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How does inner armor work?


thu
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I got a BB with 12''belt + 4''1st inner +2'' 2nd inner + 12'' barbette, so I supposed a 30'' protection. Fact was ammo detonation received from a direct penetration hit. Have I made a wrong calculation?

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1 hour ago, thu said:

I got a BB with 12''belt + 4''1st inner +2'' 2nd inner + 12'' barbette, so I supposed a 30'' protection. Fact was ammo detonation received from a direct penetration hit. Have I made a wrong calculation?

The system does not work purely additively.
When a shell penetrates the 12 inch belt, then it loses a large portion of its penetration power and checks to penetrate the next layer of armor. This is done successively and then if the shell reaches the barbette, it has to have enough penetration to pierce it.

So the overall protection can be up to 30 inches in your example, but not always 30 inches, and so sometimes, depending on the circumstances, it can be defeated by a large shell.

EDIT:
The Citadel armor schemes save a lot of weight compared to pure armor equivalence, which could be impossible without this system, as in your example, 30 inches of armor would cost a tremendous amount of extra tons, and if the tonnage would be available, then it would be restricting you to use it for other vital aspects of your ship. 

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6 hours ago, Nick Thomadis said:

The system does not work purely additively.
When a shell penetrates the 12 inch belt, then it loses a large portion of its penetration power and checks to penetrate the next layer of armor. This is done successively and then if the shell reaches the barbette, it has to have enough penetration to pierce it.

So the overall protection can be up to 30 inches in your example, but not always 30 inches, and so sometimes, depending on the circumstances, it can be defeated by a large shell.

EDIT:
The Citadel armor schemes save a lot of weight compared to pure armor equivalence, which could be impossible without this system, as in your example, 30 inches of armor would cost a tremendous amount of extra tons, and if the tonnage would be available, then it would be restricting you to use it for other vital aspects of your ship. 

I still don't entirely understand how this system works after the explanation. With the old models before the Citadel rework, penetration was a 1 or 0. After this, it's harder to understand when a shell should penetrate the inner armor of a ship.

So, for example (if you took out the RNG) how would a shell perform when it has ~80 inches of pen, and hits a 30 inch belt and a 15 inch back layer (assuming 0 armor quality)? Mainly I'm wondering, how much actual penetration is lost as a result of this, and does fusing make a difference in determining wether the shot actually goes through or not.

Edited by AdmiralObvious
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Two 5" plates are easier to penetrate than a single 10" plate. This isn't game-machanics, this is real-world physics.

That's why you can't just add the thickness of the seperate armour layers together.

So lets say for example that each time a shell passes completely through a layer of armour it loses 3/4 of the penetration of said armour. You have 20 main belt, and then two layers of inner belt 10 and 5" thick.
The shell comes in with enough penetration to go through 29" of armour.
Just by adding up the values you'd think you have 35" armour vs 29" penetration will hold... but it won't.

After punching through your main belt it loses 15" (3/4 of 20") penetration, so it hits the first inner belt with 14" pen, which is still enough, so it goes through that as well, but loses speed again and thus comes down to 11.5" (14 remaining pen minus 3/4 of 10). And now it hits the final layer with 11.5 pen vs 5" plate and goes through with 10.25 penetration left.

That of course is a simplified model, since I just picked out random numbers and am disregarding a lot of factors that are also going on (like factoring in armour material, propellant and bursting charge, barrel length, angle both horizontally and vertically and so on).

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It is a very complex question. Usually one thick plate is better than multiple thinner plate equal total thickness, but multiple thinner plate with good calculation and design can also have good defence. It called spaced armour.

In real world, armour above the main armour deck can : 1. Detonate the aerial bomb 2. Prevent fragment 3. Damage or destroy the AP cap. 

Scharnhorst and Bismarck is the typical spaced armour. A 1.97 inch armour above the main armour deck. Their calculation is that it equals 6 inch normal design.

Higher the main armour deck, bigger defensed volume. But the cost is stability.(KGV)

Lower main armour deck can save weight, but the cost is survivability.(Richelieu and Nelson)

But in the game we don't have air attack, and I don't think there is fragment and cap peel. So just make a thick plate.

 

preview

 

preview

preview

File:KGV Tirpitz armour and underwater protection.png - Wikimedia Commons

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On 7/23/2022 at 3:11 AM, Norbert Sattler said:

Two 5" plates are easier to penetrate than a single 10" plate. This isn't game-machanics, this is real-world physics.

That's why you can't just add the thickness of the seperate armour layers together.

So lets say for example that each time a shell passes completely through a layer of armour it loses 3/4 of the penetration of said armour. You have 20 main belt, and then two layers of inner belt 10 and 5" thick.
The shell comes in with enough penetration to go through 29" of armour.
Just by adding up the values you'd think you have 35" armour vs 29" penetration will hold... but it won't.

After punching through your main belt it loses 15" (3/4 of 20") penetration, so it hits the first inner belt with 14" pen, which is still enough, so it goes through that as well, but loses speed again and thus comes down to 11.5" (14 remaining pen minus 3/4 of 10). And now it hits the final layer with 11.5 pen vs 5" plate and goes through with 10.25 penetration left.

That of course is a simplified model, since I just picked out random numbers and am disregarding a lot of factors that are also going on (like factoring in armour material, propellant and bursting charge, barrel length, angle both horizontally and vertically and so on).

Laminated armor, that is, an attempt to emulate a thick plate via slapping two thinner plates on top of each other, is weaker, yes. But properly designed multi-layer armor is much more effective than a monolithic plate in many cases, one of which was mentioned by @UncleAi in armored decks. The first layer of armor is able to cause damage to the projectile, saps its energy, and, if sufficiently thick, starts its fuse. If the next armor plate is thick enough and at an appropriate distance, the shell may shatter against it or explode prematurely. Additional layers of armor also limit damage due to spalling or splinters, by having some armor between the fragments and the delicate internals. The effects of spaced armor are one of the reasons that the "turtleback" armor scheme was so effective before ranges got too far and air attack became common. Shells that made it through the main belt would be severely blunted, greatly slowed, and have their fuses set, leading them to explode on, glance off of, or simply shatter against the sloped deck armor behind the belt.

You can see some of these ideas in the armor scheme shown for the KGV battleships above, where the main armor belt has an additional layer of armor behind it, presumably to catch splinters and prevent explosions from propagating inwards. There is another layer after that over the magazines, further improving the likelihood of shell failure and reducing the chances of collateral damage. You can also see that the fuel oil is kept between the main belt and inner layer, which would further hamper enemy shells due to oil's much higher density and viscosity compared to air.

It's really quite complicated, and as far as I'm aware we don't really have any definitive empirical answers to just how effective various spaced armor schemes were, such as the Italian "decapping belt." Honestly, I'd suspect that there's not much tangible benefit to having more than about three total layers of armor anywhere, maybe four over the magazines. By the time you're up to four or five layers, those last one or two are probably protecting very little of the ship. As a result, I'd expect the system to work something like this:

  • The first armor layer acts as expected. It's a slab of steel.
  • Having a second layer of sufficient thickness leads to the armor being better than the sum of its parts. I'd expect this to take the form of a buff to the first layer's effective thickness if the second layer is substantial enough, with the total thickness (including buff) being the number to beat for shells. Full pens become rarer due to the improved armor, and partial pens become blocked shots or have their damage reduced considerably (depending on how close they were to a pen, and the thickness of the second layer).
  • The third layer and on serve mostly to reduce damage taken, rather than change hit types, and reduce the chance of critical hits. If a shell has made it through your two thickest layers of armor, it's likely quite deep in the ship at this point due to spacing, and clearly had a lot of power behind it, so you should still be taking some damage at this point. Third and on layers, being so deep in the ship, would likely be found only over highly important areas, primarily the magazines. As such, they should reduce the chances of ammo detonation in particular and critical hits in general.
Edited by Dman1791
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On 7/22/2022 at 8:49 AM, Nick Thomadis said:

The system does not work purely additively.
When a shell penetrates the 12 inch belt, then it loses a large portion of its penetration power and checks to penetrate the next layer of armor. This is done successively and then if the shell reaches the barbette, it has to have enough penetration to pierce it.

So the overall protection can be up to 30 inches in your example, but not always 30 inches, and so sometimes, depending on the circumstances, it can be defeated by a large shell.

EDIT:
The Citadel armor schemes save a lot of weight compared to pure armor equivalence, which could be impossible without this system, as in your example, 30 inches of armor would cost a tremendous amount of extra tons, and if the tonnage would be available, then it would be restricting you to use it for other vital aspects of your ship. 

It would be very helpful to have some idea of what this penetration-reduction formula is.  Be a lot easier to do things like scale our armor to the main guns of our ship.  Is it half each time, 3/4-1/2-1/2? etc.

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@Dman1791I know, as I said in my post I was massively simplifying to explain the game-mechanics.

But your post made me think something: The game needs something in addition to penetration and partial penetration.

Unless it triggers an ammo detonation, we don't see a difference in the logs between a detonation within the main armour, but outside the citadel and a detonation within the citadel.

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