Bismarck and Iowa

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Dave Saxton
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Re: Bismarck and Iowa

Postby Dave Saxton » Sun Jan 15, 2017 9:01 pm

spicmart wrote:With Bismarck's turrets having really so little armor compared they must have been way more easily knocked out? That must have been a serious disadvantage if one looks at the armor of other BBs' turrets.


Bismarck's turret face plates were 14.2-inches thick. This does not compare badly with European practice. For example, KGV's face plates were 12.75-inches (not counting the backing plate which is not significant to the effective thickness). Vanguard’s were 13-inches. Littorio’s were 14-inches.

Richelieu’s were thicker at 17-inches, but there were only two turrets, and Germans engineers reported that the quality of the French plates were of deplorable quality, so more was needed.

Which reminds me that with thick armour plates, increasing thickness does not provide a linear increase in protective quality. Beyond about 12.75-inches each incremental increase in thickness provides less and less improvement in protection. A 17 -inch plate does not provide 3-inches more protection than a 14-inch plate of the same armour.

Looking at the Bismarck’s turrets starting from the top, the roof plates were 130mm and this is the amount required in keeping with an outer immunity zone of 30,000 meters.

But as Iranon commented, there were trade-offs to consider when it came to protecting turrets rather than just providing an theoretical immunity zone against a particular gun from one range point to another. For example, the infamous angled facets of 180mm homogeneous armour represent a trade- off. They were angled-back 65 degrees from the normal. They did not provide protection from beyond 23,000 meters battle range to plunging fire, where they were unlikely to take such a hit, but they traded that off for better protection, because of the presented obliquity, at ranges of less than 20,000 meters, where they were more likely get hit. This additional short range protection was particularly needed should they find themselves embroiled in battle with light forces slinging smaller caliber higher velocity ordinance.

Likewise, the various angles of the heavy face plates we find on various designs probably has to do with trade-offs, such as improving the chances of breaking up or deflecting high velocity ordinance at ranges that really can't be protected against partial or complete perforation anyway.
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Re: Bismarck and Iowa

Postby Dave Saxton » Sun Jan 15, 2017 9:16 pm

spicmart wrote:Bismarck's TDS rating was relatively low, also nominally inferior to Richelieu's iirc. The extensive subdivision of Bismarck to counter that is said to be as effective as the french TDS approach? I always thought that torpedo protection on german ships was outstanding.
But 250 kg TNT does not seem much. How much explosives did ww2 torpedo warheads pack?
If that was more than the torpedo bulkhead was assumed to take, did that mean that it would be breached with great certainty?


Sometimes ratings do not reflect physical realities, or actual performance.

The Japanese did comprehensive testing of various TDS designs, including the type used by the Germans. They found that the Bismarck's system type was equal in performance to that used by the North Carolina class, and these were the better realistic designs. The reason they did not use either similar systems on their own Yamato class was because they did not want any liquid loading to hamper possible counter flooding and pumping strategies. They selected a less well performing system with no liquid loading, anticipating that any system could eventually be overpowered by underwater weapons.
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Re: Bismarck and Iowa

Postby spicmart » Sun Jan 15, 2017 10:47 pm

Thanks for the explanation.

They found that the Bismarck's system type was equal in performance to that used by the North Carolina class, and these were the better realistic designs.


Did you mean Richelieu instead of North Carolina? I remember it being Richelieu, also.

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Re: Bismarck and Iowa

Postby alecsandros » Mon Jan 16, 2017 8:54 am

Iranon wrote:
@ alecsandros: I'm not aware of specific American or German views on this, but the British came to the conclusion that the damage potential of a shell scales almost exclusively with the power of its bursting charge (Bismarck ahead of Iowa by 7% or so). There were also concerns that a heavy shell around a small burster may underperform (ability to ensure proper fragmentation, insufficient velocity of splinters).


Exactly, that was the British view on the subject, and thus British 14" APC rounds carried more heavy explosive charge then either German and US APC shells of 15" and 16" respectively.

German tests (of unknown methodology) came to the conclusion that "1 x 380mm APC shell explosion in the machinery area of a BB would leave the machinery completely unusable", whereas "1 x 280mm APC shell explosion would damage the machinery, but it would be repairable. 2 more x 280mm hits would be required to produce same amount of damage as 1 single 380mm shell hit).

Other then that, the essential aspect, IMHO, is kinetical energy.

It's true that velocity matters much more then mass in the kinetical energy typical formula. However, mass is not to be brushed aside... At 500 meters per second, Iowa's shell had a K.E. of 153 Mega Joules, versus 100 Mega Joules for Bismarck's shells (both with cap attached).
That extra 53% more K.E. can be a huge difference, both in perforating impacts, as well as (or more importantly in ?) non-perforating impacts, against rounded surfaces, heavy armor plates, etc. Sustaining a non-perforating hit on a turret, by a shell carrying 153 MJ is more devastating then sustaining a non-perforating hit in the same conditions, by a shell carrying 100 MJ of kinetical energy.

----

I would add that , according to most metallurgical research that I've read, a bigger shell caliber almost always ensures more actual perforation of plate, then a similarly built projectile, travelling at the same velocity and under the same impact conditions.

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Re: Bismarck and Iowa

Postby alecsandros » Mon Jan 16, 2017 8:56 am

spicmart wrote:Bismarck's TDS rating was relatively low, also nominally inferior to Richelieu's iirc.

... Allthough not directly comparable, I can't help saying:
- Bismarck resisted 2 torpedo hits, with the 3rd jamming her rudders, but not causing extensive flooding or endangering the ship
- Richelieu took 1 torpedo hit, that completely wrecked the stern of the ship, extensive flooding caused the ship to settle on the bottom of the harbor.

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Re: Bismarck and Iowa

Postby Alberto Virtuani » Mon Jan 16, 2017 1:26 pm

Alecsandros wrote: "Richelieu took 1 torpedo hit, that completely wrecked the stern of the ship"

Richelieu (like Littorio at Taranto) extensive damage (ships on the harbor bottom) was much magnified by the shallow water effect, but, for sure, the internal subdivision of Bismarck was superior (and proved to be more watertight).


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Re: Bismarck and Iowa

Postby alecsandros » Mon Jan 16, 2017 1:33 pm

True ...
Some also say that the shock that damaged Richelieu was amplified by the sympathetic detonation of some floating mines , existing in the vecinity of the battleship. It's possible.

Anyway, as you said, Bismarck apparently took less flooding and damage overall (despite being hit by multiple torps, not just 1)

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Re: Bismarck and Iowa

Postby Alberto Virtuani » Mon Jan 16, 2017 1:52 pm

Hi Alec,
yes I agree.
Even a modified Vittoio Veneto (water-tightness improved compared to Taranto), that took a "similar" torpedo hit at Matapan, did survive, due to the redundancy of her screws and auxiliary rudders system, but took an enormous quantity of water onboard compared to Bismarck.....


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Re: Bismarck and Iowa

Postby spicmart » Mon Jan 16, 2017 7:27 pm

Iranon wrote:@spicmart: Bismarck's torpedo defense system was rated to withstand 250kg of TNT, expectation was that damage inwards of the TDS from larger explosions would be contained rather than prevented - Bismarck featured extensive subdivision. The rating seems quite conservative; German assumptions of the time were generally pessimistic.


Damage inwards of the torpedo belt would mean that vitalia were damaged, right?
Can you elaborate on this? I don't quite understand. So the bulkhead was quite weak?

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Re: Bismarck and Iowa

Postby Dave Saxton » Tue Jan 17, 2017 3:22 am

spicmart wrote:
Iranon wrote:@spicmart: Bismarck's torpedo defense system was rated to withstand 250kg of TNT, expectation was that damage inwards of the TDS from larger explosions would be contained rather than prevented - Bismarck featured extensive subdivision. The rating seems quite conservative; German assumptions of the time were generally pessimistic.


Damage inwards of the torpedo belt would mean that vitalia were damaged, right?
Can you elaborate on this? I don't quite understand. So the bulkhead was quite weak?


The bulkhead was not weak. It was constructed of Ww armour plate, which was very ductile and strong. The bulkhead extended from the very bottom to above the main armoured deck as one continuous piece. There was no joint at the point of the main armoured deck or at the double bottom to fail and leak.

The system used a liquid load right against the bulk head and with a void outboard. The liquid load helped slow splinters before reaching the armoured bulkhead. Shear wave components of a shock wave also can not travel through a liquid. It also distributed the load from the shock wave over a wide area of the bulkhead. The energy from the explosion would then be expended by deforming the armoured bulkhead.

Of course any system may eventually be overcome or may encounter a weapon, such as the Japanese long Lance torpedo, that can not realistically be really defended against. It would be foolish not to anticipate and plan contingencies for when the system may be defeated. I believe this is what Iranon is alluding to.
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Re: Bismarck and Iowa

Postby spicmart » Tue Jan 17, 2017 12:58 pm

How can Richelieu underwater protection can be described and rated?

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Re: Bismarck and Iowa

Postby Dave Saxton » Tue Jan 17, 2017 5:06 pm

spicmart wrote:How can Richelieu underwater protection can be described and rated?


The Richelieu featured an internal and sloped main belt which complicated design. There was the outer shell of 10mm Ducol construction steel which wrapped around the keel and covered the sides. Inboard of this, below and outboard of the lower tip of the belt is a void space. The double bottom turned upward inboard of the outer void to meet the point where the bottom of the main belt and the sloped section of the splinter deck meet. The bulkheads making up the double bottom extension were not thick, from 8-13mm construction steel. Inboard of this were fuel tanks making up the liquid load. Inboard of the liquid load were a series of thin bulkheads of 7-10 mm thickness, spaced very close together. This represents, in my opinion, a weakness as the liquid load is not bound inboard by a single heavy armoured bulkhead. Moreover, these thin, weak, bulkheads terminate at the bottom of the splinter deck with joints that could fail and leak. The splinter deck was already below the waterline. If the joint where the double bottom extension, the lower tip of the main belt, and the slopes of the splinter deck, meet should fail, then flooding up and over the TDS system and the splinter deck is likely.

There was a large compartment filled with a type of foam forward of the main magazine to prevent a heavy trim forward in the case of widespread flooding, and some sources say that some voids were filled with the foam to prevent heavy lists. My drawing does not show that. However, given the width of the system of about 7 meters at its widest point it would have been wise to prevent complete flooding of the void spaces in the case of underwater damage.

In my opinion, the system was inferior to the Bismarck's and the North Carolina's, and also the Vanguard's.
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Re: Bismarck and Iowa

Postby Byron Angel » Wed Jan 18, 2017 12:25 am

Re comparison of shell effects, it can also be argued that optimizing the number and velocity of projectile fragments may not be as important as ensuring that a projectile whose detonation can produce a sufficient number of effective fragments is physically able reach a critical location within the target ship.

In other words, a case of the optimal being the enemy of the sufficient.

B

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Re: Bismarck and Iowa

Postby RF » Wed Jan 18, 2017 9:19 am

alecsandros wrote:In terms of anti-torpedo protection, Bismarck had stronger defense.


But it still failed to stop the ship from being crippled - and ultimately sunk.
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Re: Bismarck and Iowa

Postby RF » Wed Jan 18, 2017 9:21 am

paul.mercer wrote:
Iowa, without a doubt, she was a much more modern design with armour at least as heavy if not heavier than Bismarck and of course mounting 9 x 16" main armament and better AA weapons. As for resistance against bombs and torpedoes its hard to say, after all two of the largest battleships Yamato and Musashi which had even heavier armour were sunk by a combination of bombs and torpedoes.


I would agree completely with this assessment.
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