Bombs under water

[InProgress]

I am really curious about this since you can drop bombs on ships with delay and if it's under ship it's a total destruction, if next then mostly heavily damaged or also destroyed. In cliffs of dover bomb has 14 delay if it will realise itself during dive bombing. Are these bombs floating somehow?

 

It's hard to say in game but maybe someone knows historical data. What is better to drop bombs with no delay and hit ship or with delay at ship. Or maybe to water next to ship. While bomb with no delay that hits water seems to do little or nothing but if bomb explode under water in clod it does big damage, not sure how it is in bos but I think more less the same.

 

How about in real life? Because I have mixed feelings about bomb exploding under water and destroying ship completely.

 

50/70kg 4x and 250/500kg 1x

Edited August 28, 2017 by InProgress

[[CPT]CptJackSparrow]

Silent Hunter IV.

 

G7e under the keel.

 

Kill shot.

[-=PHX=-SuperEtendard]

An underwater explosion close to a ship hull can do tons of damage. In WW2 torpedos featured magnetic detonators so they could explode just below the ship, increasing their effectivity a lot (a single torpedo may break the ship's keel and sink it, while it would take more hits from a side approach with contact fuse). However early in the war torpedos had problems with these detonators, both US and German alike.

 

It might be possible for a bomb to do a similar thing... but it would be needed that the bomb activates with enough delay to explode at the right spot from the ship (1 or 2 meters appart), I think that while possible it would be unlikely to have this sort of catastrophic effect. It would depend in the time delay, speed and altitude at which the bomb is dropped.

 

Imho the best bombing against ships are either skip bombing so the bomb explodes close to the waterline, or with time delay AP-bomb that penetrates the upper structure of the ship then explodes inside the hull.

Edited August 28, 2017 by -=PHX=-SuperEtendard

[TP_Silk]

The Tirpitz was sunk by this method (essentially anyway, there was more to it than simply that).

 

One thing to remember is that even battleships didn't really have a well armoured hull all the way around, they relied on a 'belt' of armour that extended both above and below the waterline to prevent hull breach.

 

 

Oh, and the famous bouncing bombs that 617 Squadron used to take out the dams relied on exploding next to the dam wall and using water pressure to do part of the work of both shaping and enhancing the charge.

Edited August 28, 2017 by TP_Silk

[JtD]

To sink ships it is most effective to have bombs explode close to the ship with a little delay, so that they do not sink past the ship. Bombs going off in the water near the ship work to the same principles as mines or torpedoes, which as you may know pose a much higher threat than the same amount of explosives inside a shell/grenade.

 

The best place for a bomb to go off would be right below the keel of the ship. This combines maximum effect of the bomb with closest distance to the hull. Below the ship is always good, because the gas created by the explosion goes up and will go through the ship, even if it blows up some distance below.

 

A bomb going off next to the ship can be similarly effective, but requires fairly close proximity, otherwise the blast goes up and misses the ship.

 

Bombs going off in the hull of the ship, (i.e. direct hit with little delay) can cause a lot of internal damage (fires, machinery, ...) and are also capable of rupturing the hull, but are less likely to do so then bombs going off inside the water next to the ship.

 

Bombs going off in the superstructure of the ship (i.e. direct hits without delay) may cause significant damage, including fires, and are capable of destroying the ship, but are less likely to sink it.

 

You need HE bombs to maximize the effect of them going of in the water, but at least general purpose or for larger ships (which we don't have in game yet) even (semi) armour piercing bombs for direct hits.

 

Size of bombs is a question of target size and hit probability, but with small bombs (100kg and less) you can pretty much forget about anything but direct hits.

[InProgress]

Hmm interesting.. I never noticed bombs sinking after long delay, even this 14s explode normal. Anybody knows what was mostly used tactic during battle of Britain? To sink ships, I watched some clips and seemd like they used some delay but don't know if aiming at ships or water.

 

I know about this jumping thingy bomb, like when you throw rock and it jumps on water, tried it few times but seems more troubling than dive bombing that I love so much

 

Also from what I saw mostly Germans used 4 small bombs and one bigger 250kg. I like to do things historical :> I know I could just keep taking 500kg and 2x250kg or even 1000kg but it does not feel right.

 

But then if they used 4x small ones 50-70kg then hitting water was not any good?

 

Talking about cargo ships now, I guess big destroyers or something like this would need lots of bombs and combined effort of other pilots to sink them.

Edited August 28, 2017 by InProgress

[-SF-Disarray]

Skipping the bomb into the side of the ship, called 'top mast bombing' by some, was used with some effect. When done just perfectly the bomb goes off at or near the water line of the ship. So long as the ship doesn't have much in the way of an armor belt this will cause fatal flooding. Though I imagine delayed bombing near the ship would cause some serious damage to ships as well; with the added benefit of not requiring the skill and timing of a top mast drop. The thing you have to remember in this case is that water reacts very differently to explosions than air does. The principal difference is water doesn't compress like air will. The end result is a bomb going off near a ship under water will impart a massive amount of force over distance. While the same bomb going off on the surface of the water will impart less force over distance as the air compresses, effectively dampening the effect on the ship; think of the air as being like a car's shock absorbing system and you won't be far off. This is why magnetic detonating torpedoes work so well, they don't have to hit the target directly and they can impart huge forces at an angle the ship just isn't built to cope with. This non-compressible nature of water is also what makes depth charges work so well against submarines without having to actually strike the hull of the boat.

 

The reason, I suspect, you see large groups of planes attacking larger warships is, in part, due to the increased ordinance required to take them down. Though I think it is more likely due to the fact that these war ships tended to be very well armed against air attack in most cases. Even a relatively poorly armed ship, say with only a hand full of anti-aircraft batteries, could deal with one or two planes with little problem. Throw five or ten planes into the air and you start overwhelming the ability of the guns to cope and thus more bombs make it to target and the drop on those bombs can be more accurate because the planes aren't having to dodge the same volume of fire. You might also be supersized at the amount of bombs that are required to sink some of these warships, even the large battleships. Get one bomb through the deck and into the fuel bunker or, god forbid, the magazine and the whole ship will be destroyed, even if it is a relatively small bomb. The USS Arizona displaced almost 27,000 tons and was felled by only four bombs, the last of which punched into the forward magazine causing a devastating explosion. Granted the bomb that did this was a modified 1000 Kg armor piercing shell but it had a lot of ship to kill.

[InProgress]

Yeaa I know direct hit can be fatal

 

So what use is 4x 50/70kg bombs against ships?

Edited August 28, 2017 by InProgress

[JtD]

Four bombs obviously have a higher chance to hit than just one. Unlikely to sink anything bigger than a river steamboat, unless they set off some sort of chain reaction. Still, even if not sinking anything, a direct hit is always damaging and may put a vessel out of service. War in real life is not as binary as in a computer game, a hit with a small bomb is better than a miss with a big one..

[Venturi]

It is much better for bombs to explode near the target and under water. Damage is primarily from hydraulic effect through the surrounding fluid. Fluids are in-compressible. Therefore, more energy is delivered to the target than an explosion in air, which is very compressible and dissipates much more energy.

 

I am surprised more people don't know this.

It is the same reason depth charges are so effective.

[Venturi]

50kg bombs are not a joke. They just aren't big enough to cause direct destruction of a tank unless they drop right on it. They might still de-track that tank if right next to it.

 

I imagine a near miss within a few meters, with a 50kg bomb on an unarmored hull would be more than sufficient to punch a hole in the hull. People forget merchant men were sunk with 8.8cm Uboat deck guns very frequently in the war.

[-SF-Disarray]

To be fair, JtD, nukes when tested against US warships in the 1950s didn't even destroy some of the larger ships outright when detonated in relative proximity. It is really quite difficult to destroy anything that well build by sheer explosive power, they were built to avoid just that. If you look at the primary weapons designed to kill warships of the day they all worked by penetrating the exterior protection and detonating inside. The hope was that they would cause some catastrophic damage, this being the ideal, but more important goal was to kill the men on board. This has been the trend in naval warfare for quite a long time: sinking ships is extraordinarily difficult, especially when they are made of wood. Better to kill everyone on the ship, or at least enough of them to make the ship ineffective. This was no different in WW 2, with a notable exception being the wide spread use of submarines which were primarily tasked with actually sinking ships.

[Pharoah]

Good point re skip bombing....with BoK I'm assuming both sides will have shipping. I'm assuming we should be able to do skip bombing as well if we tried? i know they used it to good effect in the pacific war.

[DD_Arthur]

 I'm assuming we should be able to do skip bombing as well if we tried?

 

 

You can try skip bombing now.

[AndyJWest]

You can try skip bombing now.

 

Isn't the idea to have the bomb hit the hull above the waterline, and then either penetrate or sink? Given how low the BoS riverboats are in the water, there isn't much hull to hit, and the bomb is liable to skip right over, I'd have thought.

[ShamrockOneFive]

Isn't the idea to have the bomb hit the hull above the waterline, and then either penetrate or sink? Given how low the BoS riverboats are in the water, there isn't much hull to hit, and the bomb is liable to skip right over, I'd have thought.

 

I have done it with those steamboats and the small gunboats but most of the time my bombs are skipping right over them. Its a tough go to get it right.

 

Han has done it mind you

 

[unreasonable]

To be fair, JtD, nukes when tested against US warships in the 1950s didn't even destroy some of the larger ships outright when detonated in relative proximity. It is really quite difficult to destroy anything that well build by sheer explosive power, they were built to avoid just that. If you look at the primary weapons designed to kill warships of the day they all worked by penetrating the exterior protection and detonating inside. The hope was that they would cause some catastrophic damage, this being the ideal, but more important goal was to kill the men on board. This has been the trend in naval warfare for quite a long time: sinking ships is extraordinarily difficult, especially when they are made of wood. Better to kill everyone on the ship, or at least enough of them to make the ship ineffective. This was no different in WW 2, with a notable exception being the wide spread use of submarines which were primarily tasked with actually sinking ships.

 

Except for the weapons that terrified surface ship commanders, the torpedo and the mine, and the weapon that terrified submarine commanders, the depth charge. Breaching the shell of the ship below the waterline and defeating compartmentalization (if any) is the most efficient way to kill ships. WW2 ships were rarely made of wood (I am sure you know that ).

 

I have never seen an analysis done by ship or by tonnage, (anyone got one?)  but I would guess that the majority of surface ships sunk during WW2 were done in by torpedoes;  if you count warships only the proportion might be smaller, but I would still expect torpedoes to be the number one cause of sinking. 

[[_FLAPS_]Grim]

If aimed for the wheelhouse or whatever is the biggest structure on the deck, you can hit every ship with skip bombing at the moment.

I usually take a short fuse (2-3 sec) so the bomb doesnt sink to deep.

Small boats are harder to hit but much more likely to take damage from a near miss.

[Myscion]

The US navy did a analysis of ship losses and reasons after the war. Submarine incidents as well including reports from the crews. It's all be declassified. 

 

You can access more reports from the left side bar

 

Gun fire and bombs

 

Torpedoes and mines

 

The most surprising impression I got from these reports is how fragile ships are. For the destroyers 3-4 hit near the water line is near fatal. And these are highly compartmentalized and well trained crews.

 

In BOS I imagine most crews are not trained as well and ships are older. That said I imagine most ships would simply beach them selves if too badly shoot up. 

[InProgress]

I remember watching documentary about Bismarck, they said that big ships were shooting at water with main guns so it would hit attacking planes and make them crash hope it will be in Pacific or kuban. This kind of attack vr heavily armed ship seems very dangerous, especially that few seconds when you fly straight.

 

But back to bombs, I know you won't destroy ship with 1x 50kg. I meant if these 50kg will actually do anything if dropped right and explode really close to the side or under ship?

 

I know it will probably depend on different ships but I would like to focus on cargo ships and smaller ships like destroyers.

 

@up

That looks nice, lots to read but thanks

Edited August 29, 2017 by InProgress

[Wulf]

Yes that's correct about using the main batteries on warships to shoot at the sea surface in front of attacking torpedo bombers.  Hitting a water spout at speed would be like hitting a brick wall.

 

And of course the thing to remember about an effective bomb attack on a ship is that it's somewhat similar to an effective cannon attack on an aircraft. You want a short delay of the explosive charge to allow the cannon round or bomb to penetrate the outer skin of the vessel (aircraft) so that the explosive force is delivered to the structure of the target rather than the superstructure or skin.  That is why bombs used against ships were often armour piercing - to improve their penetration prior to detonation.

[Utopioneer]

I have done it with those steamboats and the small gunboats but most of the time my bombs are skipping right over them. Its a tough go to get it right.

 

Han has done it mind you

 

https://www.youtube.com/watch?v=BMHrGvCn9c0

I had a lot of fun getting my first top mast bombing run right. Looking forward to trying it in kuban, but does anybody know if waves will affect the skip trajectory? Edited August 29, 2017 by Utopioneer

[unreasonable]

The US navy did a analysis of ship losses and reasons after the war. Submarine incidents as well including reports from the crews. It's all be declassified. 

 

You can access more reports from the left side bar

 

Gun fire and bombs

 

Torpedoes and mines

 

The most surprising impression I got from these reports is how fragile ships are. For the destroyers 3-4 hit near the water line is near fatal. And these are highly compartmentalized and well trained crews.

 

In BOS I imagine most crews are not trained as well and ships are older. That said I imagine most ships would simply beach them selves if too badly shoot up. 

 

Such a good forum this! Good link. 

 

Obviously the USN, unlike the RN, did not have to worry much about mines. I think the main problem for destroyers is that being long and narrow they can easily lose stability and capsize quickly if compartments flood one one side. Also the engine rooms were not especially well compartmentalized.

 

Anyway, I am really looking forwards to strafing and bombing ships even if we do not have a torpedo in Kuban, if only because I will be able to see them, unlike most of the land targets!

[Venturi]

Read the following:

It goes on to say that the most effective Japanese bombs were the 67kg and 250kg varieties.

[Retnek]

But back to bombs, I know you won't destroy ship with 1x 50kg.

Hm, 50 kg bombs were good enough to sink large ships, if they started a fire ... ships are able to stand enormous internal damage by large bombs (or grenades), as long as the hull remained intact mostly. But the crew had to control the fire, that was the key for survival in most cases. 50 kg bombs exploding in the water directly next to a riveted hull of an old trade steamer might have produced serious problems, same for small ships or submarines.

[InProgress]

Tested it today and it's pfff... not a single bomb 250 or 70 did anything when I was dropping them next to ship, at least no visual effects. Even 4x 70kg direct hit on ship with 3s delay did nothing, no fire no smoke. I was testing 1000kg as well, no serious effects, even exploding under "nose" of ship did nothing. I got effects with 1800kg, 15s delay when dropping it RIGHT in front of ship so it would swim under it way further actually killed it. 250kg bomb with delay exploding inside ship sinked it. 0 damage if it was next to it, only 1800 was able to sink ship when landing really close to the side.

 

Tested it on this big metal cargo ship in Stalingrad. So from what I can see in game and this topic, dropping bombs in water is super useless, single 250 can do the job when direct hit, 70kg seems also useless, better to fly with 3x 250 :/

 

Maybe test was not 100% accurate, was flying for like 30min, dropping bombs on ship and next to it. But really could not get any kills or even visible damage with anything but 1800kg when dropping bombs in water.

 

I dropped 50kg from hs129 on tower of ship, it actually made little fire but it does not spread. Was really disappointed when saw 4x70kg exploding after 3s delay and nothing, ship keeps going, same speed, no smoke, bombs hit 2-3m in front of tower.

Edited August 31, 2017 by InProgress

[Venturi]

3s might be too long. That would put them quite deep, maybe 20-30ft from keel. But I agree that even 50kg bombs in the water with maybe 1s delay, if they are skip bombed or dropped within a meter or two, ought to do some damage. Ship sinking is also not a "all or nothing" event. 

 

You can have a ship listing but hanging on... then one more hole in it sinks it.

[InProgress]

I did even 15s worked with 1800 under ship. But ok, will try 1s tomorrow. But either way it's far more effective (at least in game) to hit ship, not water.

 

Maybe problem is that these russian cargo ships are quite shallow and it does not work like it does on normal cargo ships that swim on the sea in clod.

 

https://steamuserimages-a.akamaihd.net/ugc/866235915497764275/2762DC2B31FD1480CA72A6FEB060C45D4596F300/

Vs

https://steamuserimages-a.akamaihd.net/ugc/865109822939437257/0F6AD7EAEB887EA52B4CB991358626004692486C/

Edited August 31, 2017 by InProgress

[unreasonable]

Remember that a WW2 torpedo typically had about 500lbs - 225kg of TNT in it's warhead.  By comparison, a German SC250 weighs 250 kg but only has 130kg of HE.  To get a 225kg charge of HE would require a SC500. - about 10 SC50s.

 

Secondly, torpedos were triggered by contact fuses in WW2 - later ones by proximity when the torpedo could be directed right under the ship.  The optimal distance for the detonation is right next to the skin of the ship.  The blast pressure wave diffuses in proportion to the cubed root of the distance.

 

So for pressure index at 100% at distance one,  79% at distance 2, 47% at distance 10, 22% at distance 100.  

 

So bombs really will work best when they hit. A near miss from a small bomb like an SC50 or SC250 would have to be right next to the hull - and I mean almost in contact - to do significant damage.

Edited September 1, 2017 by unreasonable

[Venturi]

Torpedos were used to sink 2000T destroyers to 10000T merchantmen... to cruisers and bigger.

 

Surely a 50kg bomb detonating a few feet from the hull of a unarmored small ship, barge, or PT boat would destroy it? And would do some hull damage to even larger merchantmen.

 

That is 60-70 POUNDS of TNT........ let's not get lost in the numbers, and remember what exactly we are discussing here, and what it can do.

Tanks are VERY tough customers. Do not let your sim experiences with AFVs make you willfully ignorant of what high explosives can do...

I'm quite aware of the inverse square law. https://forum.il2sturmovik.com/topic/15691-effectiveness-german-70kg-sd-bombs/?p=251404

 

What I'm saying is that the energy transmitted through water is more than that transmitted through air... but at a shorter distance.

Obviously a direct hit is the best scenario for "small" bombs - if you consider that "small" in this regard - a 50kg bomb - means the same explosive impact of TWO 155mm artillery shells (12.5lbs TNT apiece - M107).

Edited September 1, 2017 by Venturi

[unreasonable]

Torpedos were used to sink 2000T destroyers to 10000T merchantmen... to cruisers and bigger.

 

Surely a 50kg bomb detonating a few feet from the hull of a unarmored small ship, barge, or PT boat would destroy it? And would do some hull damage to even larger merchantmen.

 

That is 60-70 POUNDS of TNT........ let's not get lost in the numbers, and remember what exactly we are discussing here, and what it can do.

Tanks are VERY tough customers. Do not let your sim experiences with AFVs make you willfully ignorant of what high explosives can do...

I'm quite aware of the inverse square law. What I'm saying is that the energy transmitted through water is more than that transmitted through air... but at a shorter distance.

Obviously a direct hit is the best scenario for "small" bombs - if you consider that "small" in this regard - a 50kg bomb - means the same explosive impact of TWO 155mm artillery shells (12.5lbs TNT apiece - M107).

 

Well the SC50 is about the smallest regularly used air dropped bomb, if you exclude cluster sub-munitions.  

 

I agree that smaller vessels would be more fragile - I am not sure how strong is the ship inProgress is attacking or for that matter how close are his near misses.  But what looks "right next to" from the cockpit might be 20 metres. 

 

Perhaps there is some data somewhere on the effectiveness of near misses.  This issue is exactly about the numbers, it is just physics.  

 

BTW please knock off the ad-hominem crap.  

[Venturi]

Well I just dropped a 250kg bomb about 3m off the bow of a barge, and it did nothing. So, that is a good indication of where we are.

[Venturi]

By the way, as I was floating down in my parachute (AAA fire), the submarine right next to the barge was shooting at me. Nice touch.

 

One other thing, I did land a 500lb'er on a barge directly, and it immediately sunk. The thing that struck me was how little fire and smoke there was, considering how much diesel fuel must have been on board that thing.

[JtD]

I hope for and expect ship damage modelling to receive some extra attention before we move to the Pacific. I suppose it will already be an issue for Kuban, but right now some things appear to be very simplistic. Good enough for the odd river barge on the Volga, but not quite good enough for naval action on open seas.

[unreasonable]

Here is an interesting tit-bit from the wiki page on depth charges on the WW1 UK depth charge.

 

"There were initially two sizes—Type D, with a 300 lb (140 kg) charge for fast ships, and Type D* with a 120 lb (54 kg) charge for ships too slow to leave the danger area before the more powerful charge detonated.^[2][3]"

 

"Initial depth settings were 40 or 80 ft (12 or 24 m)"

 

"Even slower ships could safely use the Type D at below 100 ft (30 m) and at 10 kn (19 km/h; 12 mph) or more,"

 

ie this suggests that a 54kg TNT (D*) charge could not damage the hull of a WW1 frigate or destroyer if it exploded at 12m depth somewhere close to the stern, perhaps 20 metres or so away. Also damage might not necessarily imply a hull breach or anything visible - maybe machine mountings damaged etc. But it might if it was closer.  

 

Sink rate is about 2.5 m/s, so it takes the charge about 12 seconds to get to a depth of 30m, at 19kph ship will have moved about 60 m, so straight line distance between explosion and ship is about 70 metres, so that is the safe distance for a 140kg charge underwater, at least the one the RN used at that time.

 

Well I just dropped a 250kg bomb about 3m off the bow of a barge, and it did nothing. So, that is a good indication of where we are.

 

I agree that would seem wrong.

[Venturi]

Thanks for the data, good to have numbers to back up assertions.

[InProgress]

Haven't do new test yet, but i was testing it yesterday, I was using quick battle and free camera, slow time, I know exactly where bombs hit, some were even directly next to the ship 1m or less.

 

50kg was just fooling around with hs129, did not expect to do anything with it. Like I said, only 1800 close to the ship killed it, even 1000 did not. Another thing is that 70kg also did nothing. Tested it 2 times, once I hit with all 4 bombs directly and no damage at all, once 2 hit and 2 missed but were just directly next to ship, 0 damage as well.

 

I think we can say that bombs vs ships isn't well made for now.

 

Fire does not seem to spread, cargo if it's ammo or fuel does not make any chain reaction and no big boom. Maybe they transport food only

Edited September 1, 2017 by InProgress

[Retnek]

Tested yesterday 2 x 500 kg from a Pe-2 skip-bombing with 5 sec fuse against that 1600 to - destroyer. It looked like the bomb stuck in the hull like a dart, should have made a video ... first bomb from first run took out some guns and damaged ship heavily, second bomb sunk it.

[Arfsix]

     It would appear from films and detailed reports, that it is very difficult to sink a warship by dropping a bomb in the water along side.  The following abstract goes into detail concerning possible bomb damage and for the rivet counters, provides the math behind the conclusions.

 

​      THE EFFECT OF AN UNDERWATER EXPLOSION ON A SHIP

       http://www.amw.gdynia.pl/library/File/ZeszytyNaukowe/2015/ZN%20AMW_2015_2/Szturomski.pdf

 

      The short answer  from the table below is that a 300Kg bomb must fall within 19 meters of the ship to sink the ship.

 

                    Table 3. The dependence of the distance from the explosion epicenter to the ship in the function of explosive charge mass contained in the mine and the corresponding to the effects of the shockwave on the ship.

 

Detonation                 Mine mass (TNT) [Kg]      
wave pressure   150     300     500     800     1200                             Explosion effects
[Mpa]                Distance following the Cole's formular [m]         
      4                    51       65       78       90       102                              Safe for warships
      8                    28       35       42       49        56                               Damage to mechanisms and appliances
    12                    19       24       30       34        39                               Deformations and likelihood of cracks in hull sheet plating
    16                    16       19       23       27        30                               Total loss of maneuver and combat capabilities. Llikelihood of ship sinking.
 

Edited September 1, 2017 by Arfsix

[unreasonable]

@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.