Multiple Deck - Single Deck

[Jefgte]

Single deck
Multiple deck

Some BB SS of us are with Single Deck armor (ex:100mm).
But Weather Deck is not 0 mm...

What is the SS thickness of Weather Deck in Single Armored Deck config?

[The Rock Doctor]

I just assume it's got ~10-15mm of steel that is counted as part of the ship's hull.

[TacCovert4]

I agree.  About a quarter inch of structural steel with teak on top.  I presume that the weather deck is structural,  as even unarmored ships obviously have decks. 

Currently I denote my decks as main and a splinter under main.  Eventually I'll start doing 3 decks, a decapping deck, main deck, and splinter deck. 

A decapping deck would lie above the armor belt, and would detonate he shells and bombs, and initiate ap weapons while causing their penetration caps to be damaged.   The main deck lies on top of the belt and would stop anything, hopefully.   And a splinter deck, well that's supposed to deflect spalling from the main deck,  or lower velocity splinters or flash from a breach of the main deck.

[Kaiser Kirk]

The SS deck armor values I consider to be in addition to basic hull structure, which includes the standard mild steel decks.

Tinkering with one of the protected cruisers I want to rebuild,
it has 286 tons of deck armor and 1878 tons hull structure.
deleting the deck armor, the hull structure increases to 2,164tons, +286 tons.

So in the case of a single 25mm deck, SS assumes it is fitted IN PLACE of the hull steel.?

I know by time of the HMS Arthuesa, this was done. Homogeneous 'B' plate could be used for structural steel for belt and deck armor, saving weight. I presume that and the move to more destroyer like machinery is the 1920 cruiser tech.

The problem is - hull structure changes with all sorts of things. For example, upgrading an engine, suddenly the hull and fittings weigh more.
Failure of SS. Oh well. But since the armor wt and hull wt changed 1:1 there's probably a calculation in there.

I think the next question is - what about thicker decks or multiple decks?
Upgrading that cruiser's engine to 1920, hull becomes 3804t with no deck.

So...how does SS handle this?
Single 25mm protective deck = 286+3518 = 3804 replaces hull structure
Single 50mm protective deck = 572t+3232t =3804 replaces hull structure

MULTIPLE 25mm Protective decks = 286t+3669t =3955 replaces hull structure +149t ??
MULTIPLE  50mm Protective decks = 572t+3383t =3955 replaces hull structure +149t ??

Single 50mm ARMOR deck = 572t+3383t =3955 replaces hull structure +149t ??
MULTIPLE  50mm ARMOR decks = 572t+3383t =3955 replaces hull structure +149t ??

So on this ship, 149t would be 13.5mm of deck armor...which is about right for a hull structure mild steel deck.

Conclusion :
SS seems to treat single Protective decks as replacing hull steel.
Multiple decks, or Armor decks  are in addition to the hull steel.

What practical effect would this have?
Not much.

As I recall a scrap from Okun, laminated plates are roughly 0.8* effective, while separate plates are *.5 effective.
Somewhere I have a chart- probably SeeKrieg - showing armor effectiveness by era, mild steel is like 0.2 or 0.4 compared to harvied.

So imagine a ship with a 25mm  upperdeck and 75mm main deck.
As people abandon upperbelt armor, a floating upper armor deck makes little sense, but for this we'll do it.
It would also have a mild steel weather deck, then the upper deck laminated to mild hull steel, then and say 1 more, then main laminated to hull steel.

So (13.5*.5*.4) + (25)+(13.5*.8*.4) + (13.5*.5*.4) + (75)+(13.5*.8*.4) 
..yeah I don't want to do that calculation. But each layer of hull decking is +2.7mm separate and 4.32mm laminated,
for +14.04 from the hull plating.

ok back to football, darn Indy just scored. I'm sure if I had been staring intently at the TV, it would have spurred the Raiders to better efforts....yeah...

[TacCovert4]

I would generally ignore the structural decks as it relates to anything.   

I do a splinter deck under my main armor deck because I'm trying to prevent splinters from piercing the vitals due to spelling or small deck penetrations.  Hence my splinter deck is always roughly the splinter defense thickness for the main deck if it was a shell.