Bismark Sinks Then Resurfaced Upsidedown ?

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

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Vic Dale
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Re: Bismark Sinks Then Resurfaced Upsidedown ?

Post by Vic Dale » Sat Jan 10, 2009 6:04 pm

To Legend.

If the ship has taken enough water to go under but with her main turrets still attached, the sudden loss of 4 thousand tons would add greatly to her bouyancy. For all we know the rate of her sinking once she was completely immersed could have been extremely slow and the sudden release of the turrets could indeed have brought her to the surface again. Whether or not such a thing was observed in Piorun is another matter.

It could have happened, is all that I am saying. We don't know how much air was still in the hull when she went down, but we do know she went very slowly and this I think was by design. Planned in her DC centre to ensure A. that she would definitely go under but B. that she would go under slowly enough to permit as many men as possible to get out. Such calculations would include the ship's turrets. The weight of steel above water water would force her down, but as she immersed this downward force would diminish. I believe she did hang for a good while before slowly slipping below.

A submarine can theoretically hang on it's periscope as it finds the balance between that which is immersed and that which is exposed. If very fine flooding control can be acheived the balance between weight and bouyancy can be found. Then if the volume of water equal to the volume on the periscope is added, the boat will go down very slowly and may even sit on layers of higher density water. This could have happened to Bismarck. She was inverted and this would prevent air escaping from the hull. She might go down extremely slowly, her weight overcoming bouyancy by only a very small margin, then if she was suddenly relieved of her turrets, "up" she would surely come, as if 4,000 thousand tons of bouyancy had been added.

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Re: Bismark Sinks Then Resurfaced Upsidedown ?

Post by lwd » Sat Jan 10, 2009 6:37 pm

While theoretically possible considering that Bismark had numerous holes in her upper surface and would have been gaining water pretty quickly as she submerged and then would have a fair amount of momentum downward the turrets dropping off would have to overcome the additional water taken on plus the downward momentum. It seams improbable to me.

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Re: Bismark Sinks Then Resurfaced Upsidedown ?

Post by Vic Dale » Sun Jan 11, 2009 4:24 pm

To LWD.

There were very few holes below water and those few would have been isolated through Damage Control measures during the battle and the preceding days. So the only way ingress could continue after the ship inverted, would be by compression of air trapped in the hull. I don't think very much was boiling up from the wreck, at least nothing of such seems to have been reported.

A further thought has occurred, the turrets are scattered over a large area. Yet such relatively small structures weighing so much and with so little ability to trap air inside them would have sunk very fast and if they came out together should be located very near to eachother. This has to mean that the turrets came out one at a time to make their descent and if so the hull's inversion would have to be such that they hung for a while before detaching, so the weight of the turrets may very well have carried the ship down, compressing trapped air as she went and when they came out, the now lighter hull may have arrested and then began to rise again. If this occurred I can see nothing to stop her reaching the surface again. As with the submarine, finding the balance is practically impossible.

I agree, this is highly theoretical - but possible.

Any engineers about who can work out the maths on this one?

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Re: Bismark Sinks Then Resurfaced Upsidedown ?

Post by lwd » Sun Jan 11, 2009 5:53 pm

As she turns over a lot of trapped air will be allowed to escape. There's also the scuttleing effects. Even just leaving water tight hatches open will have considerable impact then there's the effect of the openings in the hull.

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Re: Bismark Sinks Then Resurfaced Upsidedown ?

Post by Vic Dale » Sun Jan 11, 2009 6:24 pm

The scuttling applies to the engine rooms only and there are no interconnecting doors or openings between compartments below the armoured deck. The only way into the ship's separate subdivisions was vertically via hatches let into the armoured deck. The ship's water-tight intergrity would largely maintain, even though the engine rooms were open to the sea.

As the inverted hull immersed, most of the air in the ship below/above the turtle deck would be trapped.

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Re: Bismark Sinks Then Resurfaced Upsidedown ?

Post by Legend » Sun Jan 11, 2009 11:38 pm

Still, 4,000 tons being relieved from a sinking 40,000 ton wreck. I really don't see there being much of a dispute here. The engine rooms took up a great deal of space, meaning the water filled superstructure, upper decks (punctuerd by shells), engine rooms (scuttling), and other dead weights should be bringing her down without doubt. She may have slowed on the descent, but not by much. I don't see how a sudden 4,000 ton alleviance will bring a 40,000 ton hull, traveling at about 30-40 kilometers per hour toward the bottom, to a standstill and then BACK UP. It might be true for a little plastic toy in the bathtub, but not the Atlantic's largest battleship. When she went under, she went all the way under, into the mud. She is lying immersed up to her WATERLINE. Now, she did plow her way under partly, but the impact area the Mir's landed in was deep enough to show how much force she was making going down. Her outer armor plates blew straight off for pete's sake! Don't tell me throwing multiple tons of krupp steel a few dozen meters through water is an easy job! :stop: :negative:
AND THE SEA SHALL GRANT EACH MAN NEW HOPE, AS SLEEP BRINGS DREAMS.

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Re: Bismark Sinks Then Resurfaced Upsidedown ?

Post by Vic Dale » Mon Jan 12, 2009 6:38 am

To Legend.

If the ship went down with her weight plus flooding due to scuttling, she might go very slowly, but at a certain point the air in her would compress removing all bouyancy. That is what I appealed for an engineer for, to tell us when that depth might be reached. My guess is that all bouyancy would be gone at 2 miles down and from there she would descend under her own weight slowed only by water resistance. So the result would be exaclty the same.

I believe that just as an object will fall at a given rate in atmosphere so a ship will descend into the depths at a rate determined by water resistance.

I see a heavy impact whatever happens 2 miles up.

I don't think there is a figure for stating how fast a ship will sink, because they all do so with differing amounts of air trapped inside them. The fact that the turrets are so scattered indicates that Bismarck moved some way after sinking and that the turrets fell out one by one. Like a submarine, the hull would still have bouyancy even though below water. If there was sufficent weight to make her just go under with the bulk of her internal structure still filled with air, the loss of a single turret could add 1000 tons of bouyancy. It might act like a submarine blowing "Q".

It is important to remember when thinking about this sort of thing, that the 40,000 ton hull was floating until shortly before she went under and it seems she slipped under very slowly with men being able to walk on the bottom for a time.

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Re: Bismark Sinks Then Resurfaced Upsidedown ?

Post by lwd » Mon Jan 12, 2009 4:02 pm

Vic Dale wrote:... but at a certain point the air in her would compress removing all bouyancy....
The air can either exist in a water tight compartment or open to the sea. In a water tight compartment it's the crush depth or failure depth of the comparment that's important. I doubt that this occures at any great depth for most comparments. There's simply no reason to engineer the cable and pipe fixtures to hold out 10s of meters of water. As for compressing water that is open to the ocean as a rule of thumb for every 30 feet (or 10m if you prefer) the pressure goes up by one atmosphere. The equation of relevance is PV=nRT. If you neglect the change in temperature with depth nRT is a constant so you need only calculate when the density of air reaches that of water. According to http://www.elmhurst.edu/~chm/vchembook/ ... tygas.html the density of air is .00128 g/mL and that of water is ~1. So you would need a pressure of ~800 atmosphers to equalize the density. That's ~8km down.
I believe that just as an object will fall at a given rate in atmosphere so a ship will descend into the depths at a rate determined by water resistance.
Objects do have a "terminal" velocity in either medium but it can be signficantly effected by orrientation (a human body in freefall has a terminal velocity of ~120 mph spread eagle or ~180 mph head or feet first with arms and legs in tight) and in the case of a ship changeing shape and density can effect the terminal velocity.

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Re: Bismark Sinks Then Resurfaced Upsidedown ?

Post by Vic Dale » Mon Jan 12, 2009 5:22 pm

To LWD

Thanks for that.

My thinking is that compartmentalisation would mostly fail within water tight compartments but would hold longer at the main bulkheads bearing in mind that the transverse bulkheads are stressed to bear the force of the sea in very heavy weather with a section open to the sea. My estimate is that the ship could go down to a couple of hundred feet and those bulkheads should hold. Or modern ships had shell-plating no thicker than the internal bulkheads and they could take a real pounding from the sea day in, day out without ever failing, so I don't see there being much problem with Bismarck carrying herself down ot 200 feet or more and remaining intact.

The sections containing the engines were blown to the sea with the shattering of the condenser castings with the demolition charges, but that was all, the rest of the ship would be sound and without blowing those charges could have remained afloat for days. The demoliton charges were aimed at sinking the ship, but slowly so that everyone could get off. She remained bottom up for a good while before slowly disappearing. I think there was a good deal of bouyancy trapped inside her and would not easily come out, because the hull was largely intact.

In such a case the differential between weight and bouyancy could be very slight and below the surface it would become very calm. So there would be no shocks to dislodge turrets which had not already come out. If she is sinking slowly with her turrets in position, the loss of them could tip the balance. As the pressure builds, the air is forced up inside the ship and the water rises. If a turret comes out due to the ship inverting more, the loss of weight could overcome the downward motion and start her going up again. Water would be forced down and out of the hull and greater bouyancy would be felt. The motion upwards might have a stroking effect causing her to invert more fully so the the remaining turrets could come out.

I think it is possible, though how likely is anyone's guess.

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Re: Bismark Sinks Then Resurfaced Upsidedown ?

Post by lwd » Mon Jan 12, 2009 6:02 pm

Certainly possible. I just don't think lightly. Note that a few ponds of overpressue from guns were enough to damage at least parts of both the Yamato and Iowa classes from what I recall reading. Indeed over pressure effects were one reason the US didn't want to build 18" gunned ships (again from my sometimes fallible memory). At 200 feet you are talking about ~7 atmospheres of overpressure. That's almost 100lbs per sq inch. Which translates to about 7 tons per sq foot.

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Re: Bismark Sinks Then Resurfaced Upsidedown ?

Post by Geoff Leet » Mon Feb 02, 2009 6:08 pm

Does anyone know where Polish naval records are kept? The sighting of the Bismark resurfacing would surely be recorded in the destroyer's log. It is probably written in Polish!
Geoff Leet. 1-02-09.

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