Bombs under water

[Arfsix]

@Arfsix - greetings, hope you are keeping well!  

 

Good table - one clarification.  If the mine mass in the table is = the TNT mass of the mine, which I think it is,  then for an airdropped bomb the bomb mass would usually be nearly double that figure, what with casing and fins.  So 300kg of TNT would require a 500kg bomb.

 

Also looking at the pdf you can see just how huge naval mines really were.  

 

     Thanks for asking. Galveston is 40 miles south of Houston, but we are more or less dry. We only received 25 inches of rain compared to Houston's 50 inches. It did remind me of the rainy seasons in Asia. 

 

      I cited the table to show how close the explosion had to be to the hull. Almost any delay of the fusing would allow the bomb to be too deep for any significant damage. IMHO, one would be better off in trying for direct hits on the vessel, rather than trying to lay a bomb along side!  

[Venturi]

I think a better way to look at this is by graph, with pressures. It seems to me that dropping a bomb very near a ship ought to be at least as damaging as dropping it ON the ship.

 

 

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-------------------------------------------------------

 

By the way, contact or 1s delay fusing would result in explosions of the bomb only a few meters below the surface.

 

Also, thank you for the data.

[unreasonable]

Apart from the pure physics of it I think the issue is also the difference between damage - as assessed by those in the ship - and visible effects as assessed by an attacking pilot, in addition to judging the distance of a near miss.

 

The table, redrawn, says:

 

Detonation                    
wave pressure                               Explosion effects

[Mpa]                        
  0 -  4                                             Safe for warships
  5 -  8                                            Damage to mechanisms and appliances
  9 - 12                                           Deformations and likelihood of cracks in hull sheet plating
 13 -16                                           Total loss of maneuver and combat capabilities. Llikelihood of ship sinking.
 

Note that there could be damage at any level except the last without any effects immediately visible from the air. Even the last might take a minute or two to become evident.  The ships mentioned in the text did not sink, after all, despite their being contact explosions caused by mines, not near misses. Neither did the two USN ships recently damaged in collisions. (What on earth is going on there? But that is another story).

 

The section of the report you have extracted shows the pictures from the section on contact explosions just above the heading starting the section on influence explosions, which are described - and illustrated - as much less destructive (because the gas bubble does not contact the skin). This is potentially misleading if anyone thinks that the red highlighted box in any way relates to the illustrations above it.  

Edited September 2, 2017 by unreasonable

[Venturi]

I have precisely outlined both a graph showing the pressure vs distance and the text associated with it in the report. It plainly says, HULL BREACH, if pressure is above 8Mpa and within 20m distance. 

 

For a 1kg explosive, this occurs at 5m

For a 10kg explosive, this occurs at 10m

For a 50kg explosive, this occurs at 17m

For 250 and 1000kg explosives, this occurs at 20m (maximum distance)

 

Explosives which drop nearer than their breach threshhold obviously will generate bigger compromise of the hull.

I would suspect that armored hulls, or hulls which are thicker, have greater resistance and thus for a given pressure, will result in smaller breaches.

Edited September 2, 2017 by Venturi

[Venturi]

Contrast this with dropping a 50kg bomb directly on a ship, which likely will not generate ANY hull breach. Maybe it will generate fires, which would generate SECONDARY explosions, which would breach the hull, however.

[unreasonable]

Where does it say " HULL BREACH, if pressure is above 8Mpa and within 20m distance."?

 

The red highlighted text does not say "hull breech" it says "penetration of the hull".  It goes on to say that these penetrations have a linear character, ie that they are cracks.  The diagram for contact explosion says "breech".  The word breech is used in the text above in the context of a contact explosion.

 

The words "hull breech threshold" appear on that diagram because you have put them there - they are not in the original.  

 

The diagram for a close influence explosion (fig.7) which you did not show says "linear cracks" at the centre of the affected area - no "hull breech" mentioned there at all or indeed in the entire section of influence explosions.

 

Table 2. "Effects of action of shockwave caused by influence explosion" is probably what the devs should look at since it is considerably more detailed. This says, in part,   MPa 8-12 "Deformation and cracking of the hull..."  

 

Precision is indeed good. 

[Venturi]

Hull Breach = Loss of watertight integrity = Cracks and deformation of the hull

 

BIGGER Hull Breach = SUNK

 

If you like, I'll revise the table using the OTHER table... which is not in contradiction with what I posted, by the way.

 

That is, ship sinks with impact of

 

1kg = 3m distance

10kg = 7m distance

50kg = 12m distance

250kg and 1000kg = 20m distance

 

Obviously, the size of the explosion has to take into account the size of the ship. A thorough breach of the hull by a 1kg explosive may not have a large enough radius of impact to do sink a destroyer. But a couple of 50kg bombs a few meters from the hull would probably be a lot more likely to do so.

 

Still, looks like that "puny" 50kg bomb does something, even if it missed, huh?

 

And, indeed, precision is good.

 

Edited September 2, 2017 by Venturi

[JtD]

You are all aware that as with every other information, this 15 page article isn't the complete and total truth. If you think for a second that 1kg of TNT will cause "Total loss of maneuver and combat capabilities. Likelihood of ship sinking" if exploded three meters away from a modern, major warship, you need to think again (Fig 4 & Table 3). I suppose the author has good reason to start his chart with a minimum of 150kg TNT, and I suppose you'll still need to do a lot of your own thinking.

 

I found the gas bubble size chart quite useful, it gives a good impression of minimum effective distance.

 

Also, this forum has a quote function, which works much better than a screenshot with a red square on it.

Edited September 2, 2017 by JtD

[unreasonable]

From a player point of view it is important to bear in mind that 10 metres is just the wingspan of a Spitfire - even 50 meters seen from an aeroplane would look like a near miss.  Damage may not be evident immediately from the air - ships can take hours to sink.  

 

Again the label "Breach sufficient to sink ship" is just something that Venturi has made up. No-where does the report say that - at best it says that the labelled level of pressure might be sufficient to sink a ship, eventually. The examples of actual damage pictured in the report were of much higher pressures, plus the gas bubble - and the ships did not sink.

 

From table 2.

 

16–27 Likelihood for the ship to sink. Cracking of bulkheads and widespread destruction

of mechanisms and appliances. High number of death cases among crew

members. If the ship does not sink she can be considered for repairs

 

250–350 Possible immediate sinking of the ship. If the ship does not sink, the destruction

is so serious that she will be beyond repair

 

350–500 Possible breaking of the ship, her capsizing and sinking. If the ship does not

sink, the destruction is so serious that she will be beyond repair

 

above 500 Immediate sinking

 

* * *

 

I assume that Jason or someone has this or similar studies and will be able to incorporate some of them into the game as the Pacific development starts.

[tavern_knight]

I had been watching youtube showing the RAF's campaign against the Tirpitz and realized that I had read about another German battleship that had been taken out very similar but done about 22-23 years earlier (July 21, 1921). After doing google research, I had my answer and somehow fell down a "rabbit hole" that brought me here. Plus, on reading this forum sub-set of "Bombs under water," I realized that the information I found wasn't even mentioned; so I decided "throw my 'hat' into the ring" with it.

 

The article is "Billy Mitchell and the Battleships;" the website is in plain text: " https://www.airandspaceforces.com/article/billy-mitchell-ostfriesland/ "

 

General Mitchell's plan was to use six 2,000-lb. bombs to be dropped around the Ostfriesland and let the hydraulic action of the water, hammer the ship's hull simultanously. Apparantly, it worked; said battleship sank between 10-20 minutes.  

Edited December 10, 2023 by tavern_knight

[danielprates]

Now that's great necroing right there

[tavern_knight]

Never mind my previous comments...

Those that don't learn from history, are doomed to repeat it.

 

Mods, if the above comment upsets the member(s), just close out my account.

There's other websites to visit and learn from.

[Dragon1-1]

As a matter of fact, this even works on land to some extent: Tallboy bomb, which was used to sink Tirpitz, was designed to be dropped near the target and go deep into the earth, destroying it with the seismic wave. Indeed, on bridges and such near misses were often more effective than a direct hit. On water, any bomb that doesn't just blow up on contact with the surface (fuze settings matter here) will do more damage when it hits very close, instead of directly hitting the superstructure, particularly if the ship is armored.

 

In fact, modern torpedoes are set to explode under the hull, not directly next to it. You can't armor against that, the ship just breaks in half.

[Avimimus]

As an aside - the RP-3 25lb AP rocket in game can be shot through the water into ships. This was their purpose in real life... they would be arched under the water and retain enough energy to penetrate the hulls of ships below the waterline. Obviously this would only work on more lightly built ships, but it was apparently effective.

 

No one advertised it, but this was modelled in the sim! With the right angle one can send the rockets a long way underwater... (very dependent on angle).

 

Unfortunately, while the behaviour of the rockets is modelled, flooding isn't. So it is almost always better to carry the 60lb HE SAP rocket than it is to use dedicated AP weapons (similarly, HE beltings on cannons usually work better than AP beltings against ships in game).

 

  

On 12/10/2023 at 1:26 PM, danielprates said:

Now that's great necroing right there

 

Yeah, but it is an interesting thread. One people can still learn from.

[danielprates]

35 minutes ago, Avimimus said:

Yeah, but it is an interesting thread. One people can still learn from.

 

Thus me calling it "great necroing". Did @tavern_knight just asked moderators to delete his account just because of my positive remark? Hehehe I swear man, some people here....

[Avimimus]

1 hour ago, danielprates said:

 

Thus me calling it "great necroing". Did @tavern_knight just asked moderators to delete his account just because of my positive remark? Hehehe I swear man, some people here....

 

I gather. I'm not going to do it though. He'd have to work much harder (and try harder at break rules - not work harder at contributing to the forum - that doesn't get one banned).