[tec] "bouyancy problem"

[Redlance88]

I understand it that at a depth below 250m or so it is very difficult to keep the sub from going to the bottom for good. Basically flank speed to maintain that depth or sink further and crush. My question is this, is this a bug or is this the way that they worked then. it's not as simple a question as it may seem. as a scuba diver, I know that near the surface one often has to add weight just to be able to stay underwater, but as you go deeper , you have to keep adding air to a Buoyancy control device to keep control of your depth and to keep from rapidly sinking. to me this sounds like the same thing is happening to the subs, and here is the kicker, after a certain depth there is no more volume for the trim tanks to keep the sub at the ordered depth , to to maintain depth you need up force from the dive plains. just like on the surface you need negative on the plains to force the sub underwater. ( I think ya can still dive a u-boat without them, but it would take a bit longer) the depths that this sort of effect would happen may be all wrong, but just thinking before it is (fixed) make sure it needs fixing.
I welcome comments from any more in the know than I.

[kylania]

The main problem with going below 250m was the whole 'bring crushed like an egg' thing. :03:

There have been some bugs with holding depth below 180m though, apparently the same bug from SH4.

[vonTorpitz]

Interesting question. If what you are discussing actually was the case during the war, then the U-Boat commander would have always had to run his e-motors at flank speed in order keep the boat at an even depth. But if he is at over 200m depth then he is obviously evading an attack and would obviously not want to run so loudly for extended periods. Seems like a catch 22 and an interesting one if its true. However, I think its fairly unlikely because I'm fairly sure the trim and ballast tanks had a large role to play in bouyancy along side boat speed, probably enabling the commander to run silent.

[Sgtmonkeynads]

to to maintain depth you need up force from the dive plains. just like on the surface you need negative on the plains to force the sub underwater.

Has anyone ever checked the diveplanes in the game to see if they are trying to keep depth or are set in neutral when traveling forward at such a depth. Being in neutral would cause a crashdive of sorts at deep depths.

Makes you wonder if the diveplanes in the Game should be reversed at a certain level inorder to make this effect take place ? Very interesting !
I can't beleive all the stuff one can learn on this forum.

[Redlance88]

"There have been some bugs with holding depth below 180m though" Ooops, 180m then....

in regards to always having to run e- motors, no that's not what I am suggesting. What I am saying is that the deeper you go, the less effective trim tanks would be until a critical depth where you would have to be moving forward to maintain depth. before that you could try to establish a hover and just sit as a depth with no motors on. but beyond that depth you start to loose ground and need to move faster and faster through the water the deeper you go just to stay at a commanded depth, and if you were to slow down or stop you would sink, regardless of how much air you put into the trim tanks. now as I understand it Main ballast tanks are another story. they flood all the way at the surface just to get the boat under water. blowing the tanks at most any depth should create an Uncontrolled assent to the surface provided they are undamaged.
as always I am working with what I understand to be facts, and I may be totally misinformed on those facts.
My assumption here is that this effect is perhaps intentionally in the game, but perhaps too strong a force, or set too shallow, or we all just think it is set too shallow. I have had no luck finding any information on max hover (no dive plane effect) depth for German U boats of any kind.

[Trublion]

I would have no issues with not being able to keep buoyancy at 180m without help from the e-engines, however what bothers me if the fact that when ordering my sub to dive to 80m I end up at 150-160m. This make evading very tricky.
Oh and the dive planes are not at zero, but are indeed trying to get back to the set depth and by the look of it, my sub sinks from the rear... Is there any mass setting for the sub in the .zon file that could create this issue?

[TheBlobThing]

Are you guys sure it's not until 180m?

[Kromus]

I would have no issues with not being able to keep buoyancy at 180m without help from the e-engines, however what bothers me if the fact that when ordering my sub to dive to 80m I end up at 150-160m. This make evading very tricky.
Oh and the dive planes are not at zero, but are indeed trying to get back to the set depth and by the look of it, my sub sinks from the rear... Is there any mass setting for the sub in the .zon file that could create this issue?

I did edit *.sim file for each sub to get stable sub at 140m w/o using engines (see my VIIB and C mod where I did change mainly "mass" values, sub could hold about 200m at 4 knots). The problem is that sub becomes very unresponsive to waves on surface - acts very much like "sub on rails".
So it seems you need to choose if you want more realistic surface behavior or underwater depth holding. I really want to know if theres some other workaround.

[kemeri]

May be such "bouyancy problem" could help to simplify the modding of the U-boat's dead stop depth keeping instability, as it has been done AFAR in GWX (positive dead stop) and in NYGM (negative dead stop). And to make it more complex and realistic then before :DL.

[Trublion]

It makes sense, I have been using a mod for more realistic surface behavior...

[vickers03]

where is the problem in taking over the GWX sub values to sh5?

looking at the GWX submerged displacement vs. surfaced, this is your bouyancy (type 7b):
857/753=1,138 (you can work with a factor),
mass is set slightly less than surfaced displacement;
in GWX it's 752,8.
gc_height=2,35 (might be too much in sh5)

adapt this to the other subs.

don't forget to edit the data/Cfg/sim.cfg to get rid of
the sub on rails:

[Mech]
Waves amplitude=0.60
Waves attenuation=0.03

[Ducimus]

Have you tested that? :O:

[Kromus]

where is the problem in taking over the GWX sub values to sh5?

don't forget to edit the data/Cfg/sim.cfg to get rid of
the sub on rails:

[Mech]
Waves amplitude=0.60
Waves attenuation=0.03

Since when ";AI surface ships sensors cfg file" has to do something with "sub on rails" effect? Just curious :hmmm:

Edit: No joy, just tried them (taken from uboat.net actually) at full stop ordering to P depth falls down to 16 then slowly up to 14-5 to 25 it falls down to 31 then up to 28 and ordering to 100m it falls into oblivion... Like I said, it`s not that simple as someone thinks.

[Ducimus]

Since when ";AI surface ships sensors cfg file" has to do something with "sub on rails" effect? Just curious :hmmm:

http://id.mind.net/~zona/mstm/physics/waves/introduction/introductionWaves.html
http://id.mind.net/~zona/mstm/physics/waves/partsOfAWave/waveParts.htm

[vickers03]

Have you tested that? :O:
yea well.. up to some extent:D
at least i can dive around like in sh3

Since when ";AI surface ships sensors cfg file" has to do something with "sub on rails" effect? Just curious :hmmm:
[Mech]
Waves amplitude=0.60
Waves attenuation=0.03


this defines the wave influence on all surface vessels

[Kromus]

this defines the wave influence on all surface vessels

Ok I give it a shot

[Ducimus]

Ok I give it a shot

Don't be surprised if you end up with some ahh..... side effects. Tuggin on those variables will fix sub on rails for sure, but it's much akin to being a kitten tuggin on a ball of yarn. Two biggest side effects to look out for is

- AI visual sensors changing drastically one way or another.
- surface ships randomly sinking/exploding for no apparent reason. (crash depth issue with damage zones in zones.cfg if i remember correctly)

To minimize the chance of that happening, Be gentle, don't adjust it drastically. Only as needed, and very carefully, and deliberatly.

[Kromus]

Don't be surprised if you end up with some ahh..... side effects. Tuggin on those variables will fix sub on rails for sure, but it's much akin to being a kitten tuggin on a ball of yarn. Two biggest side effects to look out for is

- AI visual sensors changing drastically one way or another.
- surface ships randomly sinking/exploding for no apparent reason. (crash depth issue with damage zones in zones.cfg if i remember correctly)

To minimize the chance of that happening, Be gentle, don't adjust it drastically. Only as needed, and very carefully, and deliberatly.

Thx for warning and info :up:

Yes I just tried changing original values (0.3->0.03 and 0.75->0.6) and sub was like "running through the waves" no pitch/roll anything. So definately this is the way so thx both for this. Problem seems to be those side effects now :-?

[Ducimus]

>>no pitch/roll anything.

CG_Height in the sub's sim file. Default is 1. In previous games this was a little under or a little over 2. Here you have to be careful again or you'll have a sub doing 360's along its long axis, or end up upside down if rammed or something. One additional thing i noticed was that on deck, in rough weather and this adjusted to say 2.X.. i found myself catapuled onto the UZO as if i was standing on it. My "feet" being launched right off the conning tower deck. So, again, adjust carefully. Hope you like restarting the game alot. (insert DRM rant here).

With stock enviormental settings and waves, i found ehh 1.8 or 1.9 (i forget, but i think 1.8) to be the most i could set it before having the "catapult onto the UZO" feeling.

Hmmm.. i guess the camera doesn't move with the boat? :hmmm:

[vickers03]

Yes I just tried changing original values (0.3->0.03 and 0.75->0.6)sorry but you're not looking carefully enough,
it should be 0.3->0.6 and 0.75->0.03, a big difference.

here's my modded 7a, take a close look at ALL values
and compare with sh3/GWX stuff.
http://www.filefront.com/16047457/sh3gwx_to_sh5_7a_test.7z

[Kromus]

sorry but you're not looking carefully enough,
it should be 0.3->0.6 and 0.75->0.03, a big difference.

here's my modded 7a, take a close look at ALL values
and compare with sh3/GWX stuff.
http://www.filefront.com/16047457/sh3gwx_to_sh5_7a_test.7z

Yes I noticed that it did the opposite thing :P I`ll look at your file later gotta go sleep, gn.

Edit:

http://www.filefront.com/16048001/7b_test.zip

My try with VIIB but still with original values in sim.cfg used (will be messed up if sh3 sim.cfg values used)! Now for real, cya tomorow.

[Redlance88]

so we have some idea of what values can be adjusted, and it sounds like with the right "tweaking" of some of them we might be able to get a boat that will be able to maintain a depth at all stop but beyond that depth will need progressively more forward motion to not sink to oblivion. and to me that sounds correct in terms of real world physics. so now the question becomes what are accurate values for the historical subs, and at what depth did this become a factor if at all. if that depth is beyond crush depth the point becomes moot. and nothing is needed beyond any adjustment to keep the effect from happening too soon( shallow). thoughts?

[Bilge_Rat]

just to add some real world data which may or may not have a bearing.

Normally, a submarine will trim to have a slightly positive buoyancy and will use a slight downward angle on the planes and forward motion to maintain a set depth. The theory being that if power should be lost for any reason, the sub will gently rise to the surface.

the trim for a boat is dynamic and directly influenced by the depth. Air provides buoyancy and its effect is influenced by depth. As you go deeper, air is compressed and loses its buoyancy. A boat which is positively buoyant at 50 meters will be negatively buoyant at 150 meters at the same trim since the air in the ballast tanks will be compressed letting in more water.

normally, when a boat dives from, say, 50 meters down to 150 meters, the diving officer will have to rest the trim by pumping additional air in the ballast tanks to again achieve a slight positive trim.

All these factors also explain why you sometimes hear stories about crews losing control of the depth. If the wrong buoyancy, plane angle, speed is set, the boat may easily go past the set depth before they are able to bring it back to an equilibrium.

Although in theory, it may be possible for a sub to maintain depth while motionless, it practice it would be too difficult.

of course, none of these factors have ever been properly represented in a subsim and they may not have a bearing on the discussion here.

[Redlance88]

just to add some real world data which may or may not have a bearing.

Normally, a submarine will trim to have a slightly positive buoyancy and will use a slight downward angle on the planes and forward motion to maintain a set depth. The theory being that if power should be lost for any reason, the sub will gently rise to the surface.

the trim for a boat is dynamic and directly influenced by the depth. Air provides buoyancy and its effect is influenced by depth. As you go deeper, air is compressed and loses its buoyancy. A boat which is positively buoyant at 50 meters will be negatively buoyant at 150 meters at the same trim since the air in the ballast tanks will be compressed letting in more water.

normally, when a boat dives from, say, 50 meters down to 150 meters, the diving officer will have to rest the trim by pumping additional air in the ballast tanks to again achieve a slight positive trim.

All these factors also explain why you sometimes hear stories about crews losing control of the depth. If the wrong buoyancy, plane angle, speed is set, the boat may easily go past the set depth before they are able to bring it back to an equilibrium.

Although in theory, it may be possible for a sub to maintain depth while motionless, it practice it would be too difficult.

of course, none of these factors have ever been properly represented in a subsim and they may not have a bearing on the discussion here.

actually this is exactly the sort of thing I am trying to get at. so as the creator of this thread it has a lot of bearing to the discussion I am trying to have. I am trying to figure out how well all of this can be incorporated into the game being as it seems that a lot of the foundation for it is in the code just a question of what is realistic and what is reasonable. I think it is fair to say that trimming a sub for a specific depth in wwII was more an art than a science. but need to keep the rest of the game playable too. so we can find out the rate of compression volume at specific depths, so we can relate that to the total max volume of the ballast tanks to determine at what point there isn't enough left to keep the sub from being negative buoyant ( I suspect that that total is beyond crush depth but perhaps not) and then figure out a rate for "up force /knot of speed" from the planes and the rest it just trying to make the values match the assumptions. I think we can do this....... so time to track down some volume of air per atmosphere of depth charts and displacement values for type VII subs also what is the max compressed air capasity of the sub at 100% being as that info is modeled in the game as well use up too much compressed air and ya can't surface. but ya might be able to maintaiin a depth till ya run out of fuel. ( that would suck. ) but in a morbid way be really cool.

[Hitman]

I understand it that at a depth below 250m or so it is very difficult to keep the sub from going to the bottom for good. Basically flank speed to maintain that depth or sink further and crush. My question is this, is this a bug or is this the way that they worked then. it's not as simple a question as it may seem. as a scuba diver, I know that near the surface one often has to add weight just to be able to stay underwater, but as you go deeper , you have to keep adding air to a Buoyancy control device to keep control of your depth and to keep from rapidly sinking. to me this sounds like the same thing is happening to the subs, and here is the kicker, after a certain depth there is no more volume for the trim tanks to keep the sub at the ordered depth , to to maintain depth you need up force from the dive plains. just like on the surface you need negative on the plains to force the sub underwater. ( I think ya can still dive a u-boat without them, but it would take a bit longer) the depths that this sort of effect would happen may be all wrong, but just thinking before it is (fixed) make sure it needs fixing.
I welcome comments from any more in the know than I.

What I can add is that because of the huge pressure over the steel, it is bounced inwards at great depths and as such the actual volume of the UBoat is decreased even more, making it heavier when compared to the water because it displaces less of it. I can't say how much this effect causes, but I know it exists. It might be neglectable or not, but it was known and mentioned in WW2 documents/books, though I can't right now tell from memory where I readed it :hmmm: