Nagato protection

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marcelo_malara
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Nagato protection

Post by marcelo_malara » Sat May 23, 2020 3:51 pm

Hi guys. Look at this armour section of Nagato.


Image


What surprises me is the thickness of the horizontal protection:

-weather deck 26mm

-upper deck 70mm

-armoured deck 100mm

This amounts to 196mm, while Bismarck´s total is 130mm. Are the number for Nagato ok?



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hans zurbriggen
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Re: Nagato protection

Post by hans zurbriggen » Sat May 23, 2020 6:38 pm

Hello,
to Marcelo Malara writing: "What surprises me is the thickness of the horizontal protection".
I do not know if values reported are correct. My notes (unfrotunately I don't have the source) say:
1) weather deck in total 25 mm
2) upper armor deck 25+25+19 and
3) lower armor deck 51 mm total over magazines and 25 mm over machines
as built

1) 25 mm added over existing plates (total 50 mm)
2) no change (total 69)
3) 15 mm addded over existing plates (total 66 over magazines and 40 over machines)
after rebuilt

If your reported figures are more correct, then thickness may be impressive, but efficiency of armour layers is much less: if thumb rule that multiple layers of steel are equivalent to square root of the sum of the squared single thicknesses is valid, then Nagato's 3 decks are equivalent to 18mm, 41mm and 50 mm of homogeneous armor only, thus less than 110 mm in total: a WWI layout not comparable to WWII schemes obtained with single thick plates.

hans

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Re: Nagato protection

Post by marcelo_malara » Sat May 23, 2020 8:39 pm

Most detailed description I have is from Whitley´s Battleship of WWII:

-forecastle deck 1", 1.25" around uptakes

-upper deck 1" + 1" + 3/4"

-lower deck 2" (don´t distinguish over machinery or over magazines), 3 x 1" on the slopes

As modified:

-forecastle deck 1" + 1" (so added 1")

-upper deck as built

-lower deck: "..and the continuing of the lower armoured deck to the uptakes with 1" D steel on two layers of 1" HT steel", this will actually be 2" + 3" added

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Re: Nagato protection

Post by marcelo_malara » Sat May 23, 2020 8:46 pm

Look at this:

http://www.navweaps.com/index_lundgren/ ... lArmor.php

Quiet difficult to put all in words!

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Re: Nagato protection

Post by hans zurbriggen » Sat May 23, 2020 10:19 pm

Hello Marcelo,
I agree, very difficult to get to synthesis of the scheme. This is common to many WWI era battleships: Hood is even more complex, with a quite thick "sum of decks" (not armor grade steel) but a very poor efficiency.
Key point (that is valid for all values mentioned) is that thickness of Nagato was achieved by superimposing several thin armor layers (more easy to build) and not with a thick single plate. That means that, using the thumb formula (multiple thicknesses of steel are equivalent to square root of the sum of the squared single thicknesses), effective thickness is not so much. Then there can also be concerns re. efficiency of 3 multiple decks vs a single armor deck.
Equivalent total thickness is no more than 110 mm in the best case. KGV's had 120 mm (150 over mags), Bismarck had 50 + 80 (50 + 100 over mags), SD and Iowa had 38 + 127 mm, Yamato had 200 mm, all decks being built with single thick armor grade steel plates.

hans

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Re: Nagato protection

Post by dunmunro » Sat May 23, 2020 11:51 pm

KGV had a 30mm weatherdeck, a 150mm over 12.5mm D steel MAD and then a 38mm splinter deck over the magazines, with several 12mm decks between the armoured decks.

Over the machinery there was a 30mm weatherdeck, and a 122mm MAD over a 12.5mm D steel deck.

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Re: Nagato protection

Post by hans zurbriggen » Sun May 24, 2020 7:43 am

Hello Mr.Dunmunro,
KGV non armor grade steel layers (or construction steel over which armor deck is simply posed) are not counted for protection effectiveness, not being able to de-cap an APC shell and not adding any protection against an intact shell body.
I do not know if SD and Iowa 38 mm weather deck was an armor grade deck or not (I have never studied American BB's). Can someone confirm ?

hans

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Re: Nagato protection

Post by dunmunro » Sun May 24, 2020 9:43 am

hans zurbriggen wrote:
Sun May 24, 2020 7:43 am
Hello Mr.Dunmunro,
KGV non armor grade steel layers (or construction steel over which armor deck is simply posed) are not counted for protection effectiveness, not being able to de-cap an APC shell and not adding any protection against an intact shell body.
I do not know if SD and Iowa 38 mm weather deck was an armor grade deck or not (I have never studied American BB's). Can someone confirm ?

hans
D steel was an improved HTS and was used as armour. it was used on the weatherdeck and splinterdecks. It was similar, albeit not quite as good as USN STS.

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Re: Nagato protection

Post by hans zurbriggen » Sun May 24, 2020 1:17 pm

Hello Mr.Dunmunro,
D steel is a naval construction steel, not an armor grade steel, having hardness and tensile strength (around 50 kg/square mm) inferior to armor grade ones (e.g. German Wh n/A (85 kg/square mm), not even comparable to Ww n/A (70 kg/square mm), used for torpedo bulkhead and spliter protection only).
Even considering 12.5 D steel under 150 mm MAD as armor grade, equivalent thickness of the MAD (multiple thicknesses of steel are equivalent to square root of the sum of the squared single thicknesses) would be 150.5 mm, therefore the 12.5 layer is non significant in terms of added protection, being a structural layer of the ship.
The 30 mm weather deck, even considering it as armor grade, is too thin to ensure safe de-capping of large caliber shells, that would have to defeat 'only' the MAD, having lost only the ballistic cap and very few velocity.
The lower (below MAD) layer is only a splinter protection as any intact shell would penetrate it.
So said, I personally consider KGV horizontal protection one the best among all battleships, clearly inferior only to Yamato, but superior to American SD and Iowa, at least equivalent to Bismarck (depending on two layers vs single layer scheme efficiency evaluation).

hans

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Re: Nagato protection

Post by marcelo_malara » Sun May 24, 2020 4:59 pm

Good post Hans. Is there any article on the web about all these materials?

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Re: Nagato protection

Post by dunmunro » Sun May 24, 2020 9:40 pm

hans zurbriggen wrote:
Sun May 24, 2020 1:17 pm
Hello Mr.Dunmunro,
D steel is a naval construction steel, not an armor grade steel, having hardness and tensile strength (around 50 kg/square mm) inferior to armor grade ones (e.g. German Wh n/A (85 kg/square mm), not even comparable to Ww n/A (70 kg/square mm), used for torpedo bulkhead and spliter protection only).
Even considering 12.5 D steel under 150 mm MAD as armor grade, equivalent thickness of the MAD (multiple thicknesses of steel are equivalent to square root of the sum of the squared single thicknesses) would be 150.5 mm, therefore the 12.5 layer is non significant in terms of added protection, being a structural layer of the ship.
The 30 mm weather deck, even considering it as armor grade, is too thin to ensure safe de-capping of large caliber shells, that would have to defeat 'only' the MAD, having lost only the ballistic cap and very few velocity.
The lower (below MAD) layer is only a splinter protection as any intact shell would penetrate it.
So said, I personally consider KGV horizontal protection one the best among all battleships, clearly inferior only to Yamato, but superior to American SD and Iowa, at least equivalent to Bismarck (depending on two layers vs single layer scheme efficiency evaluation).

hans

D steel was armour grade and was used for that purpose just as STS was:
Average Post-WWI Extra-High-Strength "D" Silicon-Manganese HT Steels

Ship construction, light armor up to 2" (5.08cm), and anti-torpedo bulkheads.
http://www.navweaps.com/index_nathan/me ... _HT_Steels
http://www.navweaps.com/index_nathan/me ... pt2009.php
There are various methods for calculating the resistance of multiple plate layers, and it's not possible to reduce it to a single formulae. Similarly the decapping of AP shells and bombs is very complex.

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Re: Nagato protection

Post by dunmunro » Mon May 25, 2020 5:02 am

This is a schematic of the armour over the KGV (Its from the Lion class in Allied Battleships but KGV was the same) magazines:

The placement of the splinter protection, and the distance from the MAD to the magazines adds considerably to the protection of the magazines, as a shell or bomb is likely to detonate well above the magazines even if it can penetrate the MAD, and the same is not true for many KM and USN designs, where the magazines are directly below the MAD.
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KGV_CT.jpg
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Re: Nagato protection

Post by hans zurbriggen » Mon May 25, 2020 7:33 am

Hello Mr.Dunmunro,
"D steel was armour grade": here we can agree to disagree. It may have been used by some Navies for protection in some schemes (mostly when better steel was unavailable and/or only as splinter protection) but it does not have hardness and tensile strength quality (see the data I have posted above) to be considered an armor grade steel to defeat large caliber APC shells: it' s just a very strong construction steel.
However this is not important, as the thickness of the weather deck is anyway so limited (30 mm) that (even if it would have been built with the best existing armor grade homogeneous steel) it cannot de-cap a shell (formulas may be complex but below 1 caliber almost everybosy agrees that there is no chance to de-cap an APC shell) and therefore it adds almost nothing (like all the intermediate 'light' bulkheads) to the overall protection against battleships fire. Thanks for posting the scheme below. It shows that the 30 mm weather deck is ignored (as protective layer) also by "Allied Battleships".
If we count all construction steel layers, then "Hood" would have been very well protected with around 250 mm steel over mags (while she was absolutely not) and "Littorios" would show an impressive 229 mm over mags at centerline (while 'only' 186 armor grade protection was present).
Re. 37 mm spliner protection, this is present only around mags (that were among the best protected ones among all battleships, I know), however all other vitals in KGV have 'only' 124 mm MAD to protect them.
The 'thumb' formula for the equivalent thickness of armors is the widely accepted one, I have seen others but all of them reduce the structural layer below an armor deck to almost nothing in terms of contribution.

Still I wonder weather the 38 mm weather deck on SD and Iowa was armor grade or not (I mean, same armor grade quality as the MAD).

hans

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Re: Nagato protection

Post by Thorsten Wahl » Mon May 25, 2020 8:47 am

the upper deck on american Battleships was made of STS (sample Iowa class)
Image

the main armor deck of Iowa class was a laminate
Image


Comparison D-Steel vs St-52

comment imperial-Elongation and DIN-Dehnung (delta5) are not comparable as the german specification uses a relatively longer specimen
D Steel an armour grade material??? wishful thinking IMHO




Image
Last edited by Thorsten Wahl on Mon May 25, 2020 9:30 am, edited 4 times in total.
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Re: Nagato protection

Post by dunmunro » Mon May 25, 2020 9:20 am

hans zurbriggen wrote:
Mon May 25, 2020 7:33 am
Hello Mr.Dunmunro,
"D steel was armour grade": here we can agree to disagree. It may have been used by some Navies for protection in some schemes (mostly when better steel was unavailable and/or only as splinter protection) but it does not have hardness and tensile strength quality (see the data I have posted above) to be considered an armor grade steel to defeat large caliber APC shells: it' s just a very strong construction steel.
However this is not important, as the thickness of the weather deck is anyway so limited (30 mm) that (even if it would have been built with the best existing armor grade homogeneous steel) it cannot de-cap a shell (formulas may be complex but below 1 caliber almost everybosy agrees that there is no chance to de-cap an APC shell) and therefore it adds almost nothing (like all the intermediate 'light' bulkheads) to the overall protection against battleships fire. Thanks for posting the scheme below. It shows that the 30 mm weather deck is ignored (as protective layer) also by "Allied Battleships".
If we count all construction steel layers, then "Hood" would have been very well protected with around 250 mm steel over mags (while she was absolutely not) and "Littorios" would show an impressive 229 mm over mags at centerline (while 'only' 186 armor grade protection was present).
Re. 37 mm spliner protection, this is present only around mags (that were among the best protected ones among all battleships, I know), however all other vitals in KGV have 'only' 124 mm MAD to protect them.
The 'thumb' formula for the equivalent thickness of armors is the widely accepted one, I have seen others but all of them reduce the structural layer below an armor deck to almost nothing in terms of contribution.

Still I wonder weather the 38 mm weather deck on SD and Iowa was armor grade or not (I mean, same armor grade quality as the MAD).

hans
The weatherdeck thickness was 31mm and was made from the same D steel as the magazine splinter deck.

This is from Nathan Okun's article Decapping revisited:
The plate thicknesses assume any kind of ductile steel or even wrought iron. There doesn't seem to be any kind of visible trend as to stronger decapping plates being able to be thinner...
http://www.navweaps.com/index_tech/tech-085.php
So decapping is not a function of plate characteristics.

Okun states that .0805 calibre plate thickness begin to be effective for decapping at high obliquity.

Okun's various articles gives all the pertinent information regarding naval steel qualities, and D steel compares well and was quite suited for use as light armour.

It's not a question of "counting" plate thickness but of analyzing the trajectory path and the resistance of each plate in the projectile's path, and determining if the projectile can penetrate each plate, and if so where it will burst, if it is still fit to burst. Then determining if the projectile burst can present a threat to the magazine. One cannot simply pretend that plates don't exist. Even thin D steel decks will rapidly decelerate shell splinters, for example.

The USN used STS steel on the weather deck.

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