns (4x4 guns), 0.10lbs / 0.05kg shells, 1934 Model
Machine guns in deck mounts
on side, evenly spread, all raised mounts
Weight of broadside 616 lbs / 279 kg
Shells per gun, main battery: 300
10 - 21.7" / 550 mm above water torpedoes

Armour:
- Belts: Width (max) Length (avg) Height (avg)
Main: 1.18" / 30 mm 380.58 ft / 116.00 m 8.43 ft / 2.57 m
Ends: Unarmoured
Upper: 1.18" / 30 mm 52.49 ft / 16.00 m 8.01 ft / 2.44 m
Main Belt covers 112 % of normal length

- Gun armour: Face (max) Other gunhouse (avg) Barbette/hoist (max)
Main: 1.18" / 30 mm 0.79" / 20 mm 1.18" / 30 mm
2nd: 0.79" / 20 mm - -
3rd: 0.79" / 20 mm - -

- Armour deck: 1.18" / 30 mm, Conning tower: 1.18" / 30 mm

Machinery:
Oil fired boilers, steam turbines,
Geared drive, 4 shafts, 56,298 shp / 41,998 Kw = 32.84 kts
Range 20,000nm at 12.00 kts (Bunkerage = 1,817 tons)

Complement:
316 - 411

Cost:
£2.154 million / $8.616 million

Distribution of weights at normal displacement:
Armament: 77 tons, 1.4 %
Armour: 604 tons, 11.1 %
- Belts: 189 tons, 3.5 %
- Torpedo bulkhead: 0 tons, 0.0 %
- Armament: 36 tons, 0.7 %
- Armour Deck: 371 tons, 6.8 %
- Conning Tower: 8 tons, 0.1 %
Machinery: 1,620 tons, 29.8 %
Hull, fittings & equipment: 1,810 tons, 33.3 %
Fuel, ammunition & stores: 1,223 tons, 22.5 %
Miscellaneous weights: 100 tons, 1.8 %
-All for future growth (read: radar)

Overall survivability and seakeeping ability:
Survivability (Non-critical penetrating hits needed to sink ship):
5,038 lbs / 2,285 Kg = 84.5 x 4.9 " / 125 mm shells or 1.0 torpedoes
Stability (Unstable if below 1.00): 1.22
Metacentric height 2.5 ft / 0.8 m
Roll period: 13.1 seconds
Steadiness - As gun platform (Average = 50 %): 80 %
- Recoil effect (Restricted arc if above 1.00): 0.43
Seaboat quality (Average = 1.00): 1.30

Hull form characteristics:
Hull has low quarterdeck
and transom stern
Block coefficient: 0.440
Length to Beam Ratio: 10.67 : 1
'Natural speed' for length: 26.21 kts
Power going to wave formation at top speed: 57 %
Trim (Max stability = 0, Max steadiness = 100): 62
Bow angle (Positive = bow angles forward): 30.00 degrees
Stern overhang: 3.28 ft / 1.00 m
Freeboard (% = measuring location as a percentage of overall length):
- Stem: 27.23 ft / 8.30 m
- Forecastle (20 %): 19.36 ft / 5.90 m
- Mid (50 %): 19.36 ft / 5.90 m
- Quarterdeck (20 %): 11.48 ft / 3.50 m (19.36 ft / 5.90 m before break)
- Stern: 11.48 ft / 3.50 m
- Average freeboard: 18.41 ft / 5.61 m

Ship space, strength and comments:
Space - Hull below water (magazines/engines, low = better): 110.9 %
- Above water (accommodation/working, high = better): 141.9 %
Waterplane Area: 16,977 Square feet or 1,577 Square metres
Displacement factor (Displacement / loading): 119 %
Structure weight / hull surface area: 62 lbs/sq ft or 305 Kg/sq metre
Hull strength (Relative):
- Cross-sectional: 0.71
- Longitudinal: 1.35
- Overall: 0.76
Caution: Hull subject to strain in open-sea
Hull space for machinery, storage, compartmentation is adequate
Room for accommodation and workspaces is excellent
Ship has slow, easy roll, a good, steady gun platform
Good seaboat, rides out heavy weather easily

Another refit into idiot proof AA cruisers and escorts.

Nice and cheap. Sure the engines and generally the hull is getting worn out but they give you some capability for 5 years or so before they need to be disposed of.

A couple of duple 105mm AA mountings, not the more complex and harder to operate 125mm.

A couple more 35mm mountings. You don't have a quad do you?

Removal of the catapult. Its not really useful for their new mission and saves some weight and space.

That would be another option. You're suggesting a simple 25% refit, then, versus the 50% re-engining version I posted?

Haven't got a quad 35 yet. What's the argument for a quad 35 versus two twins? Less deck space?

25% is a cheaper. I imagine they're fairly worn out by all the wars India has been in.

A quad 35mm so its possible to have more guns firing fore/aft. Deckspace isn't really the issue, its just impossible to have two twins with the same arcs.

Quoted

The original springstyle tells me the secondaries are subject to being washed down in a seaway, but I'm not sure if the bow will change that or if it's more an average freeboard issue.

That's because they're set as if they were casemates, instead of deck mounts.

I like the idea, but then again I've always liked weird conversions to get additional mileage out of ancient hulls. ;-)

Quoted

Originally posted by Swamphen

Quoted

The original springstyle tells me the secondaries are subject to being washed down in a seaway, but I'm not sure if the bow will change that or if it's more an average freeboard issue.

That's because they're set as if they were casemates, instead of deck mounts.

I like the idea, but then again I've always liked weird conversions to get additional mileage out of ancient hulls. ;-)

Then I might have a proposition for you: I've got more ancient cruisers than I know what to do with. Fancy converting a few into high-speed long-line trolling fishing boats, or something funky like that?

Oh sure, take a thread with wholesome family values and turn it into a crass, blatant advertisement...

Quoted

Originally posted by RLBH

Then I might have a proposition for you: I've got more ancient cruisers than I know what to do with. Fancy converting a few into high-speed long-line trolling fishing boats, or something funky like that?

What I would do if I was you is convert some of your larger old cruisers into fast transports.

I´d turn them into razorblades and by me something shiny new from the money I make selling them.... ;o)

I am referring to the British of course.

J, RA may have a point in pointing out your hulls may be more worn out than anybody else due to all the action they´ve been in. Action always means lots of high speed runs and less maintenance due to lack of time. I´d seriously think about scrapping them and build something new. However, I´m not sure where Asir will lead you and a newly build vessels need more time to become reality than just rebuilding something old.

That CLAA probably is what you needs - at least it has superb seaboat ratings.

I thought about similar convertions for my smaller scout cruisers but decided that scraping/selling them and replacing them with smaller CLAA's was the way to go.

The point made about their condition seems valid but cost also could be a factor. If some of the hulls have seen little battle they could make good candidates for a simple refit (25%). A fast transport version seems like a good short term refit option till more purpose build designs get built.

The ships' age and condition hadn't escaped me; I know that Colombo herself, for example, took some hits at As Salif in 1920, so probably has lingering quirks as a result.

Asir isn't doing anything to push me down the road to CLAA - the Sauds and Yemenis don't have airpower to teach me anything thus far. And although I'll consider converting existing tonnage for the purpose, it's unlikely I'll build new CLAA while constrained by treaty. Two larger CL would offer more overall flexibility in use. If we find ourselves without limits after 1936, then it's a possibility.

Fast transports are a nice idea, but probably not the best use of my limited cruiser tonnage.

It's quite possible that I will merely retain the class in their current guise until they're 20 years old or I build replacements (whichever comes first). They'll be adequate for trade protection in most scenarios.

I'd go for the 25% refit. Even if they only last five years more at least you've brought another five years of useful service. Why build newer AA escorts when these can do the job. By 1940 you'll be able to build better ships with better armaments and you'll gain the operational experience of operating these ships.

One thing too consider - if too small a hull then there is little use as AAA battery because of hull movement in other than light seas. So CLAAs probably shouldn´t be smaller than 5kts.

Quoted

Fast transports are a nice idea, but probably not the best use of my limited cruiser tonnage.

Can you describe it as 'experimental'?

They seem a little small for an aircraft and catapult.

Reboilering would reduce the number of funnels.

Cheers,

They are perfectly suited for AA conversions, because of the fact that they are old. Why build a new ship for a threat that does not exists? I would go with the cheaper refit as the battleships they are to escort are slower than them.

Course Australia prefers old ships taking up Indian Tonnage. ;-)


High speed fishing boats? Sounds interesting...