Idiots guide to....

Warship design and construction, terminology, navigation, hydrodynamics, stability, armor schemes, damage control, etc.
HMSVF
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Idiots guide to....

Post by HMSVF » Sat Mar 20, 2021 1:53 pm

Shells and armour plate please!

I read a lot online in regards to shell performance and the quality of armoured plate and see a lot of very complicated mathematics! Now Ill be honest I feel like a limbo dancer sometimes when I read posts about this subject because everything goes over my head!

I have a few questions for my more learned contributors !

When they tested shells I assume that they took some from batches and passed them depending on their performance? Doesn't this mean that there is a risk that a fair few might not perform as intended due to manufacturing faults. Also could fairly small differences in manufacture make big differences in performance - for example the wall of the shell is minutely thinner than say a comparable shell or metal itself is minutely different?

I suppose I have the same questions in regards to armour plate. Would faults (for want of a better word) not visible to the human eye mean that a plate may not be as resistant as designed.

Finally what is obliquity ? I've always assumed that it was the angle that a shell hit a plate,it that correct? Now for a really dumb question. When talking about angles of obliquity are they from a vertical perspective (i.e like a falling shell) or a horizontal perspective,or both? Wouldn't the pitching and rolling of a ship alter this potentially in any case unless the said vessel was in a flat calm?



The reason I ask is that I see a lot of talk about what a shell should do and what an armoured plate should resist but just wondered whether it was as simple or as clean as that.


You are all probably chuckling to yourself in regards to my daft questions,but I thought I would ask!




Best wishes

HMSVF

OpanaPointer
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Re: Idiots guide to....

Post by OpanaPointer » Sat Mar 20, 2021 4:36 pm

Measure the angle of line of flight and the flat face of the armor gives the angle of obliquity.

dunmunro
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Re: Idiots guide to....

Post by dunmunro » Sat Mar 20, 2021 10:11 pm

HMSVF wrote:
Sat Mar 20, 2021 1:53 pm
Shells and armour plate please!

I read a lot online in regards to shell performance and the quality of armoured plate and see a lot of very complicated mathematics! Now Ill be honest I feel like a limbo dancer sometimes when I read posts about this subject because everything goes over my head!

I have a few questions for my more learned contributors !

When they tested shells I assume that they took some from batches and passed them depending on their performance? Doesn't this mean that there is a risk that a fair few might not perform as intended due to manufacturing faults. Also could fairly small differences in manufacture make big differences in performance - for example the wall of the shell is minutely thinner than say a comparable shell or metal itself is minutely different?

I suppose I have the same questions in regards to armour plate. Would faults (for want of a better word) not visible to the human eye mean that a plate may not be as resistant as designed.

Finally what is obliquity ? I've always assumed that it was the angle that a shell hit a plate,it that correct? Now for a really dumb question. When talking about angles of obliquity are they from a vertical perspective (i.e like a falling shell) or a horizontal perspective,or both? Wouldn't the pitching and rolling of a ship alter this potentially in any case unless the said vessel was in a flat calm?



The reason I ask is that I see a lot of talk about what a shell should do and what an armoured plate should resist but just wondered whether it was as simple or as clean as that.


You are all probably chuckling to yourself in regards to my daft questions,but I thought I would ask!




Best wishes

HMSVF
check out: http://www.panzer-war.com/

and click on " program tool "

The Naval Armor and Ballistics program is very useful and educational.

dunmunro
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Location: Langley BC Canada

Re: Idiots guide to....

Post by dunmunro » Sat Mar 20, 2021 10:12 pm

dunmunro wrote:
Sat Mar 20, 2021 10:11 pm
HMSVF wrote:
Sat Mar 20, 2021 1:53 pm
Shells and armour plate please!

I read a lot online in regards to shell performance and the quality of armoured plate and see a lot of very complicated mathematics! Now Ill be honest I feel like a limbo dancer sometimes when I read posts about this subject because everything goes over my head!

I have a few questions for my more learned contributors !

When they tested shells I assume that they took some from batches and passed them depending on their performance? Doesn't this mean that there is a risk that a fair few might not perform as intended due to manufacturing faults. Also could fairly small differences in manufacture make big differences in performance - for example the wall of the shell is minutely thinner than say a comparable shell or metal itself is minutely different?

I suppose I have the same questions in regards to armour plate. Would faults (for want of a better word) not visible to the human eye mean that a plate may not be as resistant as designed.

Finally what is obliquity ? I've always assumed that it was the angle that a shell hit a plate,it that correct? Now for a really dumb question. When talking about angles of obliquity are they from a vertical perspective (i.e like a falling shell) or a horizontal perspective,or both? Wouldn't the pitching and rolling of a ship alter this potentially in any case unless the said vessel was in a flat calm?



The reason I ask is that I see a lot of talk about what a shell should do and what an armoured plate should resist but just wondered whether it was as simple or as clean as that.


You are all probably chuckling to yourself in regards to my daft questions,but I thought I would ask!




Best wishes

HMSVF
check out: http://www.panzer-war.com/

and click on " program tools "

The Naval Armor and Ballistics program is very useful and educational.

HMSVF
Senior Member
Posts: 285
Joined: Sun Jun 17, 2018 10:15 am

Re: Idiots guide to....

Post by HMSVF » Sat Mar 20, 2021 11:23 pm

Thanks everybody!

Bill Jurens
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Re: Idiots guide to....

Post by Bill Jurens » Mon Mar 22, 2021 1:55 am

I have to admit that I'm somewhat skeptical that the Naval Armor and Ballistics program "...is very useful and educational", at least for long-range naval gunfire.

It appears to (still) be based on MCTRAJ, a small-arms ballistic program which, due to scaling issues, really doesn't model big artillery shells very well, and also appears to be based upon what amounts to a 'flat-fire' trajectory regime, thus neglecting the effects of changes in air density as the projectile travels on an elevated trajectory. If this is true, it's useful, perhaps, for armored-vehicle simulations, but not for long-range naval gunfire.

Also, my sense of many of the penetration models is that they are in most cases poorly documented, with answers worked out via highly-problematical algorithms.

But I may be wrong, so comment and correction is welcome...

Bill Jurens

dunmunro
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Re: Idiots guide to....

Post by dunmunro » Mon Mar 22, 2021 6:04 am

Bill Jurens wrote:
Mon Mar 22, 2021 1:55 am
I have to admit that I'm somewhat skeptical that the Naval Armor and Ballistics program "...is very useful and educational", at least for long-range naval gunfire.

It appears to (still) be based on MCTRAJ, a small-arms ballistic program which, due to scaling issues, really doesn't model big artillery shells very well, and also appears to be based upon what amounts to a 'flat-fire' trajectory regime, thus neglecting the effects of changes in air density as the projectile travels on an elevated trajectory. If this is true, it's useful, perhaps, for armored-vehicle simulations, but not for long-range naval gunfire.

Also, my sense of many of the penetration models is that they are in most cases poorly documented, with answers worked out via highly-problematical algorithms.

But I may be wrong, so comment and correction is welcome...

Bill Jurens
Given the title of the thread...it seems apropos.

The Ballistics calculator in NAaB 2.3 has (and can be tinkered with to give) a fair approximation of range table data, and some indication of how obliquity effects penetration.

pgollin
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Re: Idiots guide to....

Post by pgollin » Mon Mar 22, 2021 1:31 pm

.

Contrary to what many interested parties imply, in WW2 (and earlier) there was NO absolute measure of the properties of shell, versus armour (and vice versa).

Yes there were acurate measures of metallurgy, hardnesses, etc... but these were not definitive as they were usually destructive and only showing certain small areas (e.g. a shell, or piece or armour might be sawn through and then hardness tests performed on the cross-section).

Shells were proved against armour, AND, armour against shells - all relative.

At least for the RN they specially ordered batches of armour which was to be made to the exact standards with lots of efforts being used by the manufacturer(s) and inspectors that everything was exactly right. These plates (different thicknesses and specs for different types of shell) were then put aside and used only in testing. So armour was reasonablysimple, shell however was made in many, many batches and each batch had at least one shell tested against the standardised armour. If it passed, fine, if not at least one more shell would be test fired before the batch was approved or rejected. All the tests would be observed to see how the shell/armour performed, a certain percentage of shells would be section ed to check internal conditions.

That seems simple enough, but every so often a shell would under- (or over-) perform by an unexpected degree and then both the shell and armour would be sectioned and minutely examined to see if there was a defect/difference which could be learnt from.

All this sounds very scientific and accurate, but apart from the normal statistical variance, it was actually based on empirical measures. When the Ordnance Board started to run short of standardised 12-inch plates in the 30's they could not instantly just get an equal batch of plates. They commisioned new plates, BUT the process was very long winded, included tests against large batches of shell (a large percentage of which had been tested against the "old" standard tests). After all the tests and a large statistical exercise a new set of standard conditions were set - BUT, these were not absolute, merely the best relative measures.

.

paul.mercer
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Re: Idiots guide to....

Post by paul.mercer » Tue Mar 23, 2021 10:17 am

Gentlemen,
Like HMSVF, i have always been confused by the mathematics (for want of a better word) of the shell v armour controversy, would I be right in assuming that where a shell hits and whether or not it penetrates amour is to a certain extant a matter of luck?
Its one thing to test the effectiveness on a static target at a known range, but surely the moment of firing from a rolling ship at another rolling ship will determine what angle the shell leaves and at what angle the shell actually hits and whether or not it will penetrate. After all, gunnery officers firing at each other over several miles are hoping for a hit on their opponent, but not actually aiming at any particular spot.
Please don't blow me out of the water on this one!

Bill Jurens
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Re: Idiots guide to....

Post by Bill Jurens » Tue Mar 23, 2021 7:22 pm

No 'blowing out of the water' required, or appropriate.

Certainly the precise location of a particular shell hit, except in very unusual circumstances is largely a random process, which one might well characterize as being represented by 'luck'.

What is little appreciated is the inherent variability experienced even in what are often seen to be well-controlled tests. In that regard, it's useful to revisit some of the intricate minuets that were danced amongst armor/projectile clients and manufacturers, which were often very important insofar as whole lots were often rejected or accepted on the basis on one or two test plates or perhaps fifteen projectiles. The armor manufacturers, supplying plates in batches of a hundred or so, would -- of course -- like the 'test plate' chosen to be the best one possible, and the attacking projectile(s) to be selected from the worst of those available, provided these could be identified (which -- to a trained metallurgist -- would represent more than sheer guesswork. Similarly, if projectiles were being tested, the supplier would like the test plate to be amongst the worst looking of the batch. Deciding exactly what plate of the batch was to be the tested one, or which group of projectiles was to be the ones employed in testing, was often the product of a rather lengthy, intricate, and sometimes quite confrontational process, with the subsequent 'ballistic limit' often not quite representative of the mean. Both sides were 'working the system'.

As I've mentioned before, a 3% variation in plate quality, a 3% variation in projectile quality, and a 3% variation in 'other unspecified variables', assuming a roughly normal distribution, results in an overall uncertainty of about (3^2 + 3^2 + 3^2)^0.5, i.e. a bit over 5%. That’s quite a bit, especially when one notes that in many cases writers are calculating ‘quality factors’ etc. to three decimal places, i.e. one part in a thousand. Based upon sample sizes that were, in most cases, very small indeed…

After a certain point the exercise becomes meaningless. One might, for example, refine the average lifetime of a Swede from (say) 74.335 years to 74.212 years, but that’s really not going to tell you much of real value concerning any individual Swede. Now see how well you do when you only have six Swedes in the sample...

Bill Jurens

HMSVF
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Re: Idiots guide to....

Post by HMSVF » Thu Mar 25, 2021 10:51 pm

Bill Jurens wrote:
Tue Mar 23, 2021 7:22 pm
No 'blowing out of the water' required, or appropriate.

Certainly the precise location of a particular shell hit, except in very unusual circumstances is largely a random process, which one might well characterize as being represented by 'luck'.

What is little appreciated is the inherent variability experienced even in what are often seen to be well-controlled tests. In that regard, it's useful to revisit some of the intricate minuets that were danced amongst armor/projectile clients and manufacturers, which were often very important insofar as whole lots were often rejected or accepted on the basis on one or two test plates or perhaps fifteen projectiles. The armor manufacturers, supplying plates in batches of a hundred or so, would -- of course -- like the 'test plate' chosen to be the best one possible, and the attacking projectile(s) to be selected from the worst of those available, provided these could be identified (which -- to a trained metallurgist -- would represent more than sheer guesswork. Similarly, if projectiles were being tested, the supplier would like the test plate to be amongst the worst looking of the batch. Deciding exactly what plate of the batch was to be the tested one, or which group of projectiles was to be the ones employed in testing, was often the product of a rather lengthy, intricate, and sometimes quite confrontational process, with the subsequent 'ballistic limit' often not quite representative of the mean. Both sides were 'working the system'.

As I've mentioned before, a 3% variation in plate quality, a 3% variation in projectile quality, and a 3% variation in 'other unspecified variables', assuming a roughly normal distribution, results in an overall uncertainty of about (3^2 + 3^2 + 3^2)^0.5, i.e. a bit over 5%. That’s quite a bit, especially when one notes that in many cases writers are calculating ‘quality factors’ etc. to three decimal places, i.e. one part in a thousand. Based upon sample sizes that were, in most cases, very small indeed…

After a certain point the exercise becomes meaningless. One might, for example, refine the average lifetime of a Swede from (say) 74.335 years to 74.212 years, but that’s really not going to tell you much of real value concerning any individual Swede. Now see how well you do when you only have six Swedes in the sample...

Bill Jurens
Hi Bill,

Doesn't a lot depend on other factors as well? Wasn't HMS Lion nobbled at Dogger Bank by a shell that didn't defeat the plate but did break the plates supporting structure leading to fairly substantial flooding?

I suppose what I'm wondering is that in real life there are no absolutes but probabilities.

I read a lot online where its stated that "X2 would happen and here is the programme to prove it. I just wonder whether given all the variables that this is a little optimistic.


Thanks for your time (and patience probably!)


HMSVF

paul.mercer
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Re: Idiots guide to....

Post by paul.mercer » Fri Mar 26, 2021 10:50 am

Gentlemen,
In other threads some of you have very patiently explained to me why a one ton bomb dropping vertically from an aircraft is more likely to penetrate deck armour than a one ton shell arriving at an angle, I regret that I'm still a bit puzzled on this, at Pearl Harbour I believe it has been said that the 'bombs' were converted battleship shells, but it would appear that as the attack was at fairly low level then surely they would not have had time to fall vertically but according to the pictures taken at the time they appear to have penetrated through the deck and into the magazine of at least one ship.
In other words, is a bomb dropped from an aircraft going to arrive that much faster than one of the same size arriving from a ship and penetrate further?
Also on the theoretical side, if a gun could be made to fire at a high enough angle would not the shell eventually reach its maximum height and then start to fall vertically under its own weight and therefore do the same amount of damage as if dropped from an aircraft?

Bill Jurens
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Re: Idiots guide to....

Post by Bill Jurens » Fri Mar 26, 2021 11:23 pm

Mr. Mercer wrote:
"In other threads some of you have very patiently explained to me why a one ton bomb dropping vertically from an aircraft is more likely to penetrate deck armour than a one ton shell arriving at an angle, I regret that I'm still a bit puzzled on this, at Pearl Harbour I believe it has been said that the 'bombs' were converted battleship shells, but it would appear that as the attack was at fairly low level then surely they would not have had time to fall vertically but according to the pictures taken at the time they appear to have penetrated through the deck and into the magazine of at least one ship.
In other words, is a bomb dropped from an aircraft going to arrive that much faster than one of the same size arriving from a ship and penetrate further?"
Your confusion on this point is legitimate. In most situations -- I hesitate to say all, but I suspect this is nearly true in reality -- the projectile will tend to deliver considerably more kinetic energy than a bomb will, although there are circumstances where vertical penetration might be better for a bomb vs a projectile.
As an example, let us take a one-ton 16" shell and compare it with a one-ton typical bomb delivered by a level bomber. Let us also assume that the bomb and the projectile are geometrically similar regarding metal thicknesses, etc., and make a small allowance for the fact that due to its fins, etc., the bomb, overall, will tend to have a somewhat higher drag function than a projectile will.
For a maximum ordinate (drop height) of 3000 meters, the projectile will strike at an angle of fall of about 31 degrees at around 425 m/s, delivering about 92.25 mJ of energy axially, and about 24.3 mJ vertically. The bomb will strike at an angle of fall of about 70 degrees at a velocity of about 250 m/s, delivering 32.8 mJ axially, and 29 mJ vertically.
So, the projectile delivers a lot more energy overall, but about 15% more energy vertically against horizontal armor. So, overall, it should do a little better. But, all things considered, i.e. taking axial kinetic energy into account, the projectile does much much better. It doesn’t arrive faster, but it does deliver more energy in a vertical direction.
You are correct in your observation that if the gun was made to fire at a high angle (like a mortar does) the projectile would probably end up falling with about the same vertical velocity as a bomb would because the horizontal component of velocity at the maximum ordinate would be quite small. It might even do better regarding penetration of horizontal armor because the bomb, equipped with fins, would tend to stabilize nose down, where the spin-stabilized projectile might end up falling in a near horizontal orientation. This necessity to ‘turn over’ at the top of the trajectory is one reason why mortar rounds tend to have fins, and not be spin stabilized.
Hope this helps…
Bill Jurens

paul.mercer
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Re: Idiots guide to....

Post by paul.mercer » Sat Mar 27, 2021 9:55 am

Once again Bill, many thanks for your advice.

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