Hood v Vittorio Veneto

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Alberto Virtuani
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Re: Hood v Vittorio Veneto

Post by Alberto Virtuani » Fri Jun 03, 2016 8:17 am

Maciej wrote: "......exact British structure corresponds to
72 mm external plate ( Littorio had 70 )
300 mm internal plate ( Littorio had 280 )
508 mm of space ( Littorio had 250 ).............
...........it corresponds to Littorio’s:
100 mm external
280 mm internal
508 mm space ........"
Hi Maciej,
therefore, none of these two British tested structures corresponds (even in scale....) to Littorio thicknesses and distances, disregarding here the layout and the materials.....

The most critical parameter are IMHO outer plate thickness (influencing the quantity of the "precession motion") and mostly the distance between plates that is neither enough to allow full de-capping nor the good one to ensure that the shell is hitting the inner plate with an unfavorable inclination due to the same "precession motion", while the cap is detached but still "rides" the shell.


Based on what I see, I don't think that these British tests (not supported by a theoretical work contradicting Pugliese theory) can be used to dismiss the Littorio's ship design. tested with the actual ships array.

Bye, Alberto
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Re: Hood v Vittorio Veneto

Post by Maciej » Fri Jun 03, 2016 12:43 pm

The most critical parameter are IMHO outer plate thickness (influencing the quantity of the "precession motion") and mostly the distance between plates that is neither enough to allow full de-capping nor the good one to ensure that the shell is hitting the inner plate with an unfavorable inclination due to the same "precession motion", while the cap is detached but still "rides" the shell.
I can take it, except one point.
In British report, there is something that “experiment using flash photography show that the armour cap is removed from A.P.C. B.C. shot by impact with thin mild steel or armour plate targets at all velocities above critical velocity”
than description how in various velocities cap could be removed, what would be variance of velocity and so on.
Than
The removal of an armour piercing cap by a thin front plate has an obvious application in the arrangement of divided armour, since, with the cap removed, she shot will be subject to shatter on a face hardened plate, the type of failure the A.P.C. B.C. shot is designed to avoid”
(bold is mine)

So we back to shell design.
APC BC was designed to avoid damage in condition with cap removed….
So no shatter in that situation, so no clear advantage of such configuration….

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Re: Hood v Vittorio Veneto

Post by Dave Saxton » Fri Jun 03, 2016 1:27 pm

Maciej wrote: I can take it, except one point.
In British report, there is something that “experiment using flash photography show that the armour cap is removed from A.P.C. B.C. shot by impact with thin mild steel or armour plate targets at all velocities above critical velocity”
than description how in various velocities cap could be removed, what would be variance of velocity and so on.
Than
The removal of an armour piercing cap by a thin front plate has an obvious application in the arrangement of divided armour, since, with the cap removed, she shot will be subject to shatter on a face hardened plate, the type of failure the A.P.C. B.C. shot is designed to avoid”
(bold is mine)

So we back to shell design.
APC BC was designed to avoid damage in condition with cap removed….
So no shatter in that situation, so no clear advantage of such configuration….
Hi Maciej,

I think you are mis-interrupting the meaning in the English language here. It could be re-worded to say that: " APC BC shells shatter on impact against face-hardened plate if the cap is not present, thereby defeating the design purpose of fitting the shell with a cap in the first place, if the cap is removed."

How the design avoids this type of failure (shattering against FH plate) is by fitting the cap. That is the meaning. Not that the shell can avoid this type of failure with out a cap. Why fit a cap in that case? So APC BC shell design does shatter if the cap is removed and the velocity is sufficient.
Entering a night sea battle is an awesome business.The enveloping darkness, hiding the enemy's.. seems a living thing, malignant and oppressive.Swishing water at the bow and stern mark an inexorable advance toward an unknown destiny.

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Re: Hood v Vittorio Veneto

Post by Dave Saxton » Fri Jun 03, 2016 2:08 pm

Alberto Virtuani wrote:
The most critical parameter are IMHO outer plate thickness (influencing the quantity of the "precession motion") ....
Precession is slow developing. It can be described as a slow orbit around the axis of trajectory. In the case of the small Italian inter-space, the other component of yaw, nutation, would be the factor here. Nutation is a rapid and instant wobble. However precession could be starting, and combined with nutation would insure that the cap, if riding, or the head of the shell if the cap is already destroyed, does not strike nose on.
Entering a night sea battle is an awesome business.The enveloping darkness, hiding the enemy's.. seems a living thing, malignant and oppressive.Swishing water at the bow and stern mark an inexorable advance toward an unknown destiny.

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Re: Hood v Vittorio Veneto

Post by alecsandros » Fri Jun 03, 2016 3:38 pm

@Maciej, Dave,
APCBC is short for armour-piercing capped ballistic cap. The APCBC is designed to resist shatter indeed. :cool:

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Re: Hood v Vittorio Veneto

Post by Alberto Virtuani » Sat Jun 04, 2016 7:52 am

Hi all,
once we are all in agreement that the actual Littorio class array has never been tested by other navies than RM, therefore Pugliese theory has been contradicted neither by tests nor by a theoretical work, let's move to shell design.


Could anyone please elaborate on the APCBC shells ?

I'm not an expert at all, but I understand APCBC shells are simply shells fitted with a ballistic cap AND a windscreen (aerodynamic cap), as N.Okun, in his later article (kindly posted by Duncan: http://www.navweaps.com/index_tech/tech-085.htm), mentions for US nomenclature:
N.Okun article states: ""......APCBC" for AP projectiles with both AP caps and windscreens"
Am I wrong ?

Are these instead the shells that N.Okun defines as "Type 2" caps, thus designed to enhance penetration at high obliquity ? :think:

Anything else ?

Bye, Alberto
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Re: Hood v Vittorio Veneto

Post by Dave Saxton » Sat Jun 04, 2016 3:46 pm

Alberto Virtuani wrote:
Could anyone please elaborate on the APCBC shells ?

I'm not an expert at all, but I understand APCBC shells are simply shells fitted with a ballistic cap AND a windscreen (aerodynamic cap),

Thorsten and Tommy can probably provide more detailed information.

Caps were developed to help AP shells survive the impact against armour. Indeed, Krupp Cemented armour was developed specifically to shatter AP shell on impact. Harder and larger caps were developed in turn. Better armour formulations were developed in turn. Many WW1 and earlier shells had comparatively soft caps. Soft capped shells still had problems surviving impact with face hardened armour.

During the inter-war years harder, but also larger and heavier caps were the trend. For example, the difference between the 2110 lb and 2240 lb USN 16" shells was the size and the weight of the cap. The Germans found that a larger and heavier cap does help aid penetration. I have a late war US document that describes the purpose of the cap was both to protect the shell and to aid penetration. It states that upon impact, the cap helps to stress the armour and helps the shell dig in before it is destroyed. Then once penetration is started, and the cap is destroyed, the head of the shell can better push through the remaining armour like a "flat nosed punch." Removing the cap reduces the penetration capabilities of the shells and causes the shell to shatter against heavy face hardened armour.

The Germans found that removing the cap is also good in case of deck hits. Removing the cap reduces the weight and therefore the kinetic energy of the shell. Not only does the weight of the cap go away but also the momentum/velocity of that portion of the weight too. With larger and heavier caps this reduction is more significant. The weight of the cap can be more than 13% of the overall shell weight. The Germans found that there was a further significant reduction of penetration of de-capped shells if the deck armour had a tensile strength at least or exceeding 80kg/mm2 (130ksi)

Penetration at acute obliqueness is mostly the function of the shape of the head of the main body of the shell that the cap is fitted over. A sharply pointed head shape is more likely to deflect or "scoop" at more acute striking angles, but striking closely to the normal the penetration is greater. British and Italian shells had relatively sharp pointed shells of 1.4 calibers radius. American shells were much rounder shaped, being almost hemispherical in nose shape. late in the war the USN changed to an even more blunt nose shape to improve oblique penetration further. The Germans found that a nose shape of 0.93 caliber radius provides almost as good oblique performance as a hemispherical head shape but without the large trade off in normal striking performance. The rounder the nose shape, the easier it is to knock the cap off, is another trade off.

The British tested captured Italian 15" shells along side their own. They found that Italian shells were highly likely to scoop in the case of oblique hits , but that the fuse was more likely to survive the "base slap" intact.

Base slap was major problem. When a shell strikes at an oblique striking angle it will momentarily change trajectory more away from the normal which causes the base of the shell to slap against the plate during penetration or when scooping, usually distorting or breaking the fuse cavity, destroying the functionality of the fuse. The longer the shell, the more likely this was the case. The Italian fuse cavity was better protected against base slap because it was located deeper up into the shell.
Entering a night sea battle is an awesome business.The enveloping darkness, hiding the enemy's.. seems a living thing, malignant and oppressive.Swishing water at the bow and stern mark an inexorable advance toward an unknown destiny.

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Re: Hood v Vittorio Veneto

Post by Dave Saxton » Sat Jun 04, 2016 4:01 pm

The ballistic cap in the case of APC shells would avoid confusion if it is called the '"windscreen". The trend was to more aerodynamic windscreen shapes to preserve more velocity down range. Thus the new 1938 British 15" shell had a 6 crh windscreen replacing the 4 crh windscreen. The German L/4.4 had a 10 crh windscreen. The 1938 British 15" shell also had a boat tail base shape for improved aerodynamics. There is some controversy if this degraded long range accuracy.

The Germans had the only supersonic wind tunnels to test shell aerodynamics. One innovation was called "wasting" or a slight coke bottle shape. This can be seen on the USN 16" 1900 lb HE shells post war if you look closely enough.
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Re: Hood v Vittorio Veneto

Post by Maciej » Sat Jun 04, 2016 4:23 pm

once we are all in agreement that the actual Littorio class array has never been tested by other navies than RM, therefore Pugliese theory has been contradicted neither by tests nor by a theoretical work, let's move to shell design.
You have one veto.
See those pictures in scale. Test done in Italy, actually with onu 320 mm shell, on picture 356 shell and 381 to see the difference
Italy.png
Italy.png (21.74 KiB) Viewed 1752 times
Now British test - again in scale. All shells were tested.
British.png
British.png (23.9 KiB) Viewed 1752 times
Both on the same picture. In Puegliese theory, if I remember correctly, 600 mm distance is needed to allo decap 381 mm shell.
So I put that version of structure with 381 and 406 mm shells inside to show what is going on.
Under there is simply British test rescaled by 2 linerary. (there were other combination - the same distance, but main plate 280, and external 102 - rescaled )
See difference for Yourselfe. If whole thing is so sensitive to that distance...
both.png
(33.3 KiB) Not downloaded yet

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Re: Hood v Vittorio Veneto

Post by Maciej » Sat Jun 04, 2016 4:49 pm

I think you are mis-interrupting the meaning in the English language here. It could be re-worded to say that: " APC BC shells shatter on impact against face-hardened plate if the cap is not present, thereby defeating the design purpose of fitting the shell with a cap in the first place, if the cap is removed."
Possibly. That's why forums are good to correct such mistakes.
How the design avoids this type of failure (shattering against FH plate) is by fitting the cap. That is the meaning. Not that the shell can avoid this type of failure with out a cap. Why fit a cap in that case?
For two purposes.
1. To protect shell from shattering. There were shells which always shatter against KC plates, if are not fitted with caps. Specially older ones. But later not always had to shatter.
2. To help to penetrate armour. Penetration capability of shell is simply improved with cap, even if uncapped shell will not shater.

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Face HD 7.1 test

Post by Maciej » Sat Jun 04, 2016 8:54 pm

BTW
Just to satisfy my curiosity.
I checked penetration parameters of Italy 15" shells predicted by Face Hard ( with all known comments about that program )
If we include 15 degree slope of belt, at ~16 km Italian 15" shell fired from Littorio ( new gun ) hit at 14.8" armour, returned "plate holed, shell damaged".
With Italian plate, and no backing material. With any backing will be no penetration.
If we include any gun worn - say 30 shots, limit will be something like 14" solid plate.

So - whole thing was designed to protect against Iittorio's guns at 16 km. Lets say it protects to avoid any confusion.
14.8" single plate ( from Italian steel ) will protect at 16 km.

British conclusions - against 14-15" shell Littorio's structure will be as protective as ~360-370 mm solid plate. 360-370 mm = ~14.2-14.6"

I think in both cases we have agreement. There is simply no any real difference between results on both countries. At last in conclusions of protective scheme of Littorio class ( if we include differene in armour quality, and if Face Hard gives more or less accurate results )

So British conclusions - from any practical point of view better to put single plate of the same thickness. Less complicated structure, difference in protection minimal if any.

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Re: Hood v Vittorio Veneto

Post by Alberto Virtuani » Sat Jun 04, 2016 9:53 pm

@Dave Saxton_:
Hi Dave, thanks for the precious info. I really need to study a bit more the shells design..... :oops:

Maciej wrote: "If we include 15 degree slope of belt, at ~16 km Italian 15" shell fired from Littorio ( new gun ) hit at 14.8" armour, returned "plate holed, shell damaged"."
Hi Maciej,
the Italian tests were done (even using a 320 mm shell) to simulate a 381 mm shell and they confirmed the theory that the array was able to fully defeat the Italian 381 mm shell, with no penetration ("the inner plate brilliantly resisted the attack") from 16 km. The ideal fighting distance for the Italian ships was indeed considered to be 16 km.

This is quite different from the above results of Face Hard that foresee "plate holed and shell damaged" (but still active or not ???). In addition, 14,8" are 375,9 mm steel, a bit more than 360-370mm. I see quite a difference here and also compared to the British results.

Which is the thickness of armor for which Face Hard gives "no penetration at all and shell destroyed" for the Italian gun at 16 km ? This would be the equivalent thickness of the array, in case that the Italian design is working, of course. :wink:



Regarding the tests themselves, I do agree that 320 mm shell is not the same as 381 mm shell, but the Italian tests were done on the actual array fitted on Littorio, they were used just to corroborate Pugliese theoretical work, and they did.
British tests were done on several different arrays, not respecting, even in scale, the proportions of the actual Littorio arrangement and mostly they were supporting no theory that contradicts Pugliese one.....


Bye, Alberto
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"There's always a danger running in the enemy at close range" (Adm.W.F.Wake-Walker)

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Re: Hood v Vittorio Veneto

Post by Maciej » Sat Jun 04, 2016 10:37 pm

Which is the thickness of armor for which Face Hard gives "no penetration and shell destroyed" for the Italian gun at 16 km ? This would be the equivalent thickness of the array, in case that the Italian design is working, of course. :wink:
14.6" - full penetration
14.7" - partial penetration. Plug generated, shell pass through, but in broken condition
15.8" - partial penetration. Plug generated, shell pass through, but in broken condition ( and all values between of course )
15.9" - partial penetration. Some shell elements could pass, but not whole shell. Shell broken.
16.0" - no penetration

British were considering full penetration....

And still in mind - calculations from Face Hard are more or less accurate. +/- 5-10% difference in calculated thickness could happen. Depends on shells/armour combination.
And difference 0.1" ( ~2.5 mm ) are quite less than actual production tolerance in thickness of armour.
I simply wanted to check exact border.
Last edited by Maciej on Sat Jun 04, 2016 10:41 pm, edited 1 time in total.

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Re: Hood v Vittorio Veneto

Post by Maciej » Sat Jun 04, 2016 10:40 pm

they were used just to corroborate Pugliese theoretical work, and they did.
I ask a tricky question
Who evaluates whether the test results confirm the theory?
In the 30's, of course.
"Independent experts" or Pugliese?

Take me right - I'm not saying that whole thing not works. It works in some situations quite well.
What I'm questioning is some extreme large advance of such structure over single plate.
Last edited by Maciej on Sat Jun 04, 2016 11:04 pm, edited 1 time in total.

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some speculations

Post by Maciej » Sat Jun 04, 2016 11:03 pm

And one more thing to consider.
I don’t know much about Italy’s practice, so I could be very wrong, but from pure technical point of view.

~1.5 meters behind Littorio’s belt there is 36 mm bulkead. Clearly splinter protection.
After that bulkhead next 3 to 6 meters ( depends on area, plates are not parallel ) there is next 24 mm plate.
I know that Littorio was large, but not so large. I could imagine, that designers wanted to add protection in extreme short distance, but if that was not required I doubt it was the case.
My feelings (not based on any hard data – just pure engineer point of view) is that designers expected in normal situation that some splinters, shell fragments will be thrown into the hull, so those bulkheads are placed to stop them. If splinters were not expected – why waste so much mass? It was total ~60 mm and area virtually the same as covered by belt armour. Clearly mass that counts something.
And even more – I think they expected quite large fragments. From experience of WWI (Italy was allied to British, so even if had not enough damaged own ships to analyse, had some aces to British data) it was clear that 36 mm is not enough to stop large splinters. Small and say medium that should stop. But largest no. So next bulkhead was added. We can for long debate what was better - one plate 60 mm thick, or two separated. But if designed believed at spaced array - putting two separate bulkheads was quite logical.
If I’m right that pushes “relative performance” closer to 14.5” than 16”.

My opinion of course – again based only on own “feelings”, not any hard historic data.

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