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Midshipman_Hornblower

AP Mechanics DEEP Dive

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The recent upending of HE penetration and IFHE caused me to look at that subject in a lot of detail.  Which in turn showed me I didn't understand as well as I thought I did in the beginning.  And that, in turn, made me realize that my understanding of AP mechanics was rather shallow...well, ok, woefully inadequate.  So...trying to understand better, and I've run into a couple questions.  This seems to get complicated in a hurry, so sorry, this will be longer than I'd prefer.

Ok, AP round hits.  First off, check for overmatch.  If overmatch, I assume (?) the fuse arms, and the shell sails onward.  That much is fairly clear.  It's what happens after that that's worrying me.  Many ships have rather complicated layers of internal armored bulkheads and decks.  So, I assume (that word again) that the shell makes all the same checks every time it meets an armored structure, up till the time it either explodes, or it sails out the far side of the ship before exploding.

Question 1 is, can people who know more verify that's what happens?

Question #2 is, what, specifically, happens to shells that ricochet?  Do they cease to exist?  Or does the ricochet just change their flight path, but they continue onward?  This obviously doesn't matter if the shell ricochets off the outer hull, but would seem to be pretty important if it ricochets off an internal structure.  If the shell continues onward, and encounters additional armored structures, does is continue making overmatch and penetration checks, etc?  Seems like it must, though I don't believe I've seen anything that actually spells that out.

Here's a (rather complicated) example.  I was looking at the Surrey's armor diagram, and noticed that the forward end of her citadel is rather oddly shaped.  Most of the citadel box projects slightly above the waterline, but there's a small piece that projects forward.  That portion is well below the waterline, but it's upper deck protection is a mere 6 mm of armor.  So, imagine for a second that Surrey takes an AP hit from dead ahead, from an Alaska (305 mm guns), at long range, so the shell is plunging downward.  The shell passes just above the #2 turret, so the first thing it hits is the forward superstructure (13 mm), which it overmatches.  Then I assume it continues downward, and the next thing it encounters is the aux machinery room forward bulkhead (19 mm), and again overmatches.  At this point, much depends on the trajectory, but the simplest possibility is it plunges on downward and hits that thin (6 mm) top of that forward projection of the citadel, which obviously is yet another overmatch, and puts the thing in the citadel (assuming it didn't already detonate somewhere along the line).

Another, more complicated scenario would follow the above, but after penetrating the aux room bulkhead, it could hit a little further back, impacting the forward upper citadel bulkhead (140 mm).  No overmatch this time.  No idea what would happen then...maybe it pens, maybe it shatters, but given the angle, I think the most likely result would be a ricochet. 

And now we finally get to the heart of the matter.  If the shell ricochets off that citadel bulkhead, is that the end of the matter?  In other words, does the shell no longer exist?  OR...does it ricochet downward, where it immediately would hit that 6 mm section of forward citadel roof, and end up in the citadel anyway?

Sorry again for the length of the post, but it's a fairly complicated topic, and my ignorance is abundant.

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1 minute ago, Midshipman_Hornblower said:

The recent upending of HE penetration and IFHE caused me to look at that subject in a lot of detail.  Which in turn showed me I didn't understand as well as I thought I did in the beginning.  And that, in turn, made me realize that my understanding of AP mechanics was rather shallow...well, ok, woefully inadequate.  So...trying to understand better, and I've run into a couple questions.  This seems to get complicated in a hurry, so sorry, this will be longer than I'd prefer.

Ok, AP round hits.  First off, check for overmatch.  If overmatch, I assume (?) the fuse arms, and the shell sails onward.  That much is fairly clear.  It's what happens after that that's worrying me.  Many ships have rather complicated layers of internal armored bulkheads and decks.  So, I assume (that word again) that the shell makes all the same checks every time it meets an armored structure, up till the time it either explodes, or it sails out the far side of the ship before exploding.

Question 1 is, can people who know more verify that's what happens?

First off, overmatch is only checked for if the AP shell can't pen the effective thickness of the armor, (taking angle into account) or the angle is past the autobounce threshold. It's basically a last resort to see if the shell will pen.

Once it arms, it will check for additional internal penetrations, if something is hit before the shell explodes.

AFAIK, if the shell passes through enough armor to arm the fuse, it's usually going to explode before it gets a second armor layer. Almost certainly it will not get to penetrate a third.

I could be wrong on this though.

 

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41 minutes ago, Midshipman_Hornblower said:

Ok, AP round hits.  First off, check for overmatch.  If overmatch, I assume (?) the fuse arms, and the shell sails onward.  That much is fairly clear.  It's what happens after that that's worrying me.  Many ships have rather complicated layers of internal armored bulkheads and decks.  So, I assume (that word again) that the shell makes all the same checks every time it meets an armored structure, up till the time it either explodes, or it sails out the far side of the ship before exploding.

Fuse doesn't automatically arm after overmatch. Fuse check is made normally, shell at high angles where overmatch has a much better shot at making the fuse check but it's not certain. Fuse can arm if shell penetrates between two hull zones(i.e. bow->upper casemate) in addition to on penetration of armor.

43 minutes ago, Midshipman_Hornblower said:

Question #2 is, what, specifically, happens to shells that ricochet?  Do they cease to exist?  Or does the ricochet just change their flight path, but they continue onward?  This obviously doesn't matter if the shell ricochets off the outer hull, but would seem to be pretty important if it ricochets off an internal structure.  If the shell continues onward, and encounters additional armored structures, does is continue making overmatch and penetration checks, etc?  Seems like it must, though I don't believe I've seen anything that actually spells that out.

Ricochet changes flight path. See for instance German BB turtlebacks don't make shells disappear inside the ship.

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Welcome to the most complicated part of the game, some which we actually don't know all the details. There is a lot of info out from people who have dug into it, but you have to search pretty well. Hopefully some of those guys will chime in

Armor penetration for AP depends on caliber and velocity. The issue is that the velocity calculation is quite realistic, and so complicated. It's of course based on distance (due to air drag), and several coefficients in the game. I don't think we know the actual formula, but people have worked out the empirical penetrations. The other big factor is angle, which trips a ricochet check. It also increases effective armor thickness.

Looks like you have a decent understanding of how the ricochet checks work. The important thing is the fuse. Each fuse has an arming thickness, when encountering that thickness of armor the fuse arms and starts a timer. When that timer runs out, the shell explodes. Depending on where it is, that's the damage it does. That's why ships like smolensk often overpen, the shell fuse arms, but because the ship is so narrow the shell has exited the other side before it explodes, causing only overpen damage.

Now on internal armor. The same mechanics apply. A shell hits the first layer of armor, and arms. Penetrating and continuing while the timer counts down. If it encounters a second piece of armor, the same checks apply, but remember the velocity (and so penetration) is decreased by each layer of armor. So a shell may penetrate the first layer, but then not have enough (or ricochet) to pen the next layer.

So your first example is correct, assuming the fuse timer is long enough for that to happen, the Surry would just get blapped.

Second example also correct, the 140mm plate would depend on angle.

Third, yes, ricochets still exist. If you slow a replay down you can actually see shells ricochet off an armor belt. And yes, it's possible that the shell ricochets off the 140mm plate, and then pens the 6mm plate. It depends on trajectory and angle of course, but it is possible. Assuming the timer hasn't run out. This mechanic is responsible for a lot of funky citadels that happen, such as DD guns citadeling BBs. I believe KMS BBs have (or had, may have been patched) a weird armor set up near the second turret which can trap a shell and direct it down into the citadel. So yeah, ricochets definitely still exist, and are responsible for a lot of weird things.

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OP should kno just a lil tiny wee bit about this, hes an annapolis grad..furthermore since this is gen disc i jus have a simple request is there a list of said ships or is it pretty much by nation but on CV DB's wwhere do i find the info on which ships i can cit from which tier cv's etc..cause i spend a lot of time trying to cit russian and fench BB's to avail..now i havent tried em all but the few of each i tried all i could get was pens..and im sure this is an old question but ii tried to do a search and only things that came up were AP DB nerf etc..thx

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On 3/20/2020 at 4:32 PM, Lert said:

 

It would be nice if that video were complete and correct, but sadly it's neither. 

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