Some questions regarding Bismarck's armor scheme

Discussions about the history of the ship, technical details, etc.

Moderator: Bill Jurens

RobertsonN
Member
Posts: 179
Joined: Wed Jan 05, 2011 9:47 am

Re: Some questions regarding Bismarck's armor scheme

Post by RobertsonN » Sun May 05, 2019 11:21 pm

It is perhaps useful to study, as in Figs 12 and 13 of the paper by Hoyer (which appears elsewhere on this site), the curves showing the critical velocities needed for penetration and that of the projectile terminal velocity with range and inclination. If the critical velocity is below the terminal velocity then penetration is improbable depending on how great the difference is. In Fig. 12 the critical velocity for the Obere Zone (penetration of the decks) is a curve almost at right angles to the terminal velocity curve. With this configuration of curves adding a bit more protection is going to have a limited effect..But for the inner limit the critical velocity curve for 3 dez (upwards of 30 deg off the beam) is a curve that runs a bit above the terminal velocity curve and which below 7500 m is about parallel to it. These curves do not cross so protection is offered over a wide range of distances. With this type of critical velocity curve adding a bit or even redistributing some protection from belt to scarp can move the whole curve from a little below the terminal velocity curve to a little above it. In the Bismarck scheme (using the Gercke multiplate formula and taking into account the energy lost in plug ejection from the belt) the critical velocity curve for penetration lay a little below the terminal velocity curve in the case of the 40.6 cm APC while for the very similar H class scheme the critical velocity lay a little above it.

Many years ago in a piece on Bismarck, Nathan Okun also commented on this feature of the critical velocity curve for the inner limit of the protection scheme of Bismarck,

Neil Robertson

Thorsten Wahl
Senior Member
Posts: 732
Joined: Mon Apr 27, 2009 4:17 pm

Re: Some questions regarding Bismarck's armor scheme

Post by Thorsten Wahl » Tue May 07, 2019 9:23 am

RobertsonN wrote:
Sun May 05, 2019 4:16 pm
The mention of the paper by Hoyer has drawn my attention to something I had overlooked before. Namely, I had thought that the curves Vg in Figs 12 and 13 were curves of terminal velocity (from its shape) rather than of the velocity at which the shell fractures on impact. Also generally in GKdos 100 at 40 dez it is stated 'no intact penetration. At this obliquity the shell is broken on penetrating the KC plate. However, in Figs 12 and 13 the shell breaks even at low obliquity. It should not do so against the belt so near normal impact. Perhaps breakage was on the scarp. Certainly, the Wh penetration curves in Gkdos 100 state that this armor type did not break these shells. However, the curves given are for perforation, which required a high velocity at high obliquity. Perhaps shells that struck the same armor at lower velocity did break (and did not penetrate).
...
Neil Robertson
As far as I can remember correctly Hoyer did not used the original figures from GKDos 100 / Gercke Formula but used modified curves with slightly different C and B values for his explanation of the functionality of the Böschungsdreieck. Possibly because of confidentiality reasons.

Additionally the explanations for capped and uncapped penetration of homogenous armor for the same projectile are not completely satisfying.
He only says that capped and uncapped pentration for a given projectile should be (roughly) the same. But this is only true for relatively low obliquity impacts without yaw(projectile orientation with regards to the movement path).

But the complete curve for the capped projectile appears to run (at least for certain angular ranges) somewhat flatter and due to cap breakage ther may be additional discontinuities in the pentration function at higher obliquity.

-without cap at zero obliquity the uncapped projectil helds a advantage of 10-15 per cent lower velocity for complete pentration depending on % Cap- proportion on projectile weight.
-with cap at a impact at about 30 degrees obliquity the capped projectil then helds the advantage. The slight advantage for the capped projectile appears also valid for heavy british WW2 type armor piercing projectiles at about sixty degrees obliquity.

Ther is also a american explanation somewhere on DTIC.mil and also in the DEFE or SUPP reports from the National Archives Kew. (capped and uncapped high obliquity impacts on relatively thin armor plates(<35% caliber); varying head shape and cap type)

The reason for that different behavior can be seen on photographic high speed recordings.
The heavier the cap the less is the turning moment towards plate during impact.
the projectile therfor moves more sideways without or with a smaller Cap - the required hole for the projectile to pass trough the armor plate is somewhat smaller. And also the energy required to dig this hole is smaller.
The effect becomes more pronounced as the obliquity increases.

Further, the projectile more likely Scoops, when it became more deflected towards plate.
Meine Herren, es kann ein siebenjähriger, es kann ein dreißigjähriger Krieg werden – und wehe dem, der zuerst die Lunte in das Pulverfaß schleudert!

RobertsonN
Member
Posts: 179
Joined: Wed Jan 05, 2011 9:47 am

Re: Some questions regarding Bismarck's armor scheme

Post by RobertsonN » Tue May 07, 2019 7:39 pm

RobertsonN wrote:
Sun May 05, 2019 11:21 pm
It is perhaps useful to study, as in Figs 12 and 13 of the paper by Hoyer (which appears elsewhere on this site), the curves showing the critical velocities needed for penetration and that of the projectile terminal velocity with range and inclination. If the critical velocity is below the terminal velocity then penetration is improbable depending on how great the difference is. In Fig. 12 the critical velocity for the Obere Zone (penetration of the decks) is a curve almost at right angles to the terminal velocity curve. With this configuration of curves adding a bit more protection is going to have a limited effect..But for the inner limit the critical velocity curve for 3 dez (upwards of 30 deg off the beam) is a curve that runs a bit above the terminal velocity curve and which below 7500 m is about parallel to it. These curves do not cross so protection is offered over a wide range of distances. With this type of critical velocity curve adding a bit or even redistributing some protection from belt to scarp can move the whole curve from a little below the terminal velocity curve to a little above it. In the Bismarck scheme (using the Gercke multiplate formula and taking into account the energy lost in plug ejection from the belt) the critical velocity curve for penetration lay a little below the terminal velocity curve in the case of the 40.6 cm APC while for the very similar H class scheme the critical velocity lay a little above it.

Many years ago in a piece on Bismarck, Nathan Okun also commented on this feature of the critical velocity curve for the inner limit of the protection scheme of Bismarck,

Neil Robertson
Just to correct an error in the above post. The second sentence which reads:

'If the critical velocity (for penetration) is below the terminal velocity then penetration is improbable ...'

should of course say:

'If the critical velocity (for penetration) is above the terminal velocity then penetration is improbable ...'

Neil Robertson

Post Reply