General Discussions
This is the place to discuss general issues related to the U-boat war or the war at sea in WWII.
Re: Wreckage
Posted by:
kurt
()
Date: November 20, 2001 03:41PM
<HTML>I may have been 'the guy' who talked about what happens when a boat sinks. I posted some on that in regards to suggestions on the board about raising sunken U-boats.
To re-iterate the basics, when a ship (or sub) starts to sink, there are often secondary explosions - explosives, depth charges, steam boilers. If the ship is at a high angle as it slips beneath the waves, a lot of heavy machinery can tear loose and careen around - boilers or generators can fall through bulkheads and tear up the ship, cargo can fall and rip open bulkheads. Water filling the ship often bursts internal bulkheads. The strain of the ship shifting to high and unussual attitudes as it sinks under the waves can break up or destroy the ship - often tearing it apart. The Titanic was torn into three pieces by just this when it's stern was raised up out of the water.
As the ship goes below the surface and plunges to the ocean depths, all the remaining pockets of bouyancy - air pockets, tanks, etc, get crushed, and the vessel becomes denser and denser as it drops. If a boat sinks in very deep water the vessel can hit some very high speeds before it hits the floor. The Titanic was supposed to be doing 40 - 50 knots, I believe. The result is tremendous damage - a vessel sunk in deep water is usually wrecked and structurally damaged beyond possibility of raising.
Another problem is that even in the ocean depths bacteria will leech out the metal from the hull - iron eating bacteria that gradually turn the hull to dust. These icicles of iron are clearly visible in the movie 'Titanic' - in another few decades the wreck will be gone, at least as a recognizable shape of a ship. A deep wreck that has sat for a few decades is mostly rotted out, even if the basic shape remains.
For a deep submersible sub (like the Thresher and the Scorpion, but unlike a U-boat) the damage dynamics are different. The Thresher hull was made of high strength steel that could stand several thousand feet of depth - as the Thresher plunged below crush depth the hull imploded - the brittle steel hull shattering into tiny shards. Only shattered pieces were found on the ocean floor - or so I remember from a documentary.
The Scorpion was theorized to have suffered a torpedo explosion. This blew out the hatch of the forward torpedo room, allowing it to flood but not be crushed - it was the only section to be found intact, but with the hatch missing.
As the Scorpion plunged below crush depth, the remaining portion of the hull was crushed like a telescope - engine room pushed forward into the main living areas, so the whole hull was found crushed together - telescoped - but with the forward torpedo room intact and untouched.
The difference is that when a deeply submerged (several thousand feet) sub collapses, the force is incredible, and the structure will either be crushed or shattered instantly. I could also add that for the victims trapped in the hull, when it finally does collapse, rather than drowning, they either are crushed by the instant exposure to several thousand psi water, or are incenerated if they are caught in an air pocket - air suddenly compressed to several thousand psi will be as hot as a blowtorch.
The long and the short of it is that any wreck that has fallen to the bottom of the ocean depths (not several hundred, but many thousands) of feet is almost certainly destroyed structurally, even if it still appears to be intact. It was of no surprise to those in the silent service when the the (CIA's) Glomar Challenger's attempt to raise a sunken Soviet sub ended in disaster when the sub fell apart in its giant claw's grasp.</HTML>
To re-iterate the basics, when a ship (or sub) starts to sink, there are often secondary explosions - explosives, depth charges, steam boilers. If the ship is at a high angle as it slips beneath the waves, a lot of heavy machinery can tear loose and careen around - boilers or generators can fall through bulkheads and tear up the ship, cargo can fall and rip open bulkheads. Water filling the ship often bursts internal bulkheads. The strain of the ship shifting to high and unussual attitudes as it sinks under the waves can break up or destroy the ship - often tearing it apart. The Titanic was torn into three pieces by just this when it's stern was raised up out of the water.
As the ship goes below the surface and plunges to the ocean depths, all the remaining pockets of bouyancy - air pockets, tanks, etc, get crushed, and the vessel becomes denser and denser as it drops. If a boat sinks in very deep water the vessel can hit some very high speeds before it hits the floor. The Titanic was supposed to be doing 40 - 50 knots, I believe. The result is tremendous damage - a vessel sunk in deep water is usually wrecked and structurally damaged beyond possibility of raising.
Another problem is that even in the ocean depths bacteria will leech out the metal from the hull - iron eating bacteria that gradually turn the hull to dust. These icicles of iron are clearly visible in the movie 'Titanic' - in another few decades the wreck will be gone, at least as a recognizable shape of a ship. A deep wreck that has sat for a few decades is mostly rotted out, even if the basic shape remains.
For a deep submersible sub (like the Thresher and the Scorpion, but unlike a U-boat) the damage dynamics are different. The Thresher hull was made of high strength steel that could stand several thousand feet of depth - as the Thresher plunged below crush depth the hull imploded - the brittle steel hull shattering into tiny shards. Only shattered pieces were found on the ocean floor - or so I remember from a documentary.
The Scorpion was theorized to have suffered a torpedo explosion. This blew out the hatch of the forward torpedo room, allowing it to flood but not be crushed - it was the only section to be found intact, but with the hatch missing.
As the Scorpion plunged below crush depth, the remaining portion of the hull was crushed like a telescope - engine room pushed forward into the main living areas, so the whole hull was found crushed together - telescoped - but with the forward torpedo room intact and untouched.
The difference is that when a deeply submerged (several thousand feet) sub collapses, the force is incredible, and the structure will either be crushed or shattered instantly. I could also add that for the victims trapped in the hull, when it finally does collapse, rather than drowning, they either are crushed by the instant exposure to several thousand psi water, or are incenerated if they are caught in an air pocket - air suddenly compressed to several thousand psi will be as hot as a blowtorch.
The long and the short of it is that any wreck that has fallen to the bottom of the ocean depths (not several hundred, but many thousands) of feet is almost certainly destroyed structurally, even if it still appears to be intact. It was of no surprise to those in the silent service when the the (CIA's) Glomar Challenger's attempt to raise a sunken Soviet sub ended in disaster when the sub fell apart in its giant claw's grasp.</HTML>
| Subject | Written By | Posted |
|---|---|---|
Wreckage
|
J.G.W. | 11/20/2001 04:01AM |
|
Re: Wreckage
|
oliver | 11/20/2001 12:40PM |
|
Re: Wreckage
|
kurt | 11/20/2001 03:41PM |