Passing thermal layer and DC's attack?

[GakunGak]

These are two questions:
1. Passing thermal layer makes me invinsible to passive sonar at ahead slow or with silent running? Is it working for real or it is just for show?
2. When under attack by destroyer, what is the best evasion tactic?

[NefariousKoel]

1) Yes it is in. I have noticed that some of my more distant contacts were lost after passing the layer. However, it won't make you invisible. At least, it shouldn't. Enemy destroyers should still be able to detect you, but they have to be much closer to you than normal.

[daft]

Don't know any definitive answers to any of your questions, but I usually wait until the destroyer is almost on top of me and starts speeding up for his attack run. I ring up flank speed and and give a little rudder to either side of his path (depending on the angle of his run) to get out of the kill zone. As soon as things settle down after the detonation I slow down, go to silent running and creep a little deeper depending on how close the ash cans came.

[GakunGak]

But when you are at ahead slow, what the good use of decoys?

[PeriscopeDepth]

The layer certainly causes some transmission loss, but does NOT make you invisible IRL in most cases.

PD

[daft]

But when you are at ahead slow, what the good use of decoys?

I've never used the decoys in SH4 so I don't really know how effective they are yet.

[Dowly]

But when you are at ahead slow, what the good use of decoys?

There´s two ways how I use the decoys. If the DD is close, I fire one up go to flank speed for a 2-3 seconds and change my depth. But if the DD is far away, like if I am leaving a port which I raided just moments ago, I fire up the decoy and continue on silent run.

[GakunGak]

But when you are at ahead slow, what the good use of decoys?

I've never used the decoys in SH4 so I don't really know how effective they are yet. What I really meant was what the good use when you have to be far away from them, and when you speed up, destroyers will hear you anyway....
So, to not being heard at all is the all-stop ring?:huh:

[RedHammer]

That`s why, as previously explained, when far away, fire decoys, run silent, go deeper. Just keep away from those deadly ash can`s until those DD`s are empty of them.


S! to all

Your Friend in the Pacific

RH

[GakunGak]

So the destroyers can run out of depth charges???!!!
Oh my!!!:rock: :rock: :rock: :rock: :rock:

[HannesGM]

Yes, they run out, eventually. Either that, or the crew had their lunch break coming up :D

I also noticed that in SH3 - only occasionally - that the DDs seemed to run out of DCs - they'd still circle over my position, but never throw any more DCs. This was after several hours - literal hours - spent with 4 DDs overhead...

[GakunGak]

This is really good news, man, as this adds more to the realism....:up:

[Psycluded]

The strangest thing happened to me this morning, actually. To preface, I had already dove below 250 ft in the area to find where my chief of the watch called out "passing the thermal layer", so I knew where it was, in general. My plan, as is usual, is to get within radar contact range of the convoy, so I can get a snapshot view of the formation, how they're manuvering, if at all, and the direction and speed of travel.

This time, their direction was northerly, so I submerged, sprinted north and placed myself perpendicular to their track and called an all-stop about 800m from where I knew the closest freighter would pass. I was at 250 ft, in silent running mode, watching the auto-updated map as my sonarman called in the contacts.

The first attack went perfectly. With zero forward motion, I hovered up to periscope depth when the first freighter's stern passed parallel with my bow, popped the attack scope out of the water and did a quick 360-degree scan. The closest escort was the starboard side escort (looking from the convoy's point of view) and he was astern of me at a range of about 1000 yards, off on a random search.

I lit off all 6 tubes at the juiciest targets and immediately dropped the scope back down, dove to 250 ft and moved northwest (underneath the convoy) to reposition for attack. As I was passing the first freighter (underwater mind you... he was in two pieces), I heard depth charges go off behind me, so I hit F11 and went out to look. Sure enough, that DD that was DCing where I had been, or near enough to it.

The only thing I can think of, since I'd never seen this happen in SH3 or SH4 so far, is that he must have caught me before I passed the thermocline, and that the layer in that area must have created a convergence zone, causing him to misinterpret my location.

I gotta wonder if these kinds of advanced sound behavioral characteristics are modeled in SH4. I mean, I know how to use them from playing Dangerous Waters, but if it works in SH4 as well? It would explain the gross range mis-estimations my sonarman gives me from time to time (docked ships whose range estimates put them cleanly on the beach, etc).

[JackChen]

My guess is the destroyer just came over and throw some DC's at your last known position, you know, pass the motion of I am your escort and I am doing something about your loss.

If they knew where are you are specifically, I guess they would be tracking and not throwing DC's at empty seas.

[Steeltrap]

The escorts will use the tracks of your torps to estimate your position when you fired them and attack that area fairly immediately. I'm guessing that's what you saw.

I've noticed the depth changing abilities of the subs seem to be grossly inflated. Would take well over half an hour for a US sub to get back to periscope depth from around 300' under usual circumstances (pretty sure that's what Dick O'Kane says in Wahoo).

As for being able to control your depth like that while stationary, that's just nonsense.

[NEON DEON]

The escorts will use the tracks of your torps to estimate your position when you fired them and attack that area fairly immediately. I'm guessing that's what you saw.

I've noticed the depth changing abilities of the subs seem to be grossly inflated. Would take well over half an hour for a US sub to get back to periscope depth from around 300' under usual circumstances (pretty sure that's what Dick O'Kane says in Wahoo).

As for being able to control your depth like that while stationary, that's just nonsense.

Lets see.

300 - 60 = 240

240 / 30 = 8

8 feet a minute rise?

I dont think he was trying very hard.;) ;) ;)

[NefariousKoel]

The escorts will use the tracks of your torps to estimate your position when you fired them and attack that area fairly immediately. I'm guessing that's what you saw.

I've noticed the depth changing abilities of the subs seem to be grossly inflated. Would take well over half an hour for a US sub to get back to periscope depth from around 300' under usual circumstances (pretty sure that's what Dick O'Kane says in Wahoo).

As for being able to control your depth like that while stationary, that's just nonsense.
Lets see.

300 - 60 = 240

240 / 30 = 8

8 feet a minute rise?

I dont think he was trying very hard.;) ;) ;)
LOL.

In Steeltrap's defense he probably read 'seemed like 30 minutes' as "it took 30 minutes."

That's what paraphrasing gets you.

[E.Hartmann]

How do I go deeper than the 165'. (Besides having a hole in my boat!! :rotfl: )

[Floyd]

How do I go deeper than the 165'. (Besides having a hole in my boat!! :rotfl: )

Click below the depth gauge to get the second, larger scale.

[Ayari]

Yes, they run out, eventually. Either that, or the crew had their lunch break coming up :D

I also noticed that in SH3 - only occasionally - that the DDs seemed to run out of DCs - they'd still circle over my position, but never throw any more DCs. This was after several hours - literal hours - spent with 4 DDs overhead...

I have seen them run out of hedgehogs in SH3 also

[walsh2509]

Can anyone tell me if the devs have modeled the Japanese DC's on historic data, the japanese only set there DC's to 100ft until a Congressman May let it slip that the Japanese were not having much luck with there hunting of US subs as there DC's were set to low. This was printed in a few newspapers and the japanese got to hear about it and started to set there DC's deeper AFTER mid 43.

So if this is modeled correctly then no japanese DC should go deeper than 100ft up until mid43.

[JackChen]

There's got to be a smart Jap somewhere who's realising he's not getting any subs.

[aurgolo]

I always go for the same tactic since SH3:

1) I run slow at 60 mt or deeper and wait until the destroyer is almost on top of my tail
2) then I ring up flank speed and give hard rudder to port or starboard in order to follow the DD direction
3) In this way I to get out of the kill zone and ask for periscope deph
4) Reduce speed to standard and ask for 0 degrees rudder
5) when at periscope depth I have the DD just in front of the bow at around 3-400 metres and fire a torpedo (perfect shot position)
5) i use this tactic since SH3 and is quite impossible to miss the shot. It works in 95% of cases (according to my experience). I the shot is missied is because the sub gets periscope depth too close to the DD (less than 300 mt) that's why is important to reduce velocity (of course some practice is needed for different sub types according to: ascent rates, submerged speed, etc etc)

Hope it helps

Ciao ciao

andrea

[GTHammer]

I read in some other thread that the destroyers have unlimited DC's (or at least they aren't given a set number in the game files)...I think it was redwine that said something about this...I'll look for the thread. Interesting about the 100 ft max thing 'til 43 though...I'll have to make alot of noise down deep and try it out.

[Torpex752]

Thermal layers vary, so their ability to hide a sub should & would realistically vary. If the game models that I do not know.
The speed by which a sub changes depth varies as well, there are a number of variables that need to be understood. There is no one speed for changing depth, so in one instance an hour would be fast in another, an hour would be slow. So I am sure Dick OKane was speaking about a specific situation and not the "rule".

:cool:
Frank

[vindex]

I go under the thermal layer, run at 1/3, AND rig for silent running. All three are essential ... they can still find you if they know where to look, but it'll be pretty hard for them.

If they are actively pinging you and doing a depth charge run, they know where you are so you better run for it -- briefly, and then go quiet again. Otherwise, remain wery wery quiet.

[Cobra_mkII]

These are two questions:
1. Passing thermal layer makes me invinsible to passive sonar at ahead slow or with silent running? Is it working for real or it is just for show?
2. When under attack by destroyer, what is the best evasion tactic?


Just to prove the layer is modelled-
Flavoured to Taste modified the thermal layer:

"/DATA/CFG/SIM.CFG
------------------------
- ai cannons max fire range from 6K to 9K
- Ai cannons / Max error angle from 3 to 4
- lost contact time from 15 to 30 mins
- visual / enemy surface factor from 400 to 150
- visual / enemy speed factor from 15 to 9
- Visual / light factor from 1.0 to 2.0 (2.0 to 1.75)
- hydrophone / sensitivity from 0.03 to 0.04
- hyrophone / waves factor from 0.5 to 0.95
- hydrophone / noise factor from 1 to 0.35
- hydrophone / thermal layer attun from 3.0 to 2.0
- sonar / detecton time from 20 to 10
- sonar / thermal layer attun from 5.0 to 4.0"

So run silent run deep;)

If I have been detected I run and dive at flank, just before the thermal layer I launch a decoy, switch to silent running and turn away. My flank speed will allow me to drift away from the decoy (which is above the thermal layer) while I creep away below it.

[TheSatyr]

I creep beneath the layer. If I get dropped on I go to flank and get out of the way,then start creeping again once the noise from the DCs settle down. I never use decoys since the US subs never had them in WW2...including them in the game is one of my biggest beefs with the game...completely un-historical and un-realistic. (Sort of like having Lancasters with upside down US markings...heh).

Course if I'm caught in shallow water my tactics change. I still creep but I try to keep heading towards deeper water. And when I go to flank when I get dropped on I keep my course heading towards deeper water and hope the DCs drop behind me.

[Farinhir]

The reason you become more difficult to detect under a thermal layer is because sound travels at different speeds with different pressure and temps in the water. This along with the cylindrical spreading and signal absorbtion from the layer make it harder to find a sub that is under a thermal layer. There are more factors that would cause this. One is the fact that sound likes to bend in a path that will allow it to move slower. Another is "Ray Propagation Theory". Sound in water can be represented as a vector or ray.

Ray Propagation Theory states that:

1: RAYS will change direction when passing through two mediums of different density. This is Snell's Law. Crossing a thermal layer would count as passing through two mediums of different density.

2: Sound will bend towards the region of slower sound speed.

Because of these factors, when you cross a thermal layer you can find that most of the area is a shadow zone.

A good source of information on this is a powerpoint found on Berkley's navsci area (something I stumbled upon). Most of my information is from there.

Source PPT:
http://navsci.berkeley.edu/ns401/NS401%20Fall%2006/Lecture09-Underwater%20Sound%20mjh.ppt

Read the instructor notes that were included with the slides. They give a lot more info.

CHeers,
~F~

[GakunGak]

@Farinhir: THNX for the link, ya rule!!!!!!!:rock:

[STEED]

I know one thing I am sick to death every so often setting out on patrol hearing about every ten seconds Passing thermal layer in that robot voice. :hulk:


Moving on, when I attack a convoy on silent running nice and deep and if all is in place I slowly come up to have a look and make my final decision.

[John Channing]

Hardly a "robot"...

http://www.subsim.com/radioroom/showthread.php?p=538032#post538032

post #86

JCC

[tycho102]

These are two questions:
1. Passing thermal layer makes me invinsible to passive sonar at ahead slow or with silent running? Is it working for real or it is just for show?

2. When under attack by destroyer, what is the best evasion tactic?

1. In the stock game, it attenuates sound by something like 30%. Several mods change this down to 20% or less.

2. Dive as deep as possible. Run at 1kt when they're right over you, 2kts when they've moved off a little bit, 3 or 4 knots when you can. Your best best is to always dive at 4 knots just after firing a salvo, and turning ninety or more degrees to take you away from the firing position. Once you get some depth (60+ meters) and the torpedoes have impacted, reduce speed as the destroyers close in. You are better off using approach and attack configurations which don't put you in the position of being detected. The "dead stick" approach works in every case I've used it, in deep water.

[GakunGak]

These are two questions:
1. Passing thermal layer makes me invinsible to passive sonar at ahead slow or with silent running? Is it working for real or it is just for show?

2. When under attack by destroyer, what is the best evasion tactic?

1. In the stock game, it attenuates sound by something like 30%. Several mods change this down to 20% or less.

2. Dive as deep as possible. Run at 1kt when they're right over you, 2kts when they've moved off a little bit, 3 or 4 knots when you can. Your best best is to always dive at 4 knots just after firing a salvo, and turning ninety or more degrees to take you away from the firing position. Once you get some depth (60+ meters) and the torpedoes have impacted, reduce speed as the destroyers close in. You are better off using approach and attack configurations which don't put you in the position of being detected. The "dead stick" approach works in every case I've used it, in deep water.
What about after firing the fish I flank to 300+ feet and dead stop, launch decoys, port/stbrd 90* at silent running....:dead:

[Torpex752]

I read in the book "Silent Running" that the Japanese depth charges were not the pressure switch activated type like the US. According to the book it was activated by a timer. Its the first I ever read about it being described that way. has anyone any other information?

I also wonder why they (the devs)didnt make the depth charges with a "Click" then bang? I know the click was suppose to be the firing mechanism detonating miliseconds prior to the main charge. Just curious.

Frank "Torpex" Kulick
Subsim Staff :cool:

[TwinStackPete379]

Yesterday i successfully used a decoy at 73% realism. I crept into a large convoy, popped my shots, they started looking for me, they were getting close but not on attack passes. I dove to just above the thermal at 4knts (hoping to make noise to get their attention, which i did judging from the pings) popped the decoy at 4knts dropped below thermal, and kicked it up to 6 knts just to get some extra distance. they took the bait. I was then able to set up on another shot on another merchant on the back rank while they circled in vain around the decoy. even after the decoy expires, they still linger, freeing you up in a different part of the convoy.

[DigitalAura]

Also, if you notice, the DD's will often stop altogether. When they do this, you know they're 'listening' for you... that's when you have to ALL STOP (or run really, really, silent). Once they start up again, you can gun it faster if you need to (if you notice they've found you anyways and are on course to intercept).

[GOZO]

How do I go deeper than the 165'. (Besides having a hole in my boat!! :rotfl: )


"Shift D" does it as well.:cool:

/OB

[ddiplock]

I was in my Balao sub the other day, all the way down at 570ft, nearly 200ft past test depth, under DC attack from a sub chaser and a destroyer who'd spotted me.

Despite me being that deep, and below the thermal layer, they were constantly getting a fix on me with their ASDIC. Did the Japs actually become very good sub hunters later in the war??

In the end I actually got bored and re-loaded the game and headed in a different direction as I couldnt' seem to shake them even with my constant maneuvering. lol

[Rockin Robbins]

Yes, the Japanese did get much better toward the end of the war. But their elite crews were well thinned out, as were their escort fleet. If a sub found themselves unlucky enough to get stuck below a crack escort with a veteran crew they were in big trouble indeed!

[TwinStackPete379]

yeah digital, i thought that too, when they slow down or stop, i assumed they were listening hard, so usually drop deeper and slow to 1 knt waiting to hit the evasive turn