Bismarck/Tirpitz = most powerfull European battleships

Discussions about the history of the ship, technical details, etc.

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Dave Saxton
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Re: Bismarck/Tirpitz = most powerfull European battleships

Post by Dave Saxton »

Hi Phil,

This is why the Germans found that a min distance between de-capping plate and the main armour was required. IIRC, Gercke commented that the min interspace to insure de-capping is ~60cm.

In the one set of tests which included a Tirpitz based array it was found that APC shells were "always de-capped" by such an array by the time it reached the main armour, although the test array was not constructed with the correct interspace distance.
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phil gollin
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Re: Bismarck/Tirpitz = most powerfull European battleships

Post by phil gollin »

I think quoting just one set of tests is rather pointless. Certainly the British found numerous contradictory results.

As I said for yaw effect the post mid-50s tank guys are probably much better informed, and post 1990 hydrodynamacists for penetration in general.

.
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Re: Bismarck/Tirpitz = most powerfull European battleships

Post by Thorsten Wahl »

But Thorsten should be able to tell us what he meant...
I differenciate between
"deflection towards plate normal additional - reduces the efficiency of plate 2"
deflection.jpg
deflection.jpg (26.86 KiB) Viewed 1760 times
and

"Additional some kind of yaw could be introduced, this means direction of flight differ significantly from orientation of the shell, here the remaining distance between the plates was of essential importance. (too low distance could improve penetration abilities of the shell, so this could be an contraproductive feature)"
Certainly the British found numerous contradictory results.
here you are, depending on the orientation of head at the impact on the second plate the performance may be increased or decreased. The tests show a dependency from the flightdistance between both plates and also obliquity

Image

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As far as I know the british tests consider the removal of the cap as the main factor in decreasing pentration performance
there are several modes of failure of the cap
the cap may be deformed
the cap may be broken (instant effect best case)
the cap may be removed(as whole/or fragments) from the projectile(this requires sufficient space between the plates second best)
(for this case the Littorio system RHA-foreplate and FH-main plate was probably not wide enough to complete decapping)
Postby JtD » Fri Sep 24, 2010 6:14 am
http://www.combinedfleet.com/okun_biz.htm
Ever read through this?
her you can find this statement
38 CM C/34 FIRING PSGR. M. K. L/4,4 AT VARIOUS BELT ARMOR DESIGNS
USS SOUTH DAKOTA 20.3 (18.5) 16.4 (15) NEVER (Shatter)

this is not true the so called decapping plate(outer hull) was never able to decap major naval projectiles. this article was superceded by decapping revisited at http://www.navweaps.com/index_tech/tech-085.htm
many people rever to the articles at combined fleet and take them at the last wisdom but some content was obsolete and requires an update I think.
I dont have any problems with Nathan Okuns work, as it was outstanding and delivers a lot of usable Informations on armor and armor pentration. I cannot call him a "opus dei".
...........
so they try to minimize projectile degradation by decapping caused by the impact on the first plate. But progress wasnt that succesful

The end of the story was , no battleships became a real opponent for US/RN warships past ww2, so further development of better guns and shells for major naval guns were never necessary and high order research can be considered as wasting of ressources.
As I said for yaw effect the post mid-50s tank guys are probably much better informed, and post 1990 hydrodynamacists for penetration in general.
Modern research can give us some clue on mechanisms of pentration of spaced arrays. So its no cheating if you look at results of modern research, to conclude on the effectivenes of a ww2 spaced array.
Thats why i gave the link so broad.
http://www.dtic.mil/srch/search?searchv ... zation=YES
Its on your decision to restrict the search and to read whatever you want. (I will be never able to read all existent ballistic literature,so my wisdom is also very limited, so its a matter of common research and (peaceful) discussion to get the best result.)
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Re: Bismarck/Tirpitz = most powerfull European battleships

Post by alecsandros »

phil gollin wrote: As I said for yaw effect the post mid-50s tank guys are probably much better informed, and post 1990 hydrodynamacists for penetration in general.
.
The problem with the tests you mention is that they don't use battleship shells. It is well known that a host of behaviors of large-caliber shells do not apply to medium or small-caliber naval guns (take for instance underwater performance).

The behavior of the German 15" shells was well documented by Krupp in the 30s thanks to high-speed cameras. The quality and quantity of the tests performed by them was very serious. The findings, at least the ones I know about, were that
- 50mm whotan plates always induced a certain amount of yaw to the perforating shell (though the amount varied with shell mass, shape and impact velocity)
- large-caliber shells had a good chance of base-slap during penetration.
- at normal angles of penetration (up to 35* from the horizontal?), the 50mm high-quality homogenous armor was enough to de-cap shells up to 16" in diameter.

So, in the end, the problem with these tests and experiments is that they weren't repeated after teh second world war. And they can not be repeated now, because the necessary "tools" are missing: functional Japanese 18" guns.. ? functioning 15" German guns.. ?
So the only option for us right now is to learn more about historical testing with full-scale battleship shells, and try to interpolate the results of various testings... (British, German, American, etc)
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Re: Bismarck/Tirpitz = most powerfull European battleships

Post by Dave Saxton »

Hi Phil,
phil gollin wrote:I think quoting just one set of tests is rather pointless. Certainly the British found numerous contradictory results.

As I said for yaw effect the post mid-50s tank guys are probably much better informed, and post 1990 hydrodynamacists for penetration in general.

.
I would agree that there may be a few cases were de-capping was not effected, but on the whole de-capping by systems designed to do so, was the rule and not the exception to the rule. For future AP shell design the RN committe post war reccomended AP shells without caps for deck penetrators, because of the very high probability of deck protection systems designed to remove the cap, removing the cap, and making further deck penetration of the main armour rather difficult. The Germans also found that keeping the cap on was more of a problem than knocking one off, provided the de-capping plate was heavy enough per caliber for the striking angle. They tried welding, cap screws, and plastic epoxies, all with negligable improvement to standard methods. This was one reason they did not adopt an even blunter head shape of nearly hemisperical shape, because it was fairly easy to remove the cap from such shells, compared to sharper head shapes.
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Re: Bismarck/Tirpitz = most powerfull European battleships

Post by Dave Saxton »

Thorsten Wahl wrote:...here you are, depending on the orientation of head at the impact on the second plate the performance may be increased or decreased. The tests show a dependency from the flightdistance between both plates and also obliquity

Image
Modern (1990) American research into yawed oblique impact contradicts this, but as Phil says there is contradictory data. The American research found that it still required more than 10% more energy for nosed down impact compared to non yawed impact during oblique penetration. The different result may be due to the obliquity though. The American study concerned more accutely oblique impact, as would be the case of horizontal rather than vertical armour.


Nose up impact with horizontal armour required yet much more velocity compared to nosed down impact or unyawed impact. Here the distance between yaw inducing plate and the main plate becomes very important because the greater the distance within reason , the more time there is for the effect of precession (which most likely results in a nose up yaw by the point of impact) to become manifest. This illustrates why it was very important to place the panzer deck on the German designs relative to the weather deck, such that they did.

One of the things mentioned in APP 30 was that blunter head shape shells had a slower rate of post penetration precession compared to the standard 1.4 caliber radius shells, and so had the array been constructed with the proper interspace it would have performed even better against more blunt nose penetrators.
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Re: Bismarck/Tirpitz = most powerfull European battleships

Post by JtD »

Dave Saxton wrote:Note that 80mm+50mm=130 mm, and I seriously doubt that is coincidental. It's enterily plausible that because of de-capping and other factors touched upon that they knew that c1h/c could be raised to the point that VII>=VI, and they could attain at least 1:1 effective thickness.
Actually, the only way to "increase c1h/c" is to produce a crappy thick plate. If you have evidence that German 130mm plate were awful, please show.

Considering that decapping is something that loses most of its effect against homogeneous armour and that the lower deck was of that type, it is not plausible that 50+80 defeat physics.
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Re: Bismarck/Tirpitz = most powerfull European battleships

Post by Dave Saxton »

But de-capping does not lose most of its effectiveness against homogenous armour in all cases. That is not a true premise. If the homogenous armour has a tensile strength of greater 80kg/mm2, a de-capped shell requires considerably greater necessary velocity compared to a capped shell of equal mass, particuarly where we are talking about accutely oblique striking angles. Many examples where we have neceassary velocities matching or exceeding that of a single plate are using homogenous armour from the main plate. An homogenous main plate can be as effective as a cemented main plate, although it may be for different reasons.

The use of cemented armour in a decapping array is usually operating on a different principle than intact penetration or else rejecting the shell. In de-capping arrays which employ cemented armour as the main plate, the usual principle is that a de-capped will shatter if it strikes the main armour above a certain velocity. The main plate has to be just thick enough to reject the shell if it is travelling below the min shatter velocity. A de-capping array to produce shatter usually provides plate and shell debris barriers behind the main plate.

I'm not worried about semantics and exact mathamatical terms, because the known factors that require more necessary velocity to penetrate the main plate can produce a condition of effective thickness matching or exceeding that of a single plate as observed in many cases, even with homogenous plates. If the result can be observed it must be within the possible physical parameters.
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Re: Bismarck/Tirpitz = most powerfull European battleships

Post by JtD »

Dave Saxton wrote:...If the homogenous armour has a tensile strength of greater 80kg/mm2, a de-capped shell requires considerably greater necessary velocity compared to a capped shell of equal mass, particuarly where we are talking about accutely oblique striking angles. Many examples where we have neceassary velocities matching or exceeding that of a single plate are using homogenous armour from the main plate. An homogenous main plate can be as effective as a cemented main plate, although it may be for different reasons...
Please show the examples.
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Re: Bismarck/Tirpitz = most powerfull European battleships

Post by phil gollin »

Dave Saxton wrote:
........ For future AP shell design the RN committe post war reccomended AP shells without caps for deck penetrators, because of the very high probability of deck protection systems designed to remove the cap, removing the cap, and making further deck penetration of the main armour rather difficult. ............


(I wrote a nice answer that "disappeared")

Not quite. There were several ideas post-war (including the one that won out = "why bother"). The real work went into cruiser calibre (especially 5.25-inch) penetration.

For large calibres, the real idea was that existing battleships were essentially invulnerable at likely battle ranges ("say" 24,000 yards-plus) - and difficult at even short ranges. The RN thought that a higher capacity (about half-way between AP and HC) shell with deck penetration as good as or better than an AP shell AND (very important) the ability to be rejected in an explodable condition was needed so as to attack decks with the bonus of destruction of command and control facilities, electronics, communications and the superstructure in general.

.
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Re: Bismarck/Tirpitz = most powerfull European battleships

Post by RF »

Dave Saxton wrote: . Note that the Bismarck's turrets tops were 130mm single plate Wh to attain an IZ requirement to 30,000 meters vs 15" shell fire. It would be highly unlikely that they would design and accept a deck protection system, which did not provide a min deck protection at least matching this specification.
I recall in reading that comment that Bruno turret apparently had its roof blasted off by a 16 inch shell from Rodney.
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Re: Bismarck/Tirpitz = most powerfull European battleships

Post by JtD »

Didn't a 1600lb AP bomb at about 300m/s velocity and an angle of impact of about 70° penetrate the 50+100mm arrangement on Tirpitz?
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Re: Bismarck/Tirpitz = most powerfull European battleships

Post by lwd »

I noticed in the file gsap_088 (part of the zip package linked by Thorsten) it states something to the effect that a plate thickness of .2 D required to decap a projectile. Now some latter infromation shows that this is very conservative but it implies that the the deck if it was designed to decap was designed to decap 250mm and over the magazines only 400mm projectiles. Rather brings to question whether or not decapping was the purpose.
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Re: Bismarck/Tirpitz = most powerfull European battleships

Post by Bgile »

RF wrote:
Dave Saxton wrote: . Note that the Bismarck's turrets tops were 130mm single plate Wh to attain an IZ requirement to 30,000 meters vs 15" shell fire. It would be highly unlikely that they would design and accept a deck protection system, which did not provide a min deck protection at least matching this specification.
I recall in reading that comment that Bruno turret apparently had its roof blasted off by a 16 inch shell from Rodney.
I think that was the back of the turret, not the top.
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Re: Bismarck/Tirpitz = most powerfull European battleships

Post by Thorsten Wahl »

lwd wrote:I noticed in the file gsap_088 (part of the zip package linked by Thorsten) it states something to the effect that a plate thickness of .2 D required to decap a projectile. Now some latter infromation shows that this is very conservative but it implies that the the deck if it was designed to decap was designed to decap 250mm and over the magazines only 400mm projectiles. Rather brings to question whether or not decapping was the purpose.
0.2 D in the line of flight if i understand the meaning right
so 50 mm thickness at 60° obliquity should be equivalent to 100 mm in flight direction


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against 1600 lbs AP bombs at 300m/s and 20° obliquity no existing horizontal protection scheme should be able to defeat such a piece
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