Naval History Forums

Bill Jurens wrote:
Thanks to Jose for his excellent work solving my access problem. The new password you provided works perfectly!

Bill Jurens

Ok Bill,
Looking forward to seeing your new projects!

Cheers,
Alex

Hello Alecsandros:

I see where you are coming from now. My apologies if I came across as a bit defensive; I was fairly severely 'burnt' by the forward magazine explosion fiasco some years ago, and am certainly reluctant to revisit those sorts of speculations (including "Prinz Eugen did it" and "It was all faulty propellant handling/storage") again.

For what it is worth, I did do some additional armor calculations prior to the 2001 expedition to Hood, but didn't find anything too exciting. For what it's worth, even taking the armor and the ballistic limit to be c. 240mm still would yield only 50% useful penetrations, i.e. even at the so-called 'n.b.l.' only 50% of projectiles will successfully penetrate. That being said, it's pretty clear that something big must have penetrated somewhere. The wreckage itself yields no clue, and probably never will, unless one eventually finds a plate with a hole in it.

Now that I am retired, I am hoping to do a rather complete rework of the original Loss of Hood paper. Although I don't expect any dramatic new conclusions, some additional information can indeed be added, e.g. the fact that the rudder position indicates that Hood had already begun her final turn.

Thanks to Jose for his excellent work solving my access problem. The new password you provided works perfectly!

Bill Jurens

Hi Bill,
No offense intended there,
Just some bits and bolts that may bring the article more up to date.
For example, the portion where the effects of 38cm shells against heavy armor plate are discussed.
As I undrstand it, German 38cm L4.4 was tested against contemporary German FH armor, meaning the Krupp "new type" cemented armor.

Hood's armor plates were of 1920s vintage, substantialy less resistant to penetration/perforation than the more modern plates [such as KGV class armor plates]

[To put it very short, Hood's FH armor was probably similar in quality to WW1 Krupp FH armors, that was probably ~ 20% less resistant to penetration than WW2 Krupp FH armors...]

----

To be more precise, this part of the article:

"For this angle, corresponding to a shot approaching from 37° forward of the beam, the resolved obliquity would have been approximately 43.85°.53 German armor penetration curves, redrawn below,54 indicate that at the predicted striking velocity of 530 meters per second, the penetration for an intact projectile into face-hardened armor would have been approximately 240mm. An intact penetration of the 305mm main belt would therefore have been improbable, although either of the thinner sections would have been easily perforated."

could be updated:
the 305mm section of the main armor belt was probably similar to 305 x 0.8 = 244mm Krupp KC n/A... pretty close to what the penetration curve says (240mm)...
Another discussion could be done around the probability of the main belt of Hood to successfully decap the AP cap of a German 38cm shell. My intuition is that that kind of armor (1920s vintage) would not always ensure decaping of this kind of shell, meaning that deeper penetrations in a fit state to burst would be possible...

Cheers,
Alex

Alexandros suggested that there were some portions of my paper that needed revisiting. I visited the wrecks of Hood and Bismarck in 2001, and prepared a complete description of my observations there, at the same time noting that there did not appear to be any significant issues with my previous paper, i.e. that there were really no 'surprises' found on the bottom which would invalidate my previous work.

Barring the rather blatant baloney regarding a forward magazine explosion which has been put forth by 'television experts' on various pseudo documentaries on the subject -- which can be dismissed out of hand as unworthy of serious consideration -- I am unaware of any recent work in this area which might suggest my original paper was in any way substantively inadequate. In that regard, might you be a bit more specific regarding areas where 'revisiting' might be appropriate?

dunmunro wrote:For those of you who haven't read it, or haven't read the updated version, here is Bill Jurens article on the sinking of the Hood:

http://www.navweaps.com/index_inro/INRO_Hood_p1.htm

Yes, but there are a few things there that need to be revisited...

wm Jurens wrote:

Yes, all things being equal, a smaller projectile will be more affected by local turbulence. This is not really a stability issue however, as the term is commonly used, and the differences overall are not large. I doubt if anyone would be shooting in 35 m/s winds anyway, as -- if my equations are correct -- this amounts to a wind of about 80 miles per hour. That's a special case. Basically, stability -- at least as traditionally defined -- is nearly independent of caliber.



Bill Jurens

Thanks Bill,
Just to clarify :
The 40m/s wind I was thinking would occur higher up on the trajectory, not at the initial firing point (basicaly a few meters elevation). The high-point of a naval shell trajectory can easily be several kilometers high, and there are other meteo conditions up in the air...

--

Of course, you are using stability in the ballistic sense of the word, as Thorsten pointed out.
I was reffering to "stability" as in "pattern consistency"... because the discussion concerned the hit ratio of Prinz Eugen compared to Prince of Wales.

Cheers,
Alex

Regarding projectile stability.

I have been having great difficulty posting to this board lately. The following is a re-written re-post of material submitted yesterday, which apparently did not make it on to the thread. This post may stand on its own, but if the other appears as well, there will be some redundancy. I do hope this one makes it.

Alecsandros wrote:

"Just a quick though - doesn't the smaller mass of the smaller projectile make the wind turbulences more evident ? I'm guessing a 1000kg shell mantains it's trajectory better than a 100kg shell from the same family of shells, when facing high-winds of 30-40m/s ?"

Yes, all things being equal, a smaller projectile will be more affected by local turbulence. This is not really a stability issue however, as the term is commonly used, and the differences overall are not large. I doubt if anyone would be shooting in 35 m/s winds anyway, as -- if my equations are correct -- this amounts to a wind of about 80 miles per hour. That's a special case. Basically, stability -- at least as traditionally defined -- is nearly independent of caliber.

To IWD:

You are apparently confusing the drag coefficient and the ballistic coefficient. The ballistic coefficient may be simply defined essentially as mass/(drag coefficient * cal^2). The drag coefficient takes into account the effects of projectile shape and is essentially independent of projectile mass. The caliber has a very great effect on the mass, so larger projectiles will have a much greater ballistic coefficient even though the drag coefficient (which is dependent upon shape) may remain the same. It is incorrect to conclude that projectiles of the same shape but of differing caliber will have (nearly) identical ballistic coefficients. As an aside, it's worth noting that In spin-stabilized projectiles, 'stability', as the term is normally used, is essentially independent of drag coefficient or ballistic coefficient.

As noted earlier, in properly designed gun systems, dispersion is primarily related to trajectory length and (what is nearly the same thing) time-of-flight. The effect of projectile caliber, per se -- though by no means non-existent -- is rather small. The increase in dispersion at range is primarily due to the fact that smaller projectiles, for comparable initial velocities, suffer proportionately more drag and therefore require a larger angle of departure to reach any given range. This results in a longer trajectory and an increased time of flight. If range were measured in projectile calibers instead of absolute units such as yards or meters, little difference would be apparent.

Hope this helps...

Bill Jurens

lwd wrote:Just guessing but if the shapes are the same then the ballistic coeffiecents should at least be close. Givent that the force of the wind will be porportional to the area presented which is going to vary as the square of the linear dimensions and the acceleration will vary as this force divided by the mass which will vary as the cube of the linear dimensions. So all other factors (including velocity) being the same I think you are correct the larger projectiles hould experiance less "windage".

..... The rules of thumb as I understand them were that, all other things being equal, dispersion varied approximately directly with range and inversely and directly with gun caliber. In other words, at a range (say, 16.000 yards) where a 12in salvo from a well calibrated gun battery could achieve a 100 yard pattern, the best that could be achieved by a similarly calibrated 6in battery would be about 200 yards, and that both patterns would be doubled in dimensions at twice the range.


B

For those of you who haven't read it, or haven't read the updated version, here is Bill Jurens article on the sinking of the Hood:

http://www.navweaps.com/index_inro/INRO_Hood_p1.htm

PoW gunnery report:
http://www.hmshood.org.uk/reference/off ... 09guns.htm

PoW salvo ranges with short/over/straddle per salvo:
http://www.hmshood.org.uk/reference/off ... encIVa.gif

PoW salvo rounds/salvo:
http://www.sfu.ca/~dmunro/PoW_salvo_a.jpg

Alecsandros:

You are correct insofar as a smaller projectile will have a much smaller mass than a larger one will, and will therefore be somewhat more susceptible to buffeting. The effects would not be that great unless atmospheric conditions were extreme. I doubt if anyone would be shooting anything at all in 40 m/s wind velocities; if my calculations are correct that's equivalent to about 90 miles per hour.

IWD:

You are confusing drag coefficient with ballistic coefficient. The ballistic coefficient (here described in somewhat simplifed form for the purposes of this discussion) is proportional to mass/(drag coefficient * cal^2) and increases very rapidly with caliber. Projectiles of the same shape might be expected to have similar drag coefficients as the drag coefficient is, in most cases, basically independent of size, but the drag coefficent is not really closely linked to the ballistic coefficient at all. Drag is defined by projectile shape. In practical terms -- as in the simplified formula above -- the ballistic coefficient is really related to both caliber and shape, caliber controlling the mass and shape controlling the drag coefficient.

It is, overall, correct to state that in general smaller projectiles are somewhat less accurate than larger ones, and although some of this is due to the factors you mention, the primary cause of increased dispersion can be generally related to the need for a smaller projectile to traverse a longer trajectory length and experience a longer time of flight to reach a given range.

My original question related to the issue of projectile stability to describe this phenomenon, but in reality stability, as the term is conventionally applied, is not very closely linked to the ballistic coefficient or the drag coefficient at all; it's mostly controlled by spin -- or, in the case of longer projectiles -- via fins.

Hope this helps...

Bill Jurens

Just guessing but if the shapes are the same then the ballistic coeffiecents should at least be close. Givent that the force of the wind will be porportional to the area presented which is going to vary as the square of the linear dimensions and the acceleration will vary as this force divided by the mass which will vary as the cube of the linear dimensions. So all other factors (including velocity) being the same I think you are correct the larger projectiles hould experiance less "windage".

Wm Jurens wrote:
For spin-stabilized projectiles, one can nominalize stability for a given range band by changing the twist of the rifling; in general terms, it will be found that the higher the angle of departure, the slower the best possible twist will be. A lot also has to do with projectile length; so far as stability is concerned, longer bullets, e.g. 4.5 caliber long projectiles, will generally do less-well than shorter ones as range increases.

Bill Jurens

Hello Bill,
Thanks for the insights,

Just a quick though - doesn't the smaller mass of the smaller projectile make the wind turbulences more evident ? I'm guessing a 1000kg shell mantains it's trajectory better than a 100kg shell from the same family of shells, when facing high-winds of 30-40m/s ?

Thanks,
Alex

Pandora wrote:

lwd wrote:

Pandora wrote:...or it could have been anything but the fact is that it was 3 straddles and 3 hits.

That was essentially my point.

...then do we agree that 3 hits out of 3 straddles requires a lot of luck?

NO. We agree that there were 3 hits and 3 straddles as I have stated it's not at all clear that all 3 hits were assoicated with the straddles or even that there were 3 straddles (isn't one of them questionable?).

.. haven't you read it? all other salvos were seen as short or over.

And all the shell splashes from each of these salvoes was accounted for? Or could there for instance been a 3 gun salvo where 2 shorts were observed and no longs or conversely one where 2 longs were observed and no shorts? I haven't seen the detailed descritpion of each salvo by any means and no one has linked it to my knowledge or reported it in this thread.

exactly and since the odds are so low, even if you straddle, to get a hit luck has a lot to do.

LIkewise not to hit is a matter of luck.

lwd wrote:

Pandora wrote:...or it could have been anything but the fact is that it was 3 straddles and 3 hits.

That was essentially my point.

...then do we agree that 3 hits out of 3 straddles requires a lot of luck?

lwd wrote:

lwd wrote:Then how do you explain the hits, straddles, and near straddles?

good luck maybe?

For one straddle/hit/near straddle that wouldn't be an unreasonable speculation however given 3 hits, 3 straddles, and more "effective" salvos it becomes very problematic.

I dont have that impression but you are entitled to their own opinion

lwd wrote:

I dont know of any "near straddles", just 2 straddles + 1 other probable resulting in 3 hits, total salvos 18.

I strongly suspect that's what they meant by "effective salvo". It would really help to have the form that contains info each salvo by PoW.

haven't you read it? all other salvos were seen as short or over.

lwd wrote:

lwd wrote:PoW fired 18 salvos and 55 rounds that works out to just a bit over 3 rounds per salvo. Furthermore her first salvo was with 6 guns and her second with 5 I believe. If you take out these two ranging salvos then we have 16 salves and 44 rounds which is 2.75 rounds per salvo. The implication is clear she could have had a good range and still not straddled on a number of occasions. It's even possible that one or more of the hits were on salvos that didn't straddle.

ummm, getting hits without straddling the taget, that is what I call good luck!

For any particular salvo it would indeed be good luck. However if you are only firing two shells if you get a straddle the only way to get a hit is an underwater hit or one that passes through the ships upper works. With one shell you obviously can't straddle yet there are indeed records of hits. Look at the number of ships sunk by submarine deck guns for instance. Even with 3 shells if one hits the odds on a straddle (not counting the cases mentioned above) is still only 50%.

exactly and since the odds are so low, even if you straddle, to get a hit luck has a lot to do.

lwd wrote:Which would indeed suggest that it isn't at all unreasonable to think that one of PoW hits may have come from a salvo that didn't straddle.

problem is that all PoW salvos that didn't straddle were reported as short or over.