OT: sinking speed of merchants

[panda124c]

Depends on the cargo, a ship full of machinery will sink a lot faster than a ship full of cork. With the same size hole.

Q-Ships use to use cork as cargo so that they could keep afloat even after being torpedoed, just to get the sub.

And we are not even going to mention ammunition ships....... [:-]

[rtrapasso]

Early in the war, 1 torp was enough to sink most merchants...

Later in the war, the US (and presumably other Allies) started building merchies with shock mounted equipment. This caused these ships to be much more resistant to torpedoes (supposedly). Before the shock mounting, the force of an explosion would knock machinery off its mounts, causing power failure and loss of pumping capacity. The ship would usually founder as a result.

If you read the accounts of U-boat campaign, the Allied Merchies become more and more resistant to torpedoes as the war progressed, esp. after mid-1943.

[MineSweeper]

Even Tankers were tough to take down with one torpedo....read one account that a U-boat hit a dynamite cargo ship(5,000 tons of TNT) with one torpedo in the Gulf of Mexico....the ship sunk and was going down to the bottom and Kaboom, the U-boat was seriously damaged.....

[rogueusmc]

ORIGINAL: MineSweeper

Even Tankers were tough to take down with one torpedo....read one account that a U-boat hit a dynamite cargo ship(5,000 tons of TNT) with one torpedo in the Gulf of Mexico....the ship sunk and was going down to the bottom and Kaboom, the U-boat was seriously damaged.....

I it turn it's belly up?...[:D]

[mlees]

From Nelson to Vanguard, Warship design and development, 1923-1945, by D. K. Brown, Naval Institute Press, ISBN 1-59114-602-x, pg 159:
 

Of 134 ships hit by one torpedo, 99 sank, and of the 35 which reached port, 17 were not repaired (ie constructive total loss). The smaller ships, corvettes and frigates, had little chance of surviving, and, in fact, only 2 out of 34 got home. Destroyes did a little better with 11 out of 48 surviving, and if the smaller, older ships are omitted, these figures improve to 11 out of 39. However, of the 10 repaired, none rejoined in less than 8 months. Of 15 destroyers hit by two torpedoes, 2 survived, while, not surprisingly, both those hit by three torpedoes sank. The sloops and frigates did even better with nearly half surviving (22 out of 47), and three of those lost were scuttled for immediate tactical reasons. That 16 were not repaired was due to the ready availability of replacements.

 
He is speaking only of the RN warship experience, here, not merchant ships.
 
The author eventually explains why more sloops and frigates survived two torpedoes than destroyers. From page 163, "back breaking":
 

Not surprisingly, there is an indication that the more highly-stressed ships were more likely to break their back. The most vulnerable ships were destroyers, highly stressed, and with a break of forecastle amidships which would much increase the stress locally. They were also shallow, keel to deck, which meant that a hit would destroy a higher proportion of the hull girder than in a deeper ship. The converse of this is seen in the sloops with low stress and a deep hull. USN experience is somewhat similar, of 30 sunk by above water attack, 6 broke their back (37%), whilst of 27 sunk by underwater weapons, 19 (70%) broke their back.

 
 
I am a bit hazy, at the moment, on were to find the stats for the damages inflicted by the US Silent Service on the Japanese...

[msieving1]

ORIGINAL: mlees

I am a bit hazy, at the moment, on were to find the stats for the damages inflicted by the US Silent Service on the Japanese...

I don't have any stats, but the Naval Historical Center has a 1944 manual of US submarine doctrine online. In chapter 4, section 6, paragraph 4614, there's a table that shows the expected number of torpedo hits required to sink various types of ships. A merchant ship is expected to need two hits to ensure sinking. The manual does note, though, that this is higly variable depending on circumstances.

[Charbroiled]

ORIGINAL: MineSweeper

Even Tankers were tough to take down with one torpedo....read one account that a U-boat hit a dynamite cargo ship(5,000 tons of TNT) with one torpedo in the Gulf of Mexico....the ship sunk and was going down to the bottom and Kaboom, the U-boat was seriously damaged.....

I don't have the book (Operation Drumbeat) with me, but IIRC, there was a tanker hit by 2 torpedos off of the East Coast of the US. The crew started to abandon ship and the ship started sinking. The U-boat commander, thinking he had a kill, and afraid to still be in the area at sunup left the scene. Th crew reboarded the ship and managed to make it to port.

[rtrapasso]

ORIGINAL: Charbroiled

ORIGINAL: MineSweeper

Even Tankers were tough to take down with one torpedo....read one account that a U-boat hit a dynamite cargo ship(5,000 tons of TNT) with one torpedo in the Gulf of Mexico....the ship sunk and was going down to the bottom and Kaboom, the U-boat was seriously damaged.....

I don't have the book (Operation Drumbeat) with me, but IIRC, there was a tanker hit by 2 torpedos off of the East Coast of the US. The crew started to abandon ship and the ship started sinking. The U-boat commander, thinking he had a kill, and afraid to still be in the area at sunup left the scene. Th crew reboarded the ship and managed to make it to port.

Tankers often (usually?) could withstand more than 1 torp, unless they were carrying something like avgas. This is especially true when travelling in ballast (i.e. without cargo).

[Feinder]

ORIGINAL: mlees
I am a bit hazy, at the moment, on were to find the stats for the damages inflicted by the US Silent Service on the Japanese...

JANAC records for tonnage credited to each US Submarine. If you go to the home page, it's also a very comprehensive (excellent) site.

JANAC Records for each USN sub

[rtrapasso]

ORIGINAL: Feinder

ORIGINAL: mlees
I am a bit hazy, at the moment, on were to find the stats for the damages inflicted by the US Silent Service on the Japanese...

JANAC records for tonnage credited to each US Submarine. If you go to the home page, it's also a very comprehensive (excellent) site.

JANAC Records for each USN sub

Unfortunately, like many reports done just at the close of the war, there are some really glaring inaccuracies in it, so take it all with a (very large) pinch of salt...

[mlees]

Thanks Feinder! Nice find indeed!

Unfortunately for this topic, a brief glance did not show how many torps it took to sink their targets.

[Panther Bait]

ORIGINAL: rtrapasso

ORIGINAL: Charbroiled

ORIGINAL: MineSweeper

Even Tankers were tough to take down with one torpedo....read one account that a U-boat hit a dynamite cargo ship(5,000 tons of TNT) with one torpedo in the Gulf of Mexico....the ship sunk and was going down to the bottom and Kaboom, the U-boat was seriously damaged.....

I don't have the book (Operation Drumbeat) with me, but IIRC, there was a tanker hit by 2 torpedos off of the East Coast of the US. The crew started to abandon ship and the ship started sinking. The U-boat commander, thinking he had a kill, and afraid to still be in the area at sunup left the scene. Th crew reboarded the ship and managed to make it to port.

Tankers often (usually?) could withstand more than 1 torp, unless they were carrying something like avgas. This is especially true when travelling in ballast (i.e. without cargo).

That makes sense, really. Since a tanker is designed to carry liquid cargo, it likely has some additional pumping capacity relative to a straight AK.

Also, assuming there are not a lot of exterior fires to deal with, the tanker would likely have more ability to shift cargo to trim the ship or even pump the cargo overboard to lighten it. That assumes that there is some compartmentalization in the tanker, of course.

[tsimmonds]

ORIGINAL: herwin

ORIGINAL: niceguy2005

That is a really good question wild Wille. I can see how it might be highly variable depending on where the torp strikes.

Just out of curiousity how many torpedos did Indianapolis take?

Four.

Source? Every source I can find says two, from DANAFS to Morison to Friedman to ussindianapolis.org.

[panda124c]

From

http://njscuba.net/artifacts/ship_tanker.html

note the number of tanks contained in a tanker each water tight (of course).

The T2 was the backbone of the wartime tanker fleet, and far more numerous than the other types. The T2 tanker design was first adapted from SS Mobilfuel and SS Mobilube, built for the Socony-Vacuum Company ( later to become Mobile Oil. ) these standard T2s were 501 feet 6 inches in total length, with a beam of 68 feet. Rated at 9,900 tons gross (GRT), with a deadweight of 15,850 tons, standard T2s displaced about 21,100 tons. Steam turbines driving a single propeller at 12,000 shaft horsepower delivered a top speed of 15 knots. The T2-A type tanker was an early design variation. Bigger but faster, they were 526 feet in total length, displaced about 22,445 tons, and were rated at 10,600 tons gross with a deadweight tonnage of 16,300 - yet they attained a top speed approaching 16½ knots. Only a few of each type were built.

By far the most common variety of the T2-type tanker was the T2-SE-A1, another commercial design already being built in 1940 by the Sun Shipbuilding Company for Standard Oil Company of New Jersey. These were 523 feet long, 68 feet beam, with 10,448 GRT and DWT of 16,613. Their turbo-electric propulsion system delivered 6,000 shaft horsepower, with maximum thrust of 7,240 horsepower, which produced a top-rated speed of about 15 knots with a cruising range of up to 12,600 miles. After Pearl Harbor, the United States Maritime Commission ordered this model built en masse, and 481 were built in extremely short production times.

The T2-SE-A1 had 9 sets of tanks. Tanks 2 through 9 had a main center tank carrying 391,500 gallons, and two side tanks ( one port, one starboard ) carrying about 165,000 gallons each. Tank number one consisted of only two side by side tanks, divided by a common bulkhead, as this tank set was only 13 feet 6 inches long. Tank sets 2 through 9 were 36 feet 6 inches long. Total cargo was about 5,930,000 gallons, about 141,200 barrels. There was also a small dry cargo space of about 15,200 cubic feet located forward of Tank Number 1 above the deep tank for a very small amount of dry cargo.

There were two pump rooms, one forward and one aft. The main pump room was aft, and contained six pumps. There were three large capacity pumps of 2,000 gallons per minute which were driven by electric motors located in an adjacent machinery space. There were also two 400 GPM pumps and one 700 GPM pump. In the forward pump room was one 700 GPM pump and 300 GPM pump which were reciprocating pumps used for fuel transfer and stripping.