Nagato protection

Warship design and construction, terminology, navigation, hydrodynamics, stability, armor schemes, damage control, etc.
Thorsten Wahl
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Re: Nagato protection

Post by Thorsten Wahl » Tue May 26, 2020 4:34 pm

Dave Saxton wrote:
Tue May 26, 2020 4:00 pm
I also have primary documentation on ST52 and D Steel

see my post Thorsten Wahl » Mon May 25, 2020 8:47 am
Meine Herren, es kann ein siebenjähriger, es kann ein dreißigjähriger Krieg werden – und wehe dem, der zuerst die Lunte in das Pulverfaß schleudert!

dunmunro
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Re: Nagato protection

Post by dunmunro » Tue May 26, 2020 6:35 pm

hans zurbriggen wrote:
Tue May 26, 2020 12:38 pm
Hello,
to Mr.Dunmunro writing: "...your stubbornness in refusing to acknowledge the totality of KGV's deck..."
I am extremely disappointed to see these kind of personal comments, especially as I would have so much to say regarding the same attitude from your side.

I have no problem admitting my mistake regarding the D-steel post WWI data, but I see you don't acknowledge your mistakes re. mixing nichel steels of WWI era with WWII armor grade steels, re. KGV deck being sufficient for de-capping (when it was not, per your own sources) and re. D-steel being an armor grade one (Brinell hardness of pure construction steel ST52=150, D-steel =170, armor grade (e.g.Wh /nA)=250, everyone can make up his mind based on what you yourself posted as reference).

Therefore, despite we all (since the beginning) agree about 'we have to examine the entire protective scheme', I will discontinue this by now unproductive discussion with you re.KGV, hoping you will do the same, to avoid very unpleasant drifts, being back to Nagato protection.

hans
I didn't mix D steel with WW2 armour grade steels; I stated that D steel was used as armour and had good armour qualities. KGV's weather deck is capable of decapping AP projectiles, and we've both agreed to this. There is no arbitrary cutoff or category which determines whether or not a plate's resistance should be examined when looking at a protective scheme. This has been my consistent message here.

Bill Jurens
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Re: Nagato protection

Post by Bill Jurens » Tue May 26, 2020 6:52 pm

Another very important thing that is being neglected here is the effect of the supporting 'grillage' of beams etc., underneath the deck armor. The deck plating is not just floating in space. It's really impossible (or at least unsafe) to generalize, but in practical terms if one works the geometry for most ships it was pretty difficult for a large caliber shell to make it through the deck plating without intercepting some usually fairly substantial structural members underneath until angles of fall exceeded 30 degrees or so. It's a probability game that throws a fairly important 'wild-card' into the discussion.

Whether or not this underlying supporting structure may be properly counted as 'armor' or not has never really been clearly defined or discussed, so far as I know, on fora like this, but you can be assured that -- like it or not -- it acted that way. And it should be considered.

Bill Jurens.

hans zurbriggen
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Re: Nagato protection

Post by hans zurbriggen » Tue May 26, 2020 8:03 pm

Hello,
I agree with Mr.Jurens consideration about structural elements and I would add that in case of Bismarck's, Nelson's and Littorio's (plus of course Nagato's), having also a third deck between the 2 armor decks, this adds thickness and other structural elements to be 'defeated'. Also, the subdivision above the MAD of these ships provided by transversal and longitudinal bulkheads (of a steel comparable to D-steel), would present to an incoming shell much more probability to hit structural elements and vertical bulkheads before reaching the MAD than in a design that has the two armor deck separated only by one level. Difficult to say, however, if these elements really play against the shell or not, IMHO.

hans

Mostlyharmless
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Re: Nagato protection

Post by Mostlyharmless » Wed May 27, 2020 10:34 pm

Nagato's rebuild is designed to prevent what happened to Hood happening to Nagato. The machinery spaces end up only protected at their 1920 standard whilst the magazines are quite well protected against WW2 shells, although there seem to be a few weak points such as the top of the lower barbette at frame 77. However, some weight was wasted because armour was added to defend against the IJN's Type 91 shells, which were not likely to fired at Nagato (the Inboard Barbette Protection).

hans zurbriggen
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Re: Nagato protection

Post by hans zurbriggen » Thu May 28, 2020 7:50 am

Hello Mr. Mostlyharmless,
point I had made is that merely adding a layer of armour over another, does not add much extra protection (e.g. the tumb formula: multiple thicknesses of steel are equivalent to square root of the sum of the squared single thicknesses). Weak points (e.g. due to discontinuities between machinery and mags areas) are anyway present as you correctly point out. Mags themselves may have been adequately protected, machinery was not.
This was a common problem to all WWI rebuilt battleships that, even presenting high thicknesses after rebuilding, were still not comparable to WWII single plate decks design in terms of protective efficiency.
A rebuilt Hood would possibly not been blown up, but would have been disabled anyway because she would never have been a KGV anyway, due to this limitation, as well as a rebuilt QE. On the other side, effectively replacing existing decks with a single plate would have meant destroying the ship and simply build a new one.

hans

dunmunro
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Re: Nagato protection

Post by dunmunro » Thu May 28, 2020 4:58 pm

For a discussion of multiplate laminated armour see:

http://www.navweaps.com/index_nathan/mu ... ePlate.php

Okun's rule of thumb is to take the effective thickness of a laminated plate as .7 x the thinnest plate + the full thickness of the thicker plate.

Thorsten Wahl
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Re: Nagato protection

Post by Thorsten Wahl » Fri May 29, 2020 9:25 am

Okun's rule of thumb is to take the effective thickness of a laminated plate as .7 x the thinnest plate + the full thickness of the thicker plate.
the .7 number was taken from Navy Depatment Bureau of Ships
Meine Herren, es kann ein siebenjähriger, es kann ein dreißigjähriger Krieg werden – und wehe dem, der zuerst die Lunte in das Pulverfaß schleudert!

Byron Angel
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Re: Nagato protection

Post by Byron Angel » Sat May 30, 2020 12:31 am

My understanding is that an important concept underlying use of multiple armored decks rather than a very heavy single deck. IIRC, these multiple decks were intended to compromise the attacking projectile (or bomb) in several ways:

The uppermost and thinnest deck was to hopefully -
> de-cap the projectile
> activate the projectile fuze as early as possible in its path through the ship.
> cause the projectile/bomb to yaw.

The cumulative effects of the above would hopefully cause a detonation prior to the projectile reaching the second (thickest) armored deck ...or... perhaps even prevent the projectile from piercing the second deck altogether.

The third (lowest) deck (of medium thickness) was intended to be sufficiently strong to prevent any fragments or blast from reaching the ship's vitals (machinery, ammunition, etc).

FWIW.

B

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