1919: Analysis of Hood's magazine protection

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Pandora
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Re: 1919: Analysis of Hood's magazine protection

Post by Pandora » Sat Aug 17, 2013 12:36 am

dunmunro wrote:
Pandora wrote:
dunmunro wrote:So a 15in shell could penetrate 7in + 1in HTS of side armour inclined at ~40 degs and still go through a 2in scarf at 10degs and still perforate a 2in deck inclined at 70 degs. This shows how very vulnerable Scharnhorst's deck was to plunging fire and it even implied that Bismarck was vulnerable through her upper 145mm ( 5.7in) belt.
I can't find where in that paper are Scharnhorst and Bismarck mentioned?
I can't believe that you are unable to draw the obvious comparisons and conclusions.
so your reasoning is: OK Hood armor was penetrated, BUT wait a moment, German armor could be penetrated too!
If that makes you feel better that's fine.

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Re: 1919: Analysis of Hood's magazine protection

Post by dunmunro » Sat Aug 17, 2013 1:30 am

Pandora wrote:
dunmunro wrote:So a 15in shell could penetrate 7in + 1in HTS of side armour inclined at ~40 degs and still go through a 2in scarf at 10degs and still perforate a 2in deck inclined at 70 degs. This shows how very vulnerable Scharnhorst's deck was to plunging fire and it even implied that Bismarck was vulnerable through her upper 145mm ( 5.7in) belt.

so your reasoning is: OK Hood armor was penetrated, BUT wait a moment, German armor could be penetrated too!
If that makes you feel better that's fine.


The RN target was designed to test Hood's armour scheme, but it also provides a useful analogue to Bismarck, which also featured an upper belt of similar thickness and a similar deck armour arrangement, so the results are of interest in examining Bismarck and Scharnhorst's vulnerability to plunging fire, which has been debated in many threads, here and elsewhere.

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Re: 1919: Analysis of Hood's magazine protection

Post by dunmunro » Sat Aug 17, 2013 2:03 am

Pandora wrote:
If I asked is because I don't know how to use that software. :(
OK, I ran the armour thickness, inclination and SV using a 15in "greenboy" AP shell through NaAB:
http://www.panzer-war.com/Naab/NAaB.html
which incorporates an earlier version of facehard into a win32 program with a GUI.

I opened two NAaB windows and used the first to produce the results of striking the 7in+1in belt and then in the 2nd window I used a decapped 15in greenboy with the estimated SV for the remaining plates; the end result was that penetration of the final plate would not occur, albeit the results were close as NAaB predicted partial penetration of 1.6in of HTS, if I've done it all correctly.

The other interesting result from the 1919 trial is that a 15in shell was able to penetrate a 2in HTS weatherdeck, a 3in MAD and a 2in HTS crown over the magazine with a deck separation very similar to Bismarck and Scharnhorst.

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Re: 1919: Analysis of Hood's magazine protection

Post by alecsandros » Sat Aug 17, 2013 8:50 am

dunmunro wrote: The other interesting result from the 1919 trial is that a 15in shell was able to penetrate a 2in HTS weatherdeck, a 3in MAD and a 2in HTS crown over the magazine with a deck separation very similar to Bismarck and Scharnhorst.
HTS and RHA and Whotan and STS are completely different materials with completely different properties.

HTS was the British equivalent of GErman ST52 (construction steel)

Regardless, the Bismarck class featured 50mm whotan upper deck (with probably 80mm around barbettes) , and 95mm thick whotan MAD above magazines (80mm thick above machinery)

Distance between upper deck and MAD was around 5.5meters at centerline of the ship.
Last edited by alecsandros on Sat Aug 17, 2013 10:15 am, edited 1 time in total.

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Re: 1919: Analysis of Hood's magazine protection

Post by alecsandros » Sat Aug 17, 2013 10:00 am

dunmunro wrote: The drawing clearly shows that the target's 7in+1in HTS armour was penetrated at 40 degs inclination, and the shell went on to penetrate another 2in scarf, .75in bulkhead and perforated a 2in HTS deck after striking it at 70 degrees inclination.
... The drawing shows a 20* descent angle for the shell, and the 10* declination of the armor belt.

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Re: 1919: Analysis of Hood's magazine protection

Post by dunmunro » Sat Aug 17, 2013 5:33 pm

alecsandros wrote:
dunmunro wrote: The drawing clearly shows that the target's 7in+1in HTS armour was penetrated at 40 degs inclination, and the shell went on to penetrate another 2in scarf, .75in bulkhead and perforated a 2in HTS deck after striking it at 70 degrees inclination.
... The drawing shows a 20* descent angle for the shell, and the 10* declination of the armor belt.
The drawing labelled "Sketch of actual target" shows the inclination of the various plates, including 40degs for the 7in plate, and the path of the shell:

Image

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Re: 1919: Analysis of Hood's magazine protection

Post by Thorsten Wahl » Sat Aug 17, 2013 7:42 pm

duncan were the test with the target "scetch of target for next trail" carried out. what was the result.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
the naab prediction did not consider yaw, trajectory change, change of head shape.

as already said several times the Germans estimate the protective effect of Bismarcks horizontal protection as beeing 150 mm (for parts below the main armored deck). The same evaluation can be found in SUPP 6-481 Underwater performance of shells and the US report on Hurlich "Spaced armor" came to 110-130 percent additional protection for proper constructed spaeced array compared to single plates at high obliqity impact.
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Re: 1919: Analysis of Hood's magazine protection

Post by dunmunro » Sat Aug 17, 2013 8:46 pm

Thorsten Wahl wrote:duncan were the test with the target "scetch of target for next trail" carried out. what was the result.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
the naab prediction did not consider yaw, trajectory change, change of head shape.

as already said several times the Germans estimate the protective effect of Bismarcks horizontal protection as beeing 150 mm (for parts below the main armored deck). The same evaluation can be found in SUPP 6-481 Underwater performance of shells and the US report on Hurlich "Spaced armor" came to 110-130 percent additional protection for proper constructed spaeced array compared to single plates at high obliqity impact.
Yes, NAaB doesn't consider those factors (except for trajectory change) and so it might be optimistic, however the actual trials, by definition, did consider these, for example this test:
Image
Result. 15" A.P.C. shell perforated all plates, presumed "whole", shell being buried in ground and not recovered. The shell turned down about 15° while perforating the "armour" deck (i.e. centre plate of target).
and is a very interesting result.
This result is even more interesting:
Image
Shell perforated all plated and buried itself deep in the ground- probably it wil be recovered whole.
as the MAD is now 3 HTS plates = 120lb + a 100lb armour plate = 5.5in total and it still penetrated all plates! Note that the plate separation for these tests was 17.5 to 18.5ft (~5.5m).

I found this drawing:
Image
http://www.navweaps.com/index_inro/INRO_Hood_p1.htm

and it shows the 15in shell being deflected by the 3in HTS deck, however what it does not show is that the 7in+1in plate was inclined at 40degs (representing a 20deg AoF and a 20 degree inclination on the plate) as per "sketch of target for next trial".

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Re: 1919: Analysis of Hood's magazine protection

Post by alecsandros » Mon Aug 19, 2013 5:14 am

dunmunro wrote:
and it shows the 15in shell being deflected by the 3in HTS deck, however what it does not show is that the 7in+1in plate was inclined at 40degs (representing a 20deg AoF and a 20 degree inclination on the plate) as per "sketch of target for next trial".
...
Duncan,
one of the proposals following those trials was:

"2. These trials showed that neither 3" mild steel nor 2½" armour quality steel added to the main deck are sufficient to keep out the 15" A.P.C. shell at this angle of impact. It was therefore proposed (C. Sec C.1527/18 attached) to complete H.M.S. "HOOD" without any further additional deck armour and to press on with D.N.C.'s trials of improved "special treatment steel" plates etc. in hopes of producing plating which would meet the case without adding undue weight, and at a cost less than that of "armour quality" plating. This poilicy was carried out & ? (illegible handwriting)? trials are pending."

The "special treatment steel" was probably the rolled homogenous armor used in later British battleships.

There is an important quality difference there that should not be overlooked...

Nevertheless, the 15" British APC fired from the L42 guns was a very dangerous shell, and had good horizontal perforating power...

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Re: 1919: Analysis of Hood's magazine protection

Post by Dave Saxton » Tue Aug 20, 2013 12:58 pm

dunmunro wrote:
Dave Saxton wrote:Your comparing apples to oranges. :negative:
Why so?

The spacing, geometric relationships between the plates, the materials, and the effective thickness' are all completely different.
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Re: 1919: Analysis of Hood's magazine protection

Post by Dave Saxton » Tue Aug 20, 2013 1:35 pm

alecsandros wrote:Nevertheless, the 15" British APC fired from the L42 guns was a very dangerous shell, and had good horizontal perforating power...
Only at long range. The British found none of their battleship shells could defeat 6" modern homogenous armour at less than 32,000 yards in firing range testing. At short and medium range it will most likely scoop off of high quality homogenous armour due to its head shape.

To go back to the original faulty presumption behind this, lets look at the mythological 14" hit on Scharnhorst at 19,500 meters but leave out any effects of de-capping ...ect... We could treat the 80mm-95mm panzer deck just as if it was the only armoured deck, as in all or nothing design in our analysis:

The angle of fall is ~17*. I repeat the angle of fall is ~17*, or 73* from the normal. It is going to scoop most likely. Even using a popular computer model which does not properly account for the head shape of the British shell and their want to scoop, the penetration is less than 80mm. It is 71mm. This is particularly the case once we also factor in those other factors unique to the German armouring scheme and materials properties.

Remember this was a stern chase, so target angle is going to be rather oblique for a hit to pass over the main belt through the thinn upper belt and reach the panzer deck intact. Even if by chance the mythological hit just happened to come in and pass over the main belt at a time when the target angle was not very oblique, it will at least be fused. The distance to be covered to reach the panzer deck at 17* angle of fall is more than 16 meters. The shell will explode well before that. In order for the mythological hit to happen; the odds are rather long indeed.
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: 1919: Analysis of Hood's magazine protection

Post by Dave Saxton » Tue Aug 20, 2013 1:52 pm

Thorsten Wahl wrote:as already said several times the Germans estimate the protective effect of Bismarcks horizontal protection as beeing 150 mm (for parts below the main armored deck). The same evaluation can be found in SUPP 6-481 Underwater performance of shells and the US report on Hurlich "Spaced armor" came to 110-130 percent additional protection for proper constructed spaeced array compared to single plates at high obliqity impact.

That's right. The actual vulnerability to "plunging fire" is no greater than it is for KGV.
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: 1919: Analysis of Hood's magazine protection

Post by alecsandros » Wed Aug 21, 2013 5:43 am

Dave Saxton wrote:
alecsandros wrote:Nevertheless, the 15" British APC fired from the L42 guns was a very dangerous shell, and had good horizontal perforating power...
Only at long range. The British found none of their battleship shells could defeat 6" modern homogenous armour at less than 32,000 yards in firing range testing. At short and medium range it will most likely scoop off of high quality homogenous armour due to its head shape.
At long range, of course.
The 15"/L42 was a much dangerous horizontal perforator than most contemporary shells.

Adding some gun wear and possible slight inclinations of the target-ship, the 381mm shell could probably perforate some ~ 130-140mm of RHA at 23km or more.

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