AHQ: U-boat sinking rate to achieve victory?

Thanks for the lesson in torpedo design. :) :cool: :cool: I obviously don't know enough.

I was actually not trying to reduce fuel capacity. I was accepting there would be a range reduction consequent to increased fuel burn to produce a higher cruising speed. (More power requires more fuel.) I hoped to mitigate it somewhat with better hydrodynamic qualities (greater fineness). Was that estimated reduction too low?
Well as you could see from the numbers going from cruising at 10 knots to 15 Knots doubles the required energy input and that is for an absolutely perfect system where there is no waste converting the chemical energy of the fuel into kinetic energy and zero hydrodynamic drag or other factors increasing the energy requirements. In practice a good diesel engine is about 50% efficient(and no you can't do much better though explaining why gets into yet more physics) and you can reduce drag but not eliminate it, though I suspect your proposal for more guns will eliminate any gains from tweaking the hull shape. Look at the shape of modern attack sub hulls versus their WWII counterparts. They are streamlined, have no exterior attachments and of course have practically limitless power courtesy of nuclear plants.

And before it occurs to anyone, yes there are chemical fuels that offer greater energy density than diesel but they tend to be toxic, explosive, toxic and explosive, or cryogenic so they really aren't an option.

ETA: Just to re-emphasize those numbers from the Kinetic Energy equation represent the absolute best case. All real world systems fall far short of that perfect system and the goal is simply to get as close as possible. There is no tweak or modification that can take you below the numbers generated by that equation.
 
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I used to watch the DDE/h's alternate between having the sonar dome then the props out of the water as they came alongside for resupply.
I’ve been around 400 feet under the North Atlantic and the boat was moving slightly back and forth. You surface guys can have it. I’ll take my nice steady boat any day.
 
Yeah, that does want more fuel aboard. As noted, ballast tank conversions & fewer torpedoes?
Seawater fouling of fuel intakes is a big problem.
For surfaced running, I don't see the connection.
For the underwater depth charge dispsy dodo after the botched attack on the freighter, the turning fight between sub and escort, any unneeded drag on the sub makes a lot of difference, especially in the first turn out and the knuckle.
 
Well as you could see from the numbers going from cruising at 10 knots to 15 Knots doubles the required energy input and that is for an absolutely perfect system where there is no waste converting the chemical energy of the fuel into kinetic energy and zero hydrodynamic drag or other factors increasing the energy requirements. In practice a good diesel engine is about 50% efficient(and no you can't do much better though explaining why gets into yet more physics) and you can reduce drag but not eliminate it, though I suspect your proposal for more guns will eliminate any gains from tweaking the hull shape. Look at the shape of modern attack sub hulls versus their WWII counterparts. They are streamlined, have no exterior attachments and of course have practically limitless power courtesy of nuclear plants.

And before it occurs to anyone, yes there are chemical fuels that offer greater energy density than diesel but they tend to be toxic, explosive, toxic and explosive, or cryogenic so they really aren't an option.

ETA: Just to re-emphasize those numbers from the Kinetic Energy equation represent the absolute best case. All real world systems fall far short of that perfect system and the goal is simply to get as close as possible. There is no tweak or modification that can take you below the numbers generated by that equation.
It’s interesting to see a discussion of energy needed. Even modern SSNs have design trade offs due to energy requirements. The 688 class had its hull thickness lowered so they could go fast enough to keep up with CBGs. This lowered their test depth by quite a bit. The Virginia class went back to 637 class speed. One of the reasons was to achieve a 33 year core life.
 
Yeah, that does want more fuel aboard. As noted, ballast tank conversions & fewer torpedoes?
Double the fuel at the very least, not factoring in the effect of going faster on the hydrodynamic drag values and of course the increased weight of all that equipment like radar and electromechanical computer that you want to add. Remember real world ships do far worse than the theoretical system, a lot of the chemical energy in the fuel you are trying to convert into kinetic energy and velocity is going to be lost and while you can reduce that with streamlining and more efficient engines you cannot eliminate it.
 
Double the fuel at the very least, not factoring in the effect of going faster on the hydrodynamic drag values and of course the increased weight of all that equipment like radar and electromechanical computer that you want to add. Remember real world ships do far worse than the theoretical system, a lot of the chemical energy in the fuel you are trying to convert into kinetic energy and velocity is going to be lost and while you can reduce that with streamlining and more efficient engines you cannot eliminate it.
On the efficiency front, it is also important to note that even at Thermodynamic maximum efficiency you are not transferring all energy produced by the engines into forward motion. You will have losses in efficiency with every step in the process. This will compound your fuel troubles.
 
It’s interesting to see a discussion of energy needed. Even modern SSNs have design trade offs due to energy requirements. The 688 class had its hull thickness lowered so they could go fast enough to keep up with CBGs. This lowered their test depth by quite a bit. The Virginia class went back to 637 class speed. One of the reasons was to achieve a 33 year core life.
I presume that the heavy reactors also contributed to this decision. OTOH the hulls are a lot stouter.
Double the fuel at the very least, not factoring in the effect of going faster on the hydrodynamic drag values and of course the increased weight of all that equipment like radar and electromechanical computer that you want to add. Remember real world ships do far worse than the theoretical system, a lot of the chemical energy in the fuel you are trying to convert into kinetic energy and velocity is going to be lost and while you can reduce that with streamlining and more efficient engines you cannot eliminate it.
Based on our Type IXC standard and Type IX D2 examples as noted above, the fallout hovers, triple the fuel bunkerage and you only get a 70-80% increase in range at cruise using German tech. Everything else stays roughly the same as to loadout. (Do get a slightly thicker pressure hull and 20 more meters of crush depth.).
On the efficiency front, it is also important to note that even at Thermodynamic maximum efficiency you are not transferring all energy produced by the engines into forward motion. You will have losses in efficiency with every step in the process. This will compound your fuel troubles.
Germans used direct drives which required jack in and jack out in the gearing switching from diesels to electric motors and gave them slightly better mechanical efficiency in the PTOs. American boats tended to drive on throughput through the electric motors which was operationally less mechanically PTO efficient since the electric motor was an efficiency loss step to the PTO to the screw when the diesels/generator sets turned, but operationally it was quieter and far superior tactically when it came time to switch between air breather motor apparatus and battery to power the electric motor.
 
On the efficiency front, it is also important to note that even at Thermodynamic maximum efficiency you are not transferring all energy produced by the engines into forward motion. You will have losses in efficiency with every step in the process. This will compound your fuel troubles.
Based on our Type IXC standard and Type IX D2 examples as noted above, the fallout hovers, triple the fuel bunkerage and you only get a 70-80% increase in range at cruise using German tech. Everything else stays roughly the same as to loadout. (Do get a slightly thicker pressure hull and 20 more meters of crush depth.).
This discussion has perfectly encapsulated the issue of so many 'The Nazi's do better' threads. Someone suggests a seemingly simple change and it turns out to be horribly complicated and probably unworkable. The difference is that this time rather than wrangling over the vagaries of the historical record the laws of physics settle the argument. :)
 
the laws of physics settle the argument. :)
I'm not sure it's settled, but at least the answer is definitive. :)
triple the fuel bunkerage and you only get a 70-80% increase in range at cruise
The goal is a reduction in range of about 20%...
Germans used direct drives which required jack in and jack out in the gearing switching from diesels to electric motors and gave them slightly better mechanical efficiency in the PTOs.
I did not know that. Thx.
Seawater fouling of fuel intakes is a big problem.
Noted. The U.S. figured it out, apparently, so I'm going to presume the Germans can.
For the underwater depth charge dispsy dodo after the botched attack on the freighter, the turning fight between sub and escort, any unneeded drag on the sub makes a lot of difference, especially in the first turn out and the knuckle.
Fair point, but not applicable to the issue raised, namely, the affect on range & cruise speed.
 

Vahktang

Donor
a) A minefield is a static defense, it cannot move at all, unless it's a minefield made of drifting mines, which is physically impossible.
Excuse my ignorance, why?
There are drift mines, after all, I understand.
And if you are mining shipping lanes mid-Atlantic than don’t they have to be drift mines?

And how do you train extra 400 crews without the British et al. knowing?
it’s a sport.
Yeah, that’s the ticket, submarine races, even.
And then it is attributed to ‘those wacky Germans’.

i would be interested in hearing about the car that utilizes a submarine battery.
“Our underwater boat construction is for shite. But the new planned car can seat 4 and do 200+ kilometers on one charge with no use of petrol. And is charged overnight.”
“And the French ordered a thousand and the Belgians 600.”
 

Vahktang

Donor
This seems to be the thread to being this up.
OK, again, excuse my ignorance and be your normal gracious and well informed selves when you tell me why this does not work, but:
Tethered mines on submarines

Sub gets in trouble, destroyer chasing them down, they release a mine on a tether, arming it when it is a safe distance away from the submarine.
Quick, thin hulled destroyer has to be quite close to get an effective depth charge hit.
While too close, mine goes off.
In the noise and confusion of the sinking ship (undoubtedly ruining effective hydrophone use, I assume) the sub could get away.
Yes, counter measures will come in, eventually, but, then counter counter measures could come in, etc.
Or is this only some villain/Captain Nemo type thing?

And:
secret resupply from Argentina.
“Where all these torpedos and other submarine equipment going?”
“Spanish navy.“
“Portuguese navy.“
Then ships and U-boats meet at rendezvous points, U-boats continue with extended cruises.
Or is this a total spy movie thing?

Thank you for your considered responses.
 
This seems to be the thread to being this up.
I will try to make the answers make sense.

OK, again, excuse my ignorance and be your normal gracious and well informed selves when you tell me why this does not work, but:
Tethered mines on submarines
Sub gets in trouble, destroyer chasing them down, they release a mine on a tether, arming it when it is a safe distance away from the submarine.
Well, the buoy at the end of the tether is attached to the sub and that cable is making a lot of noise and generating a wake. The destroyer will probably dogleg around the buoy , which may explode depending on whether or not the proximity fusing will work. If the buoy is about 50 or 100 meters away when it blows, the deck crew on the destroyer is going to get wet. The destroyer (unless it is built by Russians) will be fine.

The sub crew has two problems now: the cable has just fouled the screws and the destroyer is dropping depth charges on the sub while the destroyer tracking party laughs themselves silly at the people who thought dragging an explosive buoy mine behind a sub was a good idea.

Now a sub (modern era) will drag a cable behind it for a very good reason; that cable at slow speed full of hydrophones can listen behind a submarine so that it can do two things, not be surprised by someone sneaking up behind in its deaf spot, and by playing the cable out the submarine can deploy a passive sonar array long enough in length so that by interferometry, the submarine tracking party can get two or three bearing fixes on a sound source at the same time and by angle intersections of the bearing solutions develop a range and track solution on an enemy submarine or surface ship good enough to launch an active terminal guidance torpedo or missile close enough so that the weapon does not have to be wire steered. It can be fired and forgotten while the sub moves on to do other things.

If the sub gets into a jam, it drops the cable and runs like hell. When it needs to use hydrophone cable again , it unreels more from the spool case. as needed.


Quick, thin hulled destroyer has to be quite close to get an effective depth charge hit.
It is more likely that the sub will launch a torpedo at the destroyer and the destroyer will be running for its life, once the CUTIE enters the inventory.

While too close, mine goes off.
If the sub wants to escape a depth charging, and I have often wondered why this tactic was not used, myself, it could release a float charge that could rise and detonate and roil the local water with a sound bang that should reverberate off the local seafloor and make it difficult to use passive tracking to trace the sub as it escapes. Active pinging is all that is left, and of course it is a CUTIE launched at the noise source down the line of bearing and since the CUTIE will home on ping. BANG. No more destroyer.

In the noise and confusion of the sinking ship (undoubtedly ruining effective hydrophone use, I assume) the sub could get away.
Yes, counter measures will come in, eventually, but, then counter counter measures could come in, etc.

Or is this only some villain/Captain Nemo type thing?
The game of chicken is a lot more terrifying than even I described it.

And:
secret resupply from Argentina.
“Where all these torpedos and other submarine equipment going?”
“Spanish navy.“
“Portuguese navy.“
Then ships and U-boats meet at rendezvous points, U-boats continue with extended cruises.
Or is this a total spy movie thing?

Thank you for your considered responses.
Want a good analogy for how it works?

 
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I will try to make the answers make sense.





Well, the buoy at the end of the tether is attached to the sub and that cable is making a lot of noise and generating a wake. The destroyer will, probably dogleg around the buoy , which may explode depend on whether or not the peoximitty fusing will work. If the buoy is about 50 or 100 meters away when it blows the deck crew on the destroyer is going to get wet.

The sub crew has two problems now. the cable has just fouled the screws and the destroyer is dropping depth charges on the sub while the destroyer tracking party laughs themselves silly at the people who thought dragging an explosive buoy mine behind a sub was a good idea.

Now a sub will drag a cable behind it for a very good reason. that cable at slow speed full of hydrophones can listen behind a submarine so that it can do two things, not be surprised by someone sneaking up behind in its deaf spot, and by playing the cable out the submarine can deploy a passive sonar array long enough so that by interferometry, the submarine tracking party can get two bearing fixes on a sound source at the same time and by angle intersections of the bearing solutions develop a range and track solution on an enemy submarine or surface ship good enough to launch an active terminal guidance torpedo or missile close enough so that the weapon does not have to be wire steered. it can be fired and forgot.

If the sub gets into a jam, it drops the cable and runs like hell. When it needs to use hydrophone cable again , it unreels more from the spool case. as needed.




It is more likely that the sub will launch a torpedo at the destroyer and the destroyer will be running for its life, once the CUTIE enters the inventory.



If the sub wants to escape a depth charging, and I have often wondered why this tactic was not used, myself, it could release a float charge that could rise and detonate and roil the local water with a sound bang that should reverberate off the local seafloor and make it difficult to use passive tracking to trace the sub as it escapes. Active pinging is all that is left, and of course it is a CUTIE launched at the noise source down the line of bearing and since the CUTIE will home on ping. BANG. No more destroyer.



The game of chicken is a lot more terrifying than even I described it.



Want a good analogy for how it works?

Good explanation of the towed array. They don’t use interferometry just basic trig. Computer will do most of it but the Section Tracking or Fire Control Tracking party will run the numbers manually as a back up. There are always a couple of Nukes on the team since we’re more used to the math aspect. The towed array is just that. If you lose it for some reason, it’s gone. The cable that pulls it in is just cable, not part of the array. If you look at a picture of an American SSN, the hump running down the stbd side is where it’s stowed. There’s a cable reel in the fwd compartment that lets it out and in. The tube crosses through the aft ballast tanks and comes out a tube attached to the side of the port stern plane.
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Vahktang

Donor
Thank you for your reply.
Well, the buoy at the end of the tether is attached to the sub and that cable is making a lot of noise and generating a wake
Sorry.
The idea is that the mine is below the surface of the water.
It would be making noise but I do not think there would be much of a wake. That requires surface or near surface activity, right?
The sub is 160’ down, the destroyer has 20’ of hull underwater, the mine would be 15’ below the surface of the water, 145’ from the sub. A contact mine is probably going too far, though, but, that was the thought.
The sub crew has two problems now: the cable has just fouled the screws
Automatic release when it explodes, then? It then sinks past the submarine.
Sufficient floatation below the explosion so that the cable continues to be above the submarine?
Now a sub (modern era) will drag a cable behind it for a very good reason;
I seen to remember that they had similar on the Seaquest show.

once the CUTIE enters the inventory.
OK, I just googled CUTIE and got outfits and oranges. Adding naval to it did not help.
From context: a type of depth charge?
 
Thank you for your reply.
You are welcome.
Sorry. The idea is that the mine is below the surface of the water. It would be making noise but I do not think there would be much of a wake. That requires surface or near surface activity, right?
For a Paravane (weapon) (additional description) which is what you describe, it was first trialed in WWI and was intended as an underwater kite to cable snag submarines. The reverse is the same kite used to snag destroyers and relies on the cable to foul the destroyer as it crosses it, automatically dragging the kite in to bang against the hull and set off a contact horn like you would find on a Hertz Mine,

The problem with the paravane as a weapon is that it is a lot harder to cable snag a destroyer or sub than it is to torpedo or depth charge it. The only navy of which I know which persisted in the paravane kite system (Ginnochio) was the French navy which kept at it because they thought it was cheaper than stocking up on hundreds of depth charges and did not require ASDIC or sonar which also was expensive to build and maintain.

Well.. they got it wrong.
The sub is 160’ down, the destroyer has 20’ of hull underwater, the mine would be 15’ below the surface of the water, 145’ from the sub. A contact mine is probably going too far, though, but, that was the thought.
It is actually a towed underwater kite. A noisy underwater kite that has to rely on fins to maintain depth, so the speed is kind of a necessity. It is also a detriment because the towing agency is quite noisy itself.

Automatic release when it explodes, then? It then sinks past the submarine.
The cable end of a paravane tow line may... no make that probably will foul screws and tail control. Sub or destroyer is in a lot of trouble.

Sufficient floatation below the explosion so that the cable continues to be above the submarine?
I would want the cable to sink below the submarine since if it floats up, it becomes a giant arrow on the surface pointing to where the sub is.

I seen to remember that they had similar on the Seaquest show.
Towed array? Hollyweird never gets anything right.

OK, I just googled CUTIE and got outfits and oranges. Adding naval to it did not help.
From context: a type of depth charge?
CUTIE.


It is a homing torpedo developed from FIDO.
@gatordad699

You are the expert on this subject matter, but it was my understanding that the trig is for one fix or plot point which is a range only generated solution. For a track solution the minimum is three fixes or plot points to generate the track and create a predicted intended motion vector which includes target/contact rate of advance *(the interferometry bit where two sounds are compared to each other to get a speed differential which may include a doppler component, too) so that the weapon can be launched at where the target/contact is expected to be when the weapon gets there.

Shrug. Vector solution has to have a velocity component for predict lead.

McP.

P.S. Like many "impractical ideas" the towed paravane does have a happy ending in that it is used to cable cut moored underwater mines by the cable snag and drag method and in the other that in the form of a noise maker and wake maker it is used to decoy and seduce wake and screw noise chasing torpedoes away from the ship that tows the paravane. A paravane can be set to kite along in a course parallel and aft of the towing ship, which makes the kite an ideal decoy and seducer for the purpose of luring a torpedo off the true target to a false target.
THAT is when one might want the kite to have an explosive charge and contact fusing to set off and destroy the torpedo which might have a hit to kill drive through fusing of its own that is designed to ignore a kite and just drive through it.
 
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