BISMARCK armor scheme = BADEN?

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Two comments

Post by Bill Jurens » Fri Sep 03, 2010 4:06 pm

A reader recently asked exactly how the center of gravity shift was measured. Traditionally, the center of gravity of a projectile is measured from the base, and that's what was done in this case. In other words, the center of gravity would move roughly 3" aft towards the base if the cap were removed. I ignored the windscreen in the calculations.

Some comments have been made that lengthening the projectile would somewhat weaken it against oblique penetration. These comments apparently assume that the projectile actually breaks upon impact, but it is quite easy to design the projectile so that it only bends instead. Sometimes this bending can be quite spectacular. Further -- seeing as some of the discussion has revolved around the supposed effects of induced yaw -- one must keep in mind that the longer the projectile the greater the moment of inertia along the longitudinal axis the greater the resistance to a change in the orientation. Something which is round, like a cannon ball, has relatively low resistance to yaw, i.e. it is pretty much happy to orient itself in any direction even relatively light forces might take it. Once a projectile is lengthened and spin stabilized, the longer it becomes the more stable it becomes. That is one reason why rockets (and arrows) are traditionally spin-stabilized; they are so long that even a little bit of spin stabilization would otherwise cause them to fail to follow the trajectory. Although a longer projectile would indeed see higher stresses and strains if exposed to a yawed impact, because it was longer it would have a lesser tendency to yaw in the first place, i.e. it would tend to have a decreased yaw when it struck, these two factors somewhat cancelling one another out.

For what it is worth, my experience has been that it takes quite a significant change of location of the center of gravity to measurably affect the amount of induced yaw; this from studying the dynamics of projectile motion whilst passing through an adjacent blast field, i.e. the muzzle blast from an adjacent gun.

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Re: BISMARCK armor scheme = BADEN?

Post by Bgile » Fri Sep 03, 2010 5:04 pm

Thanks Bill ... I attempted to say the same thing regarding longer shells and moment of inertia at one point, and hopefully your comments will add more credence to that idea. I think I was pretty much ignored, but maybe I didn't describe it as well.

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Re: BISMARCK armor scheme = BADEN?

Post by RF » Fri Sep 03, 2010 5:41 pm

Karl Heidenreich wrote:
For the first sentence I must say that for two or three years I was of the position that the Bismarck Class was an evolved Baden and with a full array of flaws. After those years of reading the most documented and researched books on battleships design (and comparing these backed up analysis with and against the navweaps agenda) I have come back to the conclusion that Bismarck was the most sophisticated, complex and effective seabourne surface naval superiority vessel up to 1941. After that it was Tirpitz, only second to the Yamato and Musashi, the one that hold that postion until it was sunk (with a priority by the allied naval authoirities that underline this fact).
My own view, for what it is worth, is that Bismarck was an evolved Baden class, with improvements, and that it shouldn't be derogatary to identify the vessel as such. Bismarck was not perfect, as in reality there can be no absolute perfection. For its weight it offered a good combination of speed and armour protection, along with the wider beam. My only real criticism concurs with the views of the naval experts involved with the Ballard expeditions, that Bismarck was not spectacular in hitting power and that the secondary and tertiary batteries did not optimise the needs for AA defence. But that criticism is very much being wise after the event.

As an evolved improved class I would say that Bismarck offered a better improvement than the WW2 hilfskreuzer were compared to SMS Wolf, which was used as the template for their cheap conversion.....
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Re: BISMARCK armor scheme = BADEN?

Post by Thorsten Wahl » Fri Sep 03, 2010 7:34 pm

Bill your explanation is not correct

the moment of inertia for a cylinder is
J=1/2m*r²
so it depends on the radius at the square and mass by 1/2.
By increasing length you are proportionally increasing mass and also increasing proportionally the (stabilising)moment by 1/2 of the increased mass,
but at the cost of potential longer levers for acting forces. Due to the longer levers potential disturbing forces increase with 1/1 of growing length.
because of this a longer shell must precess more to compensate for the same force on the longer lever

And rockets are normally fin stabilised

You cannot stabilise exact spherical objects by rotation because any forces acting on the sphere acting directly through the main focus and so they became not influenced by rotation.
that Bismarck was not spectacular in hitting power
RF what is your definition of spectacular hitting power
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Stability...

Post by Bill Jurens » Fri Sep 03, 2010 9:53 pm

Hi Thorsten:

Thanks for the comments.

I think we are accidentally talking at cross-purposes, i.e. discussing stability along different axes. (My fault, probably, I used the term longitudinal axis in my previous memo -- even though it was techically incorrect to do so -- because in the past, I have found that it's actually clearer to many readers that way.) The stability along the axis running from end to end of the cylinder is indeed proportional to (M r^2)/2 as you have written. I am, however, talking about stability about the transverse axis, i.e. the one running through the center of gravity across the diameter. To put it another way, I am primarily interested to the resistance to end-over-end tumbling. The formula for moment of inertia along that axis, as I'm sure you know, is (m/12) (3r^2 + h^2) with h being the length. Using your formula and assuming a diameter of 1.00 and doubling the length from 2 to 4 calibers changes I from 0.196 to 0.393, so indeed what you are saying is correct, but (of course) only along that axis. Along the transverse axis however, which is the one we are interested in, the moment of inertia goes from 0.792 to 5.583. Basically that's a seven-times increase in resistance vs a two times increase in the lever arm.

You are correct about rockets, of course. My mistake entirely; I was writing carelessly and the phrase "That is one reason why rockets (and arrows) are traditionally spin-stabilized..." should have read "That is one reason why rockets (and arrows) are traditionally FIN-stabilized..." I should have proof-read more carefully.

My point is that given constant cross section, the longer an projectie becomes, the more resistant it is to yaw induction. Because the moment is proportional to the square of the length, and the mass goes up as well, for the 16"/50 2700 lb projectile, the increase from 4 to 4.5 calibers length increases the transverse moment of intertia by about 40%.

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Re: BISMARCK armor scheme = BADEN?

Post by Karl Heidenreich » Fri Sep 03, 2010 9:57 pm

Thorsten:
Bill your explanation is not correct

the moment of inertia for a cylinder is
J=1/2m*r²
so it depends on the radius at the square and mass by 1/2.
By increasing length you are proportionally increasing mass and also increasing proportionally the (stabilising)moment by 1/2 of the increased mass,
but at the cost of potential longer levers for acting forces. Due to the longer levers potential disturbing forces increase with 1/1 of growing length.
because of this a longer shell must precess more to compensate for the same force on the longer lever
That it's correct: Mr. Jurens is mistaken in the calculation of the moment of inertia of a closed cylinder. The open cylinder formula is:
I = mr^2
whilst the moment over the longitudinal axis of the closed cylinder is the one Thorsten posted.
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Re: BISMARCK armor scheme = BADEN?

Post by Karl Heidenreich » Fri Sep 03, 2010 10:09 pm

The formula for the inertia over it's radius axis (instead of the longitudinal axis) is proportional to both: r and h (as a matter of fact the moment increases more with radius 3 x r^2 instead of lenght that it's only h^2). Any increase of them will affect the moment by the square of these measures. So, not only the lenght but the radius is proportionally affected.
However is interesting because, if I remember my old textbook on dynamics, the longer a cilinder (with a constant radius) the greater the rotation moment if it hits a surface on any angle that is not a perfect 90`. If you want a more stable cylinder then you increase the radius.
I think that's why the relation to diameter and lenght is so calculated when it comes to shells.
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Another moment with moments...

Post by Bill Jurens » Fri Sep 03, 2010 10:40 pm

For a solid cylinder we have: I (longitudinal), i.e. axis running from end-to-end = (m * r^2)/2. I (transverse), i.e. across diameter I = (m/12) (3r^2+h^2)

For a tube, we have: I (longitudinal), i.e. axis running from end-to-end = (m/2) (R^2 + r^2). I (transverse) i.e. across diameter I = (m12) (3R^2 +3r^2 + h^2)

Working at first principles, I simply assumed an armor-piercing projectile might be quickly modelled as a solid cylinder. One could, of course, do the complex calculations for a more detailed geometry, but why bother?

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Re: BISMARCK armor scheme = BADEN?

Post by Dave Saxton » Sat Sep 04, 2010 4:54 am

One thing we must bear in mind is that the typical lengths of APC shells (~4.5 calibers overall length including windscreen for the 16" super heavy) are all still within the range of main body lengths that will likely develop significant yaw. In modern (1990) US tests of armor penetration by projectiles with both obliquity and yaw, even main body lengths of 10 calibers developed rather significant yawed orientation after penetration of a yaw inducing plate.
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Re: BISMARCK armor scheme = BADEN?

Post by Dave Saxton » Sat Sep 04, 2010 5:17 am

One thing I should add pertaining to Gercke's discussions on the imperative to keep the center a gravity as close to the head as possible in cases of de-capping was also his reminder that proper decremental hardening of the main body was crucial to the durability and functionality issues as well.
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Re: BISMARCK armor scheme = BADEN?

Post by tnemelckram » Sat Sep 04, 2010 8:33 am

Hi All!

Perhaps information right from the horse's mouth - the testimony of Gr. Adm. Raeder at his trial at Nurenberg - can shed some light on this interesting topic. One of the bases for the charge against Raeder of conspiring to wage aggressive war was his involvement in the design and construction of ships such as Bismarck that breached the Anglo-German Agreement or other treaties. So the Tribunal delved into the design matters.

Day 131 - Direct Examination by Raeder's Counsel, Dr Seimers:
DR. SIEMERS: The Prosecution have accused you of violating this German-English Naval Agreement, and this charge is based on Document C-23, Exhibit USA-49, in the British Delegation's Document Book 10, Page 3. This document is dated 18 February 1938. It has been mentioned repeatedly in these proceedings and begins as follows, "The actual displacement of the battleships Scharnhorst, Gneisenau and F/G is in both cases 20 percent greater than the displacement stated to the British." Then we find a list which shows that the displacement of the Scharnhorst was given as 26,000 tons but was actually 31,300 tons, and that the draught stated one meter less than was actually the case. And the "F" class, that is, the Bismarck and Tirpitz, were listed as 35,000 tons but had an actual displacement of 41,700 and a difference of 80 centimeters in draught. Therefore, according to what we have seen, there is an evident infringement of the treaty. Grossadmiral, I am assuming that you do not dispute this violation of the treaty?

RAEDER: No, in no way.
MY COMMENT: This sets the background. Raeder admits the ships were a Treaty violation. Later Seimers reads quotes from an Affidavit by Dr. Wilhelm Seuchting, a Blohm & Voss shipyard construction director, into the record.

DR. SIEMERS: Since an obvious violation of the treaty exists, we now have to consider in what light this violation should be regarded. The Prosecution have said that this violation of the treaty is criminal since it implies intended aggression. In order to save time, especially since technical problems are involved, I should like, before questioning the defendant further, to submit Document Number Raeder-15, within the scope of the documentary evidence which I have submitted with the Tribunal's permission. In my opinion, this document proves that there was no intention of aggression.

Document Number Raeder-15 is an affidavit-I beg your pardon-it is in Document Book 1, Page 94. This document deals with an affidavit deposed before a notary at Hamburg by Dr. Ing. h.c. Wilhelm Suechting and is important for the refutation of Document C-23, and for that purpose I should like to quote:
"I am the former Director of the shipbuilding yard of Blohm & Voss in Hamburg. I was with this firm from 1937 to 1945"-pardon me-"from 1907 to 1945 and I am conversant with all questions concerning the construction of warships and merchant ships. In particular, as an engineer I had detailed information about the building of battleships for the German Navy. Dr. Walter Siemers, attorney at law of Hamburg, presented to me the Document C-23, dated 18 February 1938, and asked me to comment on it. This document shows that the Navy, contrary to the previous agreement, informed the British that the battleships Scharnhorst and Gneisenau-as well as other intended constructions-had a displacement and draught of about 20 percent less than was actually the case.

"I can give some details to explain why this information was given. I assume that the information given to the British- information which according to naval agreement 4 had to be supplied 4 months before the keel was laid down-was based on the fact that the battleships Scharnhorst and Gneisenan were originally intended to have a displacement of 26,000 tons and a draught of 7.50 meters and the battleship "F" (Bismarck) a displacement of 35,000 tons and a draught of 7.90 meters, as stated.

"If these battleships were afterwards built with a greater displacement and a greater draught, the changes were the result of orders given or requests made by the Navy while the plans were being drafted and which the construction office had to carry out. The changes were based upon the viewpoint repeatedly expressed by the Navy-namely, to build the battleships in such a way that they would be as nearly unsinkable as possible. The increase of the tonnage was not meant to increase the offensive power of the ship"-I beg your pardon, Mr. President. I shall be finished in a moment-"The increase of the tonnage was not meant to increase the offensive power of the ship but was done for defensive and protective purposes."

"As time went on, the Navy attached more and more importance to dividing the hull of the battleship into a greater number of compartments in order to make the ship as unsinkable as possible and to afford the maximum protection in case of leakage. The new battleships were therefore built broad in the beam with many bulkheads, only about ten meters apart, and many longitudinal and latitudinal bulkheads outside the torpedo bulkhead. At the same time, both the vertical and the horizontal armor-plating were, as far as my information goes, heavier and composed of larger plates than those used by other navies. In order..."
MY COMMENT: Suechting's continuous involvement from 1907 through Baden through Bismarck to 1945 suggests that there was some continuity in the design and construction process for both ships. He says that the design of Bismarck and the other ships was driven toward an "unsinkable" ideal, so compartmentation, heavier armor, and other protective purposes caused the increased tonnage, not offensive considerations. That sounds the same as the Tirpitz design philosophy for German WW1 ships such as Baden. Shortly thereafter, Raeder's testimony adopts and expands upon the same themes:

DR. SIEMERS: Herr Grossadmiral, you just saw the affidavit of Dr. Suechting. I ask you: Is it true, or rather-not to confuse you I will ask-on what did the Navy base its ideas about enlarging the battleships by about 20 percent?

RAEDER: Originally there was no intention to enlarge the ships by 20 percent. But at the time when we resumed battleship construction, when we could see that we would have a very small number of battleships in any case, it occurred to us that the resistance to sinking of ships should be increased as much as possible to render the few we had as impregnable as possible. It had nothing to do with stronger armament or anything like that, but merely with increasing the resistance to sinking and to enemy guns. For this reason a new system was worked out at that time in order to increase and strengthen the subdivision of the space within the ship. This meant that a great deal of new iron had to be built into the ships. Thereby the draught and the displacement were enlarged. This was unfortunate from my point of view, for we had designed the ships with a comparatively shallow draught. The mouths of our rivers, the Elbe, Weser, Jade, are so shallow that ships with a deep draught cannot navigate all stages of the rivers. Therefore, we had these ships built broad, intending to give them a shallow draught; but by building in these many new latitudinal and longitudinal bulkheads, we increased the draught and also the displacement.

DR. SIEMERS: Were these disadvantageous changes, which took place during construction, due in part to a comparatively limited experience in battleship construction?

RAEDER: Yes. Since the designers in the High Command of the Navy and the designers and engineers in the big shipyards had not built any heavy warships for a very long time, they lacked experience. As a result, the High Command of the Navy had to issue supplementary orders to the shipyards. This in itself was a drawback which I tried hard to overcome.
MY COMMENT: Raeder adds that the designers had not built any large ships for a long time and lacked experience, which again suggests that many of the same designers for both ships.

FINAL COMMENT: As far as I can tell, the Prosecution did not produce any testimony or other evidence that contradicted these narrow factual points. That enhances the likelihood that they are credibile, accurate and not self-serving in this narrow context. Moreover, Suechting was not going to be prosecuted.

It appears that Baden and Bismarck were designed and constructed by many of the same people and the same firm. It also appears that both ships had the same basic design philosophy favoring protection over firepower, most importantly, a strong hull that is hard to sink.

On the other hand, nothing is said in this testimony about the role played by previous designs and plans in general, let alone specifically connecting the two ships. It merely says that some unspecified original circa 1930 plans were modified by numerous "change orders" that added 20 percent to the original planned displacement. It's possible that those original plans drew on old circa 1918 plans to some greater or lesser degree, but that is just unsupported speculation on my part.

It seems most reasobnable to conclude that Bismarck was influenced by German WW1 design in general rather than by Baden in particular. The design probably started by dusting off all of the late WW1 plans for ships, including some of the unbuilt classes, but then progressed to the point that the old template unrecognizab'e. To me, Bismarck looks more like some of the proposed classes than Baden. When the same people start something anew, it makes sense that they would begin where they stopped before.



SOURCE: Avalon Project - Blue Set - Trial Transcript Of Testimony Day 131: http://avalon.law.yale.edu/imt/05-16-46.asp

Also the rest of the Raeder Testimony:
Day 132: http://avalon.law.yale.edu/imt/05-17-46.asp
Day 133: http://avalon.law.yale.edu/imt/05-18-46.asp
Day 134: http://avalon.law.yale.edu/imt/05-20-46.asp

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Re: BISMARCK armor scheme = BADEN?

Post by Djoser » Sat Sep 04, 2010 1:21 pm

tnemelckram wrote: It seems most reasobnable to conclude that Bismarck was influenced by German WW1 design in general rather than by Baden in particular. The design probably started by dusting off all of the late WW1 plans for ships, including some of the unbuilt classes, but then progressed to the point that the old template unrecognizab'e. To me, Bismarck looks more like some of the proposed classes than Baden. When the same people start something anew, it makes sense that they would begin where they stopped before.
The Mackensens or the ersatz Yorcks in particular would certainly make more likely precursors of the Bismarck than the Baden, I think I mentioned that somewhere before. Yorck would have been 38,000 tons full load, a bit heavier than Baden I believe. It is often forgotten that these ships were started, and in the case of the Mackensens two were launched and worked on further during the war until they had to stop.

I think the WW I German BCs were the original fast battleships, especially when you consider they were harder to sink than the British BBs (except maybe the Queen Elizabeth class).

Great post, tnemelckram!

However I still believe the question posed by the thread has been answered. The Bismarck's armor scheme did not equal the Baden's.

The Bismarck bore similarities--just as a human bears similarities to a chimpanzee--but was an order of magnitude different. It was the next generation, just as the North Carolinas were the next generation US battleship. It seems pretty clear that whatever hiatus in construction of large warships there was, there was no lack of progress in design ability, nor in the abilty to fully utilize all the significant technological progress made since cessation of construction. None whatsoever, as far as I can tell, and the historical results in terms of the ship's offensive and defensive powers would seem to prove it.

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Re: BISMARCK armor scheme = BADEN?

Post by Dave Saxton » Sat Sep 04, 2010 3:57 pm

None but the British Nelson cass battleships had been built after the WWI era, after the moritorium took effect. The Nelsons were also based on the series of designs dating from the early 20's as well. The Germans designed and built the panzerschiffs in the late 20's and early 30's. Although these designs were not battleships they advanced the state of the art of warship design and construction, particulary for new ideas and techniques such as electric welding and several advancements in marine metalurgy. Krupp as a private firm continued its R&D the whole time. Indeed in ADM213/951 the British commented that firms such as Krupp and RMB had established most of their advanced R&D findings concering guns and armour by as early as 1935.

Some of this testimony posted by tnemelckram is bolstered by the commentary of B Hoyer in his 1943 presentation: Calculations for the Heavy Armour of Warships. Hoyer showed the various alternative armour schemes that were used and/or considered, including a thorough understanding of the AoN concept, and then commented that the Germans chose an armour scheme with scarps, because it not only provided outstanding armour protection but also worked well against flooding and the containment of plug ejections and other debris.

Bismarck is obviously a decendent of Baden just as KGV is a decendent and a major upgrade over Nelson. But Baden had none of the advancements in metalurgy, construction techniques, armour plate technology, and weapons technology that made Bismarck's design much more advanced. For example, a panzer deck and upper deck no more than 1 1/2 inches each of equal thickness ratios and of obsolete metalurgy (by later standards) of the Baden does not make for any kind of proper comparison to Bismarck's deck protection, and tells us little about the relative capability and rationals of Bismarck's design.
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Re: BISMARCK armor scheme = BADEN?

Post by Karl Heidenreich » Sat Sep 04, 2010 4:15 pm

tnemelckram's provided us with an outstanding post, which help us understand, even better, the German design process. it is obvious that the Germans had some starting point from something, which by no means is a "remake" of the previous vessel, not even an optimized version but a new ship that shared some basic characteristics.
The same can be applied to some other ships, specially those Treaty Battleships and their descendants. Let's put some special attention to the fact of the broader beam, which is an issue Friedman refers to as a favorable item in Bismarck's design.
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Re: BISMARCK armor scheme = BADEN?

Post by Dave Saxton » Sun Sep 05, 2010 3:47 pm

A fundemental difference between WWI era warships and later is the possible battle ranges. The WWI era max probable battle ranges meant that deck hits or hits which passed over the main belt could be dealt with mainly through fuse initiation. Shells would explode before they could reach the vitals assuming they were not duds. On Baden and other warships of the era a heavy main armoured deck wasn't necessary but a splinter deck was. A common error is to assume that because of the similarity of layout and the common existence of the lower deck with scarps that the Bismarck's armour protection was based on the same principles. Of course at moderate and medium ranges (by WWII standards) these factors were in play, but fuse initiation was no longer the primary governing principle of the armour protection.

We know from Hoyer and other sources that the Germans applied the immunity zone concept to the design of their warships. The specifications issued by the OKM to the designers of the Bismarck class called for a an IZ extending to 32,800 yards vs 15" shell fire. We know from Hoyer and other sources that armour protection (mainly effective thickness) required to prevent intact penetration of the vitals, within the specified IZ, became the governing principles of the design. On Bismarck we find a relatively heavy panzer deck and heavy scarps as the primary armour protection system componant, as Byron pointed out in his original post. This indicates a fundemental difference in design.

Related important factors were also de-capping and the characteristics of modern guns and shells. Conventional vertical armour designs of practical thickness were no longer sufficient to meet the IZ requirements.

Additional factors, is the effect of the heavy panzer deck and scarps on GM and stability. By placing this deck lower, it not only provided the correct amount of interspace for ballistic considerations, but it helped to provide the desired amount of GM and stability. GM is a primary factor to the amount of flooding a design can withstand or the resistance to sinking alluded to by Raeder. A wider beam provided an steady gun platform with a greater GM metric.
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