"Driftdown problem" (neg. buoyancy when submerged) addressed?

[senjorlossi]

Hi Guys,
just a quick question, since I can´t find anything about it here in the forum:

Has the problem of the negative buoyancy (sub tends to sink deeper and deeper when submerged) already been addressed in any way? I can´t see anything so far.

Good hunting,
Stefan.

[GoldenRivet]

im not sure about this SH5...

but in SH3/4 this was an issue when crash diving while already submerged.

i have not noticed this bug nearly as much in SH5 as i did in SH3

[Juliano]

I think he´s having problem after a normal dive
same problem here

sometimes I have to set speed higher than 2-3 knots to keep the same depth at 100 meters

still, I don´t know how to help or if there´s a mod to fix that (if I remember right, in real life the extra speed is indeed needed to keep depth at 100m or below, but I may be wrong)

[Ducimus]

http://www.subsim.com/radioroom/showpost.php?p=1307506&postcount=25

Problem was worse in SH4, you had to go to flank.

[Conrad von Kaiser]

Silent running at 100 feet depth gives me a very slow decent. Maybe 1 foot per minute. Not a big drop if you're sitting and watching it, but at time compression it could build up pretty quick.

[senjorlossi]

Yes, when you go deeper than 80 m the sub keeps on sinking deeper unless you command a new depth of around 60 m or less. Even at around 80 m you can see that the dive planes are in the "up" position.

I thought that it might be connectet to the "silent running" status, as water would not be pumped out of the sub to prevent any noise, but it is not.

OK, I am not a submariner in real live, but I think a well trimmed sub should be able to stay at any depth, even at low speed. Of course there is always some water leaking in, the deeper the more, as the outside water pressure rises. But it´s the Chief´s duty to pump it out at times.

[Frederf]

It's a complex issue but, no I don't think it's been fixed in any patches. Someone would have mentioned it.

Standard procedure, at least near the surface, is to set the buoyancy purposefully negative so the boat has to be moving to plane up to periscope viewing depth. This way if anything goes wrong you simply sink a little deeper instead of broach, get spotted, and die.

Keeping exact trim is rather difficult. The overall buoyancy that keeps the boat at 60m and 65m are rather close. With time and effort one can "dial it in" more or less. With surface swells near the surface it's like trying to make a house of cards with the fan on.

Sinkikng down and then hovering at 0 kts to exactly 100m would take a lot of fiddling with the trim tanks and you might wobble up and down 10s of meters as trim was changed. Speed and planes help you get to a precise depth quickly. However there's no chance that at 0 kts and 100m the boat would inexorably sink out of control as the buoyancy can be changed.

There is a point of no return for submarines known as the critical depth where maximum available buoyancy authority is insufficient to achieve positive net buoyancy but that would be well below 100m in a Type VII.

[Sailor Steve]

Way back in Aces Of The Deep you couldn't run silent forever, because the pumps had to run ocassionally to get rid of the water that always leaks into the boat. NYGM for SH3 replicated this with the 'Anti-Hummingbird' mod, so the boat would start to sink if you ran at two knots or less.

Is it possible that this behaviour was placed into SH5 intentionally?

[flakmonkey]

Way back in Aces Of The Deep you couldn't run silent forever, because the pumps had to run ocassionally to get rid of the water that always leaks into the boat. NYGM for SH3 replicated this with the 'Anti-Hummingbird' mod, so the boat would start to sink if you ran at two knots or less.

Is it possible that this behaviour was placed into SH5 intentionally?

I was going to say the same thing, i always hated being able to hover perfectly at any depth, and always concidered it a sh3/4 bug, so i was quite pleased to see it had been addressed in shv.. so you can imagine my surprise that people now think of it as a bug!!

[Frederf]

Well it is a bug. Slowly sinking to the Earth's center is not normal real-life behavior. Sure, at periscope and you hit all stop and you sink a little. Either you'd drop down to a neutral buoyancy depth some small amount or you'd drop far enough that the engineer in charge or trim would do something about it.

Better behavior is settling a random (5-20m) depth below commanded when not under speed and some fluctuation over time as the engineer tries to fine tune the trim being very worried about breaking the surface.

[U-Bones]

Well it is a bug. Slowly sinking to the Earth's center is not normal real-life behavior. Sure, at periscope and you hit all stop and you sink a little. Either you'd drop down to a neutral buoyancy depth some small amount or you'd drop far enough that the engineer in charge or trim would do something about it.

Better behavior is settling a random (5-20m) depth below commanded when not under speed and some fluctuation over time as the engineer tries to fine tune the trim being very worried about breaking the surface.

I AGREE. All stop at any survivable depth should not result in free fall.

Silent running should slowly degrade your trim, and a certain amount of "slop" should be allowed in setting trim to the desired depth. But having to go over ahead slow to prevent sinking should only happen with flooding given the depths this game is played at.

[senjorlossi]

That´s exactly what I mean.

L.G. Buchheim describes in "Das Boot" how the Chief is actually waiting for some DC explosions to break the silence and pump out some water.

[Frederf]

I was going to ask if anyone knew at what depth point a Type VII would start to feel the limits of buoyancy. Is it 100m? 300m? 1000m? Maybe modern subs have sealed main ballast tanks but the WWII variety had permanently open bottoms like an upside down drinking glass so the volume of air contracts as the ambient sea pressure increases.

I hear now with SH5 we have a scripting system so depending on how powerful that is we can run a very sophisticated arrangement of depthkeeping. Perhaps we can even get to the point that we can tell our engineer how conservative to make his trim and torpedoes upset the balance when fired.

[Morpheus]

It's a complex issue but, no I don't think it's been fixed in any patches. Someone would have mentioned it.

Standard procedure, at least near the surface, is to set the buoyancy purposefully negative so the boat has to be moving to plane up to periscope viewing depth. This way if anything goes wrong you simply sink a little deeper instead of broach, get spotted, and die.

Keeping exact trim is rather difficult. The overall buoyancy that keeps the boat at 60m and 65m are rather close. With time and effort one can "dial it in" more or less. With surface swells near the surface it's like trying to make a house of cards with the fan on.

Sinkikng down and then hovering at 0 kts to exactly 100m would take a lot of fiddling with the trim tanks and you might wobble up and down 10s of meters as trim was changed. Speed and planes help you get to a precise depth quickly. However there's no chance that at 0 kts and 100m the boat would inexorably sink out of control as the buoyancy can be changed.

There is a point of no return for submarines known as the critical depth where maximum available buoyancy authority is insufficient to achieve positive net buoyancy but that would be well below 100m in a Type VII.
Very nice explanation, thx ;)

[sergei]

Is it possible that this behaviour was placed into SH5 intentionally?

It is possible it is an intentional feature that is not working properly.
If it was tied into silent running that would be a very cool feature.
Or it is possible it is simply a bouancy model for the subs that does not work properly below 100 meters.
We do not know yet.
I have been fiddling about with the submerged displacement figure in the sim file for the Type VIIA.
By shaving some numbers off the figure I can make my sub just about hold level at 150 meters, with full up on the planes, but this tweak leads to a boat that is unresonably quick at rising from 100 meters to periscope depth. She goes up real quick! Not an ideal solution. And not something I would want to release as a mod. I was just trying to figure out how the numbers in the sim file affect the game.
I'm hoping this issue will be addressed in a future patch.

[senjorlossi]

Hi Guys,

I completed a patrol tonight and got both a new sub (VII C) and some promotion points. I gave it a try and gave the navigator some intensive training. ;)

Now I am able to hold the depth at 150 m at slow speed without problems. Couldn´t check any deeper, since I am still in the north sea on my way to the western approaches, but the problem of sinking to death seems to be fixed now.

Don´t know if it´s the new boat or the navigator´s skills, but finally I´m able to sneak away deep and slow.:woot:

[Rip]

Very nice explanation, thx ;)

Well except that Main Ballast Tanks are normally fully flooded when submerged. the tanks used to trim the boat for varying water conditions are internal to the hull and therefore air compression plays no part. Although the pressure does have an effect on the trim and drain pumps as they must overcome sea pressure when trying to lighten the boat. Inversly it can be quite easy to increase the weight of the boat by simply opening a valve and letting the pressure do it's work.

Modern submarines have a system for hovering that involves two tanks one for flooding that is vented and one for blowing ballast that would be pressurized. A large three way ball valve can be hydraulically positioned to quickly gain or loose ballast to maintain depth without any forward speed.

Rip :|\\

[Frederf]

Oops, yeah MBTs would have no effect on trim being full for diving. Are there any instances of partial MBT usage like decks awash?

[Rip]

Oops, yeah MBTs would have no effect on trim being full for diving. Are there any instances of partial MBT usage like decks awash?

I don't think so. Mostly because as you noted as you descend the air compresses and you loose buoyancy. Putting yourself in a position to loose more buoyancy as a simple function of descent than what nature already mandates would not be prudent. :hmmm:

In fact at least on submarines I have been on we left MBT vents open for some time after submerging to ensure there was as little air in them as possible. :know:

Rip

[Kromus]

Hi Guys,

I completed a patrol tonight and got both a new sub (VII C) and some promotion points. I gave it a try and gave the navigator some intensive training. ;)

Now I am able to hold the depth at 150 m at slow speed without problems. Couldn´t check any deeper, since I am still in the north sea on my way to the western approaches, but the problem of sinking to death seems to be fixed now.

Don´t know if it´s the new boat or the navigator´s skills, but finally I´m able to sneak away deep and slow.:woot:

Yes, VIIC isn`t affected as much as other subs somehow, I tried historical missions just to dive as deep as possible and it could hold depth same as yours...
Maybe some modding guys should look into this how they made this in VIIC possible? VIIB has very big problems holding even 50 m (falling to 55-57 at low speeds) and VIIA is little bit better.

[Kumando]

No this is definitely a bug i cant trim the boat at a mere 30 mts it keeps going down the only depht that the boat maintains its periscope depht.

[thruster]

i always thought that the uboats were maintained intentionally abit heavy. you couldnt stay stationary whilst submerged and still maintain your depth. i thought it was related to avoiding breaking the surface once the weight of the torpedo left the tube, or as fuel weight decreases as its burnt off, etc.

bouyancy was maintained by continual weight management, ballast juggling and importantly for uboat designs; forward momentum over the dive planes.

.....or have i missed something?

[JamesT73J]

It's not a morale / experience thing, is it? In Dangerous Waters, you need a little speed to maintain depth in some of the larger vessels. I quite like this feature; the 'hovering' behaviour is a bit naff.

[BlackSpot]

It's not a morale / experience thing, is it? In Dangerous Waters, you need a little speed to maintain depth in some of the larger vessels. I quite like this feature; the 'hovering' behaviour is a bit naff.

Hmmm possibly. I'm using the morale mod and I'm not getting any drifting :hmmm:

[sergei]

Hmmm possibly. I'm using the morale mod and I'm not getting any drifting :hmmm:

Really. Which one? I'd like to try it out, but there are now a few available.

EDIT: I think you mean this one?
http://www.subsim.com/radioroom/downloads.php?do=file&id=1568

[elve84]

I would say its normal behavior for a sub, subs don't only use balast tanks for keeping debt, they also use there dive planes for this, as you hang stil in the water there is not water going over ya dive planes and thus ya can't maintain your debt. add that up with the balast tanks leaking and no working pumps because you as you are running silance. I would say it is normal that your boat "sinks" deeper.

As the Type VIIC is more modern, it could verry well be posible that german engeneers found a way to keep better debt with this ship. That would make the game more realistic in my opinion and historicaly correct.

[BlackSpot]

Yes Sergei, I just checked.
I tested the drift last night. Went down to @ 180 m it stayed steady even when using time compression x 32. Now, whether it's the mod effecting this, I can't say.

[Frederf]

I don't think so. Mostly because as you noted as you descend the air compresses and you loose buoyancy.

I picked decks awash as an example since you're obviously not diving so it might be OK to have partial MBTs.

I always thought that the U-boats were maintained intentionally a bit heavy. you couldn't stay stationary whilst submerged and still maintain your depth. i thought it was related to avoiding breaking the surface once the weight of the torpedo left the tube, or as fuel weight decreases as its burnt off, etc.

Buoyancy was maintained by continual weight management, ballast juggling and importantly for U-boat designs; forward momentum over the dive planes.

.....or have i missed something?

Read above posts, said basically as much and you're right. The difference between that and what SH5 does is a U-boat in real life settles a little bit to its trimmed depth which may be 10-20m below where it wanted to be with planes while SH5 will just settle and settle and settle and settle very, very deep.

I would say its normal behavior for a sub, subs don't only use ballast tanks for keeping debt, they also use there dive planes for this, as you hang still in the water there is not water going over ya dive planes and thus ya can't maintain your debt. add that up with the ballast tanks leaking and no working pumps because you as you are running silence. I would say it is normal that your boat "sinks" deeper.

As the Type VIIC is more modern, it could very well be possible that German engineers found a way to keep better debt with this ship. That would make the game more realistic in my opinion and historically correct.

Settling is normal, settling 100m+ is not. Who says ballast tanks leak or that silent running is on?

[Kromus]

I found solution for this. Looked at VIIC values at goblin editor and tweaked them little bit for VIIB....

After you load everything you need (GR2 and sim files) look for:

unit_submarine
obj_hydro

change this:
mass to 620.8
surfaced displacement 629/draught4.55
submerged 730/draught6.4

With these values I could hold depth at 160m w/o moving!

I hope this helps a bit.

It definately needs more tweaking but I think it`s a good thing to start with.

[Rip]

It's not a morale / experience thing, is it? In Dangerous Waters, you need a little speed to maintain depth in some of the larger vessels. I quite like this feature; the 'hovering' behaviour is a bit naff.

Actually modern submarines are able to hover. Now whether this is realistic to a u-boat I cannot speak. But hovering is a critical skill in under ice operations. The places you can break through the ice are not always large and you must ascend and a very controllable rate.

I would say they could certainly trim the vessel to at least able to maintain depth with not much over 1 KT. Doing this at periscope depth would be much more of a challenge than say 50M.