Hull difference....german, american

[Bulkhead]

What is the basic hull difference between german and american subs?
example: When struck by a depthcharge, does the german subs stand a better chance to pull through if the DC detonate at the same distanse of the hull?
Does the size of the sub mean any in this matter?
By my knowledge the german subs whas stronger built...or am i wrong...?

[manucapo]

according to a book ive read

Wolfpack, the story of the U-boat in world was 2

it claims that
a depth charge would cause serious damage if it exploded within 30-50m from the sub
ofcourse talking about german uboats

i know it's not much information and its very generic
but who knows may be usefull to compare if somone knows a general distance for the fleet boats

[-Pv-]

I think it depends on the sub model. I might be wrong, but my understanding is all the US fleet boats were welded and only the newest German boats were welded, otherwise mosty rivets. Internal seal quality and maintenance is also a big factor. The deeper you are when you take the hit places more stress on the hull. All in all, I wonder if it matters? You learn what the game will take in SH3 and 4 and work with it.
-Pv-

[Torplexed]

A lot might depend on the quality of steel used. Krupp had a pretty darn good reputation. But, then American manufacturers had access to plenty of natural resources and didn't have factories getting bombed from the air.

[The Fishlord]

So far, it's generally accepted that while US boats were bigger (and therefore tougher to maintain), they were more well built.

Early-mid war U-boats can almost give you the impression they were patched together from spare sheets of metal; US fleet boats are a single whole. Some boats like Albacore (though being older) still withstood multiple bullseye's in situations that German boats couldn't handle.

[ReallyDedPoet]

Nice thread on the Pacific Theatre:http://www.subsim.com/radioroom/showthread.php?t=128185


RDP

[Sailor Steve]

I don't know about stronger steel, but I have read that when the Allies captured u-boats they were surprised to find that the pressure hulls were thicker, and of course therefore stronger.

As to the claim of causing serious damage at a range of 30-50 meters, Allied sources claimed a lot less:
The British claimed this DC would split a 0.875 inch (22 mm) hull at 20 feet (6.1 m) and force a submarine to surface at about twice that distance. A minol charge introduced in 1942 increased these distances to 26 feet (7.9 m) and 52 feet (15.8 m), respectively.
This note is for the British Mk VII Heavy depth charge.
http://www.navweaps.com/Weapons/WAMBR_ASW.htm

[Bulkhead]

i tried too look up any drawings and explanations on how they where built.
But the size of the subs gotta have some infuence, examples the type 7 vs gato or balao. Smaller boat is by my opinion a stronger boat because fewer weak points, and the possibility to build it stiffer without compromising the flexibility.....

[Bulkhead]

Nice thread on the Pacific Theatre:http://www.subsim.com/radioroom/showthread.php?t=128185


RDP

Great site:) :up:

[Sailor Steve]

Nice thread on the Pacific Theatre:http://www.subsim.com/radioroom/showthread.php?t=128185


RDP

Great site:) :up:
Yes, Ducimus did a great job; but does it say anything about the question at hand?

[Bulkhead]

As far as i see it doesent say anything about american and german hull structure differences..

[Mikey_Wolf]

Its basic physics, even if the US subs and the U-Boats had the exact same steel the exact same thickness, which one will dive deeper?

The U-Boat naturally, because its smaller which means when it submerges there is a smaller hole in the water and the overall area of force exerted on a U-Boat is smaller than that of the US sub.

Though I would not be surprised if the German U-Boats were thicker pressure hulled anyway, because the Germans were extremely adept at Submarine warfare they learnt a lot of lessons from the Great War.

[mcf1]

That's a nice question.
You can check this.
http://www.uboat.net/forums/read.php?20,59732,59741

[NealT]

You would think that since the U-Boat's had a deeper crush depth, they would withstand a DC attack better...

Makes sense...

[Sailor Steve]

Its basic physics, even if the US subs and the U-Boats had the exact same steel the exact same thickness, which one will dive deeper?

The U-Boat naturally, because its smaller which means when it submerges there is a smaller hole in the water and the overall area of force exerted on a U-Boat is smaller than that of the US sub.
Is that right? The pressure per square inch will be the same, but I don't know enough about it to know if the size makes a difference overall. Just asking.

@ mcf1: That's a good discussion. I wish he had quoted a source for his numbers, but he seems to know what he's talking about.

@ NealT: It does make sense. Unfortunately there is no real evidence one way or the other. I've done a lot of research over the years, and the things they never seem to mention can make you pull your hair out.:damn:

[jazman]

Its basic physics, even if the US subs and the U-Boats had the exact same steel the exact same thickness, which one will dive deeper?

The U-Boat naturally, because its smaller which means when it submerges there is a smaller hole in the water and the overall area of force exerted on a U-Boat is smaller than that of the US sub.
Is that right? The pressure per square inch will be the same, but I don't know enough about it to know if the size makes a difference overall. Just asking.


Size has nothing to do with the pressure found at a depth. You put a Gato or a Type VII at 300 feet, they face the same pressure.

[cmdrk]

Drawing from my previous readings, which hasn't been recent, it is my understanding that the Type VII's pressure hull was exposed more to direct contact with the ocean. The ballast tanks were saddled onto the pressure hull's exterior.

While the US boat's pressure hull had ballast tanks wrapped around it with an outer hull encasing the whole. The pressure hull's steel was thinner and maybe less strong than German hulls. But, the outer hull and ballast tanks should have provided some outer protection - kind of like surface ships torpedo blisters.

A lot would depend on the strength and placement of the charge. Also, it has been debated on what protective effects a greater depth offered against a well placed charge. Would the greater sea pressure already have the hull nearer to failure or would the greater sea pressure contain the explosive force in a way forcing most of the energy up where the water is less compressed?

The greater depth gave a sub more time to manuever out from under an attack and in general it was better to have the charges going off above you rather than underneath.

Just some thoughts - who knows:hmm:

[Sailor Steve]

Drawing from my previous readings, which hasn't been recent, it is my understanding that the Type VII's pressure hull was exposed more to direct contact with the ocean. The ballast tanks were saddled onto the pressure hull's exterior.

While the US boat's pressure hull had ballast tanks wrapped around it with an outer hull encasing the whole. The pressure hull's steel was thinner and maybe less strong than German hulls. But, the outer hull and ballast tanks should have provided some outer protection - kind of like surface ships torpedo blisters.
I'm pretty sure the outer hull is for hydrodynamic purposes only, and has a lot of vent holes in it. The 'pressure' hull is just that; it takes the pressure directly.

As to the debate whether the depth reduces the effective radius of the charge or makes the hull more susceptible to damage, the only answer I can think of is "Yes". Sorry, doesn't help much, but both seem to me to be true.

[ETR3(SS)]

Drawing from my previous readings, which hasn't been recent, it is my understanding that the Type VII's pressure hull was exposed more to direct contact with the ocean. The ballast tanks were saddled onto the pressure hull's exterior.

While the US boat's pressure hull had ballast tanks wrapped around it with an outer hull encasing the whole. The pressure hull's steel was thinner and maybe less strong than German hulls. But, the outer hull and ballast tanks should have provided some outer protection - kind of like surface ships torpedo blisters.

A lot would depend on the strength and placement of the charge. Also, it has been debated on what protective effects a greater depth offered against a well placed charge. Would the greater sea pressure already have the hull nearer to failure or would the greater sea pressure contain the explosive force in a way forcing most of the energy up where the water is less compressed?

The greater depth gave a sub more time to manuever out from under an attack and in general it was better to have the charges going off above you rather than underneath.

Just some thoughts - who knows:hmm:
Well drawing from my firsthand knowledge on how submarines work, the ballast tanks wouldn't provide any sort of protection from sea pressure. Reason being is the pressure of the water in the ballast tanks is equal to that of sea pressure, no matter what depth. Now the reason for that is the bottom of the ballast tanks have grates to allow sea water to come in easily when the vents are opened on the top of the ballast tank. I know thats how it worked on my boat and id assume that that part of submarine design hasnt changed.

[Penelope_Grey]

Size has nothing to do with the pressure found at a depth. You put a Gato or a Type VII at 300 feet, they face the same pressure.
Semi-True, however the Gato has a larger surface area, therefore the total area of pressure is greater than that of a U-Boat. as in.... Pressure per square inch is the same, but a Gato has a lot more inches than a U-Boat does. So will naturally not be able to go as deep due to being larger.

[AVGWarhawk]

Where in the heck is an engineer when you need one. :roll:

[seafarer]

I found this at www.submarineresearch.com

Test depth can be thought of as an engineering estimate of what pressure will be required on one side of a hull to breach the hull, taking into account such factors of hull strength as hull diameter, hull thickness, framing, and intrusions. Naval engineers tend to be conservative in their estimates and the varied factors tend to render an estimate as just that, an estimate. The engineers back into the problem by first estimating the crush depth of a hull, then creating the theoretical test depth by a applying a decimal factor to the crush depth. Different national navies apply varying factors. The United States Navy has used a factor of 1.5, but this has changed many times. Of course, computers are able to make such estimates much more trust-worthy, however, the accounts described "Steep Angles and Deep Dives" are, for the most part, in hulls designed before the advent of the computer.

In the American Navy, hull designers depend on the experience of submarines to verify their estimates. Buships requires a submarine captain to immediately notify both Buships and the Chief of Naval Operations in writing when a boat under his command exceeds test depth. The captain's professional career may be jeopardized by a zealous attention to recording a dive that went wrong. Only in wartime can a captain reasonably explain the need to exceed test depth. For this reason submarines exceeding test depth sometimes fail to make note of the dive in their deck logs.

The simplest application of determining hull strength is the hull thickness. The thicker the hull metal the stronger the hull and the deeper the test depth, assuming all other factors are constant. Prior to the Balao class U.S. submarine, hulls were built of mild steel (MS) which had a maximum tensile strength of 60,000 pounds per square inch and a yield strength of 45,000 psi with 23 percent elongation. The thickness of hull plating until about 1943 was specified in terms of the weight of a square foot of plate rather than the actual thickness, and this was gradually increased from 20 pound plate (approximately one half inch) to twenty seven and a half pounds per square inch in the Salmon (SS-182).

Another change in the Balao class was the change in material used for hulls. High tensile steel was a chromium-vanadium alloy with a maximum tensile strength of 50,000 psi with 20 percent elongation. When the composition was changed to titanium-manganese alloy, because of wartime shortages, the strength dropped to 45,000 psi. The Salmon's hull was about seven eighths of an inch thick giving her a test depth of 250 feet. Conning tower shells were thicker as protection against surface guns.

The thick-skinned boats came along in 1942 with a test depth of 412 feet. These boats had the same seven eighths inch thick hull as Salmon, but the quality of hull steel ie., high tensile strength steel had significantly improved. The crush depth of these boats was estimated to be around 450 feet. Fleet type submarines built during the Second World War were to last through much of the cold war. These boats have careers that have lasted over fifty years with many still being used by foreign navies.

Anyone know any similar figures for u-boat hull steel?

P.S. www.uboat.net mentions that type ViiB/C hulls were made from steel approx. 0.73 inches thick, but I cannot find anything about the type of steel used.

P.P.S. from www.uboatarchive.net in the REPORT ON "U-570" (H.M.S. "GRAPH") (U-570, a VIIC was captured by the British in 1941)

http://www.uboatarchive.net/U-570BritishReport.htm

page 37

Hull
The hull is of all welded construction, the only riveting being on the engine room cover plate and the flanges of the dished ends of No. 3 main ballast tank.
2. The frames are of bulb section bars with no flanges. There are 82 frames.
3. The thickness of the pressure hull plating is 0.88 in., decreasing to 0.63 in. towards the ends.
4. The keel is 1.8 ft. high and 3.6 ft. wide. It is free flooding and iron ballast is carried at the ends.
5. The thickness of the pressure plating of the conning tower is 1.26 in.
6. The endings of the pressure hull are formed with dished plates which carry the housings of the torpedo tubes. The thickness of these endings is 1.378 in.

[seafarer]

Found this in a 2003 forums post on uboat.net, but no source was given for the information (post was made by forum member "Scott" under Technologies and Operations)

Hull Structural for the Type IXC, IXC40, IXD2, XB and XXI.

The cylindrical pressure hull had a diameter of 4400mm (14.42') and was made of 18mm (,73")
steel with inside bulb tee frames 200X11 (7.88" web depth X .43" web thickness) on 700mm (27.56")
centers. The plating is gradually reduced throughout the tapered section fore and aft to 16mm (.63"),
nd the frames are correspondingly reduced to 130 X 9 (5.12" X .35"). Frame spacing remains
unchanged in the tapered sections.

The specification for the pressure hull plating and frames calls for a tensile strength of 74,000 psi
with a yoeld point of 51,300 psi. The steel was known as No. 52; the specification for plates is
KM 9104, and for the frames is KM 9103

[jazman]

Size has nothing to do with the pressure found at a depth. You put a Gato or a Type VII at 300 feet, they face the same pressure.
Semi-True, however the Gato has a larger surface area, therefore the total area of pressure is greater than that of a U-Boat. as in.... Pressure per square inch is the same, but a Gato has a lot more inches than a U-Boat does. So will naturally not be able to go as deep due to being larger.

Well, you're almost right.

Take a square inch of plate, set in a nice solid frame. The net pressure on that plate is outside pressure - inside pressure. At 350 feet, that's pretty high. Say that the plate is strong enough--for whatever reason (thickness, material, bracing). And the forces on that plate, if you do a Free Body Diagram, are evenly distributed on the outside, with an equal but opposite force spread around the edges of that plate (because it's sitting in a frame). You can intuit that the middle is going to dimple / collapse first--there are some strange forces applied in there to the material.

Say the pressure is 300 psi. On that plate, you have three hundred pounds. Around the edge of that plate, the 300 pounds are over 4 inches of the mounting frame, so it's 75 pounds/inch.

So, you make that plate a piece 9 inches square (3 x 3). The total force on the outside is now 2700 pounds, and the frame has 12 inches, so it's 225 pounds /inch. Hmm, that's a lot higher. The forces working on the material in the plate are higher throught (just do a FBD on an infinitesimally small edge piece), it will, if you slowly increase the pressure, collapse before the small plate.

But suppose you build a grid frame to hold that larger plate, where it's basically a 3x3 frame to match. Then it's all the same. It comes down to what you design it to do. The total German design--thickness, bracing, etc., was designed to operate at a deeper depth. The bracing gets a little easier if you keep the ship smaller. More bracing: Money and Construction Time, and increased complexity (with increased possibility of poor build quality), etc etc etc.

But what you get is a smaller ship, and we Yanks need our Ice Cream machines.

BTW, a long long time ago, in a Galaxy far away, I was offered a job at Electric Boat. I turned it down for warmer pastures.

[Bulkhead]

Ok ok ok.... so the pressure is the same, nothing to do with the pressure because its the same for each boat at the same depth, and its not about the size either, or surface for the pressure to work on. But its about the supporting structure inside all of the surface plating. Lets call it "the sub sceleton".... The gato needs a stronger and alot heavier sceleton to face the pressure than a type-VII. If the size is twise it may need twise the number of framework to stand the same depth i dont know.
The basic question was whats the difference between the two subs, witch after all the reading ive done in this thread (BTW, thanks for all the input) i guess it narrows down to structure, construction and building techniqs.

Please continue with all stuff you can find.

Thanks

[Palidian]

However if the hull is close to being round, size should not matter. Try smashing an egg with your hand.

http://www.wonderquest.com/egg-pressure.htm


Size has nothing to do with the pressure found at a depth. You put a Gato or a Type VII at 300 feet, they face the same pressure.
Semi-True, however the Gato has a larger surface area, therefore the total area of pressure is greater than that of a U-Boat. as in.... Pressure per square inch is the same, but a Gato has a lot more inches than a U-Boat does. So will naturally not be able to go as deep due to being larger.

[cmdrk]

Drawing from my previous readings, which hasn't been recent, it is my understanding that the Type VII's pressure hull was exposed more to direct contact with the ocean. The ballast tanks were saddled onto the pressure hull's exterior.

While the US boat's pressure hull had ballast tanks wrapped around it with an outer hull encasing the whole. The pressure hull's steel was thinner and maybe less strong than German hulls. But, the outer hull and ballast tanks should have provided some outer protection - kind of like surface ships torpedo blisters. I'm pretty sure the outer hull is for hydrodynamic purposes only, and has a lot of vent holes in it. The 'pressure' hull is just that; it takes the pressure directly.

As to the debate whether the depth reduces the effective radius of the charge or makes the hull more susceptible to damage, the only answer I can think of is "Yes". Sorry, doesn't help much, but both seem to me to be true.

I understand the pressure hull is in no way sheltered from sea pressure. The ballast tanks would have equalized pressure inside and out and thus the pressure hull would have to resist that pressure.

What I was thinking about was, what protective effect would the US boat design have against a depth charge? Wouldn't the explosive force be disipated by the outer hull and water in the ballast tanks?

My understanding of physics is limited but I thought torpedo blisters were suppose to spread the force some so the force per sq. in would be lower. And, yes it would cause detonation away from the main hull. (shrugs)

[Penelope_Grey]

@Jazman, what you have posted there I really do not understand at all, and I have an A-level in physics(not enough I think). It might be the wording, but I cannot understand your explanation, not sure if the others did, but I don't.

Simplyfying it is what I was trying to do, in simplistic terms the bigger an object is the more area there is for the pressure to exert therefore the overall sum of the pressure is higher than on a smaller object generally, this assumes that the structures/materials of said object are similar or identical.

Build quality is something that I think both the Americans and Germans did well. The Americans wanted their boats for speed and fleet purposes (speed) while the germans wanted them to operate alone and be able to go beyond the Aliied ASDIC capabilities (dive deep) and in early war the Germans did succeed at this, a U-Boat could go deeper than the allied ASDIC could.

Further, taking German U-Boat's as a main example, obviously the Kriegsmarine had deep diving in mind, now, a type IX with a slightly thicker hull, still couldn't go as deep as Type VII could. And I don't mean the VIIC/41 I mean the ordinary VIIC. From what I learned in college, build can only stave off so much.

[scrag]

The size of the ship has very little to do with it at the depths we are talking about in regards to Sea Preasure - the same argument can be stated with the overall water depth - the Pacific is deeper so the water mass is different or the salinity content is different and that will disapate the blast effect differently. While the size of the ship may contribute to how much hull is exposed to the blast - water preasuure (44 ib per sq inches for every 100 feet) treats the preasure hull the same equal way. There is a lot more to sub construction - bulkhead thickness, water tight compartment integrity, framing arrangement (external or internal frames), fixtures exposed to sea preasure i.e. trim and drain system and the pumps of the system, main induction valve and diesel exhaust - you get the idea. One thing the game leaves out (seemingly) is the improved Gato depth capabilities seen in Mid WWII to the end allowing US boats to operate 500 plus feet. The Germans also had better depth capabilities too but faced the same issues. Very often, failure of a valve or other system than the preasure hull resulted in a loss of the boat at deep depths.
To answer the question about ballast tanks water dispating a blast - nope - water does not compress so it will (practically) transmit any force equally, so the effect on a submerged U Boat would transmit the effect directly to the preassure hull. Yes you would get rippling and distortion of the metal structure but the presure hull had to restrain the additional effect of the preasure wave moving through the water. Remember the string going across the engine compartment being taught on the surface but having slack at depth - that is a practical example of the effect.

[jazman]

@Jazman, what you have posted there I really do not understand at all, and I have an A-level in physics(not enough I think). It might be the wording, but I cannot understand your explanation, not sure if the others did, but I don't.


It wasn't physics, it was engineering. I guess at some point it starts looking like Magic. Ah, the joys of Technocracy!

[Dantenoc]

Simplyfying it is what I was trying to do, in simplistic terms the bigger an object is the more area there is for the pressure to exert therefore the overall sum of the pressure is higher than on a smaller object generally, this assumes that the structures/materials of said object are similar or identical.

No, that doesn't matter... if you want to think about it in those kind of terms (it may seem intuitive to you) counter it with this: true, the bigger boat has more weight to deal with (same pressure but bigger area), but it all evens out because it is "more boat" to begin with.




A story book way of looking at it:

Imagine you and I are sections of pressure hull destined to be installed on two different but identical small subs. We are both rated to withstand a pressure equivalent to 1 unit (whatever). You get installed in your sub, I get installed in mine. Both our subs dive side by side until we both receive 1 unit in pressure. You do your thing on your sub, I do mine in my sub. Do you hold? of course you do, you were rated for 1 unit of pressure. Do I hold? yes, of course, I too was rated for 1 unit of pressure. Here is the important question: did the fact that I held, helped or hindered you in holding? No, of course not; you don't care about me, and I don't care about you. As pressure plates all we care about is doing our job of resisting pressure and will do it based on our own merits.

Now for a twist on the story: There's a screw up on the sub plant, and instead of being installed on two separate small subs, we both get installed into the same big sub. We are now being used in a different way that was originally intended, but what the heck? You're still you and I'm still me, right? so we cope as best we can. The big day comes and the sub finally goes out to sea. The big sub then dives and we reach the exact same depth as the two previous small subs... Ok, pressure plates, time to work: that's you and me! it's up to us, in a team effort, to defend the integrity of this sub! :yep: . But whait..... you start to get nervous about it... what's the pressure down here? :-? I know it's supposed to be only 1 unit because it's the same depth as before, but this sub is twice as big as the other small ones... whait, does that mean that the whole sub is receiveng 2 units of weight now?!?! oh my God, I'm only rated to withstand 1 unit of pressure :huh: !!! I don't think I can hold, the big sub is doomed :cry: !!!

But.... Time goes by and to your surprise you do hold :smug: !!!!! what happened :hmm: ? Well, true the bigger the area the bigger the weight, but the sea isn't evil and "decided" not to put the whole weight of the sea just on your section. The sea is good so pressure is allways evenly distributed. So out of the 2 units of weight crushing down on the whole sub you got 1 on your section and I got 1 on my section (for a total of 2 units). Can you manage your 1 unit? yes, you where rated for 1 unit. Can I manage my 1 unit? yes, I too was rated to withstand 1 unit. My working over here did not make your job of withstanding your 1 unit of pressure any easier or any harder. You worked out your share of the pressure based on your own merit. Viceversa, I didn't care what you or any other part of the ship was doing, I just did my thing.

So, the moral of the story is, as long as there's no "weak links" in the work force, and as long as everybody does his part, size of the boat does not matter, and all hull plate sections lived happilly ever after.

The end :|\\

P.S.: and yes, Jazman makes a fine point. It's not just about strength of the materials, but the structures that they make with them and how they're held into place.

[Palidian]

There is the issue that the command tower is not in the pressure hull, and it will collapse first.

[Sailor Steve]

No, it won't. The conning tower is it's own pressure hull.
The pressure hull, designed to withstand the sea pressure, houses most of the ship's machinery and provides the living quarters for the officers and the crew. It is divided into eight watertight compartments, separated by pressure bulkheads provided with watertight pressure resistant doors. The ninth compartment, the conning tower, in the shape of a cylinder placed on its side, is located above the control room and connects with the control room through the access hatch.
http://www.maritime.org/fleetsub/chap3.htm#3A
http://www.maritime.org/fleetsub/appendix/pages/figa-01.htm

[scrag]

One point still not elaborated on is hull fittings and Valves.
The size of the hull is partically a mute point. The single largest contributing factor to keeping water out of the people tank is the number of "openings" it has that are controled by either valves or have something stuffed through them (i.e. the shafts).