Why do Metal ships sink after a fire?

I saw this thread and immediately said “Heck, that one’s easy!” My question is, why do metal ships sink when they catch on fire? I’m always seeing news reports of ships sinking after an engine room or other sort of fire, and I’ve heard of navy ships during WW II sinking after being bombed.

A ship obviously sinks if you put enough torpedoes in it or if a bomb blows a hole in its keel. But why just a fire? Or even a secondary explosion? Is it that the explosion breaks its seams? Does a fire melt the metal? I would think that, all else being equal, you could burn out the insides of a cargo freighter and it would still float.

Really just a WAG, but there is a great big hole in the bottom of the ship that the propeller shaft goes through. Burn or melt the seal around that guy and you’d have a pretty effective scuttle valve, I’m thinking. Also, heat expansion could pop welds and/or rivets that hold the hull sections together. Most boats I’ve been on leak to some degree anyway. Stop the bilge pumps by burning out the electrical system and I’d guess “natural” leakage would eventually take over but I suspect that would take a very long time to actually sink the ship.

Sometimes that’s exactly what happens. Check out these pics of the recent Hyundai Fortune fire. Amazingly, she stayed afloat and last I heard, was heading towards port for cargo offload and salvage ops.

Some ships sink when the fuel tanks explode and, as fuel tanks often line the hull, the explosion breaches the hull. Also, once raw-water pipes in the engine room start to melt or burst, the sea water eventually floods the engine room. This flooding will most likely start to affect other compartments, as an out of control fire will begin to warp and buckle decks and bulkheads, effectively eliminating the watertight integrity of the spaces.

If you’re really lucky, the flooding will put the fire out before the fire destroys your ability to stay afloat with just a flooded engine room. :wink:

WWII ships were usually carrying things that explode (like shells for their guns, or ammo for the soldiers to use once they got to their destination). A lot of ships were sunk because fire reached the ammo.

A lot of TV shows on the history channel or the military channel have shown ships that were sunk because water came in and hit the boilers. Apparently cold sea water plus hot boilers equals a very big bang. Apparently, the bang can be big enough to blow a huge hole in the side of the ship. If the bombs don’t sink the ship, it’s not necessarily the fire afterwards that does the ship in.

For single hull boats like the Liberty Ships a fire could warp the hull, bursting welds/riveting and cause flooding.
The ammo/fuel explosions is a likelier reason.
A wrecked seal on the propeller shafts seems like a fairly unlikely cause.


Quite often water used to fight the fire will cause it to capsize.

Partial list of WWII military ships and why they sank. This is done completely from memory, so add corrections, additions, and comments. Thank you.:[ul]
[li]Royal Oak? (British battleship) torpedo[/li][li]Hood: probably magazines exploded from plunging fire[/li][li]Bismarck: Torpedoed after much damage (would have floated otherwise?)[/li][li]Graf Spee: Scuttled after blockaded at Montevideo[/li][li]Arizona: magazines exploded after bomb hit[/li][li]Oklahoma: turned turtle after torpedo hits[/li][li]Lexington: ?[/li][li]Yorktown: hit by bombs and torpedoes and remained afloat, then torpedoed by sub[/li][li]Hornet: sunk by torpedo from submarine[/li][li]Wasp: hit by bombs, fires caused gas explosions that loosened seams[/li][li]Hiryu, Soryu, Akagi, Kaga: ? (These are my big question. None were hit by torpedos but all sank after fires. Explosions? Loosened seams? USS Nautilus claimed sinking of one, but that’s been debunked by eyewitnesses.[/li][li]Juneau, Indianapolis, Northhampton: sunk by torpedos. American cruisers lacked armament and damage control features[/li][li]Yamato: partially capsized by torpedoes, as she turned turtle she exploded, possibly because of ammunition rolling around[/li][li]Yamato’s sister ship (name?): sunk after being hit by 19 torpedos[/li][/ul]

Princeton sank after being hit by a kamakasie, reason unknown. Another US carrier (Franklin?) survived several suicide hits. Damage control features of US carriers, as well as good training, allowed many of them to survive repeated hits; Yorktown I was hit at Coral Sea, repaired, hit several times at Midway, and survived again only to be sunk by a Japanese sub.

I will have to research sinkings of more modern ships. Did the Exxon Valdez sink, or just run aground?

Trivia note: Titanic and Andrea Doria took several hours to sink. In comparison, Luisitania, hit by torpedo, sank in roughly 15 minutes.

Side for those who are interested: They have found the wreck of the Graf Zeppelin, the only Nazi aircraft carrier.

I would like to know how the hull could ever get this hot, since it is sitting in cold water. Heat from the fire would just be quickly dissapated right through the metal hull (at least below the water line); I doubt a single wall hull could get hot enough to warp.

True, if the entire fire is below the water line.

Heat above the water line will cause the steel to expand, and the cold steel below the water line does not. That causes hard stress on every seam that crosses the water line.


Fear Itself: What **Triskadecamus ** said. :wink:
I doubt it could be found online, but that was the cause of at least one if not many liberty ships sinking. Additionally Liberty ships did not have the tightest quality control and I believe the bulk of them were rivets not welds. I would guess that a poorly riveted seam was far more susceptible to failure due to fire than a welded seam.
I will look for cites tonight.


Just ran aground. After the accident, she was renamed SeaRiver Mediterranean and hauled oil around Europe and Asia. IIRC, that ship was actually barred, by state law, from ever entering Alaskan waters again. 'Cuz, you know, it was the ship’s fault. :rolleyes:

Liberty ships were notoriously susceptible to catastrophic failure in the North Atlantic. While I’m no metallur… metalurgis… guy who knows about metal and stuff, I believe the problem was too much sulphur in the steel used in the hulls. When the ships plyed the cold waters of the North Atlantic, the metal fractured and, in many cases, the ships broke apart. This was also a problem with the Titanic, no?

So, I could see where fire on the inside and cold North Atlantic water on the outside would cause havoc for Liberty ships, which were susceptible to temperature related failure even without the fire.

From the Wiki article on Liberty Ships:

I search for longer than I should have and I came up with no cite supporting my statement. I think I might have been in error or I am remembering a non-liberty ship. If anyone can provide a cite, I would appreciate it, but I am going to assume I was wrong.


Even with the heat transfer on the hull, you still have the fires raging around the interior bulkheads and other structural members. Take out one or more structural bulkheads and the hull will not be able to maintain its shape very long against the sea. Once the hull begins deforming, it is just a matter of time before some seam somewhere gives out and starts letting water into the ship.


[li]Lexington: ?[/li][/QUOTE]

IIRC, damaged by torpedos and bombs, then later fell victim to fires started by an electrical short and a fuel leak (both from the damage incurred in the previous battle).

[li]Hiryu, Soryu, Akagi, Kaga: ? (These are my big question. None were hit by torpedos but all sank after fires. Explosions? Loosened seams? USS Nautilus claimed sinking of one, but that’s been debunked by eyewitnesses.[/li][/QUOTE]

IIRC, a big factor for at least three of those was unsecured munitions on the hangar deck (the planes had been prepped for a bombing run on the island, then had to be quickly refitted for attacks against armored ships, which required torpedos and armor-piercing bombs, and they hadn’t stowed away the bombs yet when the American dive bombers hit the planes on deck waiting to take off). Basically blew the tops off the ships, killed many of the officers and crews (and most of the aircrews, of course). The ships were scuttled by their crews later, I think.

IIRC, British aircraft carriers, built with combat in the confines of the English Channel in mind, were built with armored decks and so, after a kamikazi hit, they would only need to extinuish the fire on the deck and sweep the wreckage overboard, while an American carrier, built for speed in open oceans and lacking armored deck plating, would need to return to base for repairs.

IIRC, Titanic’s sister ship, Brittanic sank rather quickly after striking a mine during WWI. Unlike her sister ship’s passengers and crew, the Brittanic’s crew (fortunately, she was traveling empty back to the UK (being used as a medical transport, she tended not to carry many passengers from the US to Europe) ran for the life boats at the first sign of imminent inevitable defeat.

All ships use a lot of sea water internally for cooling equipment (mainly engines). Any fire in the engine room that is not quickly contained will cause all maner of floods. Given that most (although always all) of the ships elecrical power is generated in the engine room, it is very likley the ship will not be able to pump out the water. Without the help of other ships with portable salvage pumps, sinking is gonna happen.
Shaft seals are a big hole to the briney but usually have one or more back-up sealing systems if they give out, plus there location internally is not the most prone to damage.

SeaDog… Former Marine Engineer