Mizuho and Nisshin as CVL?

[DuckofTindalos]

Die tonnage des trägers is weniger wichtig. Ich glaube nicht das die führung der Kombinierte Flotte und die Kido Butai bereit sind, mehr flugzeuge an die begleitträger abzugeben dann sie unbedingt müssen.

Die Nisshin wurde die selbe rolle als die anderen Japanischen begleitträger einnehmen, und weil diese teoretisch 23-30 flugzeuge hätten tragen können, hätte die Japaner niemahls genug flugzeuge und piloten vorhanden.

Noch mals, wenn du ein leichter flotten-träger aus ihr machen will, dann ist 28 knoten und 28-30 flugzeugen nicht unannehmbahr. Ein begleitträger braucht reichweite mehr als geschwindichkeit. Der preis spiehlt auch eine rolle.

[DuckofTindalos]

Besides, if you give the CVE conversion a smaller air group, you can increase bunkerage for the ship herself.

[Historiker]

Ok, I think german isn't necessary - so the others will also understand... (BTW: really good german!)

Die tonnage des trägers is weniger wichtig. Ich glaube nicht das die führung der Kombinierte Flotte und die Kido Butai bereit sind, mehr flugzeuge an die begleitträger abzugeben dann sie unbedingt müssen.

Die Nisshin wurde die selbe rolle als die anderen Japanischen begleitträger einnehmen, und weil diese teoretisch 23-30 flugzeuge hätten tragen können, hätte die Japaner niemahls genug flugzeuge und piloten vorhanden.

So this is a more political and aviation personal reason? You assume there's a fixed number of pilots and this is the limiting factor for number it should carry. Is that correct?
My pilot reinforcement system limits the number of pilot and doesn't have a replacement rate. So when the pool is empty in the time its airgroups arrive, the operative losses will be horrible - which seems realistic to me.

As the japanese side still has to produce every single plane onboard, the number of planes available should be the limiting factor in game - but not in the editor.

Do you agree with me?

Noch mals, wenn du ein leichter flotten-träger aus ihr machen will, dann ist 28 knoten und 28-30 flugzeugen nicht unannehmbahr. Ein begleitträger braucht reichweite mehr als geschwindichkeit. Der preis spiehlt auch eine rolle.

The Nissin should have enough range with 11.000@18kn

The Mizuho has 8000@16
With an Akizuki engine, it'll be fast enough to operate with the carriers - with the same range (or more? According to the data, it seemss like the Akizukis engine (which has 53.000 instead of 50.000 I've written at first) is more efficient. This is as good as the Akagi.
And even with its diesels remaining in the ship, 8000 miles seem enough for me. That should be enough to escort a convoi from the home islands to new caledonia and back.


Again:
I don't intend to convince you to be wrong, nor do I intend to annoy you. I also don't intend to press my opinion into a mod against all odds. My point of view is that I'm in command and order the conversion to a carrier. In this case, I want the best possible. The best in my point of view are as many (operational) planes onboard as possible.

While I want the most potent ship, I don't want something totally unrealistic. It should be possible by technical standards - but the question of pilots and planes is the players problem, not mine. My intention is to reward a successfull economic game. If he has more planes, trained pilots, armament points, shipyard points... than usual, he should have a benefit from it.

I always shook my head when I saw huge pools of modern planes or XY points in the pool and no possibility for the player to have an immediate benefit from it. In my mod, he'll have this possibility - and this ship should be part of it.

[el cid again]

ORIGINAL: Historiker

Working on the interwar Japanese Naval-Buildup, I just read that both Nisshin and Mizuho weren't converted into carriers because they were sunk before it was needed.
This implicates, that conversions were both possible and considered.
Is there any reason why this two ships shouldn't be able to convert into carriers because of historic technical reasons in a hypothetic mod?

You are correct - that is - these classes were part of a pre war shadow program with several different design options available - depending on requirements. They might be build at submarine tenders, as fast tankers, as seaplane carriers or as fixed wing carriers. The seaplane carriers were regarded as a sort of secret weapon (see I Boat Captain). The USN had similar ideas too - and the larger AV of USN were designed with catapults. In BBO family scenarios you get them in that form. In RHS Mizuho and Nisshin appear as CVLs in most EOS family scenarios. The Nisshin appears as a CVE in BBO family if I remember correctly.

The difference between a CVE and a CVL form is engines: you can fit Chitose type steam engines and get a CVL - or keep the diesels and get a CVE.

Note that that if your scenario permits pre war planning changes - you can simply lay down these ships in the form you want them. There are more complex options - I have games in which you model engine production - but in principle the basic cost of engines is pretty similar. The Mizuho was an experimental case to evaluate a very large marine diesel engine concept - and it would actually be possible to build the ships with twice as many engines - it would just be more expensive to do that.

The problem with aircraft is somehat bogus: there were plenty of air groups ashore that might have been trained for use afloat in JNAF. This is separate from the possibility of cutting the JNAF training program in duration - permitting higher output.

[Historiker]

Note that that if your scenario permits pre war planning changes - you can simply lay down these ships in the form you want them. There are more complex options - I have games in which you model engine production - but in principle the basic cost of engines is pretty similar. The Mizuho was an experimental case to evaluate a very large marine diesel engine concept - and it would actually be possible to build the ships with twice as many engines - it would just be more expensive to do that.

Good point! I haven't thought about the concept of this mod so far.
Chitose and Chiyoda were ordered for an overall refit in early 1941. This ended in their converting to CVL towards end of November 1941 (so they start as CVL).
After this, Nisshin and Mizuho are ordered for a conversion, too - and the work on it starts with 7th of December.

Without material shortages and enough workers, I assume the conversion taking 6 month.
Equiping the Mizuho with faster engines for 28kn takes an additional 3 month, so 9 month in total.
Does everyone agree?

Does it take naval shipyards for this conversions or are merchant shipyards able to do it (that's what I think)?



What other ships can be converted?

[JWE]

ORIGINAL: Historiker
Equiping the Mizuho with faster engines for 28kn takes an additional 3 month, so 9 month in total.
Does everyone agree?

Does it take naval shipyards for this conversions or are merchant shipyards able to do it (that's what I think)?
What other ships can be converted?

Differential EHP goes as the cube of differential (increased) speed. You’ll need a lot of HP to get those 6 more knots. Simple numbers from a simple model run – 350’ lwl, 2720 dspl, 15700 sq ft wetted surface: 22 knots requires 5000 EHP, 28 knots requires 20000 EHP. Change the scale factor and convert to SHP, and you get 15000 SHP at 22 and 60000 SHP at 28. So, yeah, a 53000 SHP powerplant might do it.

But your engineering footprint goes way up – turbines are bigger than diesels and you’ll need boilers too, and also forced draught macheriny. Need more bunkerage as well – specific fuel consumption is higher. Requires more longitudinal bracing. Added weight requires addl HP. Ends up taking half the internal ship volume for the power plant, so smaller hangar, smaller ordnance stowage, fewer planes … not really a good idea.

Can be done, but requires ship to be gutted to the garboard and rebuilt. Would likely take 9 – 12 months just for the powerplant conversion. Probably easier to just build one from scratch. Much easier to increase the HP of an initial turbine installation: increase Temp and Pressure, better turbine matls – higher turbine efficiency, better reduction gearing, but basically a similar engineering footprint.

Merchant yards (irl) are quite capable of building/rebuilding just about anything that fits on the slipway.

[Historiker]

Great, thank you!

The only significant difference between Chitose and Mizuho seems to be the engine. Consequently, it should be able to be converted to a similar ship, too, right? Taking the Chitose, I assumed to have the Mizuho carrying 30 planes as well.
So taking the information given by you, I would come to the following conclusions:

1. As the Mizuho has Diesels, there's no way to increase the power significantly without rebuilding the whole ship by a massive scale.
What's strange is, that the Chitose has two engines: One Turbine and a Diesel. The Diesel has 12.800 SHP while the Mizuho's has only sightly more with 15.200. So is its Diesel only slightly bigger? If so, is it wrong to think that an Akizuki engine might be added in addition to the Diesel? (Of course, I'm pretty shure that the Mizuho wasn't prepared for this, so it's either impossible because of the design of the diesel - not its size - or it makes a reconstruction of the Diesel needed as well. In this case, a whole new engime seems to make more sense...) The Chitose has the same rante with 2kn more - with the same amount of fuel. Ifs there a way to use the space that must be available (because the only slightly more powerful Diesel can't require that much space, no?) for additional diesels, maybe sub-diesels? They are both small and reliable and should be able to run at full power quite some time. Constant 25 or 26 kn will be enough if that's a constant speed, no?

2. It seems quite difficult to make a useful CVL out of the Mizuho. So a CVE should be prefared. If I take this:

But your engineering footprint goes way up – turbines are bigger than diesels and you’ll need boilers too, and also forced draught macheriny. Need more bunkerage as well – specific fuel consumption is higher. Requires more longitudinal bracing. Added weight requires addl HP. Ends up taking half the internal ship volume for the power plant, so smaller hangar, smaller ordnance stowage, fewer planes … not really a good idea.

and am not wrong with my conclusions that the only slightly more powerful Diesels of the Mizuho can't take THAT more space than the Chitose's, there should be more room for planes, ordnance and fuel than on the Chitose, no? So a CVE would not only be converted faster, it would also carry more planes! How much more? 5? 10? or even 15?
If I take 10 to 15, a Mizuho CVE would be indeed the best solution. 40 to 45 planes with a conversion within some 6 month is an almoust perfect solution to me.


Am I wrong?

[Dili]

Mizuho have precisly the same dimensions of Chitose (less 500t in full displacement) also same number of Aircraft so probably could take more cargo in CS mod. Bar any structural difference it would make sense to change it to a CVL if there are enough air groups. Much more than those horrendus Mogami,Ise silly conversions.

[Historiker]

I have a problem for the "if there are enough airgroups" problem.

I'm thinking about to change all landbased aigroups - maybe except a handfull of training groups - to army service.
In my mod as well as in RHS EOS, army pilots also can fly carrier capable planes. That means that a huge number of airgroups can be trained on land and later be used on carriers.
But if every landbased airgroup, except the few training units, is flown by army pilots, I can allow a huge number of carriers. To supply the carriers with trained pilots will be a much more significant problem then. 10 additional carriers are useless with 25 xp pilots on them.
Doing this will eliminate the historical correct landbased fighters and bombers - but it will be the first mod that handles the problem concerning trained carrier pilots correctly.

[John 3rd]

ORIGINAL: Terminus

I'd probably turn her into a diesel-powered CVE. Fastest conversion I could do, to give my convoys some modicum of air cover.

She'd be sunk quickly, of course, but still...

I get a lot of mileage out of my CVEs!

[JWE]

Hi Historiker,

Woof! Power plant design! Ok, each type of plant has its own advantages and limitations, Rankine cycle, Otto cycle, diesel, etc.. A steam turbine (Rankine) needs to run at darn near rated power, to be efficient – maybe 83-85% of BHP. Because of the cube law, you need much less power to cruise than to run at speed. That means when you are cruising with a turbine, you need reduction gearing (very heavy) to go slow, but the turbine is still running at 85% of rated power and using gas at that rate. For a warship that cruises at maybe 12-15 knots and scoots at 30+, this is a significant wasted power/bunkerage issue.

What people did was install cruising turbines downstream, and divert just enuf steam to keep the bearings lubed on the mains. Some Navys substituted cruising diesels for the cruising turbines – got some advantages, but like all compromises, picked up some limitations.

In the 1930s and 40s the technology was not mature enough to develop low-speed diesels into the 20,000+ HP range. Medium and high-speed diesels with high power output were on the drawing boards, but were still only technical curiosities.

So … no. Chitose requires her turbines to get to the higher top speed. Mizuho will require turbines as well to get to a similar same speed. EHP is what is “required” to move a shape through the water at a given speed. There weren’t no diesels (then) that could do that, so we go back to tearing out Mizuho’s guts and adding a full-tilt-boogie turbine plant. Not goodnik.

Bottom line. Can’t get there from here. Keep Mizuho at 22 knots. It took Chitose 11 months (irl) to convert. If you give Mizuho more power, a 15 month conversion time is likely and 50% decrease of internal space utilization is warranted along with a 50% decrease in a/g capacity.

40 to 45 planes in 6 months in a CVE configuration sounds very “what if” to me. I would look more to perhaps 30 in 9 months

[Historiker]

Ok, I read abouth many of this aspects in Treue's "Deutsche Marinerüstung 1919-1942" i.e. German Naval Armament 1919-1942. IIRC, Germany was leading in Diesels. Thank you very much for your really competent help and informations!
Still, I hardly believe that Diesels 18% bigger require as much space as 2 sets GT with 5 Kampon boilers @ 44.000 SHP.

So either I'm still totally wrong - or there significantly more space inside the Mizuho. I totally accept that 18% more power doesn't mean 18% more required space and weight.

15 more planes means also additional spare parts, additional accomondation for machanics and pilots, additional ordnance...
So I take 5 additional planes and don't add engines.


I took 6 month for conversions of AK/AP to CVE from the historical data. The conversion of Chitose took roughly 9 month (late January to 1st of November).
BUT: this happened in war, with all the problems of reduced supply of material, fewer workers etc. When a late war carrier was commisioned in november 44, it gets complete in november 44 in the game as well. IMO this is wrong! Except the first few weeks or maybe months, the supply was influenced by the war. Whenever a ship with ore was sunk, fewer steel arrived which delayed the ship for weeks. INO, all ships should have the building times they would have had without that influences! It has to be the allied players work to delay the completion of ships, and not the work of the game.
Consequently, I take optimized times for all works. But I haven't increased the shipyards significantly (I took RHS data for them), so the building possible should be by far more than the industry can handle.
Both the players choice which ships to build and which to stop,  as well as the allied players bombings and ressources/oil interceptions will delay the ships commission - and not the data in the game.

[JWE]

ORIGINAL: Historiker
So either I'm still totally wrong - or there significantly more space inside the Mizuho. I totally accept that 18% more power doesn't mean 18% more required space and weight.

You are not wrong, my friend. Chitose had 23% greater internal volume than Mizuho. Chitose was designed and built with diesels AND turbines. Mizuho was designed and built with just diesels. There may well have been more volumetric efficiency in Mizuho than Chitose. So perhaps Mizuho could host a similar size a/g. Don’t know.

Conversion of Chitose took 11 months – January something to December something 1943. If you want conversions to happen faster in your mod, then more power to you. It took the US 1/3 the time to do something as the Japanese. Billions of reasons why, but that’s how it was. Japan did not and could not get those levels of efficiency out of her yards.

[Historiker]

You are not wrong, my friend. Chitose had 23% greater internal volume than Mizuho. Chitose was designed and built with diesels AND turbines. Mizuho was designed and built with just diesels. There may well have been more volumetric efficiency in Mizuho than Chitose. So perhaps Mizuho could host a similar size a/g. Don’t know.

Despite the two engines, the Chitose still hade MORE internal space free than the Mizuho at the same external size??? Or do you meen the Chitose had less space free?

The conversion happened between 26th of January to 1st of November 1943. So it took 9 month and a week. Of course, itt wasn't combat ready immediately, but the sheer building time was as I stated (according to my books).

[JWE]

Chitose had less - much less.

Don't know where your data comes from, mine says Chitose was pulled offline Jan. 16, 1943 and was re-acctepted Dec. 21, 1943. Data is always suspect.

[Historiker]

with less place used, it is able to carry a bigger airgroup than the chitose's 30.

I guess your time is the time it was pulled out of service while mine is the time they were actually working on it. We all know that while the work ends one day, it isn't immediately put into service. It runs long tests...
Maybe your time is from the day the flag was lowered to the time it was accepted by the navy again.

[Dili]

Chitose had 23% greater internal volume than Mizuho.

What is the source for this? They have the same external dimensions

There weren’t no diesels (then) that could do that, so we go back to tearing out Mizuho’s guts and adding a full-tilt-boogie turbine plant. Not goodnik.

Nishin had 2(anotehr source says 6) diesels that put the ship at 28kt with a displacement almost equal to other CS's.

[JWE]

We are not talking about Nisshin. Nisshin had 4 diesels. Two mains. Each <20,000 SHP. Very large, very heavy. Very different configuration. Apples and grapefruit.

You might want to try Gilmer & Johnson's Naval Architecture, USNI Press, or Ship Construction by Eyres.

[John 3rd]

Great detailed discussion Gents.&nbsp; Thanks for keeping it going and running into so much detail.&nbsp; Fascinating to one who knows little of this material...

[el cid again]

ORIGINAL: JWE

ORIGINAL: Historiker
Equiping the Mizuho with faster engines for 28kn takes an additional 3 month, so 9 month in total.
Does everyone agree?

Does it take naval shipyards for this conversions or are merchant shipyards able to do it (that's what I think)?
What other ships can be converted?

Differential EHP goes as the cube of differential (increased) speed. You’ll need a lot of HP to get those 6 more knots. Simple numbers from a simple model run – 350’ lwl, 2720 dspl, 15700 sq ft wetted surface: 22 knots requires 5000 EHP, 28 knots requires 20000 EHP. Change the scale factor and convert to SHP, and you get 15000 SHP at 22 and 60000 SHP at 28. So, yeah, a 53000 SHP powerplant might do it.

But your engineering footprint goes way up – turbines are bigger than diesels and you’ll need boilers too, and also forced draught macheriny. Need more bunkerage as well – specific fuel consumption is higher. Requires more longitudinal bracing. Added weight requires addl HP. Ends up taking half the internal ship volume for the power plant, so smaller hangar, smaller ordnance stowage, fewer planes … not really a good idea.

Can be done, but requires ship to be gutted to the garboard and rebuilt. Would likely take 9 – 12 months just for the powerplant conversion. Probably easier to just build one from scratch. Much easier to increase the HP of an initial turbine installation: increase Temp and Pressure, better turbine matls – higher turbine efficiency, better reduction gearing, but basically a similar engineering footprint.

Merchant yards (irl) are quite capable of building/rebuilding just about anything that fits on the slipway.

Keep it simple. The ship is later in time - so order it as a repeat Chitose.